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Description

libhttpserver is a C++ library for building high performance RESTful web servers. libhttpserver is built upon libmicrohttpd to provide a simple API for developers to create HTTP services in C++.

Programming language: C++
Latest version: v0.17.5

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README

<!--- Copyright (C) 2011-2019 Sebastiano Merlino. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License". -->

The libhttpserver reference manual

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Tl;dr

libhttpserver is a C++ library for building high performance RESTful web servers. libhttpserver is built upon libmicrohttpd to provide a simple API for developers to create HTTP services in C++.

Features:

  • HTTP 1.1 compatible request parser
  • RESTful oriented interface
  • Flexible handler API
  • Cross-platform compatible
  • Implementation is HTTP 1.1 compliant
  • Multiple threading models
  • Support for IPv6
  • Support for SHOUTcast
  • Support for incremental processing of POST data (optional)
  • Support for basic and digest authentication (optional)
  • Support for TLS (requires libgnutls, optional)

Table of Contents

Community

Appendices

  • Copying statement
  • GNU-LGPL: The GNU Lesser General Public License says how you can copy and share almost all of libhttpserver.
  • GNU-FDL: The GNU Free Documentation License says how you can copy and share the documentation of libhttpserver.

Introduction

libhttpserver is meant to constitute an easy system to build HTTP servers with REST fashion. libhttpserver is based on libmicrohttpd and, like this, it is a daemon library (parts of this documentation are, in fact, matching those of the wrapped library). The mission of this library is to support all possible HTTP features directly and with a simple semantic allowing then the user to concentrate only on his application and not on HTTP request handling details.

The library is supposed to work transparently for the client Implementing the business logic and using the library itself to realize an interface. If the user wants it must be able to change every behavior of the library itself through the registration of callbacks.

libhttpserver is able to decode certain body format a and automatically format them in object oriented fashion. This is true for query arguments and for POST and PUT requests bodies if application/x-www-form-urlencoded or multipart/form-data header are passed.

All functions are guaranteed to be completely reentrant and thread-safe (unless differently specified). Additionally, clients can specify resource limits on the overall number of connections, number of connections per IP address and memory used per connection to avoid resource exhaustion.

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Requirements

libhttpserver can be used without any dependencies aside for libmicrohttpd.

The minimum versions required are:

  • g++ >= 4.8.4 or clang-3.6
  • libmicrohttpd >= 0.9.52
  • [Optionally]: for TLS (HTTPS) support, you'll need libgnutls.
  • [Optionally]: to compile the code-reference, you'll need doxygen.

Additionally, for MinGW on windows you will need:

  • libwinpthread (For MinGW-w64, if you use thread model posix then you have this)
  • libgnurx >= 2.5.1

Furthermore, the testcases use libcurl but you don't need it to compile the library.

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Building

libhttpserver uses the standard system where the usual build process involves running

./bootstrap
mkdir build
cd build
../configure
make
make install # (optionally to install on the system)

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Optional parameters to configure script

A complete list of parameters can be obtained running 'configure --help'. Here are listed the libhttpserver specific options (the canonical configure options are also supported).

  • --enable-same-directory-build: enable to compile in the same directory. This is heavily discouraged. (def=no)
  • --enable-debug: enable debug data generation. (def=no)
  • --disable-doxygen-doc: don't generate any doxygen documentation. Doxygen is automatically invoked if present on the system. Automatically disabled otherwise.
  • --enable-fastopen: enable use of TCP_FASTOPEN (def=yes)
  • --enable-poll[=ARG]: enable poll support. Internal behavior of the INTERNAL_SELECT (yes, no, auto) [auto]
  • --enable-epoll[=ARG]: enable epoll support. Internal behavior of the INTERNAL_SELECT (yes, no, auto) [auto]
  • --enable-static: enable use static linking (def=yes)

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Getting Started

The most basic example of creating a server and handling a requests for the path /hello:

#include <httpserver.hpp>

using namespace httpserver;

class hello_world_resource : public http_resource {
public:
    const std::shared_ptr<http_response> render(const http_request&) {
        return std::shared_ptr<http_response>(new string_response("Hello, World!"));
    }
};

int main(int argc, char** argv) {
    webserver ws = create_webserver(8080);

    hello_world_resource hwr;
    ws.register_resource("/hello", &hwr);
    ws.start(true);

    return 0;
}

To test the above example, you could run the following command from a terminal:

curl -XGET -v http://localhost:8080/hello

You can also check this example on github.

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Structures and classes type definition

  • webserver: Represents the daemon listening on a socket for HTTP traffic.
    • create_webserver: Builder class to support the creation of a webserver.
  • http_resource: Represents the resource associated with a specific http endpoint.
  • http_request: Represents the request received by the resource that process it.
  • http_response: Represents the response sent by the server once the resource finished its work.
    • string_response: A simple string response.
    • file_response: A response getting content from a fail.
    • basic_auth_fail_response: A failure in basic authentication.
    • digest_auth_fail_response: A failure in digest authentication.
    • deferred_response: A response getting content from a callback.

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Create and work with a webserver

As you can see from the example above, creating a webserver with standard configuration is quite simple:

webserver ws = create_webserver(8080);

The create_webserver class is a supporting builder class that eases the building of a webserver through chained syntax.

Basic Startup Options

In this section we will explore other basic options that you can use when configuring your server. More advanced options (custom callbacks, https support, etc...) will be discussed separately.

  • .port(int port): The port at which the server will listen. This can also be passed to the consturctor of create_webserver. E.g. create_webserver(8080).
  • .max_connections(int max_conns): Maximum number of concurrent connections to accept. The default is FD_SETSIZE - 4 (the maximum number of file descriptors supported by select minus four for stdin, stdout, stderr and the server socket). In other words, the default is as large as possible. Note that if you set a low connection limit, you can easily get into trouble with browsers doing request pipelining. For example, if your connection limit is “1”, a browser may open a first connection to access your “index.html” file, keep it open but use a second connection to retrieve CSS files, images and the like. In fact, modern browsers are typically by default configured for up to 15 parallel connections to a single server. If this happens, the library will refuse to even accept the second connection until the first connection is closed — which does not happen until timeout. As a result, the browser will fail to render the page and seem to hang. If you expect your server to operate close to the connection limit, you should first consider using a lower timeout value and also possibly add a “Connection: close” header to your response to ensure that request pipelining is not used and connections are closed immediately after the request has completed.
  • .content_size_limit(size_t size_limit): Sets the maximum size of the content that a client can send over in a single block. The default is -1 = unlimited.
  • .connection_timeout(int timeout): Determines after how many seconds of inactivity a connection should be timed out automatically. The default timeout is 180 seconds.
  • .memory_limit(int memory_limit): Maximum memory size per connection (followed by a size_t). The default is 32 kB (32*1024 bytes). Values above 128k are unlikely to result in much benefit, as half of the memory will be typically used for IO, and TCP buffers are unlikely to support window sizes above 64k on most systems.
  • .per_IP_connection_limit(int connection_limit): Limit on the number of (concurrent) connections made to the server from the same IP address. Can be used to prevent one IP from taking over all of the allowed connections. If the same IP tries to establish more than the specified number of connections, they will be immediately rejected. The default is 0, which means no limit on the number of connections from the same IP address.
  • .bind_socket(int socket_fd): Listen socket to use. Pass a listen socket for the daemon to use (systemd-style). If this option is used, the daemon will not open its own listen socket(s). The argument passed must be of type "int" and refer to an existing socket that has been bound to a port and is listening.
  • .max_thread_stack_size(int stack_size): Maximum stack size for threads created by the library. Not specifying this option or using a value of zero means using the system default (which is likely to differ based on your platform). Default is 0 (system default).
  • .use_ipv6() and .no_ipv6(): Enable or disable the IPv6 protocol support (by default, libhttpserver will just support IPv4). If you specify this and the local platform does not support it, starting up the server will throw an exception. off by default.
  • .pedantic() and .no_pedantic(): Enables pedantic checks about the protocol (as opposed to as tolerant as possible). Specifically, at the moment, this flag causes the library to reject HTTP 1.1 connections without a Host header. This is required by the standard, but of course in violation of the “be as liberal as possible in what you accept” norm. It is recommended to turn this off if you are testing clients against the library, and on in production. off by default.
  • .debug() and .no_debug(): Enables debug messages from the library. off by default.
  • .regex_checking() and .no_regex_checking(): Enables pattern matching for endpoints. Read more here. on by default.
  • .post_process() and .no_post_process(): Enables/Disables the library to automatically parse the body of the http request as arguments if in querystring format. Read more here. on by default.
  • .deferred() and .no_deferred(): Enables/Disables the ability for the server to suspend and resume connections. Simply put, it enables/disables the ability to use deferred_response. Read more here. on by default.
  • .single_resource() and .no_single_resource: Sets or unsets the server in single resource mode. This limits all endpoints to be served from a single resource. The resultant is that the webserver will process the request matching to the endpoint skipping any complex semantic. Because of this, the option is incompatible with regex_checking and requires the resource to be registered against an empty endpoint or the root endpoint ("/"). The resource will also have to be registered as family. (For more information on resource registration, read more here). off by default.

Threading Models

  • .start_method(const http::http_utils::start_method_T& start_method): libhttpserver can operate with two different threading models that can be selected through this method. Default value is INTERNAL_SELECT.
    • http::http_utils::INTERNAL_SELECT: In this mode, libhttpserver uses only a single thread to handle listening on the port and processing of requests. This mode is preferable if spawning a thread for each connection would be costly. If the HTTP server is able to quickly produce responses without much computational overhead for each connection, this mode can be a great choice. Note that libhttpserver will still start a single thread for itself -- this way, the main program can continue with its operations after calling the start method. Naturally, if the HTTP server needs to interact with shared state in the main application, synchronization will be required. If such synchronization in code providing a response results in blocking, all HTTP server operations on all connections will stall. This mode is a bad choice if response data cannot always be provided instantly. The reason is that the code generating responses should not block (since that would block all other connections) and on the other hand, if response data is not available immediately, libhttpserver will start to busy wait on it. If you need to scale along the number of concurrent connection and scale on multiple thread you can specify a value for max_threads (see below) thus enabling a thread pool - this is different from THREAD_PER_CONNECTION below where a new thread is spawned for each connection.
    • http::http_utils::THREAD_PER_CONNECTION: In this mode, libhttpserver starts one thread to listen on the port for new connections and then spawns a new thread to handle each connection. This mode is great if the HTTP server has hardly any state that is shared between connections (no synchronization issues!) and may need to perform blocking operations (such as extensive IO or running of code) to handle an individual connection.
  • .max_threads(int max_threads): A thread pool can be combined with the INTERNAL_SELECT mode to benefit implementations that require scalability. As said before, by default this mode only uses a single thread. When combined with the thread pool option, it is possible to handle multiple connections with multiple threads. Any value greater than one for this option will activate the use of the thread pool. In contrast to the THREAD_PER_CONNECTION mode (where each thread handles one and only one connection), threads in the pool can handle a large number of concurrent connections. Using INTERNAL_SELECT in combination with a thread pool is typically the most scalable (but also hardest to debug) mode of operation for libhttpserver. Default value is 1. This option is incompatible with THREAD_PER_CONNECTION.

Custom defaulted error messages

libhttpserver allows to override internal error retrieving functions to provide custom messages to the HTTP client. There are only 3 cases in which implementing logic (an http_resource) cannot be invoked: (1) a not found resource, where the library is not being able to match the URL requested by the client to any implementing http_resource object; (2) a not allowed method, when the HTTP client is requesting a method explicitly marked as not allowed (more info here) by the implementation; (3) an exception being thrown. In all these 3 cases libhttpserver would provide a standard HTTP response to the client with the correct error code; respectively a 404, a 405 and a 500. The library allows its user to specify custom callbacks that will be called to replace the default behavior.

  • .not_found_resource(const shared_ptr(*render_ptr)(const http_request&) resource): Specifies a function to handle a request when no matching registered endpoint exist for the URL requested by the client.
  • .method_not_allowed_resource(const shared_ptr(*render_ptr)(const http_request&) resource): Specifies a function to handle a request that is asking for a method marked as not allowed on the matching http_resource.
  • .internal_error_resource(const shared_ptr(*render_ptr)(const http_request&) resource): Specifies a function to handle a request that is causing an uncaught exception during its execution. REMEMBER: is this callback is causing an exception itself, the standard default response from libhttpserver will be reported to the HTTP client.

Example of custom errors:

  #include <httpserver.hpp>

  using namespace httpserver;

  const std::shared_ptr<http_response> not_found_custom(const http_request& req) {
      return std::shared_ptr<string_response>(new string_response("Not found custom", 404, "text/plain"));
  }

  const std::shared_ptr<http_response> not_allowed_custom(const http_request& req) {
      return std::shared_ptr<string_response>(new string_response("Not allowed custom", 405, "text/plain"));
  }

  class hello_world_resource : public http_resource {
  public:
      const std::shared_ptr<http_response> render(const http_request&) {
          return std::shared_ptr<http_response>(new string_response("Hello, World!"));
      }
  };

  int main(int argc, char** argv) {
      webserver ws = create_webserver(8080)
          .not_found_resource(not_found_custom)
          .method_not_allowed_resource(not_allowed_custom);

      hello_world_resource hwr;
      hwr.disallow_all();
      hwr.set_allowing("GET", true);
      ws.register_resource("/hello", &hwr);
      ws.start(true);

      return 0;
  }

To test the above example, you can run the following command from a terminal:

curl -XGET -v http://localhost:8080/hello

If you try to run either of the two following commands, you'll see your custom errors:

  • curl -XGET -v http://localhost:8080/morning: will return your custom not found error.
  • curl -XPOST -v http://localhost:8080/hello: will return your custom not allowed error.

You can also check this example on github.

Custom logging callbacks

  • .log_access(void(*log_access_ptr)(const std::string&) functor): Specifies a function used to log accesses (requests) to the server.
  • .log_error(void(*log_error_ptr)(const std::string&) functor): Specifies a function used to log errors generating from the server.

Example of custom logging callback

#include <httpserver.hpp>
#include <iostream>

using namespace httpserver;

void custom_access_log(const std::string& url) {
    std::cout << "ACCESSING: " << url << std::endl;
}

class hello_world_resource : public http_resource {
public:
    const std::shared_ptr<http_response> render(const http_request&) {
        return std::shared_ptr<http_response>(new string_response("Hello, World!"));
    }
};

int main(int argc, char** argv) {
    webserver ws = create_webserver(8080)
        .log_access(custom_access_log);

    hello_world_resource hwr;
    ws.register_resource("/hello", &hwr);
    ws.start(true);

    return 0;
}

To test the above example, you can run the following command from a terminal:

curl -XGET -v http://localhost:8080/hello

You'll notice how, on the terminal runing your server, the logs will now be printed in output for each request received.

You can also check this example on github.

TLS/HTTPS

  • .use_ssl() and .no_ssl(): Determines whether to run in HTTPS-mode or not. If you set this as on and libhttpserver was compiled without SSL support, the library will throw an exception at start of the server. off by default.
  • .cred_type(const http::http_utils::cred_type_T& cred_type): Daemon credentials type. Either certificate or anonymous. Acceptable values are:
    • NONE: No credentials.
    • CERTIFICATE: Certificate credential.
    • ANON: Anonymous credential.
    • SRP: SRP credential.
    • PSK: PSK credential.
    • IA: IA credential.
  • .https_mem_key(const std::string& filename): String representing the path to a file containing the private key to be used by the HTTPS daemon. This must be used in conjunction with https_mem_cert.
  • .https_mem_cert(const std::string& filename): String representing the path to a file containing the certificate to be used by the HTTPS daemon. This must be used in conjunction with https_mem_key.
  • .https_mem_trust(const std::string& filename): String representing the path to a file containing the CA certificate to be used by the HTTPS daemon to authenticate and trust clients certificates. The presence of this option activates the request of certificate to the client. The request to the client is marked optional, and it is the responsibility of the server to check the presence of the certificate if needed. Note that most browsers will only present a client certificate only if they have one matching the specified CA, not sending any certificate otherwise.
  • .https_priorities(const std::string& priority_string): SSL/TLS protocol version and ciphers. Must be followed by a string specifying the SSL/TLS protocol versions and ciphers that are acceptable for the application. The string is passed unchanged to gnutls_priority_init. If this option is not specified, "NORMAL" is used.

Minimal example using HTTPS

#include <httpserver.hpp>

using namespace httpserver;

class hello_world_resource : public http_resource {
public:
    const std::shared_ptr<http_response> render(const http_request&) {
        return std::shared_ptr<http_response>(new string_response("Hello, World!"));
    }
};

int main(int argc, char** argv) {
    webserver ws = create_webserver(8080)
        .use_ssl()
        .https_mem_key("key.pem")
        .https_mem_cert("cert.pem");

    hello_world_resource hwr;
    ws.register_resource("/hello", &hwr);
    ws.start(true);

    return 0;
}

To test the above example, you can run the following command from a terminal:

curl -XGET -v -k 'https://localhost:8080/hello'

You can also check this example on github.

IP Blacklisting/Whitelisting

libhttpserver supports IP blacklisting and whitelisting as an internal feature. This section explains the startup options related with IP blacklisting/whitelisting. See the specific section to read more about the topic.

  • .ban_system() and .no_ban_system: Can be used to enable/disable the ban system. on by default.
  • .default_policy(const http::http_utils::policy_T& default_policy): Specifies what should be the default behavior when receiving a request. Possible values are ACCEPT and REJECT. Default is ACCEPT.

Authentication Parameters

  • .basic_auth() and .no_basic_auth: Can be used to enable/disable parsing of the basic authorization header sent by the client. on by default.
  • .digest_auth() and .no_digest_auth: Can be used to enable/disable parsing of the digested authentication data sent by the client. on by default.
  • .nonce_nc_size(int nonce_size): Size of an array of nonce and nonce counter map. This option represents the size (number of elements) of a map of a nonce and a nonce-counter. If this option is not specified, a default value of 4 will be used (which might be too small for servers handling many requests). You should calculate the value of NC_SIZE based on the number of connections per second multiplied by your expected session duration plus a factor of about two for hash table collisions. For example, if you expect 100 digest-authenticated connections per second and the average user to stay on your site for 5 minutes, then you likely need a value of about 60000. On the other hand, if you can only expect only 10 digest-authenticated connections per second, tolerate browsers getting a fresh nonce for each request and expect a HTTP request latency of 250 ms, then a value of about 5 should be fine.
  • .digest_auth_random(const std::string& nonce_seed): Digest Authentication nonce’s seed. For security, you SHOULD provide a fresh random nonce when actually using Digest Authentication with libhttpserver in production.

Examples of chaining syntax to create a webserver

webserver ws = create_webserver(8080)
    .no_ssl()
    .no_ipv6()
    .no_debug()
    .no_pedantic()
    .no_basic_auth()
    .no_digest_auth()
    .no_comet()
    .no_regex_checking()
    .no_ban_system()
    .no_post_process();
webserver ws = create_webserver(8080)
    .use_ssl()
    .https_mem_key("key.pem")
    .https_mem_cert("cert.pem");

Starting and stopping a webserver

Once a webserver is created, you can manage its execution through the following methods on the webserver class:

  • void webserver::start(bool blocking): Allows to start a server. If the blocking flag is passed as true, it will block the execution of the current thread until a call to stop on the same webserver object is performed.
  • void webserver::stop(): Allows to stop a server. It immediately stops it.
  • bool webserver::is_running(): Checks if a server is running
  • void webserver::sweet_kill(): Allows to stop a server. It doesn't guarantee an immediate halt to allow for thread termination and connection closure.

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The Resource Object

The http_resource class represents a logical collection of HTTP methods that will be associated to a URL when registered on the webserver. The class is designed for extension and it is where most of your code should ideally live. When the webserver matches a request against a resource (see: resource registration), the method correspondent to the one in the request (GET, POST, etc..) (see below) is called on the resource.

Given this, the http_resource class contains the following extensible methods (also called handlers or render methods):

  • const std::shared_ptr http_resource::render_GET(const http_request& req): Invoked on an HTTP GET request.
  • const std::shared_ptr http_resource::render_POST(const http_request& req): Invoked on an HTTP POST request.
  • const std::shared_ptr http_resource::render_PUT(const http_request& req): Invoked on an HTTP PUT request.
  • const std::shared_ptr http_resource::render_HEAD(const http_request& req): Invoked on an HTTP HEAD request.
  • const std::shared_ptr http_resource::render_DELETE(const http_request& req): Invoked on an HTTP DELETE request.
  • const std::shared_ptr http_resource::render_TRACE(const http_request& req): Invoked on an HTTP TRACE request.
  • const std::shared_ptr http_resource::render_OPTIONS(const http_request& req): Invoked on an HTTP OPTIONS request.
  • const std::shared_ptr http_resource::render_CONNECT(const http_request& req): Invoked on an HTTP CONNECT request.
  • const std::shared_ptr http_resource::render(const http_request& req): Invoked as a backup method if the matching method is not implemented. It can be used whenever you want all the invocations on a URL to activate the same behavior regardless of the HTTP method requested. The default implementation of the render method returns an empty response with a 404.

Example of implementation of render methods

#include <httpserver.hpp>

using namespace httpserver;

class hello_world_resource : public http_resource {
public:
    const std::shared_ptr<http_response> render_GET(const http_request&) {
        return std::shared_ptr<http_response>(new string_response("GET: Hello, World!"));
    }

    const std::shared_ptr<http_response> render(const http_request&) {
        return std::shared_ptr<http_response>(new string_response("OTHER: Hello, World!"));
    }
};

int main(int argc, char** argv) {
    webserver ws = create_webserver(8080);

    hello_world_resource hwr;
    ws.register_resource("/hello", &hwr);
    ws.start(true);

    return 0;
}

To test the above example, you can run the following commands from a terminal:

  • curl -XGET -v http://localhost:8080/hello: will return GET: Hello, World!.
  • curl -XPOST -v http://localhost:8080/hello: will return OTHER: Hello, World!. You can try requesting other methods beside POST to verify how the same message will be returned.

You can also check this example on github.

Allowing and disallowing methods on a resource

By default, all methods an a resource are allowed, meaning that an HTTP request with that method will be invoked. It is possible to mark methods as not allowed on a resource. When a method not allowed is requested on a resource, the default method_not_allowed method is invoked - the default can be overriden as explain in the section [Custom defaulted error messages](custom-defaulted-error-messages). The base http_resource class has a set of methods that can be used to allow and disallow HTTP methods.

  • void http_resource::set_allowing(const std::string& method, bool allowed): Used to allow or disallow a method. The method parameter is a string representing an HTTP method (GET, POST, PUT, etc...).
  • void http_resource::allow_all(): Marks all HTTP methods as allowed.
  • void http_resource::disallow_all(): Marks all HTTP methods as not allowed.

Example of methods allowed/disallowed

  #include <httpserver.hpp>

  using namespace httpserver;

  class hello_world_resource : public http_resource {
  public:
      const std::shared_ptr<http_response> render(const http_request&) {
          return std::shared_ptr<http_response>(new string_response("Hello, World!"));
      }
  };

  int main(int argc, char** argv) {
      webserver ws = create_webserver(8080);

      hello_world_resource hwr;
      hwr.disallow_all();
      hwr.set_allowing("GET", true);
      ws.register_resource("/hello", &hwr);
      ws.start(true);

      return 0;
  }

To test the above example, you can run the following command from a terminal:

curl -XGET -v http://localhost:8080/hello

If you try to run the following command, you'll see a method_not_allowed error:

  • curl -XPOST -v http://localhost:8080/hello.

You can also check this example on github.

Back to TOC

Registering resources

Once you have created your resource and extended its methods, you'll have to register the resource on the webserver. Registering a resource will associate it with an endpoint and allows the webserver to route it. The webserver class offers a method to register a resource:

  • bool register_resource(const std::string& endpoint, http_resource* resource, bool family = false): Registers the resource to an endpoint. The endpoint is a string representing the path on your webserver from where you want your resource to be served from (e.g. "/path/to/resource"). The optional family parameter allows to register a resource as a "family" resource that will match any path nested into the one specified. For example, if family is set to true and endpoint is set to "/path", the webserver will route to the resource not only the requests against "/path" but also everything in its nested path "/path/on/the/previous/one".

Specifying endpoints

There are essentially four ways to specify an endpoint string:

  • A simple path (e.g. "/path/to/resource"). In this case, the webserver will try to match exactly the value of the endpoint.
  • A regular exception. In this case, the webserver will try to match the URL of the request with the regex passed. For example, if passing "/path/as/decimal/[0-9]+, requests on URLs like "/path/as/decimal/5" or "/path/as/decimal/42" will be matched; instead, URLs like "/path/as/decimal/three" will not.
  • A parametrized path. (e.g. "/path/to/resource/with/{arg1}/{arg2}/in/url"). In this case, the webserver will match the argument with any value passed. In addition to this, the arguments will be passed to the resource as part of the arguments (readable from the http_request::get_arg method - see here). For example, if passing "/path/to/resource/with/{arg1}/{arg2}/in/url" will match any request on URL with any value in place of {arg1} and {arg2}.
  • A parametrized path with custom parameters. This is the same of a normal parametrized path, but allows to specify a regular expression for the argument (e.g. "/path/to/resource/with/{arg1|[0-9]+}/{arg2|[a-z]+}/in/url". In this case, the webserver will match the arguments with any value passed that satisfies the regex. In addition to this, as above, the arguments will be passed to the resource as part of the arguments (readable from the http_request::get_arg method - see here). For example, if passing "/path/to/resource/with/{arg1|[0-9]+}/{arg2|[a-z]+}/in/url" will match requests on URLs like "/path/to/resource/with/10/AA/in/url" but not like ""/path/to/resource/with/BB/10/in/url""
  • Any of the above marked as family. Will match any request on URLs having path that is prefixed by the path passed. For example, if family is set to true and endpoint is set to "/path", the webserver will route to the resource not only the requests against "/path" but also everything in its nested path "/path/on/the/previous/one".

    #include

    using namespace httpserver;

    class hello_world_resource : public http_resource { public: const std::shared_ptr render(const http_request&) { return std::shared_ptr(new string_response("Hello, World!")); } };

    class handling_multiple_resource : public http_resource { public: const std::shared_ptr render(const http_request& req) { return std::shared_ptr(new string_response("Your URL: " + req.get_path())); } };

    class url_args_resource : public http_resource { public: const std::shared_ptr render(const http_request& req) { return std::shared_ptr(new string_response("ARGS: " + req.get_arg("arg1") + " and " + req.get_arg("arg2"))); } };

    int main(int argc, char** argv) { webserver ws = create_webserver(8080);

      hello_world_resource hwr;
      ws.register_resource("/hello", &hwr);
    
      handling_multiple_resource hmr;
      ws.register_resource("/family", &hmr, true);
      ws.register_resource("/with_regex_[0-9]+", &hmr);
    
      url_args_resource uar;
      ws.register_resource("/url/with/{arg1}/and/{arg2}", &uar);
      ws.register_resource("/url/with/parametric/args/{arg1|[0-9]+}/and/{arg2|[A-Z]+}", &uar);
    
      ws.start(true);
    
      return 0;
    

    }

To test the above example, you can run the following commands from a terminal:

  • curl -XGET -v http://localhost:8080/hello: will return the Hello, World! message.
  • curl -XGET -v http://localhost:8080/family: will return the Your URL: /family message.
  • curl -XGET -v http://localhost:8080/family/with/suffix: will return the Your URL: /family/with/suffix message.
  • curl -XGET -v http://localhost:8080/with_regex_10: will return the Your URL: /with_regex_10 message.
  • curl -XGET -v http://localhost:8080/url/with/AA/and/BB: will return the ARGS: AA and BB message. You can change AA and BB with any value and observe how the URL is still matched and parameters are read.
  • curl -XGET -v http://localhost:8080/url/with/parametric/args/10/and/AA: will return the ARGS: 10 and AA message. You can change 10 and AA with any value matching the regexes and observe how the URL is still matched and parameters are read.

Conversely, you can observe how these URL will not be matched (al the following will give you a not found message):

  • curl -XGET -v http://localhost:8080/with_regex_A
  • curl -XGET -v http://localhost:8080/url/with/parametric/args/AA/and/BB

You can also check this example on github.

Back to TOC

Parsing requests

As seen in the documentation of http_resource, every extensible method takes in input a http_request object. The webserver takes the responsibility to extract the data from the HTTP request on the network and does all the heavy lifting to build the instance of http_request.

The http_request class has a set of methods you will have access to when implementing your handlers:

  • const std::string& get_path() const: Returns the path as requested from the HTTP client.
  • const std::vector<std::string>& get_path_pieces() const: Returns the components of the path requested by the HTTP client (each piece of the path split by '/'.
  • const std::string& get_path_piece(int index) const: Returns one piece of the path requested by the HTTP client. The piece is selected through the index parameter (0-indexed).
  • const std::string& get_method() const: Returns the method requested by the HTTP client.
  • const std::string get_header(const std::string& key) const: Returns the header with name equal to key if present in the HTTP request. Returns an empty string otherwise.
  • const std::string get_cookie(const std::string& key) const: Returns the cookie with name equal to key if present in the HTTP request. Returns an empty string otherwise.
  • const std::string get_footer(const std::string& key) const: Returns the footer with name equal to key if present in the HTTP request (only for http 1.1 chunked encodings). Returns an empty string otherwise.
  • const std::string get_arg(const std::string& key) const: Returns the argument with name equal to key if present in the HTTP request. Arguments can be (1) querystring parameters, (2) path argument (in case of parametric endpoint, (3) parameters parsed from the HTTP request body if the body is in application/x-www-form-urlencoded or multipart/form-data formats and the postprocessor is enabled in the webserver (enabled by default).
  • const std::map get_headers() const: Returns a map containing all the headers present in the HTTP request.
  • const std::map get_cookies() const: Returns a map containing all the cookies present in the HTTP request.
  • const std::map get_footers() const: Returns a map containing all the footers present in the HTTP request (only for http 1.1 chunked encodings).
  • const std::map get_args() const: Returns all the arguments present in the HTTP request. Arguments can be (1) querystring parameters, (2) path argument (in case of parametric endpoint, (3) parameters parsed from the HTTP request body if the body is in application/x-www-form-urlencoded or multipart/form-data formats and the postprocessor is enabled in the webserver (enabled by default).
  • const std::string& get_content() const: Returns the body of the HTTP request.
  • bool content_too_large() const: Returns true if the body length of the HTTP request sent by the client is longer than the max allowed on the server.
  • const std::string get_querystring() const: Returns the querystring of the HTTP request.
  • const std::string& get_version() const: Returns the HTTP version of the client request.
  • const std::string get_requestor() const: Returns the IP from which the client is sending the request.
  • unsigned short get_requestor_port() const: Returns the port from which the client is sending the request.
  • const std::string get_user() const: Returns the user as self-identified through basic authentication. The content of the user header will be parsed only if basic authentication is enabled on the server (enabled by default).
  • const std::string get_pass() const: Returns the password as self-identified through basic authentication. The content of the password header will be parsed only if basic authentication is enabled on the server (enabled by default).
  • const std::string get_digested_user() const: Returns the digested user as self-identified through digest authentication. The content of the user header will be parsed only if digest authentication is enabled on the server (enabled by default).
  • bool check_digest_auth(const std::string& realm, const std::string& password, int nonce_timeout, bool& reload_nonce) const: Allows to check the validity of the authentication token sent through digest authentication (if the provided values in the WWW-Authenticate header are valid and sound according to RFC2716). Takes in input the realm of validity of the authentication, the password as known to the server to compare against, the nonce_timeout to indicate how long the nonce is valid and reload_nonce a boolean that will be set by the method to indicate a nonce being reloaded. The method returns true if the authentication is valid, false otherwise.

Example of handler reading arguments from a request

#include <httpserver.hpp>

using namespace httpserver;

class hello_world_resource : public http_resource {
public:
    const std::shared_ptr<http_response> render(const http_request& req) {
        return std::shared_ptr<http_response>(new string_response("Hello: " + req.get_arg("name")));
    }
};

int main(int argc, char** argv) {
    webserver ws = create_webserver(8080);

    hello_world_resource hwr;
    ws.register_resource("/hello", &hwr);
    ws.start(true);

    return 0;
}

To test the above example, you can run the following command from a terminal:

curl -XGET -v "http://localhost:8080/hello?name=John"

You will receive the message Hello: John in reply. Given that the body post processing is enabled, you can also run curl -d "name=John" -X POST http://localhost:8080/hello to obtain the same result.

You can also check this example on github.

Back to TOC

Building responses to requests

As seen in the documentation of http_resource, every extensible method returns in output a http_response object. The webserver takes the responsibility to convert the http_response object you create into a response on the network.

There are 5 types of response that you can create - we will describe them here through their constructors:

  • string_response(const std::string& content, int response_code = 200, const std::string& content_type = "text/plain"): The most basic type of response. It uses the content string passed in construction as body of the HTTP response. The other two optional parameters are the response_code and the content_type. You can find constant definition for the various response codes within the http_utils library file.
  • file_response(const std::string& filename, int response_code = 200, const std::string& content_type = "text/plain"): Uses the filename passed in construction as pointer to a file on disk. The body of the HTTP response will be set using the content of the file. The other two optional parameters are the response_code and the content_type. You can find constant definition for the various response codes within the http_utils library file.
  • basic_auth_fail_response(const std::string& content, const std::string& realm = "", int response_code = 200, const std::string& content_type = "text/plain"): A response in return to a failure during basic authentication. It allows to specify a content string as a message to send back to the client. The realm parameter should contain your realm of authentication (if any). The other two optional parameters are the response_code and the content_type. You can find constant definition for the various response codes within the http_utils library file.
  • digest_auth_fail_response(const std::string& content, const std::string& realm = "", const std::string& opaque = "", bool reload_nonce = false, int response_code = 200, const std::string& content_type = "text/plain"): A response in return to a failure during digest authentication. It allows to specify a content string as a message to send back to the client. The realm parameter should contain your realm of authentication (if any). The opaque represents a value that gets passed to the client and expected to be passed again to the server as-is. This value can be a hexadecimal or base64 string. The reload_nonce parameter tells the server to reload the nonce (you should use the value returned by the check_digest_auth method on the http_request. The other two optional parameters are the response_code and the content_type. You can find constant definition for the various response codes within the http_utils library file.
  • deferred_response(ssize_t(*cycle_callback_ptr)(shared_ptr<T>, char*, size_t) cycle_callback, const std::string& content = "", int response_code = 200, const std::string& content_type = "text/plain"): A response that obtains additional content from a callback executed in a deferred way. It leaves the client in pending state (returning a 100 CONTINUE message) and suspends the connection. Besides the callback, optionally, you can provide a content parameter that sets the initial message sent immediately to the client. The other two optional parameters are the response_code and the content_type. You can find constant definition for the various response codes within the http_utils library file. To use deferred_response you need to have the deferred option active on your webserver (enabled by default).
    • The cycle_callback_ptr has this shape: ssize_t cycle_callback(shared_ptr<T> closure_data, char* buf, size_t max_size). You are supposed to implement a function in this shape and provide it to the deferred_repsonse method. The webserver will provide a char* to the function. It is responsibility of the function to allocate it and fill its content. The method is supposed to respect the max_size parameter passed in input. The function must return a ssize_t value representing the actual size you filled the buf with. Any value different from -1 will keep the resume the connection, deliver the content and suspend it again (with a 100 CONTINUE). If the method returns -1, the webserver will complete the communication with the client and close the connection. You can also pass a shared_ptr pointing to a data object of your choice (this will be templetized with a class of your choice). The server will guarantee that this object is passed at each invocation of the method allowing the client code to use it as a memory buffer during computation.

Setting additional properties of the response

The http_response class offers an additional set of methods to "decorate" your responses. This set of methods is:

  • void with_header(const std::string& key, const std::string& value): Sets an HTTP header with name set to key and value set to value.
  • void with_footer(const std::string& key, const std::string& value): Sets an HTTP footer with name set to key and value set to value.
  • void with_cookie(const std::string& key, const std::string& value): Sets an HTTP cookie with name set to key and value set to value (only for http 1.1 chunked encodings).
  • void shoutCAST(): Mark the response as a shoutCAST one.

Example of response setting headers

#include <httpserver.hpp>

using namespace httpserver;

class hello_world_resource : public http_resource {
public:
    const std::shared_ptr<http_response> render(const http_request&) {
        std::shared_ptr<http_response> response = std::shared_ptr<http_response>(new string_response("Hello, World!"));
        response->with_header("MyHeader", "MyValue");
        return response;
    }
};

int main(int argc, char** argv) {
    webserver ws = create_webserver(8080);

    hello_world_resource hwr;
    ws.register_resource("/hello", &hwr);
    ws.start(true);

    return 0;
}

To test the above example, you could run the following command from a terminal:

curl -XGET -v "http://localhost:8080/hello"

You will receive the message custom header in reply.

You can also check this example on github.

Back to TOC

IP Blacklisting and Whitelisting

libhttpserver provides natively a system to blacklist and whitelist IP addresses. To enable/disable the system, it is possible to use the ban_system and no_ban_system methods on the create_webserver class. In the same way, you can specify what you want to be your "default behavior" (allow by default or disallow by default) by using the default_policy method (see here).

The system supports both IPV4 and IPV6 and manages them transparently. The only requirement is for ipv6 to be enabled on your server - you'll have to enable this by using the use_ipv6 method on create_webserver.

You can explicitly ban or allow an IP address using the following methods on the webserver class:

  • void ban_ip(const std::string& ip): Adds one IP (or a range of IPs) to the list of the banned ones. Takes in input a string that contains the IP (or range of IPs) to ban. To use when the default_policy is ACCEPT.
  • void allow_ip(const std::string& ip): Adds one IP (or a range of IPs) to the list of the allowed ones. Takes in input a string that contains the IP (or range of IPs) to allow. To use when the default_policy is REJECT.
  • void unban_ip(const std::string& ip): Removes one IP (or a range of IPs) from the list of the banned ones. Takes in input a string that contains the IP (or range of IPs) to remove from the list. To use when the default_policy is REJECT.
  • void disallow_ip(const std::string& ip): Removes one IP (or a range of IPs) from the list of the allowed ones. Takes in input a string that contains the IP (or range of IPs) to remove from the list. To use when the default_policy is REJECT.

IP String Format

The IP string format can represent both IPV4 and IPV6. Addresses will be normalized by the webserver to operate in the same sapce. Any valid IPV4 or IPV6 textual representation works. It is also possible to specify ranges of IPs. To do so, omit the octect you want to express as a range and specify a '*' in its place. Examples of valid IPs include:

  • "192.168.5.5": standard IPV4
  • "192.168.*.*": range of IPV4 addresses. In the example, everything between 192.168.0.0 and 192.168.255.255.
  • "2001:db8:8714:3a90::12": standard IPV6 - clustered empty ranges are fully supported.
  • "2001:db8:8714:3a90:*:*": range of IPV6 addresses.
  • "::ffff:192.0.2.128": IPV4 IPs nested into IPV6.
  • "::192.0.2.128": IPV4 IPs nested into IPV6 (without 'ffff' prefix)
  • "::ffff:192.0.*.*": ranges of IPV4 IPs nested into IPV6.

Example of IP Whitelisting/Blacklisting

#include <httpserver.hpp>

using namespace httpserver;

class hello_world_resource : public http_resource {
public:
    const std::shared_ptr<http_response> render(const http_request&) {
        return std::shared_ptr<http_response>(new string_response("Hello, World!"));
    }
};

int main(int argc, char** argv) {
    webserver ws = create_webserver(8080)
        .default_policy(http::http_utils::REJECT);

    ws.allow_ip("127.0.0.1");

    hello_world_resource hwr;
    ws.register_resource("/hello", &hwr);
    ws.start(true);

    return 0;
}

To test the above example, you could run the following command from a terminal:

curl -XGET -v "http://localhost:8080/hello"

You can also check this example on github.

Back to TOC

Authentication

libhttpserver support three types of client authentication.

Basic authentication uses a simple authentication method based on BASE64 algorithm. Username and password are exchanged in clear between the client and the server, so this method must only be used for non-sensitive content or when the session is protected with https. When using basic authentication libhttpserver will have access to the clear password, possibly allowing to create a chained authentication toward an external authentication server. You can enable/disable support for Basic authentication through the basic_auth and no_basic_auth methods of the create_webserver class.

Digest authentication uses a one-way authentication method based on MD5 hash algorithm. Only the hash will transit over the network, hence protecting the user password. The nonce will prevent replay attacks. This method is appropriate for general use, especially when https is not used to encrypt the session. You can enable/disable support for Digest authentication through the digest_auth and no_digest_auth methods of the create_webserver class.

Client certificate authentication uses a X.509 certificate from the client. This is the strongest authentication mechanism but it requires the use of HTTPS. Client certificate authentication can be used simultaneously with Basic or Digest Authentication in order to provide a two levels authentication (like for instance separate machine and user authentication). You can enable/disable support for Certificate authentication through the use_ssl and no_ssl methods of the create_webserver class.

Using Basic Authentication

#include <httpserver.hpp>

using namespace httpserver;

class user_pass_resource : public httpserver::http_resource {
public:
    const std::shared_ptr<http_response> render_GET(const http_request& req) {
        if (req.get_user() != "myuser" || req.get_pass() != "mypass") {
            return std::shared_ptr<basic_auth_fail_response>(new basic_auth_fail_response("FAIL", "test@example.com"));
        }
        return std::shared_ptr<string_response>(new string_response(req.get_user() + " " + req.get_pass(), 200, "text/plain"));
    }
};

int main(int argc, char** argv) {
    webserver ws = create_webserver(8080);

    user_pass_resource hwr;
    ws.register_resource("/hello", &hwr);
    ws.start(true);

    return 0;
}

To test the above example, you can run the following command from a terminal:

curl -XGET -v -u myuser:mypass "http://localhost:8080/hello"

You will receive back the user and password you passed in input. Try to pass the wrong credentials to see the failure.

You can also check this example on github.

Using Digest Authentication

#include <httpserver.hpp>

#define MY_OPAQUE "11733b200778ce33060f31c9af70a870ba96ddd4"

using namespace httpserver;

class digest_resource : public httpserver::http_resource {
public:
    const std::shared_ptr<http_response> render_GET(const http_request& req) {
        if (req.get_digested_user() == "") {
            return std::shared_ptr<digest_auth_fail_response>(new digest_auth_fail_response("FAIL", "test@example.com", MY_OPAQUE, true));
        }
        else {
            bool reload_nonce = false;
            if(!req.check_digest_auth("test@example.com", "mypass", 300, reload_nonce)) {
                return std::shared_ptr<digest_auth_fail_response>(new digest_auth_fail_response("FAIL", "test@example.com", MY_OPAQUE, reload_nonce));
            }
        }
        return std::shared_ptr<string_response>(new string_response("SUCCESS", 200, "text/plain"));
    }
};

int main(int argc, char** argv) {
    webserver ws = create_webserver(8080);

    digest_resource hwr;
    ws.register_resource("/hello", &hwr);
    ws.start(true);

    return 0;
}

To test the above example, you can run the following command from a terminal:

curl -XGET -v --digest --user myuser:mypass localhost:8080/hello

You will receive a SUCCESS in response (observe the response message from the server in detail and you'll see the full interaction). Try to pass the wrong credentials or send a request without digest active to see the failure.

You can also check this example on github.

Back to TOC

HTTP Utils

libhttpserver provides a set of constants to help you develop your HTTP server. It would be redudant to list them here; so, please, consult the list directly here.

Back to TOC

Other Examples

Example of returning a response from a file

#include <httpserver.hpp>

using namespace httpserver;

class file_response_resource : public http_resource {
public:
    const std::shared_ptr<http_response> render_GET(const http_request& req) {
        return std::shared_ptr<file_response>(new file_response("test_content", 200, "text/plain"));
    }
};

int main(int argc, char** argv) {
    webserver ws = create_webserver(8080);

    file_response_resource hwr;
    ws.register_resource("/hello", &hwr);
    ws.start(true);

    return 0;
}

To test the above example, you can run the following command from a terminal:

curl -XGET -v localhost:8080/hello

You can also check this example on github.

Example of a deferred response through callback

#include <httpserver.hpp>

using namespace httpserver;

static int counter = 0;

ssize_t test_callback (std::shared_ptr<void> closure_data, char* buf, size_t max) {
    if (counter == 2) {
        return -1;
    }
    else {
        memset(buf, 0, max);
        strcat(buf, " test ");
        counter++;
        return std::string(buf).size();
    }
}

class deferred_resource : public http_resource {
    public:
        const std::shared_ptr<http_response> render_GET(const http_request& req) {
            return std::shared_ptr<deferred_response<void> >(new deferred_response<void>(test_callback, nullptr, "cycle callback response"));
        }
};

int main(int argc, char** argv) {
    webserver ws = create_webserver(8080);

    deferred_resource hwr;
    ws.register_resource("/hello", &hwr);
    ws.start(true);

    return 0;
}

To test the above example, you can run the following command from a terminal:

curl -XGET -v localhost:8080/hello

You can also check this example on github.

Example of a deferred response through callback (passing additional data along)

#include <atomic>
#include <httpserver.hpp>

using namespace httpserver;

std::atomic<int> counter;

ssize_t test_callback (std::shared_ptr<std::atomic<int> > closure_data, char* buf, size_t max) {
    int reqid;
    if (closure_data == nullptr) {
        reqid = -1;
    } else {
        reqid = *closure_data;
    }

    // only first 5 connections can be established
    if (reqid >= 5) {
        return -1;
    } else {
        // respond corresponding request IDs to the clients
        std::string str = "";
        str += std::to_string(reqid) + " ";
        memset(buf, 0, max);
        std::copy(str.begin(), str.end(), buf);

        // keep sending reqid
        sleep(1);

        return (ssize_t)max;
    }
}

class deferred_resource : public http_resource {
    public:
        const std::shared_ptr<http_response> render_GET(const http_request& req) {
            std::shared_ptr<std::atomic<int> > closure_data(new std::atomic<int>(counter++));
            return std::shared_ptr<deferred_response<std::atomic<int> > >(new deferred_response<std::atomic<int> >(test_callback, closure_data, "cycle callback response"));
        }
};

int main(int argc, char** argv) {
    webserver ws = create_webserver(8080);

    deferred_resource hwr;
    ws.register_resource("/hello", &hwr);
    ws.start(true);

    return 0;
}

To test the above example, you can run the following command from a terminal:

curl -XGET -v localhost:8080/hello

You can also check this example on github.

Back to TOC

Copying

This manual is for libhttpserver, C++ library for creating an embedded Rest HTTP server (and more).

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled GNU Free Documentation License.

Back to TOC

GNU Lesser General Public License

Version 2.1, February 1999

Copyright © 1991, 1999 Free Software Foundation, Inc. 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.

This is the first released version of the Lesser GPL. It also counts as the successor of the GNU Library Public License, version 2, hence the version number 2.1.

Preamble

The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public Licenses are intended to guarantee your freedom to share and change free software--to make sure the software is free for all its users.

This license, the Lesser General Public License, applies to some specially designated software packages--typically libraries--of the Free Software Foundation and other authors who decide to use it. You can use it too, but we suggest you first think carefully about whether this license or the ordinary General Public License is the better strategy to use in any particular case, based on the explanations below.

When we speak of free software, we are referring to freedom of use, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish); that you receive source code or can get it if you want it; that you can change the software and use pieces of it in new free programs; and that you are informed that you can do these things.

To protect your rights, we need to make restrictions that forbid distributors to deny you these rights or to ask you to surrender these rights. These restrictions translate to certain responsibilities for you if you distribute copies of the library or if you modify it.

For example, if you distribute copies of the library, whether gratis or for a fee, you must give the recipients all the rights that we gave you. You must make sure that they, too, receive or can get the source code. If you link other code with the library, you must provide complete object files to the recipients, so that they can relink them with the library after making changes to the library and recompiling it. And you must show them these terms so they know their rights.

We protect your rights with a two-step method: (1) we copyright the library, and (2) we offer you this license, which gives you legal permission to copy, distribute and/or modify the library.

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How to Apply These Terms to Your New Libraries

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Also add information on how to contact you by electronic and paper mail.

You should also get your employer (if you work as a programmer) or your school, if any, to sign a “copyright disclaimer” for the library, if necessary. Here is a sample; alter the names:

Yoyodyne, Inc., hereby disclaims all copyright interest in the library `Frob' (a library for tweaking knobs) written by James Random Hacker.

, 1 April 1990 Ty Coon, President of Vice

That's all there is to it!

Back to TOC

GNU Free Documentation License

Version 1.3, 3 November 2008

Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc. <http://fsf.org/>

Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.

0. PREAMBLE

The purpose of this License is to make a manual, textbook, or other functional and useful document “free” in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.

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1. APPLICABILITY AND DEFINITIONS

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2. VERBATIM COPYING

You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3.

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3. COPYING IN QUANTITY

If you publish printed copies (or copies in media that commonly have printed covers) of the Document, numbering more than 100, and the Document's license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.

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It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document.

4. MODIFICATIONS

You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:

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  • E. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.
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  • G. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document's license notice.
  • H. Include an unaltered copy of this License.
  • I. Preserve the section Entitled “History”, Preserve its Title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section Entitled “History” in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence.
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  • K. For any section Entitled “Acknowledgements” or “Dedications”, Preserve the Title of the section, and preserve in the section all the substance and tone of each of the contributor acknowledgements and/or dedications given therein.
  • L. Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section numbers or the equivalent are not considered part of the section titles.
  • M. Delete any section Entitled “Endorsements”. Such a section may not be included in the Modified Version.
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  • O. Preserve any Warranty Disclaimers.

If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version's license notice. These titles must be distinct from any other section titles.

You may add a section Entitled “Endorsements”, provided it contains nothing but endorsements of your Modified Version by various parties--for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.

You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.

The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version.

5. COMBINING DOCUMENTS

You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice, and that you preserve all their Warranty Disclaimers.

The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.

In the combination, you must combine any sections Entitled “History” in the various original documents, forming one section Entitled “History”; likewise combine any sections Entitled “Acknowledgements”, and any sections Entitled “Dedications”. You must delete all sections Entitled “Endorsements”.

6. COLLECTIONS OF DOCUMENTS

You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.

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If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document's Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.

8. TRANSLATION

Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.

If a section in the Document is Entitled “Acknowledgements”, “Dedications”, or “History”, the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.

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You may not copy, modify, sublicense, or distribute the Document except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense, or distribute it is void, and will automatically terminate your rights under this License.

However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation.

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10. FUTURE REVISIONS OF THIS LICENSE

The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See <http://www.gnu.org/copyleft/>.

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An MMC is “eligible for relicensing” if it is licensed under this License, and if all works that were first published under this License somewhere other than this MMC, and subsequently incorporated in whole or in part into the MMC, (1) had no cover texts or invariant sections, and (2) were thus incorporated prior to November 1, 2008.

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ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:

Copyright (c)  YEAR  YOUR NAME.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3
or any later version published by the Free Software Foundation;
with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
A copy of the license is included in the section entitled &ldquo;GNU
Free Documentation License&rdquo;.

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the with...Texts. line with this:

with the Invariant Sections being LIST THEIR TITLES, with the
Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.

If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.

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Thanks

This library has been originally developed under the zencoders flags and this community has always supported me all along this work so I am happy to put the logo on this readme.

        When you see this tree, know that you've came across ZenCoders.org

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      connec  SELECT * FROM table mycnf acco desc and or selector::clas  at     
     openldap string  sys.   print "zenc der " { 'a':  `ls -l` >  appe &firs    
    import Tkinter    paste( $obh  &a or it myval  bro roll:  :: [] require a   
   case `` super. +y  <svg x="100">  expr    say " %rooms 1  --account fb- yy   
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 and    main (--) import loop $$ or  end onload  UNION WITH tab   timer 150 *2  
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cout << endl   public genera   #include "b ost   ::ac myna const cast<char*> mys
ac  size_t   return ran  int (*getNextValue)(void) ff   double sa_family_t famil
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       BEQ                   BNEQZ R1 10 ANDI R1 R2                  SYS        
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          BNE            BLTZAL R1 1 LUI 001 NOOP MULTU           SLLV          
            MOV R1     ADD R1 R2  JUMP  10 1001 BEQ R1 R2 1      ANDI            
               1101  1010001100  111 001 01  1010 101100 1001  100              
                 110110 100   0  01 101 01100 100 100 1000100011                
                    11101001001  00   11  100   11  10100010                    
                        000101001001 10  1001   101000101                       
                             010010010010110101001010

For further information: visit our website www.zencoders.org

Author: Sebastiano Merlino

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*Note that all licence references and agreements mentioned in the C++ library for creating an embedded Rest HTTP server README section above are relevant to that project's source code only.