A C++11 single-file header-only cross platform HTTP/HTTPS library.

It's extremely easy to setup. Just include the httplib.h file in your code!

NOTE: This is a multi-threaded 'blocking' HTTP library. If you are looking for a 'non-blocking' library, this is not the one that you want.

Programming language: C++
License: MIT License
Tags: Networking     HTTP     Server     Client    

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A C++11 single-file header-only cross platform HTTP/HTTPS library.

It's extremely easy to setup. Just include the httplib.h file in your code!

NOTE: This library uses 'blocking' socket I/O. If you are looking for a library with 'non-blocking' socket I/O, this is not the one that you want.

Simple examples

Server (Multi-threaded)
#include "path/to/httplib.h"

httplib::Server svr;

httplib::SSLServer svr;

svr.Get("/hi", [](const httplib::Request &, httplib::Response &res) {
  res.set_content("Hello World!", "text/plain");

svr.listen("", 8080);
#include "path/to/httplib.h"

httplib::Client cli("http://cpp-httplib-server.yhirose.repl.co");

httplib::Client cli("https://cpp-httplib-server.yhirose.repl.co");

auto res = cli.Get("/hi");

SSL Support

SSL support is available with CPPHTTPLIB_OPENSSL_SUPPORT. libssl and libcrypto should be linked.

NOTE: cpp-httplib currently supports only version 1.1.1 and 3.0.

#include "path/to/httplib.h"

// Server
httplib::SSLServer svr("./cert.pem", "./key.pem");

// Client
httplib::Client cli("https://localhost:1234"); // scheme + host
httplib::SSLClient cli("localhost:1234"); // host

// Use your CA bundle

// Disable cert verification

Note: When using SSL, it seems impossible to avoid SIGPIPE in all cases, since on some operating systems, SIGPIPE can only be suppressed on a per-message basis, but there is no way to make the OpenSSL library do so for its internal communications. If your program needs to avoid being terminated on SIGPIPE, the only fully general way might be to set up a signal handler for SIGPIPE to handle or ignore it yourself.


#include <httplib.h>

int main(void)
  using namespace httplib;

  Server svr;

  svr.Get("/hi", [](const Request& req, Response& res) {
    res.set_content("Hello World!", "text/plain");

  svr.Get(R"(/numbers/(\d+))", [&](const Request& req, Response& res) {
    auto numbers = req.matches[1];
    res.set_content(numbers, "text/plain");

  svr.Get("/body-header-param", [](const Request& req, Response& res) {
    if (req.has_header("Content-Length")) {
      auto val = req.get_header_value("Content-Length");
    if (req.has_param("key")) {
      auto val = req.get_param_value("key");
    res.set_content(req.body, "text/plain");

  svr.Get("/stop", [&](const Request& req, Response& res) {

  svr.listen("localhost", 1234);

Post, Put, Delete and Options methods are also supported.

Bind a socket to multiple interfaces and any available port

int port = svr.bind_to_any_port("");

Static File Server

// Mount / to ./www directory
auto ret = svr.set_mount_point("/", "./www");
if (!ret) {
  // The specified base directory doesn't exist...

// Mount /public to ./www directory
ret = svr.set_mount_point("/public", "./www");

// Mount /public to ./www1 and ./www2 directories
ret = svr.set_mount_point("/public", "./www1"); // 1st order to search
ret = svr.set_mount_point("/public", "./www2"); // 2nd order to search

// Remove mount /
ret = svr.remove_mount_point("/");

// Remove mount /public
ret = svr.remove_mount_point("/public");
// User defined file extension and MIME type mappings
svr.set_file_extension_and_mimetype_mapping("cc", "text/x-c");
svr.set_file_extension_and_mimetype_mapping("cpp", "text/x-c");
svr.set_file_extension_and_mimetype_mapping("hh", "text/x-h");

The followings are built-in mappings:

Extension MIME Type Extension MIME Type
css text/css mpga audio/mpeg
csv text/csv weba audio/webm
txt text/plain wav audio/wave
vtt text/vtt otf font/otf
html, htm text/html ttf font/ttf
apng image/apng woff font/woff
avif image/avif woff2 font/woff2
bmp image/bmp 7z application/x-7z-compressed
gif image/gif atom application/atom+xml
png image/png pdf application/pdf
svg image/svg+xml mjs, js application/javascript
webp image/webp json application/json
ico image/x-icon rss application/rss+xml
tif image/tiff tar application/x-tar
tiff image/tiff xhtml, xht application/xhtml+xml
jpeg, jpg image/jpeg xslt application/xslt+xml
mp4 video/mp4 xml application/xml
mpeg video/mpeg gz application/gzip
webm video/webm zip application/zip
mp3 audio/mp3 wasm application/wasm

File request handler

// The handler is called right before the response is sent to a client
svr.set_file_request_handler([](const Request &req, Response &res) {

NOTE: These static file server methods are not thread-safe.


svr.set_logger([](const auto& req, const auto& res) {
  your_logger(req, res);

Error handler

svr.set_error_handler([](const auto& req, auto& res) {
  auto fmt = "<p>Error Status: <span style='color:red;'>%d</span></p>";
  char buf[BUFSIZ];
  snprintf(buf, sizeof(buf), fmt, res.status);
  res.set_content(buf, "text/html");

Exception handler

The exception handler gets called if a user routing handler throws an error.

svr.set_exception_handler([](const auto& req, auto& res, std::exception_ptr ep) {
  auto fmt = "<h1>Error 500</h1><p>%s</p>";
  char buf[BUFSIZ];
  try {
  } catch (std::exception &e) {
    snprintf(buf, sizeof(buf), fmt, e.what());
  } catch (...) { // See the following NOTE
    snprintf(buf, sizeof(buf), fmt, "Unknown Exception");
  res.set_content(buf, "text/html");
  res.status = 500;

NOTE: if you don't provide the catch (...) block for a rethrown exception pointer, an uncaught exception will end up causing the server crash. Be careful!

Pre routing handler

svr.set_pre_routing_handler([](const auto& req, auto& res) {
  if (req.path == "/hello") {
    res.set_content("world", "text/html");
    return Server::HandlerResponse::Handled;
  return Server::HandlerResponse::Unhandled;

Post routing handler

svr.set_post_routing_handler([](const auto& req, auto& res) {
  res.set_header("ADDITIONAL_HEADER", "value");

'multipart/form-data' POST data

svr.Post("/multipart", [&](const auto& req, auto& res) {
  auto size = req.files.size();
  auto ret = req.has_file("name1");
  const auto& file = req.get_file_value("name1");
  // file.filename;
  // file.content_type;
  // file.content;

Receive content with a content receiver

  [&](const Request &req, Response &res, const ContentReader &content_reader) {
    if (req.is_multipart_form_data()) {
      // NOTE: `content_reader` is blocking until every form data field is read
      MultipartFormDataItems files;
        [&](const MultipartFormData &file) {
          return true;
        [&](const char *data, size_t data_length) {
          files.back().content.append(data, data_length);
          return true;
    } else {
      std::string body;
      content_reader([&](const char *data, size_t data_length) {
        body.append(data, data_length);
        return true;

Send content with the content provider

const size_t DATA_CHUNK_SIZE = 4;

svr.Get("/stream", [&](const Request &req, Response &res) {
  auto data = new std::string("abcdefg");

    data->size(), // Content length
    "text/plain", // Content type
    [data](size_t offset, size_t length, DataSink &sink) {
      const auto &d = *data;
      sink.write(&d[offset], std::min(length, DATA_CHUNK_SIZE));
      return true; // return 'false' if you want to cancel the process.
    [data](bool success) { delete data; });

Without content length:

svr.Get("/stream", [&](const Request &req, Response &res) {
    "text/plain", // Content type
    [&](size_t offset, DataSink &sink) {
      if (/* there is still data */) {
        std::vector<char> data;
        // prepare data...
        sink.write(data.data(), data.size());
      } else {
        sink.done(); // No more data
      return true; // return 'false' if you want to cancel the process.

Chunked transfer encoding

svr.Get("/chunked", [&](const Request& req, Response& res) {
    [](size_t offset, DataSink &sink) {
      sink.write("123", 3);
      sink.write("345", 3);
      sink.write("789", 3);
      sink.done(); // No more data
      return true; // return 'false' if you want to cancel the process.

'Expect: 100-continue' handler

By default, the server sends a 100 Continue response for an Expect: 100-continue header.

// Send a '417 Expectation Failed' response.
svr.set_expect_100_continue_handler([](const Request &req, Response &res) {
  return 417;
// Send a final status without reading the message body.
svr.set_expect_100_continue_handler([](const Request &req, Response &res) {
  return res.status = 401;

Keep-Alive connection

svr.set_keep_alive_max_count(2); // Default is 5
svr.set_keep_alive_timeout(10);  // Default is 5


svr.set_read_timeout(5, 0); // 5 seconds
svr.set_write_timeout(5, 0); // 5 seconds
svr.set_idle_interval(0, 100000); // 100 milliseconds

Set maximum payload length for reading a request body

svr.set_payload_max_length(1024 * 1024 * 512); // 512MB

Server-Sent Events

Please see Server example and Client example.

Default thread pool support

ThreadPool is used as a default task queue, and the default thread count is 8, or std::thread::hardware_concurrency(). You can change it with CPPHTTPLIB_THREAD_POOL_COUNT.

If you want to set the thread count at runtime, there is no convenient way... But here is how.

svr.new_task_queue = [] { return new ThreadPool(12); };

Override the default thread pool with yours

You can supply your own thread pool implementation according to your need.

class YourThreadPoolTaskQueue : public TaskQueue {
  YourThreadPoolTaskQueue(size_t n) {

  virtual void enqueue(std::function<void()> fn) override {

  virtual void shutdown() override {

  YourThreadPool pool_;

svr.new_task_queue = [] {
  return new YourThreadPoolTaskQueue(12);


#include <httplib.h>
#include <iostream>

int main(void)
  httplib::Client cli("localhost", 1234);

  if (auto res = cli.Get("/hi")) {
    if (res->status == 200) {
      std::cout << res->body << std::endl;
  } else {
    auto err = res.error();
    std::cout << "HTTP error: " << httplib::to_string(err) << std::endl;

NOTE: Constructor with scheme-host-port string is now supported!

httplib::Client cli("localhost");
httplib::Client cli("localhost:8080");
httplib::Client cli("http://localhost");
httplib::Client cli("http://localhost:8080");
httplib::Client cli("https://localhost");
httplib::SSLClient cli("localhost");

Error code

Here is the list of errors from Result::error().

enum Error {
  Success = 0,

GET with HTTP headers

httplib::Headers headers = {
  { "Accept-Encoding", "gzip, deflate" }
auto res = cli.Get("/hi", headers);


  { "Accept-Encoding", "gzip, deflate" }
auto res = cli.Get("/hi");


res = cli.Post("/post", "text", "text/plain");
res = cli.Post("/person", "name=john1&note=coder", "application/x-www-form-urlencoded");

POST with parameters

httplib::Params params;
params.emplace("name", "john");
params.emplace("note", "coder");

auto res = cli.Post("/post", params);


httplib::Params params{
  { "name", "john" },
  { "note", "coder" }

auto res = cli.Post("/post", params);

POST with Multipart Form Data

httplib::MultipartFormDataItems items = {
  { "text1", "text default", "", "" },
  { "text2", "aωb", "", "" },
  { "file1", "h\ne\n\nl\nl\no\n", "hello.txt", "text/plain" },
  { "file2", "{\n  \"world\", true\n}\n", "world.json", "application/json" },
  { "file3", "", "", "application/octet-stream" },

auto res = cli.Post("/multipart", items);


res = cli.Put("/resource/foo", "text", "text/plain");


res = cli.Delete("/resource/foo");


res = cli.Options("*");
res = cli.Options("/resource/foo");


cli.set_connection_timeout(0, 300000); // 300 milliseconds
cli.set_read_timeout(5, 0); // 5 seconds
cli.set_write_timeout(5, 0); // 5 seconds

Receive content with a content receiver

std::string body;

auto res = cli.Get("/large-data",
  [&](const char *data, size_t data_length) {
    body.append(data, data_length);
    return true;
std::string body;

auto res = cli.Get(
  "/stream", Headers(),
  [&](const Response &response) {
    EXPECT_EQ(200, response.status);
    return true; // return 'false' if you want to cancel the request.
  [&](const char *data, size_t data_length) {
    body.append(data, data_length);
    return true; // return 'false' if you want to cancel the request.

Send content with a content provider

std::string body = ...;

auto res = cli.Post(
  "/stream", body.size(),
  [](size_t offset, size_t length, DataSink &sink) {
    sink.write(body.data() + offset, length);
    return true; // return 'false' if you want to cancel the request.

Chunked transfer encoding

auto res = cli.Post(
  [](size_t offset, DataSink &sink) {
    sink.os << "chunked data 1";
    sink.os << "chunked data 2";
    sink.os << "chunked data 3";
    return true; // return 'false' if you want to cancel the request.

With Progress Callback

httplib::Client client(url, port);

// prints: 0 / 000 bytes => 50% complete
auto res = cli.Get("/", [](uint64_t len, uint64_t total) {
  printf("%lld / %lld bytes => %d%% complete\n",
    len, total,
  return true; // return 'false' if you want to cancel the request.



// Basic Authentication
cli.set_basic_auth("user", "pass");

// Digest Authentication
cli.set_digest_auth("user", "pass");

// Bearer Token Authentication

NOTE: OpenSSL is required for Digest Authentication.

Proxy server support

cli.set_proxy("host", port);

// Basic Authentication
cli.set_proxy_basic_auth("user", "pass");

// Digest Authentication
cli.set_proxy_digest_auth("user", "pass");

// Bearer Token Authentication

NOTE: OpenSSL is required for Digest Authentication.


httplib::Client cli("httpbin.org");

auto res = cli.Get("/range/32", {
  httplib::make_range_header({{1, 10}}) // 'Range: bytes=1-10'
// res->status should be 206.
// res->body should be "bcdefghijk".
httplib::make_range_header({{1, 10}, {20, -1}})      // 'Range: bytes=1-10, 20-'
httplib::make_range_header({{100, 199}, {500, 599}}) // 'Range: bytes=100-199, 500-599'
httplib::make_range_header({{0, 0}, {-1, 1}})        // 'Range: bytes=0-0, -1'

Keep-Alive connection

httplib::Client cli("localhost", 1234);

cli.Get("/hello");         // with "Connection: close"


cli.Get("/last-request");  // with "Connection: close"


httplib::Client cli("yahoo.com");

auto res = cli.Get("/");
res->status; // 301

res = cli.Get("/");
res->status; // 200

Use a specific network interface

NOTE: This feature is not available on Windows, yet.

cli.set_interface("eth0"); // Interface name, IP address or host name


The server can apply compression to the following MIME type contents:

  • all text types except text/event-stream
  • image/svg+xml
  • application/javascript
  • application/json
  • application/xml
  • application/xhtml+xml

Zlib Support

'gzip' compression is available with CPPHTTPLIB_ZLIB_SUPPORT. libz should be linked.

Brotli Support

Brotli compression is available with CPPHTTPLIB_BROTLI_SUPPORT. Necessary libraries should be linked. Please see https://github.com/google/brotli for more detail.

Compress request body on client

res = cli.Post("/resource/foo", "...", "text/plain");

Compress response body on client

res = cli.Get("/resource/foo", {{"Accept-Encoding", "gzip, deflate, br"}});
res->body; // Compressed data

Use poll instead of select

select system call is used as default since it's more widely supported. If you want to let cpp-httplib use poll instead, you can do so with CPPHTTPLIB_USE_POLL.

Split httplib.h into .h and .cc

$ ./split.py -h
usage: split.py [-h] [-e EXTENSION] [-o OUT]

This script splits httplib.h into .h and .cc parts.

optional arguments:
  -h, --help            show this help message and exit
  -e EXTENSION, --extension EXTENSION
                        extension of the implementation file (default: cc)
  -o OUT, --out OUT     where to write the files (default: out)

$ ./split.py
Wrote out/httplib.h and out/httplib.cc



g++ 4.8 and below cannot build this library since <regex> in the versions are broken.


Include httplib.h before Windows.h or include Windows.h by defining WIN32_LEAN_AND_MEAN beforehand.

#include <httplib.h>
#include <Windows.h>
#include <Windows.h>
#include <httplib.h>

Note: cpp-httplib officially supports only the latest Visual Studio. It might work with former versions of Visual Studio, but I can no longer verify it. Pull requests are always welcome for the older versions of Visual Studio unless they break the C++11 conformance.

Note: Windows 8 or lower, Visual Studio 2013 or lower, and Cygwin on Windows are not supported.


MIT license (© 2022 Yuji Hirose)

Special Thanks To

These folks made great contributions to polish this library to totally another level from a simple toy!

*Note that all licence references and agreements mentioned in the cpp-httplib README section above are relevant to that project's source code only.