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EWS - Single .h File C Embeddable Web Server

Latest Version: 1.1.4 released September 9, 2021
Supported platforms: Linux, Mac OS X, Windows
License: BSD 2-clause

Embeddable Web Server is a web server in a single header file and has no external dependencies in the tradition of the STB libraries. It can serve static files and handle responses with C/C++ code (the server compiles in both). Here's how to use it:

  1. #include "EmbeddableWebServer.h" (and #define EWS_HEADER_ONLY if you included it somewhere else)
  2. Call acceptConnectionsUntilStoppedFromEverywhereIPv4(NULL), which will initialize a new server and block Note: If you want to take connections from a specific inteface/localhost you can use acceptConnectionsUntilStopped
  3. Fill out createResponseForRequest. Use the responseAlloc* functions to return a response or take over the connection yourself and return NULL. The easiest way to serve static files is responseAllocServeFileFromRequestPath. The easiest way to serve HTML is responseAllocHTML. The easiest way to serve JSON is responseAllocJSON. The server will free() your response once it's been sent. When compiled with Objective-C, an autoreleasepool will be created for you.
  4. Use the connectionDebugStringCreate to aid in debugging.

See the EWSDemo.cpp file for more examples like chunked transfer, HTML forms, and JSON responses.

If you want to control server setup/teardown use serverInit, serverStop, and serverDeInit and pass that same Server in acceptConnectionsUntilStopped.

Quick Example

#include "EmbeddableWebServer.h"
#pragma comment(lib, "ws2_32")

int main(int argc, char* argv[]) {
	return acceptConnectionsUntilStoppedFromEverywhereIPv4(NULL, 8080);

struct Response* createResponseForRequest(const struct Request* request, struct Connection* connection) {
	if (0 == strcmp(request->pathDecoded, "/welcome")) {
		return responseAllocHTML("<html><body><marquee><h1>Welcome to my home page</h1></marquee></body></html>");
	if (0 == strcmp(request->pathDecoded, "/status/json")) {
		static const char* statuses[] = { ":-)", ":-(", ":-|" };
		int status = rand() % (sizeof(statuses) / sizeof(*statuses));
		/* There is also a family of responseAllocJSON functions */
		return responseAllocWithFormat(200, "OK", "application/json", "{ \"status\" : \"%s\" }", statuses[status]);
	if (0 == strcmp(request->pathDecoded, "/100_random_numbers")) {
		struct Response* response = responseAllocHTML("<html><body><h1>100 Random Numbers</h1><ol>");
		for (int i = 1; i <= 100; i++) {
			heapStringAppendFormat(&response->body, "<li>%d</li>\n", rand());
		heapStringAppendString(&response->body, "</ol></body></html>");
		return response;
	/* Serve files from the current directory */
	if (request->pathDecoded == strstr(request->pathDecoded, "/files")) {
		return responseAllocServeFileFromRequestPath("/files", request->path, request->pathDecoded, ".");
	return responseAlloc404NotFoundHTML("What?!");

Features and use cases

  • Serve a debug page/dashboard for your application
  • Expose variables for debugging your 3D graphics application
  • Handle HTML GET + POST form data
  • Serve up websites for embedded touch display panels
  • Mix dynamic request handlers with static content
  • Seamless emoji support: Handles UTF-8 and international files, even on Windows (run the demo)
  • Someone is using it for robots


This server is suitable for controlled applications which will not be accessed over the general Internet. If you are determined to use this on Internet I advise you to use a proxy server in front (like haproxy, squid, or nginx). However I found and fixed only 2 crashes with alf-fuzz...


The server is implemented in a thread-per-connection model. This way you can do slow, hacky things in a request and not stall other requests. On the other hand this uses ~40KB + request body + response body of memory per connection. All strings are assumed to be UTF-8. On Windows, UTF-8 file paths are converted to their wide-character (wchar_t) equivalent so you can serve files with Chinese characters and so on.

The server assumes all strings are UTF-8. When accessing the file system on Windows, EWS will convert to/from the wchar_t representation and use the appropriate APIs.

pthreads wrapper for Windows

Since EWS uses threads we need to have a way to launch threads on all platforms. pthreads are supported on most of the operating systems this targets. Hence, EWS targets pthreads directly. EWS includes a very light wrapper for pthreads that supports thread creation, mutexes, and condition variables.

Example of launching a server thread from your app

#include "EmbeddableWebServer.h"
#ifdef WIN32
#pragma comment(lib, "ws2_32") // link against Winsock on Windows

static int counter = 0;
static struct Server server;
static THREAD_RETURN_TYPE STDCALL_ON_WIN32 acceptConnectionsThread(void* unusedParam) {
    const uint16_t portInHostOrder = 8080;
    acceptConnectionsUntilStoppedFromEverywhereIPv4(&server, portInHostOrder);
    return (THREAD_RETURN_TYPE) 0;

int main() {
    pthread_t threadHandle;
    pthread_create(&threadHandle, NULL, &acceptConnectionsThread, NULL);
    while (1) {
    // rest of the program
    return 0;

struct Response* createResponseForRequest(const struct Request* request, struct Connection* connection) {
    return responseAllocHTMLWithFormat("The counter is currently %d\n", counter);

Comparison to other really light embeddable web servers

  • yocto HTTP server - yocto has more features (WebSockets, handling deferred requests, custom headers, and can build PNG images on the fly - pretty cool) and lets you spit out the response in pieces. If you want anything custom EWS makes you take over the whole request yourself. yocto also has better MIME type detection. EWS is smaller and handles each connection on a separate thread so one slow response doesn't block the others.
  • Mongoose - mongoose is professionally supported and developed, dual-licensed under GPL and a commercial license you pay for. Mongoose has a huge amount of features. It works with or without an operating system.
  • Baraccuda - Baraccuda from Real-Time logic is a proprietary web server targetting embedded systems. I think they run with and without an OS and include lots of features like Mongoose does.

Change log


  • Fixes #10 (serverStop should not take lock if not initialized)


  • Fixes #7 (pathDecodedLength is always 0)


  • Fix build error when building with plain C rather than C++


  • When compiled with Objective-C (OBJC is defined), an autoreleasepool is created around the createResponseForRequest function invocation


  • From Daniel Barry: Check for NULL pointer after calling getifaddrs()
  • From Martin Pulec: Added macro to disable snprintf compat
  • From Martin Pulec: Improved IPv6 support
  • Stop leaking string when a directory is requested but viewing directories is disabled
  • Several functions like responseAllocHTMLWithStatus() are ignoring the status code parameter and always using 200. This is breaking functions like responseAlloc404NotFoundHTML(). The browser always gets 200 OK rather than the actual response code.
  • Fixed warnings and updated comments in various places


  • Initial release

Things I would change

If rewriting this from scratch I would change:

  • Right now all responses are allocated on the heap. They have to be built up into one single response. Instead I would allow for responses to be sent incrementally. So instead of responseAlloc you would have headerSend(connection, "Content-Type", "...") and bodySend("..."). It's a little more tricky to make that work and the onus of ordering goes on the user. Another advantage is that the user can deal with errors when sending pages.
  • Why did I not prefix all functions with something like EWS? EWSServerStart, EWSResponseAlloc. I should have done that. serverStop? Come on!