mongoose/docs

Overview

Introduction

Mongoose is a networking library for C/C++. It implements event-driven non-blocking APIs for TCP, UDP, HTTP, WebSocket, MQTT. It has been designed for connecting devices and bringing them online. On the market since 2004, used by vast number of open source and commercial products - it even runs on the International Space Station! Mongoose makes embedded network programming fast, robust, and easy.

Features

• Cross-platform: works on Linux/UNIX, MacOS, QNX, eCos, Windows, Android, iPhone, FreeRTOS, etc
• Supported hardware platforms: TI CC3200, TI MSP432, NRF52, STM32, PIC32, ESP8266, ESP32 and more
• Builtin protocols:
  • plain TCP, plain UDP, SSL/TLS (over TCP, one-way or two-way)
  • HTTP client, HTTP server
  • WebSocket client, WebSocket server
  • MQTT client
  • DNS client, async DNS resolver
• Single-threaded, asynchronous, non-blocking core with simple event-based API
• Native support for LWIP embedded TCP/IP stack
• Tiny static and run-time footprint
• Source code is both ISO C and ISO C++ compliant
• Very easy to integrate: just copy mongoose.c and mongoose.h files to your build tree

Concept

Mongoose has three basic data structures:

• struct mg_mgr - an event manager that holds all active connections
• struct mg_connection - describes a connection
• struct mg_iobuf - describes data buffer (received or sent data)

Connections could be either listening, outbound or inbound. Outbound connections are created by the mg_connect() call. Listening connections are created by the mg_listen() call. Inbound connections are those accepted by a listening connection. Each connection is described by a struct mg_connection structure, which has a number of fields. All fields are exposed to the application by design, to give an application a full visibility into the Mongoose's internals.

An application that uses mongoose should follow a standard pattern of event-driven application:

• Declare and initialise an event manager:

struct mg_mgr mgr;
mg_mgr_init(&mgr);

• Create connections. For example, a server application should create listening connections. When any connection is created (listening or outgoing), an event handler function must be specified. An event handler function defines connection's behavior.

struct mg_connection *c = mg_http_listen(&mgr, "0.0.0.0:8000", fn, arg);

• Create an event loop by calling mg_mgr_poll():

 for (;;) {
   mg_mgr_poll(&mgr, 1000);
 }

mg_mgr_poll() iterates over all sockets, accepts new connections, sends and receives data, closes connections and calls event handler functions for the respective events.

Since the Mongoose's core is not protected against the concurrent access, make sure that all mg_* API functions are called from the same thread or RTOS task.

Send and receive buffers

Each connection has a send and receive buffer:

• struct mg_connection::send - data to be sent to a peer
• struct mg_connection::recv - data received from a peer

When data arrives, Mongoose appends received data to the recv and triggers an MG_EV_RECV event. The user may send data back by calling one of the output functions, like mg_send() or mg_printf(). Output functions append data to the send buffer. When Mongoose successfully writes data to the socket, it discards data from struct mg_connection::send and sends an MG_EV_SEND event.

Event handler function

Each connection has an event handler function associated with it. That function must be implemented by the user. Event handler is the key element of the Mongoose application, since it defines the connection's behaviour. This is what an event handler function looks like:

static void fn(struct mg_connection *c, int ev, void *ev_data, void *fn_data) {
  switch (ev) {
    /* Event handler code that defines behavior of the connection */
    ...
  }
}

• struct mg_connection *c - a connection that received an event
• int ev - an event number, defined in mongoose.h. For example, when data arrives on an inbound connection, ev would be MG_EV_RECV.
• void *ev_data - points to the event-specific data, and it has a different meaning for different events. For example, for an MG_EV_RECV event, ev_data is an int * pointing to the number of bytes received from a remote peer and saved into the c->recv IO buffer. The exact meaning of ev_data is described for each event. Protocol-specific events usually have ev_data pointing to structures that hold protocol-specific information.
• void *fn_data - a user-defined pointer for the connection, which is a placeholder for application-specific data. Mongoose does not use that pointer. An event handler can store any kind of information there

Events

Below is the list of events trigged by Mongoose, taken as-is from mongoose.h. For each event, a comment describes a meaning of the ev_data pointer passed to an event handler:

enum {
  MG_EV_ERROR,     // Error                        char *error_message
  MG_EV_POLL,      // mg_mgr_poll iteration        unsigned long *millis
  MG_EV_RESOLVE,   // Host name is resolved        NULL
  MG_EV_CONNECT,   // Connection established       NULL
  MG_EV_ACCEPT,    // Connection accepted          NULL
  MG_EV_READ,      // Data received from socket    struct mg_str *
  MG_EV_WRITE,     // Data written to socket       int *num_bytes_written
  MG_EV_CLOSE,     // Connection closed            NULL
  MG_EV_HTTP_MSG,  // HTTP request/response        struct mg_http_message *
  MG_EV_WS_OPEN,    // Websocket handshake done     NULL
  MG_EV_WS_MSG,     // Websocket message received   struct mg_ws_message *
  MG_EV_MQTT_MSG,   // MQTT message                 struct mg_mqtt_message *
  MG_EV_MQTT_OPEN,  // MQTT CONNACK received        int *connack_status_code
  MG_EV_SNTP_TIME,  // SNTP time received           struct timeval *
  MG_EV_USER,       // Starting ID for user events
};

Connection flags

struct mg_connection has a bitfield with connection flags. Flags are binary, they can be either 0 or 1. Some flags are set by Mongoose and must be not changed by an application code, for example is_udp flag tells application if that connection is UDP or not. Some flags can be changed by application, for example, is_drainig flag, if set by an application, tells Mongoose to send the remaining data to peer, and when everything is sent, close the connection.

User-changeable flags are: is_hexdumping, is_drainig, is_closing.

This is taken from mongoose.h as-is:

struct mg_connection {
  ...
  unsigned is_listening : 1;   // Listening connection
  unsigned is_client : 1;      // Outbound (client) connection
  unsigned is_accepted : 1;    // Accepted (server) connection
  unsigned is_resolving : 1;   // Non-blocking DNS resolv is in progress
  unsigned is_connecting : 1;  // Non-blocking connect is in progress
  unsigned is_tls : 1;         // TLS-enabled connection
  unsigned is_tls_hs : 1;      // TLS handshake is in progress
  unsigned is_udp : 1;         // UDP connection
  unsigned is_websocket : 1;   // WebSocket connection
  unsigned is_hexdumping : 1;  // Hexdump in/out traffic
  unsigned is_draining : 1;    // Send remaining data, then close and free
  unsigned is_closing : 1;     // Close and free the connection immediately
  unsigned is_readable : 1;    // Connection is ready to read
  unsigned is_writable : 1;    // Connection is ready to write
};

Build options

Mongoose source code ships in two files:

• mongoose.h - API definitions
• mongoose.c - implementation

Therefore to integrate Mongoose into an application, simply copy these two files to the application's source tree.

The mongoose.c and mongoose.h files are, actually, an amalgamation - a non-amalgamated sources can be found at https://github.com/cesanta/mongoose/tree/master/src

Mongoose source code uses a bunch of build constants defined at https://github.com/cesanta/mongoose/blob/master/src/config.h, together with their default values.

In order to change the constant during build time, use the -D <PREPROCESSOR_FLAG> compiler option. For example, to disable both MQTT, compile the application my_app.c like this (assumed UNIX system):

$ cc my_app.c mongoose.c -D MG_MQTT_ENABLE=0

Here is a list of build constants and their default values:

Name	Default	Description
MG_ENABLE_LWIP	0	Use LWIP low-level API instead of BSD sockets
MG_ENABLE_SOCKET	1	Use BSD socket low-level API
MG_ENABLE_MBEDTLS	0	Enable Mbed TLS library
MG_ENABLE_OPENSSL	0	Enable OpenSSL library
MG_ENABLE_FS	1	Enable API that use filesystem, like mg_http_send_file()
MG_ENABLE_IPV6	0	Enable IPv6
MG_ENABLE_LOG	1	Enable LOG() macro
MG_ENABLE_MD5	0	Use native MD5 implementation
MG_ENABLE_DIRECTORY_LISTING	0	Enable directory listing for HTTP server
MG_ENABLE_HTTP_DEBUG_ENDPOINT	0	Enable /debug/info debug URI
MG_ENABLE_SOCKETPAIR	0	Enable mg_socketpair() for multi-threading
MG_IO_SIZE	512	Granularity of the send/recv IO buffer growth
MG_MAX_RECV_BUF_SIZE	(3 * 1024 * 1024)	Maximum recv buffer size
MG_MAX_HTTP_HEADERS	40	Maximum number of HTTP headers

Minimal example

This example is a simple static HTTP server that serves current directory:

#include "mongoose.h"

static const char *s_web_root_dir = ".";
static const char *s_listening_address = "http://localhost:8000";

static void cb(struct mg_connection *c, int ev, void *ev_data, void *fn_data) {
  if (ev == MG_EV_HTTP_MSG) mg_http_serve_dir(c, ev_data, s_web_root_dir);
}

int main(int argc, char *argv[]) {
  struct mg_mgr mgr;
  mg_mgr_init(&mgr);
  mg_http_listen(&mgr, s_listening_address, cb, &mgr);
  for (;;) mg_mgr_poll(&mgr, 1000);
  mg_mgr_free(&mgr);
  return 0;
}