mongoose/docs

User Guide

Introduction

Mongoose is a networking library for C/C++. It implements an 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 a 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
• Built-in 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:

1. Declare and initialize an event manager:

struct mg_mgr mgr;
mg_mgr_init(&mgr);

2. 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);

3. 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 concurrent accesses, 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 behaviour 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

Events

Below is the list of events triggered 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     struct mg_http_message *
  MG_EV_WS_MSG,     // Websocket msg, text or bin   struct mg_ws_message *
  MG_EV_WS_CTL,     // Websocket control msg        struct mg_ws_message *
  MG_EV_MQTT_CMD,   // MQTT low-level command       struct mg_mqtt_message *
  MG_EV_MQTT_MSG,   // MQTT PUBLISH received        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_draining 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_draining, 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_SOCKETPAIR	0	Enable mg_socketpair() for multi-threading
MG_ENABLE_SSI	0	Enable serving SSI files by mg_http_serve_dir()
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

NOTE: MG_IO_SIZE controls the maximum UDP message size, see https://github.com/cesanta/mongoose/issues/907 for details. If application uses large UDP messages, increase the MG_IO_SIZE limit accordingly.

Custom build

It is possible to use Mongoose on an architecture that is not yet supported by the current codebase. In order to do so, follow these steps:

1. Create a file called mongoose_custom.h, with defines and includes that are relevant to your platform. Mongoose uses bool type, MG_DIRSEP define, and optionally other structures like DIR * depending on the functionality you have enabled - see previous section. Below is an example:

#include <dirent.h>             // For DIR *
#include <stdbool.h>            // For bool
#include <sys/time.h>           // For gettimeofday()
#include <unistd.h>             // For usleep()
#define MG_DIRSEP '/'
#define MG_ENABLE_SOCKET 0      // Disable BSD socket API, implement your own

2. Add -DMG_ARCH=MG_ARCH_CUSTOM to your build flags.

3. This step is optional. If you have disabled BSD socket API, your build is going to fail due to several undefined symbols. Create mongoose_custom.c and implement the following functions (take a look at src/sock.c for the reference implementation):

struct mg_connection *mg_connect(struct mg_mgr *mgr, const char *url,
                                 mg_event_handler_t fn, void *fn_data) {
  // implement this!
}

void mg_connect_resolved(struct mg_connection *c) {
  // implement this!
}


struct mg_connection *mg_listen(struct mg_mgr *mgr, const char *url,
                                mg_event_handler_t fn, void *fn_data) {
  // implement this!
}

void mg_mgr_poll(struct mg_mgr *mgr, int ms) {
  // implement this!
}

int mg_send(struct mg_connection *c, const void *buf, size_t len) {
  // implement this!
}

Minimal HTTP server

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) {
  struct mg_http_serve_opts opts = {.root_dir = s_web_root_dir};
  if (ev == MG_EV_HTTP_MSG) mg_http_serve_dir(c, ev_data, &opts);
}

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;
}

Minimal TCP echo server

This example is a simple TCP echo server that listens on port 1234:

#include "mongoose.h"

static const char *s_listening_address = "tcp://0.0.0.0:1234";

static void cb(struct mg_connection *c, int ev, void *ev_data, void *fn_data) {
  if (ev == MG_EV_RECV) {
    mg_send(c, c->recv.buf, c->recv.len);     // Echo received data back
    mg_iobuf_delete(&c->recv, c->recv.len);   // And discard it
  }
}

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

API Reference

Core

struct mg_mgr

struct mg_mgr {
  struct mg_connection *conns;  // List of active connections
  struct mg_connection *dnsc;   // DNS resolver connection
  const char *dnsserver;        // DNS server URL
  int dnstimeout;               // DNS resolve timeout in milliseconds
};

Event management structure that holds a list of active connections, together with some housekeeping information.

struct mg_connection

struct mg_connection {
  struct mg_connection *next;  // Linkage in struct mg_mgr :: connections
  struct mg_mgr *mgr;          // Our container
  struct mg_addr peer;         // Remote peer address
  void *fd;                    // Connected socket, or LWIP data
  struct mg_iobuf recv;        // Incoming data
  struct mg_iobuf send;        // Outgoing data
  mg_event_handler_t fn;       // User-specified event handler function
  void *fn_data;               // User-specified function parameter
  mg_event_handler_t pfn;      // Protocol-specific handler function
  void *pfn_data;              // Protocol-specific function parameter
  char label[32];              // Arbitrary label
  void *tls;                   // TLS specific data
  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 resolve 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
};

A connection - either a listening connection, or an accepted connection, or an outbound connection.

mg_mgr_init()

void mg_mgr_init(struct mg_mgr *);

Initialize event manager structure: set a list of active connections to NULL, set DNS server and timeout to their default values, etc.

mg_mgr_poll()

void mg_mgr_poll(struct mg_mgr *mgr, int ms);

Perform a single poll iteration. For each connection in the mgr->conns list,

• See if there is incoming data. If it is, read it into the c->recv buffer, send MG_EV_RECV event
• See if there is data in the c->send buffer, and write it, send MG_EV_WRITE event
• If a connection is listening, accept an incoming connection if any, and send MG_EV_ACCEPT event to it
• Send MG_EV_POLL event

Each connection has two event handler functions: c->fn and c->pfn. The c->fn is a user-specified event handler function. The c->pfn is a protocol-specific handler function that is set implicitly. For example, a mg_http_listen() sets c->pfn to a Mongoose's HTTP event handler. A protocol-specific handler is called before user-specific handler. It parses incoming data and may invoke protocol-specific events like MG_EV_HTTP_MSG.

mg_mgr_free()

void mg_mgr_free(struct mg_mgr *mgr);

Close all connections, and free all resources.

mg_listen()

struct mg_connection *mg_listen(struct mg_mgr *mgr, const char *url,
                                mg_event_handler_t fn, void *fn_data);

Create a listening connection, append this connection to mgr->conns.

• url - specifies local IP address and port to listen on, e.g. tcp://127.0.0.1:1234 or udp://0.0.0.0:9000
• fn - an event handler function
• fn_data - an arbitrary pointer, which will be passed as fn_data when an event handler is called. This pointer is also stored in a connection structure as c->fn_data

Return value: created connection, or NULL on error.

mg_connect()

struct mg_connection *mg_connect(struct mg_mgr *mgr, const char *url,
                                 mg_event_handler_t fn, void *fn_data);

Create an outbound connection, append this connection to mgr->conns.

• url - specifies remote IP address/port to connect to, e.g. http://a.com
• fn - an event handler function
• fn_data - an arbitrary pointer, which will be passed as fn_data when an event handler is called. This pointer is also stored in a connection structure as c->fn_data

Return value: created connection, or NULL on error.

mg_send()

int mg_send(struct mg_connection *c, const void *data, size_t size);

Append data of size size to the c->send buffer. Return number of bytes appended.

Note: this function does not push data to the network! It only appends data to the output buffer. The data is being sent when mg_mgr_poll() is called. If mg_send() is called multiple times, the output buffer grows.

mg_printf()

int mg_printf(struct mg_connection *, const char *fmt, ...);

Same as mg_send(), but formats data using printf() semantics. Return number of bytes appended to the output buffer.

mg_vprintf()

int mg_vprintf(struct mg_connection *, const char *fmt, va_list ap);

Same as mg_printf(), but takes va_list argument as a parameter.

mg_socketpair()

bool mg_socketpair(int *blocking, int *non_blocking);

Create a socket pair for exchanging data in multi-threaded environment. The blocking socket is blocking - it should be passed to the processing task. The non_blocking socket is non blocking, it should be used by an event handler function. Return value: true on success, false on error.

IO buffers

struct mg_iobuf

struct mg_iobuf {
  unsigned char *buf;
  size_t size, len;
};

Generic IO buffer. The size specifies an allocation size of the data pointed by buf, and len specifies number of bytes currently stored.

mg_iobuf_init()

int mg_iobuf_init(struct mg_iobuf *io, size_t size);

Initialize IO buffer, allocate size bytes. Return 1 on success, 0 on allocation failure.

mg_iobuf_resize()

int mg_iobuf_resize(struct mg_iobuf *io, size_t size);

Resize IO buffer, set the new size to size. The io->buf pointer could change after this, for example if the buffer grows. If size is 0, then the io->buf is freed and set to NULL, and both size and len are set to 0. Return 1 on success, 0 on allocation failure.

mg_iobuf_free()

void mg_iobuf_free(struct mg_iobuf *io);

Free memory pointed by io->buf and set to NULL. Both size and len are set to 0.

mg_iobuf_append()

size_t mg_iobuf_append(struct mg_iobuf *io, const void *data, size_t data_size, size_t granularity);

Append data bytes of size data_size to the end of the buffer. The buffer is expanded if data_size is greater than io->size - io->len. If that happens, the io->buf can change. The resulting io->size is always set to the granularity byte boundary. Example:

struct mg_iobuf io;
mg_iobuf_init(&io, 0);                // Empty buffer
mg_iobuf_append(&io, "hi", 2, 1024);  // io->len is 2, io->size is 1024

mg_iobuf_delete()

size_t mg_iobuf_delete(struct mg_iobuf *io, size_t len);

Discard len bytes from the beginning of the buffer, and shift the remaining bytes to the beginning. If len is greater than io->len, nothing happens, so such call is silently ignored.

HTTP

struct mg_http_header

struct mg_http_header {
  struct mg_str name;
  struct mg_str value;
};

struct mg_http_message

struct mg_http_message {
  //        GET /foo/bar/baz?aa=b&cc=ddd HTTP/1.1
  // method |-| |----uri---| |--query--| |proto-|

  struct mg_str method, uri, query, proto;  // Request/response line
  struct mg_http_header headers[MG_MAX_HTTP_HEADERS];  // Headers
  struct mg_str body;                       // Body
  struct mg_str message;                    // Request line + headers + body
};

mg_http_listen()

struct mg_connection *mg_http_listen(struct mg_mgr *, const char *url,
                                     mg_event_handler_t fn, void *fn_data);

Create HTTP listener.

• url - specifies local IP address and port to listen on, e.g. http://0.0.0.0:8000
• fn - an event handler function
• fn_data - an arbitrary pointer, which will be passed as fn_data when an event handler is called. This pointer is also stored in a connection structure as c->fn_data

mg_http_connect()

struct mg_connection *mg_http_connect(struct mg_mgr *, const char *url,
                                      mg_event_handler_t fn, void *fn_data);

Create HTTP client connection.

• url - specifies remote URL, e.g. http://google.com
• fn - an event handler function
• fn_data - an arbitrary pointer, which will be passed as fn_data when an event handler is called. This pointer is also stored in a connection structure as c->fn_data

mg_http_get_request_len()

int mg_http_get_request_len(const unsigned char *buf, size_t buf_len);

Return value: -1 on error, 0 if a message is incomplete, or the length of request. The length of request is a number of bytes till the end of HTTP headers. It does not include length of HTTP body.

mg_http_parse()

int mg_http_parse(const char *s, size_t len, struct mg_http_message *hm);

Parse string s, len into a structure hm. Return request length - see mg_http_get_request_len().

mg_http_printf_chunk()

void mg_http_printf_chunk(struct mg_connection *cnn, const char *fmt, ...);

Write a chunk of data in chunked encoding format, using printf() semantic.

mg_http_write_chunk()

void mg_http_write_chunk(struct mg_connection *c, const char *buf, size_t len);

Write a chunk of data in chunked encoding format.

mg_http_serve_dir()

struct mg_http_serve_opts {
  const char *root_dir;       // Web root directory, must be non-NULL
  const char *ssi_pattern;    // SSI file name pattern, e.g. #.shtml
  const char *extra_headers;  // Extra HTTP headers to add in responses
};
void mg_http_serve_dir(struct mg_connection *, struct mg_http_message *hm,
                       const struct mg_http_serve_opts *opts);

Serve static files according to the given options. Note that in order to enable SSI, set a -DMG_ENABLE_SSI=1 build flag.

mg_http_serve_file()

void mg_http_serve_file(struct mg_connection *, struct mg_http_message *hm,
                        const char *path, const char *mimetype,
                        const char *extra_headers);

Serve static file. Note that the extra_headers must end with \r\n. Here is an example call:

mg_http_serve_file(c, hm, "a.png", "image/png", "AA: bb\r\nCC: dd\r\n");

mg_http_reply()

void mg_http_reply(struct mg_connection *c, int status_code, const char *headers,
                   const char *body_fmt, ...);

Send simple HTTP response using printf() semantic. This function formats response body according to a body_fmt, and automatically appends a correct Content-Length header. Extra headers could be passed via headers parameter.

• status_code - an HTTP response code
• headers - extra headers, default NULL. If not NULL, must end with \r\n
• fmt - a format string for the HTTP body, in a printf semantics

mg_http_get_header()

struct mg_str *mg_http_get_header(struct mg_http_message *, const char *name);

Return value of HTTP header, or NULL if not found.

mg_http_get_var()

int mg_http_get_var(const struct mg_str *, const char *name, char *buf, int len);

Decode HTTP variable name into a given buffer. Return length of decoded variable. Zero or negative value means error.

mg_url_decode()

int mg_url_decode(const char *s, size_t n, char *to, size_t to_len, int form);

URL-decode string s, n unto a buffer buf, len. Return decoded length. If form is non-zero, then + is decoded as whitespace.

mg_http_creds()

void mg_http_creds(struct mg_http_message *, char *user, int userlen, char *pass, int passlen);

Fetch authentication credential from the request, and store into the user, userlen and pass, passlen buffers. The credentials are looked up in the following order:

• from the Authorization HTTP header,
  • Basic auth fills both user and pass
  • Bearer auth fills only pass
• from the access_token cookie, fills pass
• from the ?access_token=... query string parameter, fills pass

If none is found, then both user and pass are set to empty nul-terminated strings.

mg_http_match_uri()

bool mg_http_match_uri(const struct mg_http_message *, const char *glob);

Return true if HTTP request matches a given glob pattern; false otherwise.

mg_http_upload()

int mg_http_upload(struct mg_connection *, struct mg_http_message *hm,
                   const char *dir);

Handle file upload. See file upload example.

This function expects a series of POST requests with file data. POST requests should have name and offset query string parameters set:

POST /whatever_uri?name=myfile.txt&offset=1234 HTTP/1.0
Content-Length: 5

hello

• name - a mandatory query string parameter, specifies a file name. It it created in the dir directory
• offset - an optional parameter, default 0. If it set to 0, or omitted, then a file gets truncated before write. Otherwise, the body of the POST request gets appended to the file
• Server must call mg_http_upload() when /whatever_uri is hit

So, the expected usage of this API function is this:

• A client splits a file into small enough chunks, to ensure that a chunk fits into the server's RAM
• Then, each chunk is POST-ed to the server with using URI like /some_uri?name=FILENAME&offset=OFFSET
• Initial OFFSET is 0, and subsequent offsets are non-zero
• Each chunk gets appended to the file
• When the last chunk is POSTed, upload finishes
• POST data must not be encoded in any way, it it saved as-is

mg_http_bauth()

void mg_http_bauth(struct mg_connection *, const char *user, const char *pass);

Write a Basic Authorization header to the output buffer.

mg_http_next_\multipart()

// Parameter for mg_http_next_multipart
struct mg_http_part {
  struct mg_str name;      // Form field name
  struct mg_str filename;  // Filename for file uploads
  struct mg_str body;      // Part contents
};

size_t mg_http_next_multipart(struct mg_str body, size_t offset, struct mg_http_part *part);

Parse the multipart chunk in the body at a given offset. An initial offset should be 0. Fill up parameters in the provided part, which could be NULL. Return offset to the next chunk, or 0 if there are no more chunks.

See form-upload example for a usage example.

Websocket

struct mg_ws_message

struct mg_ws_message {
  struct mg_str data;
  uint8_t flags;  // Websocket message flags
};

mg_ws_connect()

struct mg_connection *mg_ws_connect(struct mg_mgr *, const char *url,
                                    mg_event_handler_t fn, void *fn_data,
                                    const char *fmt, ...);

Create client Websocket connection.

• url - specifies remote URL, e.g. http://google.com
• opts - MQTT options, with client ID, qos, etc
• fn - an event handler function
• fn_data - an arbitrary pointer, which will be passed as fn_data when an event handler is called. This pointer is also stored in a connection structure as c->fn_data
• fmt - printf-like format string for additional HTTP headers, or NULL

mg_ws_upgrade()

void mg_ws_upgrade(struct mg_connection *, struct mg_http_message *,
                   const char *fmt, ...);

Upgrade given HTTP connection to Websocket. The fmt is a printf-like format string for the extra HTTP headers returned to the client in a Websocket handshake. Set fmt to NULL if no extra headers needs to be passed.

mg_ws_send()

size_t mg_ws_send(struct mg_connection *, const char *buf, size_t len, int op);

Send buf, len to the websocket peer. op is the Websocket message type:

#define WEBSOCKET_OP_CONTINUE 0
#define WEBSOCKET_OP_TEXT 1
#define WEBSOCKET_OP_BINARY 2
#define WEBSOCKET_OP_CLOSE 8
#define WEBSOCKET_OP_PING 9
#define WEBSOCKET_OP_PONG 10

MQTT

struct mg_mqtt_opts

struct mg_mqtt_opts {
  struct mg_str client_id;
  struct mg_str will_topic;
  struct mg_str will_message;
  uint8_t qos;         // Quality of service
  bool will_retain;    // Retain last will
  bool clean;          // Use clean session, 0 or 1
  uint16_t keepalive;  // Keep-alive timer in seconds
};

struct mg_mqtt_message

struct mg_mqtt_message {
  struct mg_str topic;
  struct mg_str data;
};

mg_mqtt_connect()

struct mg_connection *mg_mqtt_connect(struct mg_mgr *, const char *url,
                                      struct mg_mqtt_opts *opts,
                                      mg_event_handler_t fn, void *fn_data);

Create client MQTT connection.

• url - specifies remote URL, e.g. http://google.com
• opts - MQTT options, with client ID, qos, etc
• fn - an event handler function
• fn_data - an arbitrary pointer, which will be passed as fn_data when an event handler is called. This pointer is also stored in a connection structure as c->fn_data

mg_mqtt_pub()

void mg_mqtt_pub(struct mg_connection *, struct mg_str *topic,
                 struct mg_str *data);

Publish message data to the topic topic.

mg_mqtt_sub()

void mg_mqtt_sub(struct mg_connection *, struct mg_str *topic);

Subscribe to topic topic.

mg_mqtt_next_sub()

int mg_mqtt_next_sub(struct mg_mqtt_message *msg, struct mg_str *topic,
                     uint8_t *qos, int pos);

Traverse list of subscribed topics. Used to implement MQTT server when MQTT_CMD_SUBSCRIBE is received. Return next position. Initial position pos should be 4. Example:

if (ev == MG_EV_MQTT_CMD) {
  struct mg_mqtt_message *mm = (struct mg_mqtt_message *) ev_data;
  if (mm->cmd == MQTT_CMD_SUBSCRIBE) {
    int pos = 4;
    uint8_t qos;
    struct mg_str topic;
    while ((pos = mg_mqtt_next_sub(mm, &topic, &qos, pos)) > 0) {
      LOG(LL_INFO, ("SUB [%.*s]", (int) topic.len, topic.ptr));
    }
  }
}

mg_mqtt_next_unsub()

int mg_mqtt_next_unsub(struct mg_mqtt_message *msg, struct mg_str *topic,
                       int pos);

Same as mg_mqtt_next_sub(), but for unsubscribed topics. The difference is that there is no QoS in unsubscribe request.

TLS

mg_tls_init()

struct mg_tls_opts {
  const char *ca;        // CA certificate file. For both listeners and clients
  const char *cert;      // Certificate
  const char *certkey;   // Certificate key
  const char *ciphers;   // Cipher list
  struct mg_str srvname; // If not empty, enables server name verification
};
int mg_tls_init(struct mg_connection *c, struct mg_tls_opts *opts);

Initialise TLS on a given connection.

Timers

struct mg_timer

struct mg_timer {
  int period_ms;            // Timer period in milliseconds
  int flags;                // Possible flags values below
#define MG_TIMER_REPEAT 1   // Call function periodically, otherwise run once
#define MG_TIMER_RUN_NOW 2  // Call immediately when timer is set
  void (*fn)(void *);       // Function to call
  void *arg;                // Function argument
  unsigned long expire;     // Expiration timestamp in milliseconds
  struct mg_timer *next;    // Linkage in g_timers list
};

Timer structure.

mg_timer_init()

void mg_timer_init(struct mg_timer *, int ms, int flags, void (*fn)(void *), void *fn_data);

Setup a timer.

• ms - an interval in milliseconds
• flags - timer flags bitmask, MG_TIMER_REPEAT and MG_TIMER_RUN_NOW
• fn - function to invoke
• fn_data - function argument

A timer gets initialized and linked into the g_timers list:

struct mg_timer *g_timers;

mg_timer_free()

void mg_timer_free(struct mg_timer *);

Free timer, remove it from the g_timers list.

mg_timer_poll()

void mg_timer_poll(unsigned long uptime_ms);

Traverse list of timers, and call them if current timestamp uptime_ms is past the timer's expiration time.

Utility functions

mg_file_read()

char *mg_file_read(const char *path, size_t *sizep);

Read file contents into a nul-terminated malloc-ed string. It is a caller's responsibility to free() a returned pointer. If sizep is not NULL, it will return a file size in bytes.

mg_file_size()

size_t mg_file_size(const char *path);

Return file size, or 0 on failure. Empty files also report 0 length.

mg_file_write()

bool mg_file_write(const char *path, const void *buf, size_t len);

Write data to a file, return true if written, false otherwise. The write is atomic, i.e. data gets written to a temporary file first, then rename()-ed to a destination file name.

mg_file_printf()

int mg_file_printf(const char *path, const char *fmt, ...);

Write into a file path using printf() semantics. Return true on success, false otherwise. This function prints data to a temporary in-memory buffer first, then calls mg_file_write().

mg_random()

void mg_random(void *buf, size_t len);

Fill in buffer buf, len with random data.

mg_globmatch()

bool mg_globmatch(const char *pattern, int plen, const char *s, int n);

Return true if string s, n matches glob pattern pattern, plen. The glob pattern matching rules are as follows:

• ? matches any single character
• * matches zero or more characters except /
• # matches zero or more characters
• any other character matches itself

mg_next_comma_entry()

bool mg_next_comma_entry(struct mg_str *s, struct mg_str *k, struct mg_str *v);

Parse string s, which is a comma-separated list of entries. An entry could be either an arbitrary string, which gets stored in v, or a KEY=VALUE which gets stored in k and v respectively.

IMPORTANT: this function modifies s by pointing to the next entry. Usage example:

struct mg_str k, v, s = mg_str("a=333,b=777");
while (mg_next_comma_entry(&s, &k, &v))               // This loop output:
  printf("[%.*s] set to [%.*s]\n",                    // [a] set to [333]
         (int) k.len, k.ptr, (int) v.len, v.ptr);     // [b] set to [777]

mg_ntohs()

uint16_t mg_ntohs(uint16_t net);

Convert uint16_t value to host order.

mg_ntohl()

uint32_t mg_ntohl(uint32_t net);

Convert uint32_t value to host order.

mg_hexdump()

char *mg_hexdump(const void *buf, int len);

Hexdump binary data buf, len into malloc-ed buffer and return it. It is a caller's responsibility to free() returned pointer.

mg_hex()

char *mg_hex(const void *buf, int len, char *dst);

Hex-encode binary data buf, len into a buffer dst and nul-terminate it. The output buffer must be at least 2 x len + 1 big. Return value: dst pointer. The encoded characters are lowercase, for example mg_hex("hi", 2, buf) outputs 6869 and 0 byte, 5 bytes overall.

mg_unhex()

void mg_unhex(const char *buf, int len, unsigned char *to);

Hex-decode string buf, len into a buffer to. The to buffer should be at least lsn / 2 big.

mg_unhexn()

unsigned long mg_unhexn(const char *s, int len);

Parse len characters of the hex-encoded string s, return parsed value. The maximum value of len is the width of the long x 2, for example on 32-bit platforms it is 8.

mg_asprintf()

int mg_asprintf(char **buf, size_t size, const char *fmt, ...);

Print message specified by printf-like format string fmt into a buffer pointed by buf of size size. If size is large enough to hold the whole message, then a message is stored in *buf. If it does not fit, then a large enough buffer is allocated to hold a message, and buf is changed to point to that buffer. Return value: number of bytes printed.

mg_vasprintf()

int mg_vasprintf(char **buf, size_t size, const char *fmt, va_list ap);

Same as mg_asprintf() but uses va_list argument.

mg_to64()

int64_t mg_to64(const char *s);

Parse 64-bit integer value held by string s.

mg_aton()

bool mg_aton(struct mg_str str, uint32_t *ipaddr);

Parse IP address held by str and store it in ipaddr. Return true on success.

mg_ntoa()

char *mg_ntoa(const struct mg_addr *, char *buf, size_t len);

Stringify IP address ipaddr into a buffer buf, len. Return buf.

mg_time()

double mg_time(void);

Return current time as UNIX epoch, using double value for sub-second accuracy.

mg_millis()

unsigned long mg_millis(void);

Return current uptime in milliseconds.

mg_usleep()

void mg_usleep(unsigned long usecs);

Block for a given number of microseconds.

mg_crc32()

uint32_t mg_crc32(uint32_t crc, const uint8_t *buf, size_t len);

Calculate CRC32 checksum for a given buffer. An initial crc value should be 0.