c++mongoose 实现httpserver，httpclient

# 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 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](https://en.wikipedia.org/wiki/LwIP) * Tiny static and run-time footprint * Source code is both ISO C and ISO C++ compliant * Very easy to integrate: just copy [mongoose.c](https://raw.githubusercontent.com/cesanta/mongoose/master/mongoose.c) and [mongoose.h](https://raw.githubusercontent.com/cesanta/mongoose/master/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 initialise an event manager: ```c 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. ```c 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()`: ```c 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: ```c 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 ## 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: ```c 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: ```c 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](https://github.com/cesanta/mongoose/blob/master/mongoose.h) - API definitions - [mongoose.c](http