libevent(九)evhttp
用libevent构建一个http server非常方便，可参考libevent(六)http server。
主要涉及的一个结构体是evhttp:
struct evhttp { /* Next vhost, if this is a vhost. */ TAILQ_ENTRY(evhttp) next_vhost; /* All listeners for this host */ TAILQ_HEAD(boundq, evhttp_bound_socket) sockets; TAILQ_HEAD(httpcbq, evhttp_cb) callbacks; /* All live connections on this host. */ struct evconq connections; TAILQ_HEAD(vhostsq, evhttp) virtualhosts; TAILQ_HEAD(aliasq, evhttp_server_alias) aliases; /* NULL if this server is not a vhost */ char *vhost_pattern; int timeout; size_t default_max_headers_size; ev_uint64_t default_max_body_size; /* Bitmask of all HTTP methods that we accept and pass to user * callbacks. */ ev_uint16_t allowed_methods; /* Fallback callback if all the other callbacks for this connection don't match. */ void (*gencb)(struct evhttp_request *req, void *); void *gencbarg; struct event_base *base; };
值得关注的有两个成员：
callbacks，一个链表，存放用户定义的回调函数
connections，一个链表，存放所有连接，每个连接对应一个evhttp_connection
evhttp_connection结构如下:
/* A client or server connection. */ struct evhttp_connection { /* we use this tailq only if this connection was created for an http * server */ TAILQ_ENTRY(evhttp_connection) next; evutil_socket_t fd; struct bufferevent *bufev; struct event retry_ev; /* for retrying connects */ char *bind_address; /* address to use for binding the src */ u_short bind_port; /* local port for binding the src */ char *address; /* address to connect to */ u_short port; size_t max_headers_size; ev_uint64_t max_body_size; int flags; #define EVHTTP_CON_INCOMING 0x0001 /* only one request on it ever */ #define EVHTTP_CON_OUTGOING 0x0002 /* multiple requests possible */ #define EVHTTP_CON_CLOSEDETECT 0x0004 /* detecting if persistent close */ int timeout; /* timeout in seconds for events */ int retry_cnt; /* retry count */ int retry_max; /* maximum number of retries */ enum evhttp_connection_state state; /* for server connections, the http server they are connected with */ struct evhttp *http_server; TAILQ_HEAD(evcon_requestq, evhttp_request) requests; void (*cb)(struct evhttp_connection *, void *); void *cb_arg; void (*closecb)(struct evhttp_connection *, void *); void *closecb_arg; struct deferred_cb read_more_deferred_cb; struct event_base *base; struct evdns_base *dns_base; };
值得关注的成员有两个:
bufev，对应一个bufferevent
requests，一个链表，存放该连接上的所有请求，每个请求对应evhttp_request
evhttp_request结构如下:
struct evhttp_request { #if defined(TAILQ_ENTRY) TAILQ_ENTRY(evhttp_request) next; #else struct { struct evhttp_request *tqe_next; struct evhttp_request **tqe_prev; } next; #endif /* the connection object that this request belongs to */ struct evhttp_connection *evcon; int flags; /** The request obj owns the evhttp connection and needs to free it */ #define EVHTTP_REQ_OWN_CONNECTION 0x0001 /** Request was made via a proxy */ #define EVHTTP_PROXY_REQUEST 0x0002 /** The request object is owned by the user; the user must free it */ #define EVHTTP_USER_OWNED 0x0004 /** The request will be used again upstack; freeing must be deferred */ #define EVHTTP_REQ_DEFER_FREE 0x0008 /** The request should be freed upstack */ #define EVHTTP_REQ_NEEDS_FREE 0x0010 struct evkeyvalq *input_headers; struct evkeyvalq *output_headers; /* address of the remote host and the port connection came from */ char *remote_host; ev_uint16_t remote_port; /* cache of the hostname for evhttp_request_get_host */ char *host_cache; enum evhttp_request_kind kind; enum evhttp_cmd_type type; size_t headers_size; size_t body_size; char *uri; /* uri after HTTP request was parsed */ struct evhttp_uri *uri_elems; /* uri elements */ char major; /* HTTP Major number */ char minor; /* HTTP Minor number */ int response_code; /* HTTP Response code */ char *response_code_line; /* Readable response */ struct evbuffer *input_buffer; /* read data */ ev_int64_t ntoread; unsigned chunked:1, /* a chunked request */ userdone:1; /* the user has sent all data */ struct evbuffer *output_buffer; /* outgoing post or data */ /* Callback */ void (*cb)(struct evhttp_request *, void *); void *cb_arg; /* * Chunked data callback - call for each completed chunk if * specified. If not specified, all the data is delivered via * the regular callback. */ void (*chunk_cb)(struct evhttp_request *, void *); };
值得注意的是：
每个请求有自己的输入缓冲input_buffer、输出缓冲output_buffer。
总结一下evhttp:
1. 一个evhttp使用一个链表存放多个evhttp_connection，每个evhttp_connection使用链表存放多个evhttp_request。
2. 每个evhttp_connection包含一个bufferevent，每个evhttp_request包含两个evbuffer，用于输入输出缓冲。
说了半天，好像没看见同步机制，可见evhttp不适合多线程。
参考资料:
