Libevent (13) Evhttp Event Processing flow

In Libevent (vi) HTTP server, as a single-threaded HTTP server, listen not only to the arrival of each connection, but also to the I/O events on each connection.

Check the source, in Evhttp_bind_socket set the Accept callback function:ACCEPT_SOCKET_CB.

/**/staticvoidACCEPT_SOCKET_CB (structstruct  intvoid *arg) {    struct evhttp *http = arg;    Evhttp_get_request (http, NFD, Peer_sa, Peer_socklen);}

Static voidEvhttp_get_request (structEvhttp *http, evutil_socket_t FD,structSOCKADDR *SA, ev_socklen_t Salen) {    structEvhttp_connection *Evcon; Evcon=evhttp_get_request_connection (http, FD, SA, salen); if(Evcon = =NULL) {Event_sock_warn (FD,"%s:cannot get connection on"ev_sock_fmt, __func__, Ev_sock_arg (FD));        Evutil_closesocket (FD); return; }    /*The timeout can be used by the server to close idle connections*/    if(Http->timeout! =-1) evhttp_connection_set_timeout (Evcon, HTTP-timeout); /** If we want to accept more than one request in a connection, * we need to know which HTTP server it belongs     To. */Evcon->http_server =http; Tailq_insert_tail (&http->connections, Evcon, next); if(Evhttp_associate_new_request_with_connection (evcon) = =-1) Evhttp_connection_free (Evcon);}

Two important functions: evhttp_get_request_connection,evhttp_associate_new_request_with_connection .

1. evhttp_get_request_connection

/** Takes A file descriptor to read a request from. * The callback was executed once the whole request has been read. /c11>*/Static structevhttp_connection*Evhttp_get_request_connection (structevhttp*http, evutil_socket_t FD,structSOCKADDR *SA, ev_socklen_t Salen) {    structEvhttp_connection *Evcon; Char*hostname = NULL, *portname =NULL; NAME_FROM_ADDR (SA, Salen,&hostname, &portname); if(hostname = = NULL | | portname = =NULL) {        if(hostname) Mm_free (hostname); if(PortName) mm_free (portname); return(NULL); } event_debug (("%s:new request from%s:%s on"Ev_sock_fmt"\ n", __FUNC__, hostname, portname, Ev_sock_arg (FD)); /*We need a connection object to put the HTTP request on*/Evcon=evhttp_connection_base_new (http-Base, NULL, hostname, atoi (portname));    Mm_free (hostname);    Mm_free (PortName); if(Evcon = =NULL)return(NULL); Evcon->max_headers_size = http->default_max_headers_size; Evcon->max_body_size = http->default_max_body_size; Evcon->flags |=evhttp_con_incoming; Evcon->state =Evcon_reading_firstline; Evcon->FD =FD; bufferevent_setfd (Evcon ->bufev, FD); return(Evcon);}

Note the point:

1. bufferevent READCD is set through Evhttp_connection_base_new: EVHTTP_READ_CB,

WRITECB: EVHTTP_WRITE_CB.

2. Call BUFFEREVENT_SETFD

The BUFFEREVENT_SETFD code is as follows:

intBufferevent_setfd (structBufferevent *Bev, evutil_socket_t FD)    {Union Bufferevent_ctrl_data D; intres =-1; D.FD=FD;    Bev_lock (BEV); if(bev->be_ops->ctrl) Res= Bev->be_ops->ctrl (Bev, BEV_CTRL_SET_FD, &d);    Bev_unlock (BEV); returnRes;}Static intBe_socket_ctrl (structBufferevent *bev,enumbufferevent_ctrl_op op, Union bufferevent_ctrl_data*data) {    Switch(OP) { Casebev_ctrl_set_fd:be_socket_setfd (BEV, Data-FD); return 0;  CaseBev_ctrl_get_fd:data->FD = EVENT_GET_FD (&bev->ev_read); return 0;  Casebev_ctrl_get_underlying: CaseBev_ctrl_cancel_all:default:        return-1; }}Static voidBe_socket_setfd (structBufferevent *Bufev, evutil_socket_t FD)    {Bev_lock (BUFEV); Evutil_assert (Bufev->be_ops = = &bufferevent_ops_socket); Event_del (&bufev->ev_read); Event_del (&bufev->ev_write); Event_assign (&bufev->ev_read, bufev->ev_base, FD, Ev_read|ev_persist, BUFFEREVENT_READCB, Bufev); Event_assign (&bufev->ev_write, bufev->ev_base, FD, Ev_write|ev_persist, BUFFEREVENT_WRITECB, Bufev); if(FD >=0) bufferevent_enable (Bufev, Bufev-enabled); Bev_unlock (Bufev);}

Here the main set of FD read event callback BUFFEREVENT_READCB, write event callback BUFFEREVENT_WRITECB.

( here the bufferevent_enable can not be cared for, the back will be reset.) )

2. evhttp_associate_new_request_with_connection

Static intEvhttp_associate_new_request_with_connection (structEvhttp_connection *Evcon) {    structEvhttp *http = evcon->Http_server; structEvhttp_request *req; if((req = evhttp_request_new (evhttp_handle_request, http)) = =NULL)return(-1); if((Req->remote_host = Mm_strdup (evcon->address)) = =NULL) {Event_warn ("%s:strdup", __func__);        Evhttp_request_free (req); return(-1); } req->remote_port = evcon->Port; Req->evcon = Evcon;/*The request ends up owning the connection*/req->flags |=evhttp_req_own_connection; /*We didn't present the request to the user user yet, so treat it as * if the user is done with the request. This allows us to free the * request on a persistent connection if the client drops it without * sending a request     . */req->userdone =1; Tailq_insert_tail (&evcon->requests, req, next); Req->kind =evhttp_request;    Evhttp_start_read (Evcon); return(0);}

The first step is to set Evhttp_request's callback function evhttp_handle_request, and the second step calls Evhttp_start_read:

/** Reads data from file descriptor into request structure * Request structure needs to BES set up correctly.*/voidEvhttp_start_read (structEvhttp_connection *Evcon) {    /*Set up a event to read the headers*/bufferevent_disable (Evcon-Bufev, Ev_write); Bufferevent_enable (Evcon-Bufev, Ev_read); Evcon->state =Evcon_reading_firstline; /*Reset the bufferevent callbacks*/BUFFEREVENT_SETCB (Evcon-Bufev, EVHTTP_READ_CB, EVHTTP_WRITE_CB, EVHTTP_ERROR_CB, Evcon); /*If There ' s still data pending, process it next time through the * loop. Don ' t do it now; That could get recusive. */    if(Evbuffer_get_length (Bufferevent_get_input (evcon->Bufev)))  {Event_deferred_cb_schedule (Get_deferred_queue (Evcon),&evcon->READ_MORE_DEFERRED_CB); }}

As you can see, the read events of FD are added to the event loop.

Finally comb the next read event invocation process:

1. A read event occurred on FD

2. BUFFEREVENT_READCB

3. EVHTTP_READ_CB

4. Evhttp_connection_done

5. Evhttp_handle_request

6. Call the user-defined evhttp callback function

About the flow of data

When a read event occurs on the FD, the data on the FD is first read into the Evhttp_connection bufferevent, and then the data in the bufferevent is read into the input buffer of the evhttp_request.

When we use evhttp_send_reply to send data, the data is first written to the evhttp_request output buffer, then to the bufferevent of evhttp_connection, and the output buffer to the FD is written last.

Libevent (13) Evhttp Event Processing flow