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EPIPE blocks the server

I wrote a single-threaded asynchronous server in C running on Linux: the socket is not blocked, and I use epoll for polling. Tests show that the server is working fine and, according to Valgrind, there are no memory leaks or other problems.

The only problem is that when the write () command is aborted (because the client has closed the connection), the server will encounter EPIPE. I interrupt artificially by running the siege benchmarking utility with the -b option. It performs a lot of queries in a row, which work perfectly. Now I press CTRL-C and restart the siege. Sometimes I get lucky and the server cannot send a full response because client fd is not valid. As expected, errno is installed in EPIPE. I handle this situation, execute the close () function on fd, and then free the memory associated with the connection. Now the problem is that the server is blocking and is no longer responding. Here is strace's output:

epoll_wait(4, {{EPOLLIN, {u32=0, u64=0}}}, 128, -1) = 1
accept(3, {sa_family=AF_INET, sin_port=htons(55328), sin_addr=inet_addr("127.0.0.1")}, [16]) = 5
fcntl64(5, F_GETFL)                     = 0x2 (flags O_RDWR)
fcntl64(5, F_SETFL, O_RDWR|O_NONBLOCK)  = 0
epoll_ctl(4, EPOLL_CTL_ADD, 5, {EPOLLIN|EPOLLERR|EPOLLHUP|EPOLLET, {u32=144039912, u64=144039912}}) = 0
epoll_wait(4, {{EPOLLIN, {u32=144039912, u64=144039912}}}, 128, -1) = 1
read(5, "GET /user/register HTTP/1.1\r\nHos"..., 4096) = 161
send(5, "HTTP/1.1 200 OK\r\nContent-Type: t"..., 106, MSG_NOSIGNAL) = 106 <<<<
send(5, "00001000\r\n", 10, MSG_NOSIGNAL) = -1 EPIPE (Broken pipe)        <<<< Why did the previous send() work?
close(5)                                = 0
epoll_wait(4, {{EPOLLIN, {u32=0, u64=0}}}, 128, -1) = 1
accept(3, {sa_family=AF_INET, sin_port=htons(55329), sin_addr=inet_addr("127.0.0.1")}, [16]) = 5
...

(I removed printf () from the log if you're interested)

, , , , . EPOLL. epoll_wait() , (EPOLLIN). . , , write() EPIPE. "", , , .

#include "Connection.h"

static ExceptionManager *exc;

void Connection0(ExceptionManager *e) {
    exc = e;
}

void Connection_Init(Connection *this) {
    Socket_Init(&this->server);
    Socket_SetReusableFlag(&this->server);
    Socket_SetCloexecFlag(&this->server, true);
    Socket_SetBlockingFlag(&this->server, true);
    Socket_ListenTCP(&this->server, 8080, SOMAXCONN);

    // Add the server socket to epoll
    Poll_Init(&this->poll, SOMAXCONN, (void *) &Connection_OnEvent, this);
    Poll_AddEvent(&this->poll, NULL, this->server.fd, EPOLLIN | EPOLLET | EPOLLHUP | EPOLLERR);

    this->activeConn = 0;
}

void Connection_Destroy(Connection *this) {
    Poll_Destroy(&this->poll);
    Socket_Destroy(&this->server);
}

void Connection_Process(Connection *this) {
    Poll_Process(&this->poll, -1);
}

void Connection_AcceptClient(Connection *this) {
    Client *client;

    SocketConnection conn = Socket_Accept(&this->server);
    SocketConnection_SetBlockingFlag(&conn, true);

    client = New(Client);

    client->req = NULL;

    client->conn = New(SocketConnection);
    client->conn->remote = conn.remote;
    client->conn->fd = conn.fd;

    this->activeConn++;

    Poll_AddEvent(&this->poll, client, conn.fd, EPOLLIN | EPOLLET | EPOLLHUP | EPOLLERR);
}

void Connection_DestroyClient(Connection *this, Client *client) {
    // Poll_DeleteEvent(&this->poll, client->conn->fd);
    SocketConnection_Close(client->conn);

    if (client->req != NULL) {
        Request_Destroy(client->req);
        Memory_Free(client->req);
    }

    if (client->conn != NULL) {
        Memory_Free(client->conn);
    }

    Memory_Free(client);

    this->activeConn--;
}

void Connection_OnEvent(Connection *this, int events, Client *client) {
    /* error or connection hung up */
    if (client != NULL && (events & (EPOLLHUP | EPOLLERR))) {
        String_Print(String("EPOLLHUP | EPOLLERR received\n"));
        Connection_DestroyClient(this, client);
        return;
    }

    /* incoming connection */
    if (client == NULL && (events & EPOLLIN)) {
        if (this->activeConn > SOMAXCONN - 1) { /* TODO */
            String_Print(String("Too many connections...\n"));
            return;
        }

        Connection_AcceptClient(this);
        return;
    }

    /* receiving data from client */
    if (client != NULL && (events & EPOLLIN)) {
        if (client->req == NULL) {
            client->req = New(Request);
            Request_Init(client->req, client->conn);
        }

        bool keepOpen = false;

        try (exc) {
            keepOpen = Request_Parse(client->req);
        } catch(&SocketConnection_PipeException, e) {
            printf("Caught PipeException on fd=%d\n", client->conn->fd); fflush(stdout);
        } catch(&SocketConnection_ConnectionResetException, e) {
            printf("Caught ConnectionResetException on fd=%d\n", client->conn->fd); fflush(stdout);
        } finally {
            if (!keepOpen) {
                printf("Will close...\n"); fflush(stdout);
                Connection_DestroyClient(this, client);
            }
        } tryEnd;
    }
}
+1
2

sigaction(), SIGPIPE SIG_IGN. -1 errno, EPIPE, .

Linux send() MSG_NOSIGNAL write(). , . BSD- SO_NOSIGPIPE, SIGPIPE .

TCP- TCP RST . EPIPE SIGPIPE, . , , , - EPIPE SIGPIPE.

: , , strace, fcntl64(5, F_SETFL, O_RDONLY|O_NONBLOCK). O_RDONLY 0, , O_NONBLOCK. , OldFlags | O_NONBLOCK, . , -, . , F_GETFD F_GETFL, .

+6

(, , ), epoll , SIGPIPE . , SIGPIPE ( EPIPE) , . , .

+1

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