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Message-ID: <40941F92.1DDD3E67@hot.pl>
Date: Sun, 02 May 2004 00:07:14 +0200
From: Jacek Trzmiel <sc0rp AT hot DOT pl>
MIME-Version: 1.0
To: "cygwin AT cygwin DOT com" <cygwin AT cygwin DOT com>
Subject: shutdown( socket, SHUT_WR ) - unexpected behaviour
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Hi,

$ cygcheck -cd cygwin       
Cygwin Package Information
Package              Version        
cygwin               1.5.9-1        

I found some unexpected behaviour of shutdown call.  Here is example
program to reproduce problem.  It is supposed to send simple http
request to example.org, close writing part of socket, and then wait for
and print reply:

--- ShutdownTest.cpp ------------------------------------------------
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <string.h>
#include <assert.h>


const char *HOST    = "example.org";
const int   PORT    = 80;
const char *MESSAGE = "GET / HTTP/1.0\r\n\r\n";


void sendall( int sd, const char *data, int datalen )
{
    assert( data );
    assert( datalen >= 0 );
    while(datalen>0) {
        int sent = send(sd, data, datalen, 0);
        if( sent == -1) {
            perror("send");
            exit(1);
        }
        data += sent;
        datalen -= sent;
        assert( datalen>=0 );
    }
}


void recvandprintall( int sd )
{
    const int bufferlen = 65536;
    char buffer[bufferlen];

    while(true) {
        int got = recv(sd, buffer, bufferlen, 0);
        if(got == -1) {
            perror("recv");
            exit(1);
        }
        if(got==0) {
            break;
        }
        for( int i=0; i<got; ++i)
        {
            printf( "%c", buffer[i] );
        }
    }
}


void test()
{
    /* go find out about the desired host machine */
    struct hostent *he = gethostbyname(HOST);
    if (he == 0) {
        perror("gethostbyname");
        exit(1);
    }
    assert( he->h_addrtype == AF_INET );
    assert( he->h_addr_list[0] );

    /* fill in the socket structure with host information */
    struct sockaddr_in pin;
    memset( &pin, 0, sizeof(pin) );
    pin.sin_family = AF_INET;
    pin.sin_addr.s_addr = ((struct in_addr *)(he->h_addr))->s_addr;
    pin.sin_port = htons(PORT);

    /* grab an Internet domain socket */
    int sd;
    if ((sd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
        perror("socket");
        exit(1);
    }

    /* connect to PORT on HOST */
    if (connect(sd,(struct sockaddr *)  &pin, sizeof(pin)) == -1) {
        perror("connect");
        exit(1);
    }

    /* send a message to the server PORT on machine HOST */
    sendall( sd, MESSAGE, strlen(MESSAGE) );

    /* shutdown writing part of socket */
    shutdown( sd, SHUT_WR );

    /* wait for data to come back from the server and print it */
    recvandprintall( sd );

    close(sd);
}


int main()
{
    test();
    return 0;
}
--- ShutdownTest.cpp ------------------------------------------------

If you compile and run it this way:
$ g++ ShutdownTest.cpp -o ShutdownTest && ./ShutdownTest.exe

it doesn't print anything.   Commenting out shutdown call or adding some
wait before it does make program work as expected:

$ g++ ShutdownTest.cpp -o ShutdownTest && ./ShutdownTest.exe
HTTP/1.1 200 OK
Date: Sat, 01 May 2004 23:28:20 GMT
Server: Apache/1.3.27 (Unix)  (Red-Hat/Linux)
Last-Modified: Wed, 08 Jan 2003 23:11:55 GMT
[...]



1. I suppose that shutdown(sd,SHUT_WR) does not force unflushed buffers
out (i.e. discards them).  Am I right?


2. Is this bug or feature?  Manual page isn't helpful:
$ man 2 shutdown
No entry for shutdown in section 2 of the manual
$ man shutdown
No manual entry for shutdown


3. If it's a feature, then how can I manually flush buffers out before
calling shutdown?


I've googled for this problem, but haven't found any relevant
information.


Best regards,
Jacek.

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