[c] Simple C example of doing an HTTP POST and consuming the response

Handle added.
Added Host header.
Added linux / windows support, tested (XP,WIN7).
WARNING: ERROR : "segmentation fault" if no host,path or port as argument.

#include <stdio.h> /* printf, sprintf */
#include <stdlib.h> /* exit, atoi, malloc, free */
#include <unistd.h> /* read, write, close */
#include <string.h> /* memcpy, memset */
#ifdef __linux__ 
    #include <sys/socket.h> /* socket, connect */
    #include <netdb.h> /* struct hostent, gethostbyname */
    #include <netinet/in.h> /* struct sockaddr_in, struct sockaddr */
#elif _WIN32
    #include <winsock2.h>
    #include <ws2tcpip.h>
    #include <windows.h>
    #pragma comment(lib,"ws2_32.lib") //Winsock Library

#else

#endif

void error(const char *msg) { perror(msg); exit(0); }

int main(int argc,char *argv[])
{

    int i;
    struct hostent *server;
    struct sockaddr_in serv_addr;
    int bytes, sent, received, total, message_size;
    char *message, response[4096];
    int portno = atoi(argv[2])>0?atoi(argv[2]):80;
    char *host = strlen(argv[1])>0?argv[1]:"localhost";
    char *path = strlen(argv[4])>0?argv[4]:"/";
    if (argc < 5) { puts("Parameters: <host> <port> <method> <path> [<data> [<headers>]]"); exit(0); }
    /* How big is the message? */
    message_size=0;
    if(!strcmp(argv[3],"GET"))
    {
                printf("Process 1\n");
        message_size+=strlen("%s %s%s%s HTTP/1.0\r\nHost: %s\r\n");        /* method         */
        message_size+=strlen(argv[3]);                         /* path           */
        message_size+=strlen(path);                         /* headers        */
        if(argc>5)
            message_size+=strlen(argv[5]);                     /* query string   */
        for(i=6;i<argc;i++)                                    /* headers        */
            message_size+=strlen(argv[i])+strlen("\r\n");
        message_size+=strlen("\r\n");                          /* blank line     */
    }
    else
    {
                printf("Process 2\n");
        message_size+=strlen("%s %s HTTP/1.0\r\nHost: %s\r\n");
        message_size+=strlen(argv[3]);                         /* method         */
        message_size+=strlen(path);                            /* path           */
        for(i=6;i<argc;i++)                                    /* headers        */
            message_size+=strlen(argv[i])+strlen("\r\n");
        if(argc>5)
            message_size+=strlen("Content-Length: %d\r\n")+10; /* content length */
        message_size+=strlen("\r\n");                          /* blank line     */
        if(argc>5)
            message_size+=strlen(argv[5]);                     /* body           */
    }
            printf("Allocating...\n");
    /* allocate space for the message */
    message=malloc(message_size);

    /* fill in the parameters */
    if(!strcmp(argv[3],"GET"))
    {
        if(argc>5)
            sprintf(message,"%s %s%s%s HTTP/1.0\r\nHost: %s\r\n",
                strlen(argv[3])>0?argv[3]:"GET",               /* method         */
                path,                                          /* path           */
                strlen(argv[5])>0?"?":"",                      /* ?              */
                strlen(argv[5])>0?argv[5]:"",host);            /* query string   */
        else
            sprintf(message,"%s %s HTTP/1.0\r\nHost: %s\r\n",
                strlen(argv[3])>0?argv[3]:"GET",               /* method         */
                path,host);                                    /* path           */
        for(i=6;i<argc;i++)                                    /* headers        */
            {strcat(message,argv[i]);strcat(message,"\r\n");}
        strcat(message,"\r\n");                                /* blank line     */
    }
    else
    {
        sprintf(message,"%s %s HTTP/1.0\r\nHost: %s\r\n",
            strlen(argv[3])>0?argv[3]:"POST",                  /* method         */
            path,host);                                        /* path           */
        for(i=6;i<argc;i++)                                    /* headers        */
            {strcat(message,argv[i]);strcat(message,"\r\n");}
        if(argc>5)
            sprintf(message+strlen(message),"Content-Length: %d\r\n",(int)strlen(argv[5]));
        strcat(message,"\r\n");                                /* blank line     */
        if(argc>5)
            strcat(message,argv[5]);                           /* body           */
    }
    printf("Processed\n");
    /* What are we going to send? */
    printf("Request:\n%s\n",message);
        /* lookup the ip address */

    total = strlen(message);
    /* create the socket */
    #ifdef _WIN32
WSADATA wsa;
SOCKET s;

printf("\nInitialising Winsock...");
if (WSAStartup(MAKEWORD(2,2),&wsa) != 0)
{
    printf("Failed. Error Code : %d",WSAGetLastError());
    return 1;
}

printf("Initialised.\n");

//Create a socket
if((s = socket(AF_INET , SOCK_STREAM , 0 )) == INVALID_SOCKET)
{
    printf("Could not create socket : %d" , WSAGetLastError());
}

printf("Socket created.\n");

server = gethostbyname(host);
serv_addr.sin_addr.s_addr = inet_addr(server->h_addr);
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(portno);
memset(&serv_addr,0,sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(portno);
memcpy(&serv_addr.sin_addr.s_addr,server->h_addr,server->h_length);
//Connect to remote server
if (connect(s , (struct sockaddr *)&serv_addr , sizeof(serv_addr)) < 0)
{
    printf("connect failed with error code : %d" , WSAGetLastError());
    return 1;
}

puts("Connected");
if( send(s , message , strlen(message) , 0) < 0)
{
    printf("Send failed with error code : %d" , WSAGetLastError());
    return 1;
}
puts("Data Send\n");

//Receive a reply from the server
if((received = recv(s , response , 2000 , 0)) == SOCKET_ERROR)
{
    printf("recv failed with error code : %d" , WSAGetLastError());
}

puts("Reply received\n");

//Add a NULL terminating character to make it a proper string before printing
response[received] = '\0';
puts(response);

closesocket(s);
WSACleanup();
    #endif
    #ifdef __linux__ 
    int sockfd;
    server = gethostbyname(host);
    if (server == NULL) error("ERROR, no such host");
        sockfd = socket(AF_INET, SOCK_STREAM, 0);
        if (sockfd < 0) error("ERROR opening socket");
        /* fill in the structure */
        memset(&serv_addr,0,sizeof(serv_addr));
        serv_addr.sin_family = AF_INET;
        serv_addr.sin_port = htons(portno);
        memcpy(&serv_addr.sin_addr.s_addr,server->h_addr,server->h_length);
                /* connect the socket */
        if (connect(sockfd,(struct sockaddr *)&serv_addr,sizeof(serv_addr)) < 0)
            error("ERROR connecting");
                /* send the request */

    sent = 0;
    do {
        bytes = write(sockfd,message+sent,total-sent);
        if (bytes < 0)
            error("ERROR writing message to socket");
        if (bytes == 0)
            break;
        sent+=bytes;
    } while (sent < total);
    /* receive the response */
    memset(response, 0, sizeof(response));
    total = sizeof(response)-1;
    received = 0;
    printf("Response: \n");
    do {
       printf("%s", response);
       memset(response, 0, sizeof(response));
       bytes = recv(sockfd, response, 1024, 0);
        if (bytes < 0)
           printf("ERROR reading response from socket");
       if (bytes == 0)
           break;
       received+=bytes;
    } while (1);

    if (received == total)
        error("ERROR storing complete response from socket");

    /* close the socket */
    close(sockfd);
    #endif


    free(message);

    return 0;
}

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