C socket programming client sometimes don't receive server mesage - c

Question

I made a simple client program with C that sends HTTP request to a host. The last part of the code, where the client receives HTTP response from server looks like this:
int main(int argc, char *argv[])
{
// ...
char buf[BUFSIZ];
int content_length;
content_length = recv(clientfd, buf, sizeof(buf) - 1, 0);
buf[content_length] = 0;
printf("%s", buf);
fflush(stdout);
exit(EXIT_SUCCESS);
}
With this code, I often get the expected result like the following:
GET /foo HTTP/1.0
Host: 127.0.0.1:8080
HTTP/1.0 200 OK
Content-Length: 12
Connection: close
abadakedavra
But sometimes, the content of the request doesn't show up.
GET /foo HTTP/1.0
Host: 127.0.0.1:8080
HTTP/1.0 200 OK
Content-Length: 12
Connection: close
What could be the reason for this behavior?
cf. My whole client code looks like this:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#define MAX_REQUEST 10000
#define MAX_URL 2048
void error(const char *msg)
{
perror(msg);
exit(EXIT_FAILURE);
}
void parse_url(char *src, char *hostname, char *port, char *url)
{
size_t i, j = 0;
for (i = 7; src[i] != ':'; i++)
hostname[j++] = src[i];
hostname[j] = 0;
j = 0;
for (i = i + 1; src[i] != '/'; i++)
port[j++] = src[i];
port[j] = 0;
j = 0;
for (i = i + 1; src[i]; i++)
url[j++] = src[i];
url[j] = 0;
}
int main(int argc, char *argv[])
{
/*
Expect
argv[0] : ./client (Executable name)
argv[1] : -G (GET) or -P (POST)
argv[2] : http://hostname:port/url
*/
int clientfd;
char hostname[MAX_URL], port[6], url[MAX_URL];
char msg[MAX_REQUEST];
struct addrinfo hints, *listp, *p;
if (argc < 3 || (strcmp(argv[1], "-G") != 0 && strcmp(argv[1], "-P") != 0))
{
printf("Usage:\n %s -P <URL> HTTP 1.0 POST from stdin\n"
" %s -G <URL> HTTP 1.0 GET to stdin\n",
argv[0], argv[0]);
exit(EXIT_FAILURE);
}
parse_url(argv[2], hostname, port, url);
if(strcmp(argv[1], "-P") == 0) fgets(msg, MAX_REQUEST, stdin);
/* Client socket creation */
memset(&hints, 0, sizeof(struct addrinfo));
hints.ai_socktype = SOCK_STREAM; // Use TCP
hints.ai_flags = AI_NUMERICSERV; // Use numeric port arg
// Generate a list of addrinfo in listp
getaddrinfo(hostname, port, &hints, &listp);
for (p = listp; p; p = p->ai_next)
{
// Create a socket based on addrinfo struct
if ((clientfd = socket(p->ai_family, p->ai_socktype, p->ai_protocol)) < 0)
continue;
if (connect(clientfd, p->ai_addr, p->ai_addrlen) != -1)
break;
close(clientfd); // Bind fail, loop to try again
}
freeaddrinfo(listp); // Not needed anymore
if (!p) // Entire loop failed
{
error("Failed in socket binding");
}
/* Send HTTP Request */
char httpRequest[MAX_REQUEST];
if(strcmp(argv[1], "-G") == 0) sprintf(httpRequest, "GET /%s HTTP/1.0\r\nHost: %s:%s\r\n\r\n", url, hostname, port);
else if(strcmp(argv[1]), "-P" == 0) sprintf(httpRequest, "POST /%s HTTP/1.0\r\nHost: %s:%s\r\nContent-Type: plain/text\r\nContent-Length: %lu\r\n\r\n%s\n", url, hostname, port, strlen(msg), msg);
else error("Invalid request");
printf("%s", httpRequest);
send(clientfd, httpRequest, strlen(httpRequest), 0);
/* Recieve HTTP response */
char buf[BUFSIZ];
int content_length;
content_length = recv(clientfd, buf, sizeof(buf) - 1, 0);
buf[content_length] = 0;
printf("%s", buf);
fflush(stdout);
exit(EXIT_SUCCESS);
}

Answer 1

You never implemented the HTTP protocol. If you want to receive an HTTP protocol response, you need to write code that receives an HTTP protocol response in accord with the HTTP protocol. Your code just receives a bunch of bytes, so that's all you get out.