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C getting part of a string inside a string

I am trying to write code that parses an HTTP GET request and checks if "Host" is www.bbc.co.uk.

This is my working code:

char data[] = "GET /news/ HTTP/1.1\nHost: www.bbc.co.uk\nConnection: keep-alive";
    unsigned int size = strlen(data);

    if (size>3 && data[0] == 'G' && data[1] == 'E' && data[2] == 'T'){ //If GET Request
        int host_index = -1;

        for (int i=4; i<size-4; i++){
            if (data[i] == 'H' && data[i+1] == 'o' && data[i+2] == 's' && data[i+3] == 't'
                    && data[i+4] == ':' && data[i+5] == ' '){
                host_index = i+6;
            }
        }

        if ( host_index != -1 && size > host_index+11 &&
                data[host_index] == 'w' && data[host_index+1] == 'w' && data[host_index+2] == 'w' &&
                data[host_index+3] == '.' && data[host_index+4] == 'b' && data[host_index+5] == 'b' &&
                data[host_index+6] == 'c' && data[host_index+7] == '.' && data[host_index+8] == 'c' &&
                data[host_index+9] == 'o' && data[host_index+10] == '.' && data[host_index+11] == 'u' &&
                data[host_index+12] == 'k')
        {
            printf("BBC WEBSITE!\n");
        }

    }

I think this is a lot of code for not very much. How can I make this code more compact?

[Please keep it on plain C. No third-party libraries]

MANY THANKS!

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4 answers

Your code can be written more compactly, for example:

   if (!strncmp(data, "GET ", 4) && strstr(data, "\nHost: www.bbc.co.uk\n"))
       printf("BBC WEBSITE!\n");

However, although this may work 99.9% of the time, it does not process arbitrary empty space after the colon. Regular expressions would be useful, but you would need a third-party library that you don’t have.

One solution:

  if (!strncmp(data, "GET ", 4)) {
      const char *p = data;
      char buf[99 + 1];
      buf[0] = 0;
      while ((p = strchr(p, '\n')) && sscanf(++p, "Host: %99s", buf) != 1)
          ;
      if (!strcmp(buf, "www.bbc.co.uk"))
          printf("BBC WEBSITE!\n");
  }

. CR / LF "Host:". , HTTP/1.1 LWS ( ). , , sscanf :

   (sscanf(++p, "Host:%*[ \t]%99[^ \t]", buf) == 1 || 
    sscanf(p,   "Host:%99[^ \t]",        buf) == 1)

, .

+2

strstr()?

strstr(),

+4

, :

char data[] = 
    "GET /news/ HTTP/1.1\n"
    "Host: www.bbc.co.uk\n"
    "Connection: keep-alive";

char *found_host = strstr(data, "Host: ");

if (found_host != NULL) {
    found_host += sizeof("Host: ") - 1;

    char *end_of_host = strpbrk(found_host, "\r\n");

    if (end_of_host != NULL) {
        int equal = strncmp(found_host, "www.bbc.co.uk", end_of_host - found_host);
    }
}

, .

+2
char data[] = "GET /news/ HTTP/1.1\nHost: www.bbc.co.uk\nConnection: keep-alive";
unsigned int size = strlen(data);
char buff[size];
sscanf(data, "%*[^:]:%s", buff);
if(strcmp(buff, "www.bbc.co.uk")==0)
    puts("BBC");
+1

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