strcpy(s,lookup(line));
After gdb:
    Program received signal SIGSEGV, Segmentation fault.
    __strcpy_ssse3 () at ../sysdeps/i386/i686/multiarch/strcpy-ssse3.S:84


I would look for another way, for example:

    // copy line to new string
        char* temp = malloc(strlen(line) + 1);
        if(temp == NULL)
        {
            free(temp);
            return false;
        }
        strcpy(temp, line);
i don't know how is possible to resolve server without using gdb, this is a fundamental skill that you have to learn.
I also do not know what you intend to use lookup, if only returns a string with the MIME type of file, you have to analyze line and see that it fulfills the specifications