Function strcmp() doesn't find the match with the same values

I have a function that returns a response depending on the method and the path of the request.

When I use strcmp(method, "GET") it gives me -67, even if the method is exactly the same (I used printf() to see the value of method), it only works with path.

char *handle_response(char *method, char *path, char *protocol) {
    char *response;
      
    //strcmp
    if (strcmp(method, "GET") == 0 && strcmp(path, "/") == 0) {
        response = "HTTP/1.1 200 OK\r\nContent-Type: text/plain\r\n\r\nhola\n";
    } else {
        printf("Failed strcmp\n");
        printf("%s\n", method);
        printf("%s\n", path);

        printf("%d\n", strcmp(method, "GET"));
        printf("%d\n", strcmp(path, "/"));
    }
    //strstr OK
    if (strstr(method, "GET") && strstr(path, "/")) {
        response = "HTTP/1.1 200 OK\r\nContent-Type: text/plain\r\n\r\nhola\n";
    } else {
        response = "HTTP/1.1 404 Not Found\r\nContent-Type: text/plain\r\n\r\n404 Not Found";
    }
    
    return response;
}

I was able to make it work using strstr(), but it doesn't make any sense to me.

I call the handle_response() function after parsing the request:

int http_parser(char *client_socket) {
    char request[BUFFER_SIZE];
    char *method;
    char *protocol;
    char *path;
           
    strncpy(request, client_socket, sizeof(request));
    
    char *token = strtok(request, " ");
    
    if (token == NULL) {
        printf("\nInvalid Request Format!");
        return 0;
    }
    
    //METODO
    method = token;
    if (token == NULL) {
        printf("Invalid Request Method!\n"); 
        return 0;
    }
    
    //PATH
    token = strtok(NULL, " ");
    path = token;
    if (token == NULL) {
        printf("Invalid Request Path\n");
        return 0;
    }
   
    //PROTOCOL
    token = strtok(NULL, "\n");
    protocol = token;
    
    if (token == NULL) {
        printf("Invalid Request Protocol\n");
        return 0;
    }
    
    //FUNCTION CALLING handling_response()
    int client_fd = *client_socket;
    void *response = (void *)handle_response(method, path, protocol);
    send(client_fd, response, strlen(response), 0);
    
    return 1;
}

Solution

There are multiple problems in the code:

strncpy(request, client_socket, sizeof(request)) will not null terminate the string stored in request is the source string length is greater or equal to sizeof(request). strncpy is a false friend, do not use this function, use strlcpy instead.
there is a redundant test for Invalid Request Method. Store the return value of strtok() to the corresponding variable instead of using an intermediary variable token.
it is not obvious why the calls to strcmp in handle_response fail to return 0, but your printf formats do not allow you to see if there is any white space after GET or / that would explain the return values. I suggest you use this for debugging:
```
    printf("Failed strcmp:\n");
    printf("|%s| -> %d\n", method, strcmp(method, "GET"));
    printf("|%s| -> %d\n", path, strcmp(path, "/"));
```
strstr sill return a non null pointer if the first string contains the second, eg: strstr("GET\t", "GET").
it would help to print the client_socket string in case of failure: return NULL if the comparison fails and test for error in http_parser to output the original string.

Here is a modified version:

const char *handle_response(const char *method, const char *path, const char *protocol) {
    if (strcmp(method, "GET") == 0 && strcmp(path, "/") == 0) {
        return "HTTP/1.1 200 OK\r\nContent-Type: text/plain\r\n\r\nhola\n";
    } else {
        printf("Failed strcmp:\n");
        printf("|%s| -> %d\n", method, strcmp(method, "GET"));
        printf("|%s| -> %d\n", path, strcmp(path, "/"));
        return "HTTP/1.1 404 Not Found\r\nContent-Type: text/plain\r\n\r\n404 Not Found";
    }
}

int http_parser(const char *client_socket) {
    char request[BUFFER_SIZE];

    // copy the string with truncation
    size_t len = strlen(client_socket);
    if (len >= sizeof(request)) {
        len = sizeof(request) - 1;
    }
    memcpy(request, client_socket, len);
    request[len] = '\0';
    
    char *method = strtok(request, " ");
    if (method == NULL) {
        printf("\nInvalid Request Format!");
        return 0;
    }
    
    char *path = strtok(NULL, " ");
    if (path == NULL) {
        printf("Invalid Request Path\n");
        return 0;
    }
   
    char *protocol = strtok(NULL, "\n");
    if (protocol == NULL) {
        printf("Invalid Request Protocol\n");
        return 0;
    }
    
    int client_fd = *client_socket;
    const char *response = handle_response(method, path, protocol);
    send(client_fd, response, strlen(response), 0);
    
    return 1;
}