Using JSON

Ecewo supports a powerful built-in JSON library called Jansson. It’s easy to use and allows us to work with JSON objects effortlessly. For more information, refer to the official Jansson Documentation.

Creating JSON

Let’s write our hello world example again, but this time it will send a JSON object instead of a plain text.

src/handlers.c

#include "router.h"  // To handle the request and send a response
#include "jansson.h"  // To deal with JSON

void hello_world(Req *req, Res *res)
{
    // Create a JSON object
    json_t *json = json_object();

    // Add string to the JSON object we just created
    json_object_set_new(json, "hello", json_string("world"));

    // Convert the JSON object to a string
    // It is impossible to send a JSON without printing
    char *json_string = json_dumps(json, JSON_COMPACT);

    // Send the response with 200 status code
    // content-type must be "application/json" to send a json

    reply(res, "200 OK", "application/json", json_string);

    // Free the memory that allocated by cJSON
    json_decref(json);
    free(json_string);
}

src/handlers.h

#ifndef HANDLERS_H
#define HANDLERS_H

#include "router.h"

void hello_world(Req *req, Res *res);

#endif

src/main.c

#include "ecewo.h"
#include "router.h"
#include "handlers.h"

int main()
{
    get("/", hello_world);
    ecewo(4000);
    return 0;
}

Now we can recompile and send a request to http://localhost:4000/ again. We’ll receive a JSON:

{"hello":"world"}

Parsing JSON

This time, let’s take a JSON and print it to console.

src/handlers.c

#include "router.h"
#include "jansson.h"

void handle_user(Req *req, Res *res)
{
    const char *body = req->body;

    if (body == NULL)
    {
        reply(res, "400 Bad Request", "text/plain", "Missing request body");
        return;
    }

    cjson_error_t error;
    json_t *json = json_loads(body, 0, &error);
    if (!json)
    {
        reply(res, "400 Bad Request", "text/plain", "Invalid JSON");
        return;
    }

    json_t *name_obj = json_object_get(json, "name");
    json_t *surname_obj = json_object_get(json, "surname");
    json_t *username_obj = json_object_get(json, "username");

    if (!json_is_string(name_obj) || !json_is_string(surname_obj) || !json_is_string(username_obj))
    {
        json_decref(json);
        reply(res, "400 Bad Request", "text/plain", "Missing fields");
        return;
    }

    const char *name = json_string_value(name_obj);
    const char *surname = json_string_value(surname_obj);
    const char *username = json_string_value(username_obj);

    printf("Name: %s\n", name);
    printf("Surname: %s\n", surname);
    printf("Username: %s\n", username);

    json_decref(json); // Free the JSON object
    reply(res, "200", "text/plain", "Success!");
}

src/handlers.h

#ifndef HANDLERS_H
#define HANDLERS_H

#include "router.h"

void handle_user(Req *req, Res *res);

#endif

src/main.c

#include "ecewo.h"
#include "router.h"
#include "handlers.h"

int main()
{
    post("/user", handle_user);
    ecewo(4000);
    return 0;
}

Let’s recompile the program and send a POST request to http://localhost:4000/user with this body:

{
    "name": "John",
    "surname": "Doe",
    "username": "johndoe"
}

We’ll see in the console:

Name: John
Surname: Doe
Username: johndoe