Passa al contenuto principale

D01 - Esempio programma C - API HTTP REST libmicrohttpd

Esempio pratico e funzionante di programma in C che espone una API HTTP REST (es. /hello) usando una libreria leggera e molto usata: libmicrohttpd.

È ideale per:

  • servizi REST semplici

  • API interne di sistema

  • embedded / IoT

  • interfaccia con script o sistemi esterni

🚀 Esempio completo: API in C (GET /hello)

📌 Requisiti

Installa la libreria:

sudo apt-get install libmicrohttpd-dev

📄 api_server.c

#include <microhttpd.h>
#include <string.h>
#include <stdlib.h>

#define PORT 8080

// Funzione che gestisce le richieste HTTP
static int answer_to_connection(
    void *cls,
    struct MHD_Connection *connection,
    const char *url,
    const char *method,
    const char *version,
    const char *upload_data,
    size_t *upload_data_size,
    void **con_cls)
{
    const char *response_msg;

    if (strcmp(url, "/hello") == 0 && strcmp(method, "GET") == 0) {
        response_msg = "{\"message\": \"Hello from API in C!\"}";
    }
    else {
        response_msg = "{\"error\": \"Endpoint not found\"}";
    }

    struct MHD_Response *response;
    int ret;

    response = MHD_create_response_from_buffer(
        strlen(response_msg),
        (void*) response_msg,
        MHD_RESPMEM_PERSISTENT);

    MHD_add_response_header(response, "Content-Type", "application/json");
    ret = MHD_queue_response(connection, MHD_HTTP_OK, response);
    MHD_destroy_response(response);

    return ret;
}

int main() {
    struct MHD_Daemon *daemon;

    daemon = MHD_start_daemon(
        MHD_USE_INTERNAL_POLLING_THREAD, PORT, NULL, NULL,
        &answer_to_connection, NULL, MHD_OPTION_END);

    if (daemon == NULL) {
        fprintf(stderr, "Error starting server\n");
        return 1;
    }

    printf("Server running on port %d\n", PORT);
    printf("Try: curl http://localhost:%d/hello\n", PORT);

    getchar();  // Ferma il server quando premi INVIO

    MHD_stop_daemon(daemon);
    return 0;
}

🔧 Compilazione

gcc api_server.c -o api_server -lmicrohttpd

▶️ Esecuzione

./api_server

🧪 Test con curl

curl http://localhost:8080/hello

Output:

{"message": "Hello from API in C!"}

📁 Struttura del Progetto

rest_api_c/
├── src/
│   ├── api_server.c
│   ├── router.c
│   ├── router.h
│   └── utils.c
├── include/
│   ├── router.h
│   └── utils.h
├── Makefile
└── config.json   (esempio)

📌 1. src/api_server.c — Avvio server REST

#include <microhttpd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "router.h"

#define PORT 8080

static int answer_to_connection(
    void *cls,
    struct MHD_Connection *connection,
    const char *url,
    const char *method,
    const char *version,
    const char *upload_data,
    size_t *upload_data_size,
    void **con_cls)
{
    return route_request(connection, url, method);
}

int main() {
    struct MHD_Daemon *daemon;

    daemon = MHD_start_daemon(
        MHD_USE_INTERNAL_POLLING_THREAD, PORT, NULL, NULL,
        &answer_to_connection, NULL, MHD_OPTION_END);

    if (daemon == NULL) {
        fprintf(stderr, "Errore avvio server\n");
        return 1;
    }

    printf("Server REST avviato su porta %d\n", PORT);
    printf("Esempio: curl http://localhost:%d/hello\n", PORT);

    getchar();   // fermare server con INVIO
    MHD_stop_daemon(daemon);
    return 0;
}

📌 2. src/router.c — Gestione endpoint REST

#include <microhttpd.h>
#include <string.h>
#include <stdio.h>
#include "router.h"
#include "utils.h"

int route_request(struct MHD_Connection *connection, const char *url, const char *method) {
    const char *response_msg;

    if (strcmp(url, "/hello") == 0 && strcmp(method, "GET") == 0) {
        response_msg = "{\"message\": \"Hello from REST API C\"}";
        return send_response(connection, response_msg, MHD_HTTP_OK);
    }
    else if (strcmp(url, "/status") == 0 && strcmp(method, "GET") == 0) {
        response_msg = "{\"status\": \"OK\", \"service\": \"running\"}";
        return send_response(connection, response_msg, MHD_HTTP_OK);
    }
    else {
        response_msg = "{\"error\": \"Not Found\"}";
        return send_response(connection, response_msg, MHD_HTTP_NOT_FOUND);
    }
}

📌 3. include/router.h

#ifndef ROUTER_H
#define ROUTER_H

#include <microhttpd.h>

int route_request(struct MHD_Connection *connection, const char *url, const char *method);

#endif

📌 4. src/utils.c — Funzioni per risposte HTTP

#include <microhttpd.h>
#include <string.h>
#include "utils.h"

int send_response(struct MHD_Connection *connection, const char *msg, int status_code) {
    struct MHD_Response *response = MHD_create_response_from_buffer(
        strlen(msg), (void*) msg, MHD_RESPMEM_PERSISTENT);

    MHD_add_response_header(response, "Content-Type", "application/json");

    int ret = MHD_queue_response(connection, status_code, response);
    MHD_destroy_response(response);
    return ret;
}

📌 5. include/utils.h

#ifndef UTILS_H
#define UTILS_H

#include <microhttpd.h>

int send_response(struct MHD_Connection *connection, const char *msg, int status_code);

#endif

📌 6. Makefile

CC = gcc
CFLAGS = -Wall -Iinclude
LIBS = -lmicrohttpd

SRC = src/api_server.c src/router.c src/utils.c
OBJ = $(SRC:.c=.o)

TARGET = rest_api

all: $(TARGET)

$(TARGET): $(OBJ)
$(CC) $(OBJ) -o $(TARGET) $(LIBS)

clean:
rm -f $(OBJ) $(TARGET)

🧪 Test API

Compila ed esegui:

make
./rest_api

Test via curl:

curl http://localhost:8080/hello
curl http://localhost:8080/status

Output:

{"message": "Hello from REST API C"}
{"status": "OK", "service": "running"}

Tutorials:

https://www.gnu.org/software/libmicrohttpd/tutorial.html#Hello-browser-example

https://docs.oracle.com/cd/E88353_01/html/E37842/libmicrohttpd-3lib.html

 

Nessun commento
Torna in alto