# 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.
ร ideale per:
- servizi REST semplici
- API interne di sistema
- embedded / IoT
- interfaccia con script o sistemi esterni
##### ๐ **Esempio completo: API in C (GET /hello)**
๐ **Requisiti**
Installa la libreria:
sudo apt-get install libmicrohttpd-dev
๐ **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;
}
---
๐ง **Compilazione**
gcc api\_server.c -o api\_server -lmicrohttpd
โถ๏ธ **Esecuzione**
./api\_server
๐งช **Test con curl**
curl [http://localhost:8080/hello](http://localhost:8080/hello)
*Output:*
{"message": "Hello from API in C!"}
---
๐ **Struttura del Progetto**
rest\_api\_c/
โโโ src/
โ โโโ api\_server.c
โ โโโ router.c
โ โโโ router.h
โ โโโ utils.c
โโโ include/
โ โโโ router.h
โ โโโ utils.h
โโโ Makefile
โโโ config.json (esempio)
---
**๐ **1. src/api\_server.c** โ 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;
}
---
**๐ **2. src/router.c** โ 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);
}
}
---
**๐ **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
---
**๐ **4. src/utils.c** โ 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;
}
---
**๐ **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
---
****๐ **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)
---
๐งช **Test API**
*Compila ed esegui*:
make
./rest\_api
*Test via curl:*
curl http://localhost:8080/hello
curl [http://localhost:8080/status](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://www.gnu.org/software/libmicrohttpd/tutorial.html#Hello-browser-example)
[https://docs.oracle.com/cd/E88353\_01/html/E37842/libmicrohttpd-3lib.html](https://docs.oracle.com/cd/E88353_01/html/E37842/libmicrohttpd-3lib.html)