Add OTA over mqtt example

tutorials/mqtt/ota-over-mqtt/Makefile

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+PROG ?= example                   # Program we are building
+DELETE = rm -rf                   # Command to remove files
+OUT ?= -o $(PROG)                 # Compiler argument for output file
+SOURCES = main.c mongoose.c       # Source code files, packed_fs.c contains ca.pem, which contains CA certs for TLS
+CFLAGS = -W -Wall -Wextra -g -I.  # Build options
+
+# Mongoose build options. See https://mongoose.ws/documentation/#build-options
+CFLAGS_MONGOOSE += -DMG_ENABLE_LINES=1
+CFLAGS_MONGOOSE += -DMG_TLS=MG_TLS_BUILTIN
+#CFLAGS_MONGOOSE += -DMG_TLS=MG_TLS_OPENSSL -L/opt/homebrew/opt/openssl/lib -I/opt/homebrew/opt/openssl/include -lssl -lcrypto
+#CFLAGS_MONGOOSE += -DMG_TLS=MG_TLS_MBED -L/opt/homebrew/opt/mbedtls/lib -I/opt/homebrew/opt/mbedtls/include -lmbedtls -lmbedcrypto -lmbedx509
+
+ifeq ($(OS),Windows_NT)   # Windows settings. Assume MinGW compiler. To use VC: make CC=cl CFLAGS=/MD OUT=/Feprog.exe
+  PROG ?= example.exe           # Use .exe suffix for the binary
+  CC = gcc                      # Use MinGW gcc compiler
+  CFLAGS += -lws2_32            # Link against Winsock library
+  DELETE = cmd /C del /Q /F /S  # Command prompt command to delete files
+  OUT ?= -o $(PROG)             # Build output
+endif
+
+all: $(PROG)              # Default target. Build and run program
+	$(RUN) ./$(PROG) $(ARGS)
+
+$(PROG): $(SOURCES)       # Build program from sources
+	$(CC) $(SOURCES) $(CFLAGS) $(CFLAGS_MONGOOSE) $(CFLAGS_EXTRA) $(OUT)
+
+clean:                    # Cleanup. Delete built program and all build artifacts
+	$(DELETE) $(PROG) *.o *.obj *.exe *.dSYM

tutorials/mqtt/ota-over-mqtt/main.c

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+// Copyright (c) 2013-2026 Cesanta Software Limited
+// All rights reserved
+//
+// This example implements a JSON-RPC server that connects to the MQTT server
+// and expects requests on MQTT_RX_TOPIC, and sends responses to the
+// MQTT_TX_TOPIC. Only a single RPC method is implemented, "ota.update",
+// which expects parameters {"total": XX, "offset": XX, "chunk": "..."}
+// The rpc_ota_update() function handles those requests and calls Mongoose
+// ota_begin(), ota_write(), ota_end() respectively.
+//
+// Visit https://mongoose.ws/mqtt/ web page to push the firmware binary.
+
+#include "mongoose.h"
+
+#define MQTT_SERVER_URL "mqtt://broker.hivemq.com:1883"
+#define MQTT_RX_TOPIC "mg/123/rx"
+#define MQTT_TX_TOPIC "mg/123/tx"
+
+static uint8_t s_qos = 1;             // MQTT QoS
+static struct mg_connection *s_conn;  // MQTT Client connection
+static struct mg_rpc *s_rpc = NULL;   // List of registered RPC methods
+
+static void rpc_ota_update(struct mg_rpc_req *r) {
+  long ofs = mg_json_get_long(r->frame, "$.params.offset", -1);
+  long tot = mg_json_get_long(r->frame, "$.params.total", -1);
+  int len = 0;
+  char *buf = mg_json_get_b64(r->frame, "$.params.chunk", &len);
+  if (buf == NULL) {
+    mg_rpc_err(r, 1, "%m", MG_ESC("Chunk decoding error"));
+  } else if (ofs < 0 || tot < 0) {
+    mg_rpc_err(r, 1, "%m", MG_ESC("offset and total not set"));
+  } else if (ofs == 0 && mg_ota_begin((size_t) tot) == false) {
+    mg_rpc_err(r, 1, "\"mg_ota_begin(%ld) failed\"", tot);
+  } else if (len > 0 && mg_ota_write(buf, len) == false) {
+    mg_rpc_err(r, 1, "\"mg_ota_write(%lu) @%ld failed\"", len, ofs);
+    mg_ota_end();
+  } else if (len == 0 && mg_ota_end() == false) {
+    mg_rpc_err(r, 1, "\"mg_ota_end() failed\"", tot);
+  } else {
+    mg_rpc_ok(r, "%m", MG_ESC("ok"));
+  }
+  mg_free(buf);
+}
+
+static void subscribe(struct mg_connection *c, struct mg_str topic) {
+  struct mg_mqtt_opts opts = {};
+  memset(&opts, 0, sizeof(opts));
+  opts.topic = topic;
+  opts.qos = s_qos;
+  mg_mqtt_sub(c, &opts);
+  MG_INFO(("%lu SUBSCRIBED to %.*s", c->id, topic.len, topic.buf));
+}
+
+static void publish(struct mg_connection *c, struct mg_str topic,
+                    struct mg_str message) {
+  struct mg_mqtt_opts opts = {};
+  memset(&opts, 0, sizeof(opts));
+  opts.topic = topic;
+  opts.message = message;
+  opts.qos = s_qos;
+  mg_mqtt_pub(c, &opts);
+  MG_INFO(("%lu PUBLISHED %.*s -> %.*s", c->id, topic.len, topic.buf,
+           message.len, message.buf));
+}
+
+static void ev_handler(struct mg_connection *c, int ev, void *ev_data) {
+  if (ev == MG_EV_OPEN) {
+    MG_INFO(("%lu CREATED", c->id));
+    // c->is_hexdumping = 1;
+  } else if (ev == MG_EV_CONNECT) {
+    MG_INFO(("Connected"));
+  } else if (ev == MG_EV_ERROR) {
+    // On error, log error message
+    MG_ERROR(("%lu ERROR %s", c->id, (char *) ev_data));
+  } else if (ev == MG_EV_MQTT_OPEN) {
+    // MQTT connect is successful
+    MG_INFO(("%lu CONNECTED", c->id));
+    subscribe(c, mg_str(MQTT_RX_TOPIC));
+  } else if (ev == MG_EV_MQTT_MSG) {
+    // Treat this message as JSON-RPC: process an RPC request
+    struct mg_mqtt_message *mm = (struct mg_mqtt_message *) ev_data;
+    struct mg_iobuf io = {0, 0, 0, 512};
+    struct mg_rpc_req r = {&s_rpc, NULL, mg_pfn_iobuf,
+                           &io,    NULL, {mm->data.buf, mm->data.len}};
+    size_t clipped_len = mm->data.len > 512 ? 512 : mm->data.len;
+    MG_INFO(("%lu RECEIVED %.*s <- %.*s", c->id, clipped_len, mm->data.buf,
+             mm->topic.len, mm->topic.buf));
+    mg_rpc_process(&r);
+    if (io.buf != NULL && io.len > 0) {
+      publish(c, mg_str(MQTT_TX_TOPIC), mg_str_n((char *) io.buf, io.len));
+    }
+    mg_iobuf_free(&io);
+  } else if (ev == MG_EV_CLOSE) {
+    MG_INFO(("%lu CLOSED", c->id));
+    s_conn = NULL;  // Mark that we're closed
+  }
+}
+
+// SNTP timer function. Sync up time - may be needed for TLS on embedded
+static void timer_sntp(void *param) {
+  static uint64_t hourly_timer = 0;
+  uint64_t t1 = mg_now(), t2 = mg_millis();
+  if (t1 < t2 + 3600 || mg_timer_expired(&hourly_timer, 3600000, t2)) {
+    mg_sntp_connect(param, "udp://time.google.com:123", NULL, NULL);
+  }
+}
+
+static void timer_fn(void *arg) {
+  if (s_conn == NULL) {
+    struct mg_mgr *mgr = (struct mg_mgr *) arg;
+    struct mg_mqtt_opts opts = {.clean = true,
+                                .qos = s_qos,
+                                .topic = mg_str(MQTT_TX_TOPIC),
+                                .keepalive = 5,
+                                .version = 4,
+                                .message = mg_str("{\"method\":\"bye\"}")};
+    s_conn = mg_mqtt_connect(mgr, MQTT_SERVER_URL, &opts, ev_handler, NULL);
+  } else {
+    mg_mqtt_ping(s_conn);
+  }
+}
+
+int main(void) {
+  struct mg_mgr mgr;
+  mg_log_set(MG_LL_INFO);
+  mg_mgr_init(&mgr);
+
+  mg_timer_add(&mgr, 3000, MG_TIMER_REPEAT | MG_TIMER_RUN_NOW, timer_fn, &mgr);
+  mg_timer_add(&mgr, 100, MG_TIMER_REPEAT, timer_sntp, &mgr);
+
+  mg_rpc_add(&s_rpc, mg_str("ota.update"), rpc_ota_update, NULL);
+
+  for (;;) mg_mgr_poll(&mgr, 100);
+  mg_mgr_free(&mgr);
+
+  return 0;
+}

tutorials/mqtt/ota-over-mqtt/mongoose.c

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+../../../mongoose.c

tutorials/mqtt/ota-over-mqtt/mongoose.h

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+../../../mongoose.h