From 0175c84ad866e8f33a90d571e6207c6cc120075c Mon Sep 17 00:00:00 2001
From: cbdev <cb@cbcdn.com>
Date: Sun, 20 Dec 2020 13:30:11 +0100
Subject: Basic MQTT message parsing

---
 backends/mqtt.c | 54 ++++++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 50 insertions(+), 4 deletions(-)

(limited to 'backends')

diff --git a/backends/mqtt.c b/backends/mqtt.c
index 72046df..d42d1f5 100644
--- a/backends/mqtt.c
+++ b/backends/mqtt.c
@@ -86,16 +86,22 @@ static int mqtt_generate_instanceid(instance* inst){
 	return mmbackend_strdup(&(data->client_id), clientid);
 }
 
-static size_t mqtt_varint_decode(uint8_t* buffer, uint32_t* result){
+static int mqtt_pop_varint(uint8_t* buffer, size_t len, uint32_t* result){
 	size_t value = 0, offset = 0;
 	do {
+		if(offset >= len){
+			return 0;
+		}
+
 		value |= (buffer[offset] & 0x7F) << (7 * offset);
 		offset++;
 	} while(buffer[offset - 1] & 0x80);
-	return 0;
+
+	*result = value;
+	return offset;
 }
 
-static size_t mqtt_varint_encode(size_t value, size_t maxlen, uint8_t* buffer){
+static size_t mqtt_push_varint(size_t value, size_t maxlen, uint8_t* buffer){
 	//implementation conforming to spec 1.5.5
 	size_t offset = 0;
 	do {
@@ -142,8 +148,9 @@ static int mqtt_transmit(instance* inst, uint8_t type, size_t vh_length, uint8_t
 	uint8_t fixed_header[5];
 	size_t offset = 0;
 
+	//how in the world is it a _fixed_ header if it contains a variable length integer? eh...
 	fixed_header[offset++] = type;
-	offset += mqtt_varint_encode(vh_length + payload_length, sizeof(fixed_header) - offset, fixed_header + offset);
+	offset += mqtt_push_varint(vh_length + payload_length, sizeof(fixed_header) - offset, fixed_header + offset);
 
 	if(mmbackend_send(data->fd, fixed_header, offset)
 			|| mmbackend_send(data->fd, vh, vh_length)
@@ -316,9 +323,28 @@ static int mqtt_maintenance(){
 	return 0;
 }
 
+static int mqtt_handle_message(instance* inst, uint8_t type, uint8_t* variable_header, size_t length){
+	switch(type){
+		case MSG_CONNACK:
+			if(length >= 2){
+				if(variable_header[1]){
+					LOGPF("Connection on %s was rejected, reason code %d", inst->name, variable_header[1]);
+				}
+				else{
+					LOGPF("Connection on %s established", inst->name);
+				}
+			}
+			break;
+		default:
+			LOGPF("Unhandled MQTT message type 0x%02X on %s", type, inst->name);
+	}
+	return 0;
+}
+
 static int mqtt_handle_fd(instance* inst){
 	mqtt_instance_data* data = (mqtt_instance_data*) inst->impl;
 	ssize_t bytes_read = 0, bytes_left = sizeof(data->receive_buffer) - data->receive_offset;
+	uint32_t message_length = 0, header_length = 0;
 
 	bytes_read = recv(data->fd, data->receive_buffer + data->receive_offset, bytes_left, 0);
 	if(bytes_read < 0){
@@ -333,7 +359,27 @@ static int mqtt_handle_fd(instance* inst){
 	}
 
 	DBGPF("Instance %s, offset %" PRIsize_t ", read %" PRIsize_t " bytes", inst->name, data->receive_offset, bytes_read);
+	data->receive_offset += bytes_read;
+
+	//TODO loop this while at least one unhandled message is in the buffer
+	//check for complete message
+	if(data->receive_offset >= 2){
+		header_length = mqtt_pop_varint(data->receive_buffer + 1, data->receive_offset - 1, &message_length);
+		if(header_length && data->receive_offset >= message_length + header_length + 1){
+			DBGPF("Received complete message of %" PRIu32 " bytes, total received %" PRIsize_t ", payload %" PRIu32 ", message type %02X", message_length + header_length + 1, data->receive_offset, message_length, data->receive_buffer[0]);
+			if(mqtt_handle_message(inst, data->receive_buffer[0], data->receive_buffer + header_length + 1, message_length)){
+				//TODO handle failures properly
+			}
+
+			//remove handled message
+			if(data->receive_offset > message_length + header_length + 1){
+				memmove(data->receive_buffer, data->receive_buffer + message_length + header_length + 1, data->receive_offset - (message_length + header_length + 1));
+			}
+			data->receive_offset -= message_length + header_length + 1;
+		}
+	}
 
+	data->receive_offset += bytes_read;
 	return 0;
 }
 
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