using magic strings instead of magic numbers

main/network/udp.cpp

@@ -13,32 +13,20 @@ static const char *TAG = "udp-server";
 
 static const in_port_t PORT = 4213;
 
-static std::map<uint32_t, qthing::udpPacketCallback> packetCallbackMap;
+static std::map<std::string, qthing::udpPacketCallback> packetCallbackMap;
 
-void qthing::addUDPPacketCallback(uint32_t magicNumber, qthing::udpPacketCallback callback) {
-    if (packetCallbackMap.count(magicNumber) > 0) {
-        qthing::udpPacketCallback old_callback = packetCallbackMap.at(magicNumber);
-        packetCallbackMap[magicNumber] = [old_callback, callback](udpPacket packet) {
+void qthing::addUDPPacketCallback(std::string magicString, qthing::udpPacketCallback callback) {
+    if (packetCallbackMap.count(magicString) > 0) {
+        qthing::udpPacketCallback old_callback = packetCallbackMap.at(magicString);
+        packetCallbackMap[magicString] = [old_callback, callback](udpPacket packet) {
             old_callback(packet);
             callback(packet);
         };
     } else {
-        packetCallbackMap[magicNumber] = callback;
+        packetCallbackMap[magicString] = callback;
     }
 
-    ESP_LOGI(TAG, "Registered callback for packets with magic number 0x%08X", magicNumber);
-}
-
-std::string to_string(struct sockaddr_in6 sourceAddr) {
-    char addr_str[128];
-
-    if (sourceAddr.sin6_family == PF_INET) {
-        inet_ntoa_r(((struct sockaddr_in *)&sourceAddr)->sin_addr.s_addr, addr_str, sizeof(addr_str) - 1);
-    } else if (sourceAddr.sin6_family == PF_INET6) {
-        inet6_ntoa_r(sourceAddr.sin6_addr, addr_str, sizeof(addr_str) - 1);
-    }
-
-    return(std::string(addr_str));
+    ESP_LOGI(TAG, "Registered callback for packets with magic string %s", magicString.c_str());
 }
 
 static char rx_buffer[2048];  // TODO: get MTU
@@ -76,6 +64,7 @@ static void udp_server_task(void *pvParameters)
             struct sockaddr_in6 sourceAddr; // Large enough for both IPv4 or IPv6
             socklen_t socklen = sizeof(sourceAddr);
 
+            memset(rx_buffer, 0, sizeof(rx_buffer));
             int len = recvfrom(sock, rx_buffer, sizeof(rx_buffer) - 1, 0, (struct sockaddr *)&sourceAddr, &socklen);
 
             // Error occured during receiving
@@ -85,30 +74,28 @@ static void udp_server_task(void *pvParameters)
             }
             // Data received
             else {
-                ESP_LOGI(TAG, "Received %d bytes from %s:", len, to_string(sourceAddr).c_str());
-
-                if (len >= sizeof(uint32_t)) {
+                ESP_LOGI(TAG, "Received %d bytes from %s", len, to_string(sourceAddr).c_str());
+
+                std::string payload_str(rx_buffer);
+                int16_t lenBestMatch = -1;
+                qthing::udpPacketCallback callback = NULL;
+                for(auto it = packetCallbackMap.begin(); it != packetCallbackMap.end(); ++it) {
+                    if (len >= it->first.length() && payload_str.find(it->first) == 0) {
+                        lenBestMatch = len;
+                        callback = it->second;
+                    }
+                }
 
-                    uint32_t magicNumber = rx_buffer[0] << 24 |
-                                           rx_buffer[1] << 16 |
-                                           rx_buffer[2] << 8  |
-                                           rx_buffer[3];
-                    
+                if (lenBestMatch > -1) {
                     qthing::udpPacket packet = {
                         .sourceAddr = sourceAddr,
-                        .payload = rx_buffer + 4,
-                        .length = (uint16_t)(len - 4)
+                        .payload = rx_buffer,
+                        .length = (uint16_t)len
                     };
 
-                    auto iterator = packetCallbackMap.find(magicNumber);
-                    if (iterator != packetCallbackMap.end()) {
-                        auto callback = iterator->second;
-                        callback(packet);
-                    } else {
-                        ESP_LOGW(TAG, "Packet has unknown magic number 0x%08X", magicNumber);
-                    }
+                    callback(packet);
                 } else {
-                    ESP_LOGW(TAG, "Packet is too small, cannot determine magic number");
+                    ESP_LOGW(TAG, "Packet has unknown magic string");
                 }
             }
         }

main/qthing.h

@@ -130,7 +130,7 @@ namespace qthing {
     } udpPacket;
 
     typedef std::function<void(udpPacket)> udpPacketCallback;
-    void addUDPPacketCallback(uint32_t magicNumber, udpPacketCallback callback);
+    void addUDPPacketCallback(std::string magicString, udpPacketCallback callback);
     void start_udp_server();
 }