feat: Add support for PAYLOAD_TYPE_GRP_DATA

docs/companion_protocol.md

@@ -281,6 +281,33 @@ Bytes 7+: Message Text (UTF-8, variable length)
 
 ---
 
+### 6. Send Channel Data Datagram
+
+**Purpose**: Send binary datagram data to a channel.
+
+**Command Format**:
+```
+Byte 0: 0x3E
+Bytes 1-2: Data Type (`data_type`, 16-bit little-endian)
+Byte 3: Channel Index (0-7)
+Bytes 4+: Binary payload bytes (variable length)
+```
+
+**Data Type / Transport Mapping**:
+- `0x0000` is invalid for this command.
+- `0xFFFF` (`DATA_TYPE_DEV`) is the developer namespace for experimenting and developing apps.
+- Other non-zero values can be used as assigned application/community namespaces.
+
+**Note**: Applications that need a timestamp should encode it inside the binary payload.
+
+**Limits**:
+- Maximum payload length is `163` bytes.
+- Larger payloads are rejected with `PACKET_ERROR`.
+
+**Response**: `PACKET_OK` (0x00) on success
+
+---
+
 ### 6. Get Message
 
 **Purpose**: Request the next queued message from the device.

docs/faq.md

@@ -386,7 +386,7 @@ https://github.com/meshcore-dev/MeshCore/blob/main/src/Packet.h#L19
     #define PAYLOAD_TYPE_TXT_MSG 0x02 // a plain text message (prefixed with dest/src hashes, MAC) (enc data: timestamp, text)
     #define PAYLOAD_TYPE_ACK 0x03 // a simple ack #define PAYLOAD_TYPE_ADVERT 0x04 // a node advertising its Identity
     #define PAYLOAD_TYPE_GRP_TXT 0x05 // an (unverified) group text message (prefixed with channel hash, MAC) (enc data: timestamp, "name: msg")
-    #define PAYLOAD_TYPE_GRP_DATA 0x06 // an (unverified) group datagram (prefixed with channel hash, MAC) (enc data: timestamp, blob)
+    #define PAYLOAD_TYPE_GRP_DATA 0x06 // an (unverified) group datagram (prefixed with channel hash, MAC) (enc data: data_type, data_len, blob)
     #define PAYLOAD_TYPE_ANON_REQ 0x07 // generic request (prefixed with dest_hash, ephemeral pub_key, MAC) (enc data: ...)
     #define PAYLOAD_TYPE_PATH 0x08 // returned path (prefixed with dest/src hashes, MAC) (enc data: path, extra)
 

examples/companion_radio/MyMesh.cpp

@@ -58,6 +58,7 @@
 #define CMD_GET_AUTOADD_CONFIG        59
 #define CMD_GET_ALLOWED_REPEAT_FREQ   60
 #define CMD_SET_PATH_HASH_MODE        61
+#define CMD_SEND_CHANNEL_DATA         62
 
 // Stats sub-types for CMD_GET_STATS
 #define STATS_TYPE_CORE               0
@@ -91,6 +92,9 @@
 #define RESP_CODE_STATS               24   // v8+, second byte is stats type
 #define RESP_CODE_AUTOADD_CONFIG      25
 #define RESP_ALLOWED_REPEAT_FREQ      26
+#define RESP_CODE_CHANNEL_DATA_RECV   27
+
+#define MAX_CHANNEL_DATA_LENGTH       (MAX_FRAME_SIZE - 9)
 
 #define SEND_TIMEOUT_BASE_MILLIS        500
 #define FLOOD_SEND_TIMEOUT_FACTOR       16.0f
@@ -204,7 +208,8 @@ void MyMesh::updateContactFromFrame(ContactInfo &contact, uint32_t& last_mod, co
 }
 
 bool MyMesh::Frame::isChannelMsg() const {
-  return buf[0] == RESP_CODE_CHANNEL_MSG_RECV || buf[0] == RESP_CODE_CHANNEL_MSG_RECV_V3;
+  return buf[0] == RESP_CODE_CHANNEL_MSG_RECV || buf[0] == RESP_CODE_CHANNEL_MSG_RECV_V3 ||
+         buf[0] == RESP_CODE_CHANNEL_DATA_RECV;
 }
 
 void MyMesh::addToOfflineQueue(const uint8_t frame[], int len) {
@@ -564,6 +569,41 @@ void MyMesh::onChannelMessageRecv(const mesh::GroupChannel &channel, mesh::Packe
 #endif
 }
 
+void MyMesh::onChannelDataRecv(const mesh::GroupChannel &channel, mesh::Packet *pkt, uint16_t data_type,
+                               const uint8_t *data, size_t data_len) {
+  if (data_len > MAX_CHANNEL_DATA_LENGTH) {
+    MESH_DEBUG_PRINTLN("onChannelDataRecv: dropping payload_len=%d exceeds frame limit=%d",
+                       (uint32_t)data_len, (uint32_t)MAX_CHANNEL_DATA_LENGTH);
+    return;
+  }
+
+  int i = 0;
+  out_frame[i++] = RESP_CODE_CHANNEL_DATA_RECV;
+  out_frame[i++] = (int8_t)(pkt->getSNR() * 4);
+  out_frame[i++] = 0; // reserved1
+  out_frame[i++] = 0; // reserved2
+
+  uint8_t channel_idx = findChannelIdx(channel);
+  out_frame[i++] = channel_idx;
+  out_frame[i++] = pkt->isRouteFlood() ? pkt->path_len : 0xFF;
+  out_frame[i++] = (uint8_t)(data_type & 0xFF);
+  out_frame[i++] = (uint8_t)(data_type >> 8);
+  out_frame[i++] = (uint8_t)data_len;
+
+  int copy_len = (int)data_len;
+  if (copy_len > 0) {
+    memcpy(&out_frame[i], data, copy_len);
+    i += copy_len;
+  }
+  addToOfflineQueue(out_frame, i);
+
+  if (_serial->isConnected()) {
+    uint8_t frame[1];
+    frame[0] = PUSH_CODE_MSG_WAITING; // send push 'tickle'
+    _serial->writeFrame(frame, 1);
+  }
+}
+
 uint8_t MyMesh::onContactRequest(const ContactInfo &contact, uint32_t sender_timestamp, const uint8_t *data,
                                  uint8_t len, uint8_t *reply) {
   if (data[0] == REQ_TYPE_GET_TELEMETRY_DATA) {
@@ -1031,7 +1071,7 @@ void MyMesh::handleCmdFrame(size_t len) {
                         ? ERR_CODE_NOT_FOUND
                         : ERR_CODE_UNSUPPORTED_CMD); // unknown recipient, or unsuported TXT_TYPE_*
     }
-  } else if (cmd_frame[0] == CMD_SEND_CHANNEL_TXT_MSG) { // send GroupChannel msg
+  } else if (cmd_frame[0] == CMD_SEND_CHANNEL_TXT_MSG) { // send GroupChannel text msg
     int i = 1;
     uint8_t txt_type = cmd_frame[i++]; // should be TXT_TYPE_PLAIN
     uint8_t channel_idx = cmd_frame[i++];
@@ -1051,6 +1091,31 @@ void MyMesh::handleCmdFrame(size_t len) {
         writeErrFrame(ERR_CODE_NOT_FOUND); // bad channel_idx
       }
     }
+  } else if (cmd_frame[0] == CMD_SEND_CHANNEL_DATA) { // send GroupChannel datagram
+    if (len < 4) {
+      writeErrFrame(ERR_CODE_ILLEGAL_ARG);
+      return;
+    }
+    int i = 1;
+    uint16_t data_type = ((uint16_t)cmd_frame[i]) | (((uint16_t)cmd_frame[i + 1]) << 8);
+    i += 2;
+    uint8_t channel_idx = cmd_frame[i++];
+    const uint8_t *payload = &cmd_frame[i];
+    int payload_len = (len > (size_t)i) ? (int)(len - i) : 0;
+
+    ChannelDetails channel;
+    if (!getChannel(channel_idx, channel)) {
+      writeErrFrame(ERR_CODE_NOT_FOUND); // bad channel_idx
+    } else if (data_type == 0) {
+      writeErrFrame(ERR_CODE_ILLEGAL_ARG);
+    } else if (payload_len > MAX_CHANNEL_DATA_LENGTH) {
+      MESH_DEBUG_PRINTLN("CMD_SEND_CHANNEL_DATA payload too long: %d > %d", payload_len, MAX_CHANNEL_DATA_LENGTH);
+      writeErrFrame(ERR_CODE_ILLEGAL_ARG);
+    } else if (sendGroupData(channel.channel, data_type, payload, payload_len)) {
+      writeOKFrame();
+    } else {
+      writeErrFrame(ERR_CODE_TABLE_FULL);
+    }
   } else if (cmd_frame[0] == CMD_GET_CONTACTS) { // get Contact list
     if (_iter_started) {
       writeErrFrame(ERR_CODE_BAD_STATE); // iterator is currently busy

examples/companion_radio/MyMesh.h

@@ -137,6 +137,8 @@ class MyMesh : public BaseChatMesh, public DataStoreHost {
                            const uint8_t *sender_prefix, const char *text) override;
   void onChannelMessageRecv(const mesh::GroupChannel &channel, mesh::Packet *pkt, uint32_t timestamp,
                             const char *text) override;
+  void onChannelDataRecv(const mesh::GroupChannel &channel, mesh::Packet *pkt, uint16_t data_type,
+                         const uint8_t *data, size_t data_len) override;
 
   uint8_t onContactRequest(const ContactInfo &contact, uint32_t sender_timestamp, const uint8_t *data,
                            uint8_t len, uint8_t *reply) override;

src/MeshCore.h

@@ -17,6 +17,7 @@
 #define PATH_HASH_SIZE       1
 
 #define MAX_PACKET_PAYLOAD  184
+#define MAX_GROUP_DATA_LENGTH  (MAX_PACKET_PAYLOAD - CIPHER_BLOCK_SIZE - 3)
 #define MAX_PATH_SIZE        64
 #define MAX_TRANS_UNIT      255
 
@@ -100,4 +101,4 @@ class RTCClock {
   }
 };
 
-}
+}

src/Packet.h

@@ -22,7 +22,7 @@ namespace mesh {
 #define PAYLOAD_TYPE_ACK         0x03    // a simple ack
 #define PAYLOAD_TYPE_ADVERT      0x04    // a node advertising its Identity
 #define PAYLOAD_TYPE_GRP_TXT     0x05    // an (unverified) group text message (prefixed with channel hash, MAC) (enc data: timestamp, "name: msg")
-#define PAYLOAD_TYPE_GRP_DATA    0x06    // an (unverified) group datagram (prefixed with channel hash, MAC) (enc data: timestamp, blob)
+#define PAYLOAD_TYPE_GRP_DATA    0x06    // an (unverified) group datagram (prefixed with channel hash, MAC) (enc data: data_type(uint16), data_len, blob)
 #define PAYLOAD_TYPE_ANON_REQ    0x07    // generic request (prefixed with dest_hash, ephemeral pub_key, MAC) (enc data: ...)
 #define PAYLOAD_TYPE_PATH        0x08    // returned path (prefixed with dest/src hashes, MAC) (enc data: path, extra)
 #define PAYLOAD_TYPE_TRACE       0x09    // trace a path, collecting SNI for each hop

src/helpers/BaseChatMesh.cpp

@@ -353,8 +353,18 @@ int BaseChatMesh::searchChannelsByHash(const uint8_t* hash, mesh::GroupChannel d
 #endif
 
 void BaseChatMesh::onGroupDataRecv(mesh::Packet* packet, uint8_t type, const mesh::GroupChannel& channel, uint8_t* data, size_t len) {
-  uint8_t txt_type = data[4];
-  if (type == PAYLOAD_TYPE_GRP_TXT && len > 5 && (txt_type >> 2) == 0) {  // 0 = plain text msg
+  if (type == PAYLOAD_TYPE_GRP_TXT) {
+    if (len < 5) {
+      MESH_DEBUG_PRINTLN("onGroupDataRecv: dropping short group text payload len=%d", (uint32_t)len);
+      return;
+    }
+
+    uint8_t txt_type = data[4];
+    if ((txt_type >> 2) != 0) {
+      MESH_DEBUG_PRINTLN("onGroupDataRecv: dropping unsupported group text type=%d", (uint32_t)txt_type);
+      return;
+    }
+
     uint32_t timestamp;
     memcpy(&timestamp, data, 4);
 
@@ -363,6 +373,23 @@ void BaseChatMesh::onGroupDataRecv(mesh::Packet* packet, uint8_t type, const mes
 
     // notify UI  of this new message
     onChannelMessageRecv(channel, packet, timestamp, (const char *) &data[5]);  // let UI know
+  } else if (type == PAYLOAD_TYPE_GRP_DATA) {
+    if (len < 3) {
+      MESH_DEBUG_PRINTLN("onGroupDataRecv: dropping short group data payload len=%d", (uint32_t)len);
+      return;
+    }
+
+    uint16_t data_type = ((uint16_t)data[0]) | (((uint16_t)data[1]) << 8);
+    uint8_t data_len = data[2];
+    size_t available_len = len - 3;
+
+    if (data_len > available_len) {
+      MESH_DEBUG_PRINTLN("onGroupDataRecv: dropping malformed group data type=%d len=%d available=%d",
+                         (uint32_t)data_type, (uint32_t)data_len, (uint32_t)available_len);
+      return;
+    }
+
+    onChannelDataRecv(channel, packet, data_type, &data[3], data_len);
   }
 }
 
@@ -454,6 +481,31 @@ bool BaseChatMesh::sendGroupMessage(uint32_t timestamp, mesh::GroupChannel& chan
   return false;
 }
 
+bool BaseChatMesh::sendGroupData(mesh::GroupChannel& channel, uint16_t data_type, const uint8_t* data, int data_len) {
+  if (data_len < 0) {
+    MESH_DEBUG_PRINTLN("sendGroupData: invalid negative data_len=%d", data_len);
+    return false;
+  }
+  if (data_len > MAX_GROUP_DATA_LENGTH) {
+    MESH_DEBUG_PRINTLN("sendGroupData: data_len=%d exceeds max=%d", data_len, MAX_GROUP_DATA_LENGTH);
+    return false;
+  }
+
+  uint8_t temp[3 + MAX_GROUP_DATA_LENGTH];
+  temp[0] = (uint8_t)(data_type & 0xFF);
+  temp[1] = (uint8_t)(data_type >> 8);
+  temp[2] = (uint8_t)data_len;
+  if (data_len > 0) memcpy(&temp[3], data, data_len);
+
+  auto pkt = createGroupDatagram(PAYLOAD_TYPE_GRP_DATA, channel, temp, 3 + data_len);
+  if (pkt == NULL) {
+    MESH_DEBUG_PRINTLN("sendGroupData: unable to create group datagram, data_len=%d", data_len);
+    return false;
+  }
+  sendFloodScoped(channel, pkt);
+  return true;
+}
+
 bool BaseChatMesh::shareContactZeroHop(const ContactInfo& contact) {
   int plen = getBlobByKey(contact.id.pub_key, PUB_KEY_SIZE, temp_buf);  // retrieve last raw advert packet
   if (plen == 0) return false;  // not found

src/helpers/BaseChatMesh.h

@@ -111,6 +111,8 @@ class BaseChatMesh : public mesh::Mesh {
   virtual uint32_t calcDirectTimeoutMillisFor(uint32_t pkt_airtime_millis, uint8_t path_len) const = 0;
   virtual void onSendTimeout() = 0;
   virtual void onChannelMessageRecv(const mesh::GroupChannel& channel, mesh::Packet* pkt, uint32_t timestamp, const char *text) = 0;
+  virtual void onChannelDataRecv(const mesh::GroupChannel& channel, mesh::Packet* pkt, uint16_t data_type,
+                                 const uint8_t* data, size_t data_len) {}
   virtual uint8_t onContactRequest(const ContactInfo& contact, uint32_t sender_timestamp, const uint8_t* data, uint8_t len, uint8_t* reply) = 0;
   virtual void onContactResponse(const ContactInfo& contact, const uint8_t* data, uint8_t len) = 0;
   virtual void handleReturnPathRetry(const ContactInfo& contact, const uint8_t* path, uint8_t path_len);
@@ -148,6 +150,7 @@ class BaseChatMesh : public mesh::Mesh {
   int  sendMessage(const ContactInfo& recipient, uint32_t timestamp, uint8_t attempt, const char* text, uint32_t& expected_ack, uint32_t& est_timeout);
   int  sendCommandData(const ContactInfo& recipient, uint32_t timestamp, uint8_t attempt, const char* text, uint32_t& est_timeout);
   bool sendGroupMessage(uint32_t timestamp, mesh::GroupChannel& channel, const char* sender_name, const char* text, int text_len);
+  bool sendGroupData(mesh::GroupChannel& channel, uint16_t data_type, const uint8_t* data, int data_len);
   int  sendLogin(const ContactInfo& recipient, const char* password, uint32_t& est_timeout);
   int  sendAnonReq(const ContactInfo& recipient, const uint8_t* data, uint8_t len, uint32_t& tag, uint32_t& est_timeout);
   int  sendRequest(const ContactInfo& recipient, uint8_t req_type, uint32_t& tag, uint32_t& est_timeout);

src/helpers/TxtDataHelpers.h

@@ -3,9 +3,10 @@
 #include <stddef.h>
 #include <stdint.h>
 
-#define TXT_TYPE_PLAIN          0    // a plain text message
-#define TXT_TYPE_CLI_DATA       1    // a CLI command
-#define TXT_TYPE_SIGNED_PLAIN   2    // plain text, signed by sender
+#define TXT_TYPE_PLAIN          0      // a plain text message
+#define TXT_TYPE_CLI_DATA       1      // a CLI command
+#define TXT_TYPE_SIGNED_PLAIN   2      // plain text, signed by sender
+#define DATA_TYPE_DEV           0xFFFF // developer namespace for experimenting with group/channel datagrams and building apps
 
 class StrHelper {
 public: