Add reply bot module with DM-only responses and rate limiting (#9456)

* Implement Meshtastic reply bot module with ping and status features

Adds a reply bot module that listens for /ping, /hello, and /test commands received via direct messages or broadcasts on the primary channel. The module always replies via direct message to the sender only, reporting hop count, RSSI, and SNR. Per-sender cooldowns are enforced to reduce network spam, and the module can be excluded at build time via a compile flag. Updates include the new module source files and required build configuration changes.

* Update ReplyBotModule.cpp

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update src/modules/ReplyBotModule.h

Match the existing MESHTASTIC_EXCLUDE_* guard pattern so the module is excluded by default.

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update src/modules/ReplyBotModule.cpp

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Tidying up

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Ben Meadors <benmmeadors@gmail.com>

src/modules/ReplyBotModule.cpp

@@ -0,0 +1,183 @@
+#if !MESHTASTIC_EXCLUDE_REPLYBOT
+/*
+ * ReplyBotModule.cpp
+ *
+ * This module implements a simple reply bot for the Meshtastic firmware.  It listens for
+ * specific text commands ("/ping", "/hello" and "/test") delivered either via a direct
+ * message (DM) or a broadcast on the primary channel.  When a supported command is
+ * received the bot responds with a short status message that includes the hop count
+ * (minimum number of relays), RSSI and SNR of the received packet.  To avoid spamming
+ * the network it enforces a per‑sender cooldown between responses.  By default the
+ * module is enabled; define MESHTASTIC_EXCLUDE_REPLYBOT at build time to exclude it
+ * entirely.  See the official firmware documentation for guidance on adding modules.
+ */
+
+#include "ReplyBotModule.h"
+#include "Channels.h"
+#include "MeshService.h"
+#include "NodeDB.h"
+#include "configuration.h"
+#include "mesh/MeshTypes.h"
+
+#include <Arduino.h>
+#include <cctype>
+#include <cstring>
+
+//
+// Rate limiting data structures
+//
+// Each sender is tracked in a small ring buffer.  When a message arrives from a
+// sender we check the last time we responded to them.  If the difference is
+// less than the configured cooldown (different values for DM vs broadcast)
+// the message is ignored; otherwise we update the last response time and
+// proceed with replying.
+
+struct ReplyBotCooldownEntry {
+    uint32_t from = 0;
+    uint32_t lastMs = 0;
+};
+
+static constexpr uint8_t REPLYBOT_COOLDOWN_SLOTS = 8;          // ring buffer size
+static constexpr uint32_t REPLYBOT_DM_COOLDOWN_MS = 15 * 1000; // 15 seconds for DMs
+static constexpr uint32_t REPLYBOT_LF_COOLDOWN_MS = 60 * 1000; // 60 seconds for LongFast broadcasts
+
+static ReplyBotCooldownEntry replybotCooldown[REPLYBOT_COOLDOWN_SLOTS];
+static uint8_t replybotCooldownIdx = 0;
+
+// Return true if a reply should be rate‑limited for this sender, updating the
+// entry table as needed.
+static bool replybotRateLimited(uint32_t from, uint32_t cooldownMs)
+{
+    const uint32_t now = millis();
+    for (auto &e : replybotCooldown) {
+        if (e.from == from) {
+            // Found existing entry; check if cooldown expired
+            if ((uint32_t)(now - e.lastMs) < cooldownMs) {
+                return true;
+            }
+            e.lastMs = now;
+            return false;
+        }
+    }
+    // No entry found – insert new sender into the ring
+    replybotCooldown[replybotCooldownIdx].from = from;
+    replybotCooldown[replybotCooldownIdx].lastMs = now;
+    replybotCooldownIdx = (replybotCooldownIdx + 1) % REPLYBOT_COOLDOWN_SLOTS;
+    return false;
+}
+
+// Constructor – registers a single text port and marks the module promiscuous
+// so that broadcast messages on the primary channel are visible.
+ReplyBotModule::ReplyBotModule() : SinglePortModule("replybot", meshtastic_PortNum_TEXT_MESSAGE_APP)
+{
+    isPromiscuous = true;
+}
+
+void ReplyBotModule::setup()
+{
+    // In future we may add a protobuf configuration; for now the module is
+    // always enabled when compiled in.
+}
+
+// Determine whether we want to process this packet.  We only care about
+// plain text messages addressed to our port.
+bool ReplyBotModule::wantPacket(const meshtastic_MeshPacket *p)
+{
+    return (p && p->decoded.portnum == ourPortNum);
+}
+
+ProcessMessage ReplyBotModule::handleReceived(const meshtastic_MeshPacket &mp)
+{
+    // Accept only direct messages to us or broadcasts on the Primary channel
+    // (regardless of modem preset: LongFast, MediumFast, etc).
+
+    const uint32_t ourNode = nodeDB->getNodeNum();
+    const bool isDM = (mp.to == ourNode);
+    const bool isPrimaryChannel = (mp.channel == channels.getPrimaryIndex()) && isBroadcast(mp.to);
+    if (!isDM && !isPrimaryChannel) {
+        return ProcessMessage::CONTINUE;
+    }
+
+    // Ignore empty payloads
+    if (mp.decoded.payload.size == 0) {
+        return ProcessMessage::CONTINUE;
+    }
+
+    // Copy payload into a null‑terminated buffer
+    char buf[260];
+    memset(buf, 0, sizeof(buf));
+    size_t n = mp.decoded.payload.size;
+    if (n > sizeof(buf) - 1)
+        n = sizeof(buf) - 1;
+    memcpy(buf, mp.decoded.payload.bytes, n);
+
+    // React only to supported slash commands
+    if (!isCommand(buf)) {
+        return ProcessMessage::CONTINUE;
+    }
+
+    // Apply rate limiting per sender depending on DM/broadcast
+    const uint32_t cooldownMs = isDM ? REPLYBOT_DM_COOLDOWN_MS : REPLYBOT_LF_COOLDOWN_MS;
+    if (replybotRateLimited(mp.from, cooldownMs)) {
+        return ProcessMessage::CONTINUE;
+    }
+
+    // Compute hop count indicator – if the relay_node is non‑zero we know
+    // there was at least one relay.  Some firmware builds support a hop_start
+    // field which could be used for more accurate counts, but here we use
+    // the available relay_node flag only.
+    // int hopsAway = mp.hop_start - mp.hop_limit;
+    int hopsAway = getHopsAway(mp);
+
+    // Normalize RSSI: if positive adjust down by 200 to align with typical values
+    int rssi = mp.rx_rssi;
+    if (rssi > 0) {
+        rssi -= 200;
+    }
+    float snr = mp.rx_snr;
+
+    // Build the reply message and send it back via DM
+    char reply[96];
+    snprintf(reply, sizeof(reply), "🎙️ Mic Check : %d Hops away | RSSI %d | SNR %.1f", hopsAway, rssi, snr);
+    sendDm(mp, reply);
+    return ProcessMessage::CONTINUE;
+}
+
+// Check if the message starts with one of the supported commands.  Leading
+// whitespace is skipped and commands must be followed by end‑of‑string or
+// whitespace.
+bool ReplyBotModule::isCommand(const char *msg) const
+{
+    if (!msg)
+        return false;
+    while (*msg == ' ' || *msg == '\t')
+        msg++;
+    auto isEndOrSpace = [](char c) { return c == '\0' || std::isspace(static_cast<unsigned char>(c)); };
+    if (strncmp(msg, "/ping", 5) == 0 && isEndOrSpace(msg[5]))
+        return true;
+    if (strncmp(msg, "/hello", 6) == 0 && isEndOrSpace(msg[6]))
+        return true;
+    if (strncmp(msg, "/test", 5) == 0 && isEndOrSpace(msg[5]))
+        return true;
+    return false;
+}
+
+// Send a direct message back to the originating node.
+void ReplyBotModule::sendDm(const meshtastic_MeshPacket &rx, const char *text)
+{
+    if (!text)
+        return;
+    meshtastic_MeshPacket *p = allocDataPacket();
+    p->to = rx.from;
+    p->channel = rx.channel;
+    p->want_ack = false;
+    p->decoded.want_response = false;
+    size_t len = strlen(text);
+    if (len > sizeof(p->decoded.payload.bytes)) {
+        len = sizeof(p->decoded.payload.bytes);
+    }
+    p->decoded.payload.size = len;
+    memcpy(p->decoded.payload.bytes, text, len);
+    service->sendToMesh(p);
+}
+#endif // MESHTASTIC_EXCLUDE_REPLYBOT