From 2653ee01aa671318fb142a710ea6857abe03461d Mon Sep 17 00:00:00 2001
From: Morgan Diepart <morgandiepart@gmail.com>
Date: Sun, 22 Oct 2023 21:13:27 -0700
Subject: [PATCH] M17: added callsign-based squelch for incoming transmissions

---
 openrtx/include/rtx/OpMode_M17.hpp | 13 +++++++++++++
 openrtx/src/rtx/OpMode_M17.cpp     | 30 +++++++++++++++++++++++++++++-
 2 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/openrtx/include/rtx/OpMode_M17.hpp b/openrtx/include/rtx/OpMode_M17.hpp
index 537637c0..28310354 100644
--- a/openrtx/include/rtx/OpMode_M17.hpp
+++ b/openrtx/include/rtx/OpMode_M17.hpp
@@ -121,6 +121,19 @@ private:
      */
     void txState(rtxStatus_t *const status);
 
+    /**
+     * Compare two callsigns in plain text form.
+     * The comparison does not take into account the country prefixes (strips
+     * the '/' and whatever is in front from all callsigns). It does take into
+     * account the dash and whatever is after it. In case the incoming callsign
+     * is "ALL" the function returns true.
+     *
+     * \param localCs plain text callsign from the user
+     * \param incomingCs plain text destination callsign
+     * \return true if local an incoming callsigns match.
+     */
+    bool compareCallsigns(const std::string& localCs, const std::string& incomingCs);
+
 
     bool startRx;                      ///< Flag for RX management.
     bool startTx;                      ///< Flag for TX management.
diff --git a/openrtx/src/rtx/OpMode_M17.cpp b/openrtx/src/rtx/OpMode_M17.cpp
index 700896d1..1f8fdbcd 100644
--- a/openrtx/src/rtx/OpMode_M17.cpp
+++ b/openrtx/src/rtx/OpMode_M17.cpp
@@ -268,8 +268,13 @@ void OpMode_M17::rxState(rtxStatus_t *const status)
                 bool canMatch =  (streamType.fields.CAN == status->can)
                               || (status->canRxEn == false);
 
+                // Check if the destination callsign of the incoming transmission
+                // matches with ours
+                bool callMatch = compareCallsigns(std::string(status->source_address), dst);
+
                 // Extract audio data
-                if((type == M17FrameType::STREAM) && (pthSts == PATH_OPEN) && (canMatch == true))
+                if((type == M17FrameType::STREAM) && (pthSts == PATH_OPEN) &&
+                   (canMatch == true)             && (callMatch == true))
                 {
                     M17StreamFrame sf = decoder.getStreamFrame();
                     codec_pushFrame(sf.payload().data(),     false);
@@ -359,3 +364,26 @@ void OpMode_M17::txState(rtxStatus_t *const status)
         modulator.stop();
     }
 }
+
+bool OpMode_M17::compareCallsigns(const std::string& localCs,
+                                  const std::string& incomingCs)
+{
+    if(incomingCs == "ALL")
+        return true;
+
+    std::string truncatedLocal(localCs);
+    std::string truncatedIncoming(incomingCs);
+
+    int slashPos = localCs.find_first_of('/');
+    if(slashPos <= 2)
+        truncatedLocal = localCs.substr(slashPos + 1);
+
+    slashPos = incomingCs.find_first_of('/');
+    if(slashPos <= 2)
+        truncatedIncoming = incomingCs.substr(slashPos + 1);
+
+    if(truncatedLocal == truncatedIncoming)
+        return true;
+
+    return false;
+}