From 7831c5085ed435a300d906a1f940781059b0daf9 Mon Sep 17 00:00:00 2001
From: Will Greenberg <willg@eff.org>
Date: Thu, 25 Jun 2026 07:36:23 -0700
Subject: [PATCH] If a Message isn't convertable to GSMTAP, don't try

This also removes the pseudo GSMTAP packets added for measurement
results, since they add a ton of noise to PCAPs. Eventually, we should
keep track of the latest signal for a given PCI, and annotate actual
packets with that value.
---
 lib/src/diag/mod.rs      | 14 ++++++++++++++
 lib/src/gsmtap/parser.rs | 17 +++++------------
 2 files changed, 19 insertions(+), 12 deletions(-)

diff --git a/lib/src/diag/mod.rs b/lib/src/diag/mod.rs
index 6a1ca3b..4443983 100644
--- a/lib/src/diag/mod.rs
+++ b/lib/src/diag/mod.rs
@@ -156,6 +156,20 @@ impl Message {
             Err(err) => Err(DiagParsingError::HdlcDecapsulationError(err, data.to_vec())),
         }
     }
+
+    /// Returns whether this message should be parsed into a GSMTAP packet for
+    /// display in pcap files
+    pub fn is_gsmtap_message(&self) -> bool {
+        let Message::Log { body, .. } = self else {
+            return false;
+        };
+        match body {
+            LogBody::LteRrcOtaMessage { .. } => true,
+            LogBody::LteMacRachResponse { .. } => true,
+            LogBody::Nas4GMessage { .. } => true,
+            _ => false
+        }
+    }
 }
 
 #[derive(Debug, Clone, PartialEq, DekuRead, DekuWrite)]
diff --git a/lib/src/gsmtap/parser.rs b/lib/src/gsmtap/parser.rs
index 837d22b..e33f91c 100644
--- a/lib/src/gsmtap/parser.rs
+++ b/lib/src/gsmtap/parser.rs
@@ -17,6 +17,9 @@ pub enum GsmtapParserError {
 }
 
 pub fn parse(msg: Message) -> Result<Option<(Timestamp, GsmtapMessage)>, GsmtapParserError> {
+    if !msg.is_gsmtap_message() {
+        return Ok(None);
+    }
     if let Message::Log {
         timestamp, body, ..
     } = msg
@@ -31,6 +34,8 @@ pub fn parse(msg: Message) -> Result<Option<(Timestamp, GsmtapMessage)>, GsmtapP
 }
 
 fn log_to_gsmtap(value: LogBody) -> Result<Option<GsmtapMessage>, GsmtapParserError> {
+    // Note: if support for another LogBody variant is added here, it should
+    // also be added to Message::is_gsmtap_message
     match value {
         LogBody::LteRrcOtaMessage {
             ext_header_version,
@@ -156,18 +161,6 @@ fn log_to_gsmtap(value: LogBody) -> Result<Option<GsmtapMessage>, GsmtapParserEr
                 payload: msg,
             }))
         }
-        LogBody::LteMl1ServingCellMeasurementAndEvaluation { data, .. } => {
-            // frame_number reused for PCI (normally SFN in RRC frames) so all three
-            // serving-cell fields are accessible in Wireshark as gsmtap.* columns.
-            let mut header = GsmtapHeader::new(GsmtapType::QcDiag);
-            header.signal_dbm = data.get_meas_rsrp() as i8;
-            header.arfcn = data.get_earfcn().try_into().unwrap_or(0);
-            header.frame_number = data.get_pci() as u32;
-            Ok(Some(GsmtapMessage {
-                header,
-                payload: vec![],
-            }))
-        }
         LogBody::LteMacRachResponse { packet } => {
             if packet.subpackets.len() > 1 {
                 warn!(