lib: refactor gsmtap/gsmtap_parser into a single module

This'll allow us to break out more specific GSMTAP parsing into submodules more easily.
2026-07-08 09:38:10 -07:00 · 2026-06-24 12:24:01 -07:00
parent cae056d959
commit 38f476b664
7 changed files with 6 additions and 5 deletions
@@ -0,0 +1,181 @@
+use crate::diag::Message;
+use crate::diag::diaglog::{Timestamp, LogBody, Nas4GMessageDirection};
+use crate::gsmtap::{GsmtapHeader, GsmtapMessage, GsmtapType, LteNasSubtype, LteRrcSubtype};
+
+use log::error;
+use thiserror::Error;
+
+#[derive(Debug, Error)]
+pub enum GsmtapParserError {
+    #[error("Invalid LteRrcOtaMessage ext header version {0}")]
+    InvalidLteRrcOtaExtHeaderVersion(u8),
+    #[error("Invalid LteRrcOtaMessage header/PDU number combination: {0}/{1}")]
+    InvalidLteRrcOtaHeaderPduNum(u8, u8),
+}
+
+pub fn parse(msg: Message) -> Result<Option<(Timestamp, GsmtapMessage)>, GsmtapParserError> {
+    if let Message::Log {
+        timestamp, body, ..
+    } = msg
+    {
+        match log_to_gsmtap(body)? {
+            Some(msg) => Ok(Some((timestamp, msg))),
+            None => Ok(None),
+        }
+    } else {
+        Ok(None)
+    }
+}
+
+fn log_to_gsmtap(value: LogBody) -> Result<Option<GsmtapMessage>, GsmtapParserError> {
+    match value {
+        LogBody::LteRrcOtaMessage {
+            ext_header_version,
+            packet,
+        } => {
+            let gsmtap_type = match ext_header_version {
+                0x02 | 0x03 | 0x04 | 0x06 | 0x07 | 0x08 | 0x0d | 0x16 => match packet.get_pdu_num()
+                {
+                    1 => GsmtapType::LteRrc(LteRrcSubtype::BcchBch),
+                    2 => GsmtapType::LteRrc(LteRrcSubtype::BcchDlSch),
+                    3 => GsmtapType::LteRrc(LteRrcSubtype::MCCH),
+                    4 => GsmtapType::LteRrc(LteRrcSubtype::PCCH),
+                    5 => GsmtapType::LteRrc(LteRrcSubtype::DlCcch),
+                    6 => GsmtapType::LteRrc(LteRrcSubtype::DlDcch),
+                    7 => GsmtapType::LteRrc(LteRrcSubtype::UlCcch),
+                    8 => GsmtapType::LteRrc(LteRrcSubtype::UlDcch),
+                    pdu => {
+                        return Err(GsmtapParserError::InvalidLteRrcOtaHeaderPduNum(
+                            ext_header_version,
+                            pdu,
+                        ));
+                    }
+                },
+                0x09 | 0x0c => match packet.get_pdu_num() {
+                    8 => GsmtapType::LteRrc(LteRrcSubtype::BcchBch),
+                    9 => GsmtapType::LteRrc(LteRrcSubtype::BcchDlSch),
+                    10 => GsmtapType::LteRrc(LteRrcSubtype::MCCH),
+                    11 => GsmtapType::LteRrc(LteRrcSubtype::PCCH),
+                    12 => GsmtapType::LteRrc(LteRrcSubtype::DlCcch),
+                    13 => GsmtapType::LteRrc(LteRrcSubtype::DlDcch),
+                    14 => GsmtapType::LteRrc(LteRrcSubtype::UlCcch),
+                    15 => GsmtapType::LteRrc(LteRrcSubtype::UlDcch),
+                    pdu => {
+                        return Err(GsmtapParserError::InvalidLteRrcOtaHeaderPduNum(
+                            ext_header_version,
+                            pdu,
+                        ));
+                    }
+                },
+                0x0e..=0x10 => match packet.get_pdu_num() {
+                    1 => GsmtapType::LteRrc(LteRrcSubtype::BcchBch),
+                    2 => GsmtapType::LteRrc(LteRrcSubtype::BcchDlSch),
+                    4 => GsmtapType::LteRrc(LteRrcSubtype::MCCH),
+                    5 => GsmtapType::LteRrc(LteRrcSubtype::PCCH),
+                    6 => GsmtapType::LteRrc(LteRrcSubtype::DlCcch),
+                    7 => GsmtapType::LteRrc(LteRrcSubtype::DlDcch),
+                    8 => GsmtapType::LteRrc(LteRrcSubtype::UlCcch),
+                    9 => GsmtapType::LteRrc(LteRrcSubtype::UlDcch),
+                    pdu => {
+                        return Err(GsmtapParserError::InvalidLteRrcOtaHeaderPduNum(
+                            ext_header_version,
+                            pdu,
+                        ));
+                    }
+                },
+                0x13 | 0x1a | 0x1b => match packet.get_pdu_num() {
+                    1 => GsmtapType::LteRrc(LteRrcSubtype::BcchBch),
+                    3 => GsmtapType::LteRrc(LteRrcSubtype::BcchDlSch),
+                    6 => GsmtapType::LteRrc(LteRrcSubtype::MCCH),
+                    7 => GsmtapType::LteRrc(LteRrcSubtype::PCCH),
+                    8 => GsmtapType::LteRrc(LteRrcSubtype::DlCcch),
+                    9 => GsmtapType::LteRrc(LteRrcSubtype::DlDcch),
+                    10 => GsmtapType::LteRrc(LteRrcSubtype::UlCcch),
+                    11 => GsmtapType::LteRrc(LteRrcSubtype::UlDcch),
+                    45 => GsmtapType::LteRrc(LteRrcSubtype::BcchBchNb),
+                    46 => GsmtapType::LteRrc(LteRrcSubtype::BcchDlSchNb),
+                    47 => GsmtapType::LteRrc(LteRrcSubtype::PcchNb),
+                    48 => GsmtapType::LteRrc(LteRrcSubtype::DlCcchNb),
+                    49 => GsmtapType::LteRrc(LteRrcSubtype::DlDcchNb),
+                    50 => GsmtapType::LteRrc(LteRrcSubtype::UlCcchNb),
+                    52 => GsmtapType::LteRrc(LteRrcSubtype::UlDcchNb),
+                    pdu => {
+                        return Err(GsmtapParserError::InvalidLteRrcOtaHeaderPduNum(
+                            ext_header_version,
+                            pdu,
+                        ));
+                    }
+                },
+                0x14 | 0x18 | 0x19 => match packet.get_pdu_num() {
+                    1 => GsmtapType::LteRrc(LteRrcSubtype::BcchBch),
+                    2 => GsmtapType::LteRrc(LteRrcSubtype::BcchDlSch),
+                    4 => GsmtapType::LteRrc(LteRrcSubtype::MCCH),
+                    5 => GsmtapType::LteRrc(LteRrcSubtype::PCCH),
+                    6 => GsmtapType::LteRrc(LteRrcSubtype::DlCcch),
+                    7 => GsmtapType::LteRrc(LteRrcSubtype::DlDcch),
+                    8 => GsmtapType::LteRrc(LteRrcSubtype::UlCcch),
+                    9 => GsmtapType::LteRrc(LteRrcSubtype::UlDcch),
+                    54 => GsmtapType::LteRrc(LteRrcSubtype::BcchBchNb),
+                    55 => GsmtapType::LteRrc(LteRrcSubtype::BcchDlSchNb),
+                    56 => GsmtapType::LteRrc(LteRrcSubtype::PcchNb),
+                    57 => GsmtapType::LteRrc(LteRrcSubtype::DlCcchNb),
+                    58 => GsmtapType::LteRrc(LteRrcSubtype::DlDcchNb),
+                    59 => GsmtapType::LteRrc(LteRrcSubtype::UlCcchNb),
+                    61 => GsmtapType::LteRrc(LteRrcSubtype::UlDcchNb),
+                    pdu => {
+                        return Err(GsmtapParserError::InvalidLteRrcOtaHeaderPduNum(
+                            ext_header_version,
+                            pdu,
+                        ));
+                    }
+                },
+                _ => {
+                    return Err(GsmtapParserError::InvalidLteRrcOtaExtHeaderVersion(
+                        ext_header_version,
+                    ));
+                }
+            };
+            let mut header = GsmtapHeader::new(gsmtap_type);
+            header.arfcn = (packet.get_earfcn() as u16) & 0x3FFF;
+            header.frame_number = packet.get_sfn();
+            header.subslot = packet.get_subfn();
+            Ok(Some(GsmtapMessage {
+                header,
+                payload: packet.take_payload(),
+            }))
+        }
+        LogBody::Nas4GMessage { msg, direction, .. } => {
+            // currently we only handle "plain" (i.e. non-secure) NAS messages
+            let mut header = GsmtapHeader::new(GsmtapType::LteNas(LteNasSubtype::Plain));
+            header.uplink = matches!(direction, Nas4GMessageDirection::Uplink);
+            Ok(Some(GsmtapMessage {
+                header,
+                payload: msg,
+            }))
+        }
+        _ => {
+            error!("gsmtap_sink: ignoring unhandled log type: {value:?}");
+            Ok(None)
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use deku::DekuContainerWrite;
+
+    #[test]
+    fn test_arfcn_exceeding_14_bits_does_not_panic() {
+        let mut header = GsmtapHeader::new(GsmtapType::LteRrc(LteRrcSubtype::DlDcch));
+        // EARFCN 54540 (band 46) exceeds 14-bit max of 16383
+        let large_earfcn: u32 = 54540;
+        header.arfcn = (large_earfcn as u16) & 0x3FFF;
+        let msg = GsmtapMessage {
+            header,
+            payload: vec![0x00],
+        };
+        // This would panic before the fix with "bit size of input is larger than bit requested size"
+        assert!(msg.to_bytes().is_ok());
+    }
+}