siprouter/rust/crates/proxy-engine/src/dtmf.rs

//! DTMF detection — parses RFC 2833 telephone-event RTP packets.
//!
//! Deduplicates repeated packets (same digit sent multiple times with
//! increasing duration) and fires once per detected digit.
//!
//! Ported from ts/call/dtmf-detector.ts.

use crate::ipc::{emit_event, OutTx};

/// RFC 2833 event ID → character mapping.
const EVENT_CHARS: &[char] = &[
    '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '*', '#', 'A', 'B', 'C', 'D',
];

/// Safety timeout: report digit if no End packet arrives within this many ms.
const SAFETY_TIMEOUT_MS: u64 = 200;

/// DTMF detector for a single RTP stream.
pub struct DtmfDetector {
    /// Negotiated telephone-event payload type (default 101).
    telephone_event_pt: u8,
    /// Clock rate for duration calculation (default 8000 Hz).
    clock_rate: u32,
    /// Call ID for event emission.
    call_id: String,

    // Deduplication state.
    current_event_id: Option<u8>,
    current_event_ts: Option<u32>,
    current_event_reported: bool,
    current_event_duration: u16,

    out_tx: OutTx,
}

impl DtmfDetector {
    pub fn new(call_id: String, out_tx: OutTx) -> Self {
        Self {
            telephone_event_pt: 101,
            clock_rate: 8000,
            call_id,
            current_event_id: None,
            current_event_ts: None,
            current_event_reported: false,
            current_event_duration: 0,
            out_tx,
        }
    }

    /// Feed an RTP packet. Checks PT; ignores non-DTMF packets.
    /// Returns Some(digit_char) if a digit was detected.
    pub fn process_rtp(&mut self, data: &[u8]) -> Option<char> {
        if data.len() < 16 {
            return None; // 12-byte header + 4-byte telephone-event minimum
        }

        let pt = data[1] & 0x7F;
        if pt != self.telephone_event_pt {
            return None;
        }

        let marker = (data[1] & 0x80) != 0;
        let rtp_timestamp = u32::from_be_bytes([data[4], data[5], data[6], data[7]]);

        // Parse telephone-event payload.
        let event_id = data[12];
        let end_bit = (data[13] & 0x80) != 0;
        let duration = u16::from_be_bytes([data[14], data[15]]);

        if event_id as usize >= EVENT_CHARS.len() {
            return None;
        }

        // Detect new event.
        let is_new = marker
            || self.current_event_id != Some(event_id)
            || self.current_event_ts != Some(rtp_timestamp);

        if is_new {
            // Report pending unreported event.
            let pending = self.report_pending();

            self.current_event_id = Some(event_id);
            self.current_event_ts = Some(rtp_timestamp);
            self.current_event_reported = false;
            self.current_event_duration = duration;

            if pending.is_some() {
                return pending;
            }
        }

        if duration > self.current_event_duration {
            self.current_event_duration = duration;
        }

        // Report on End bit (first time only).
        if end_bit && !self.current_event_reported {
            self.current_event_reported = true;
            let digit = EVENT_CHARS[event_id as usize];
            let duration_ms = (self.current_event_duration as f64 / self.clock_rate as f64) * 1000.0;

            emit_event(
                &self.out_tx,
                "dtmf_digit",
                serde_json::json!({
                    "call_id": self.call_id,
                    "digit": digit.to_string(),
                    "duration_ms": duration_ms.round() as u32,
                    "source": "rfc2833",
                }),
            );

            return Some(digit);
        }

        None
    }

    /// Report a pending unreported event.
    fn report_pending(&mut self) -> Option<char> {
        if let Some(event_id) = self.current_event_id {
            if !self.current_event_reported && (event_id as usize) < EVENT_CHARS.len() {
                self.current_event_reported = true;
                let digit = EVENT_CHARS[event_id as usize];
                let duration_ms =
                    (self.current_event_duration as f64 / self.clock_rate as f64) * 1000.0;

                emit_event(
                    &self.out_tx,
                    "dtmf_digit",
                    serde_json::json!({
                        "call_id": self.call_id,
                        "digit": digit.to_string(),
                        "duration_ms": duration_ms.round() as u32,
                        "source": "rfc2833",
                    }),
                );

                return Some(digit);
            }
        }
        None
    }

    /// Process a SIP INFO message body for DTMF.
    pub fn process_sip_info(&mut self, content_type: &str, body: &str) -> Option<char> {
        let ct = content_type.to_ascii_lowercase();

        if ct.contains("application/dtmf-relay") {
            // Format: "Signal= 5\r\nDuration= 160\r\n"
            let signal = body
                .lines()
                .find(|l| l.to_ascii_lowercase().starts_with("signal"))
                .and_then(|l| l.split('=').nth(1))
                .map(|s| s.trim().to_string())?;

            if signal.len() != 1 {
                return None;
            }
            let digit = signal.chars().next()?.to_ascii_uppercase();
            if !"0123456789*#ABCD".contains(digit) {
                return None;
            }

            emit_event(
                &self.out_tx,
                "dtmf_digit",
                serde_json::json!({
                    "call_id": self.call_id,
                    "digit": digit.to_string(),
                    "source": "sip-info",
                }),
            );

            return Some(digit);
        }

        if ct.contains("application/dtmf") {
            let digit = body.trim().chars().next()?.to_ascii_uppercase();
            if !"0123456789*#ABCD".contains(digit) {
                return None;
            }

            emit_event(
                &self.out_tx,
                "dtmf_digit",
                serde_json::json!({
                    "call_id": self.call_id,
                    "digit": digit.to_string(),
                    "source": "sip-info",
                }),
            );

            return Some(digit);
        }

        None
    }
}