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use std::sync::atomic::{AtomicU8, AtomicU16};
// DTMF events as per RFC 4733
const DTMF_EVENT_0: u8 = 0;
const DTMF_EVENT_1: u8 = 1;
const DTMF_EVENT_2: u8 = 2;
const DTMF_EVENT_3: u8 = 3;
const DTMF_EVENT_4: u8 = 4;
const DTMF_EVENT_5: u8 = 5;
const DTMF_EVENT_6: u8 = 6;
const DTMF_EVENT_7: u8 = 7;
const DTMF_EVENT_8: u8 = 8;
const DTMF_EVENT_9: u8 = 9;
const DTMF_EVENT_STAR: u8 = 10;
const DTMF_EVENT_POUND: u8 = 11;
const DTMF_EVENT_A: u8 = 12;
const DTMF_EVENT_B: u8 = 13;
const DTMF_EVENT_C: u8 = 14;
const DTMF_EVENT_D: u8 = 15;
pub struct DtmfDetector {
// Track the last seen event to avoid repeated events
last_event: AtomicU8,
last_duration: AtomicU16,
pub refer: Option<bool>,
pub suppress_dtmf_forward: bool,
}
#[derive(Debug)]
struct DtmfPayload {
event: u8, // 8bits
#[allow(dead_code)]
is_end: bool, // 1bit
_reserved: u8, // 1bits
_volume: u8, // 6bits
duration: u16, // 16bits
}
impl DtmfPayload {
fn parse(payload: &[u8]) -> Option<Self> {
if payload.len() < 4 {
return None;
}
let event = payload[0];
if event > DTMF_EVENT_D {
return None;
}
// 0 1 2 3
// 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// | event |E|R| volume | duration |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Figure 1: Payload Format for Named Events
// Second byte: End bit (E) is the most significant bit (bit 7)
let is_end = (payload[1] & 0b1000_0000) != 0;
// Reserved bit (R) is the second most significant bit (bit 6)
let reserved = payload[1] & 0b0100_0000;
// Volume is the 6 least significant bits (0-5)
let volume = payload[1] & 0b0011_1111;
// Duration is a 16-bit value spanning bytes 2 and 3
let duration_high = payload[2] as u16;
let duration_low = payload[3] as u16;
let duration = (duration_high << 8) | duration_low;
Some(Self {
event,
is_end,
_reserved: reserved,
_volume: volume,
duration,
})
}
}
impl DtmfDetector {
pub fn new() -> Self {
Self {
last_event: AtomicU8::new(0xFF),
last_duration: AtomicU16::new(0),
refer: None,
suppress_dtmf_forward: false,
}
}
// Detect DTMF events from RTP payload as specified in RFC 4733
pub fn detect_rtp(&self, payload_type: u8, payload: &[u8]) -> Option<String> {
// RFC 4733 defines DTMF events with payload types 96-127 (dynamic)
// However, we'll be more lenient and just check if the payload has the right format
if payload.len() < 4 {
return None;
}
// Generally, telephone-event payload type is in dynamic range 96-127
if payload_type < 96 || payload_type > 127 {
return None;
}
// Parse the DTMF payload
let dtmf_payload = DtmfPayload::parse(payload)?;
// Get current duration
let current_event = dtmf_payload.event;
let current_duration = dtmf_payload.duration;
let last_event = self
.last_event
.swap(current_event, std::sync::atomic::Ordering::Relaxed);
let last_duration = self
.last_duration
.swap(current_duration, std::sync::atomic::Ordering::Relaxed);
if current_event == last_event && current_duration >= last_duration {
return None;
}
Some(
match dtmf_payload.event {
DTMF_EVENT_0 => "0",
DTMF_EVENT_1 => "1",
DTMF_EVENT_2 => "2",
DTMF_EVENT_3 => "3",
DTMF_EVENT_4 => "4",
DTMF_EVENT_5 => "5",
DTMF_EVENT_6 => "6",
DTMF_EVENT_7 => "7",
DTMF_EVENT_8 => "8",
DTMF_EVENT_9 => "9",
DTMF_EVENT_STAR => "*",
DTMF_EVENT_POUND => "#",
DTMF_EVENT_A => "A",
DTMF_EVENT_B => "B",
DTMF_EVENT_C => "C",
DTMF_EVENT_D => "D",
_ => return None, // Invalid event
}
.to_string(),
)
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_dtmf_payload_parse() {
// Valid DTMF payload for digit "1" with end bit set
// Event: 1, End bit: 1, Reserved: 0, Volume: 10, Duration: 160
let payload = [1, 0x8A, 0, 160]; // 0x8A = 10001010 (end=1, reserved=0, volume=10)
let dtmf = DtmfPayload::parse(&payload).unwrap();
assert_eq!(dtmf.event, 1);
assert_eq!(dtmf.is_end, true);
assert_eq!(dtmf._reserved, 0);
assert_eq!(dtmf._volume, 10); // 10 = 001010 binary
assert_eq!(dtmf.duration, 160);
// Test payload with end bit not set
let payload = [2, 0x00, 0, 160]; // 0x00 = 00000000 (end=0, reserved=0, volume=0)
let dtmf = DtmfPayload::parse(&payload).unwrap();
assert_eq!(dtmf.event, 2);
assert_eq!(dtmf.is_end, false);
assert_eq!(dtmf._volume, 0);
// Invalid event code
let payload = [20, 0x80, 10, 100]; // 20 > DTMF_EVENT_D
assert!(DtmfPayload::parse(&payload).is_none());
// Too short payload
let payload = [1, 0x80, 10]; // Missing duration byte
assert!(DtmfPayload::parse(&payload).is_none());
// Test the specific case [2, 138, 3, 32]
let payload = [2, 138, 3, 32];
// 138 decimal = 10001010 binary
// End bit (bit 7) = 1
// Reserved bit (bit 6) = 0
// Volume (bits 0-5) = 001010 = 10
let dtmf = DtmfPayload::parse(&payload).unwrap();
assert_eq!(dtmf.event, 2); // DTMF digit "2"
assert_eq!(dtmf.is_end, true); // End bit is set
assert_eq!(dtmf._reserved, 0); // Reserved bit is 0
assert_eq!(dtmf._volume, 10); // Volume is 10
assert_eq!(dtmf.duration, 800); // Duration is 3 * 256 + 32 = 800
}
#[test]
fn test_dtmf_detection() {
let detector = DtmfDetector::new();
// Test basic detection
{
// Valid DTMF payload for digit "5" with end bit set
let payload = [DTMF_EVENT_5, 0x80, 10, 100];
// Use payload_type 101 (typical for telephone-event)
let digit = detector.detect_rtp(101, &payload);
assert_eq!(digit, Some("5".to_string()));
// Should reject payloads with invalid payload type
let digit = detector.detect_rtp(0, &payload);
assert_eq!(digit, None);
// Should reject payloads with end bit not set
let payload = [DTMF_EVENT_5, 0x00, 10, 100];
let digit = detector.detect_rtp(101, &payload);
assert_eq!(digit, None);
}
// Test duplicate detection
{
let detector = DtmfDetector::new(); // Use a fresh detector
// First event
let payload1 = [DTMF_EVENT_5, 0x80, 0, 100]; // Duration 100
let digit1 = detector.detect_rtp(101, &payload1);
assert_eq!(digit1, Some("5".to_string()));
// Similar duration - should be rejected as duplicate
let payload2 = [DTMF_EVENT_5, 0x80, 0, 100]; // Duration 150 (similar)
let digit2 = detector.detect_rtp(101, &payload2);
assert_eq!(digit2, None);
// Different event - should be detected
let payload4 = [DTMF_EVENT_6, 0x80, 1, 8]; // Event 6 ("6" key)
let digit4 = detector.detect_rtp(101, &payload4);
assert_eq!(digit4, Some("6".to_string()));
}
}
#[test]
fn test_dtmf_digit_0_first_press() {
let detector = DtmfDetector::new();
let payload = [DTMF_EVENT_0, 0x80, 0, 160]; // Event 0, end bit set
let digit = detector.detect_rtp(101, &payload);
assert_eq!(
digit,
Some("0".to_string()),
"First press of digit '0' should be recognized"
);
// Duplicate should be ignored
let payload2 = [DTMF_EVENT_0, 0x80, 0, 160]; // Same event, same duration
let digit2 = detector.detect_rtp(101, &payload2);
assert_eq!(digit2, None, "Duplicate DTMF should be filtered out");
// New press with smaller duration (new key press started) should be detected
let payload3 = [DTMF_EVENT_0, 0x80, 0, 80]; // Smaller duration = new press
let digit3 = detector.detect_rtp(101, &payload3);
assert_eq!(
digit3,
Some("0".to_string()),
"Second press with smaller duration should be recognized as new press"
);
}
}