Driver: Split receive into its own feature (#141)

Adds the "receive" feature, which is disabled by default. When this is disabled, the UDP receive task is not compiled and not run, and as an optimisation the UDP receive buffer size is set to 0. All related events are also removed.

This also removes the UDP Tx task, and moves packet and keepalive sends back into the mixer thread. This allows us to entirely remove channels and various allocations between the mixer and an async task created only for sending data (i.e., fewer memcopies).

If "receive" is enabled, UDP sends are now non-blocking due to technical constraints -- failure to send is non-fatal, but *will* drop affected packets. Given that blocking on a UDP send indicates that the OS cannot clear send buffers fast enough, this should alleviate OS load.

Closes #131.

ARCHITECTURE.md

@@ -35,13 +35,12 @@ Audio processing remains synchronous for the following reasons:
 Songbird subdivides voice connection handling into several long- and short-lived tasks.
 
 * **Core**: Handles and directs commands received from the driver. Responsible for connection/reconnection, and creates network tasks.
-* **Mixer**: Combines audio sources together, Opus encodes the result, and encrypts the built packets every 20ms. Responsible for handling track commands/state. ***Synchronous***.
+* **Mixer**: Combines audio sources together, Opus encodes the result, and encrypts the built packets every 20ms. Responsible for handling track commands/state, and transmitting completed voice packets and keepalive messages. ***Synchronous***.
 * **Thread Pool**: A dynamically sized thread-pool for I/O tasks. Creates lazy tracks using `Compose` if sync creation is needed, otherwise spawns a tokio task. Seek operations always go to the thread pool. ***Synchronous***.
 * **Disposer**: Used by mixer thread to dispose of data with potentially long/blocking `Drop` implementations (i.e., audio sources). ***Synchronous***.
 * **Events**: Stores and runs event handlers, tracks event timing, and handles 
 * **Websocket**: *Network task.* Sends speaking status updates and keepalives to Discord, and receives client (dis)connect events.
-* **UDP Tx**: *Network task.* Responsible for transmitting completed voice packets.
-* **UDP Rx**: *Network task.* Decrypts/decodes received voice packets and statistics information.
+* **UDP Rx**: *Optional network task.* Decrypts/decodes received voice packets and statistics information.
 
 *Note: all tasks are able to message the permanent tasks via a block of interconnecting channels.*
 

Cargo.toml

@@ -19,7 +19,7 @@ audiopus = { optional = true, version = "0.3.0-rc.0" }
 byteorder = { optional = true, version = "1" }
 dashmap = { optional = true, version = "5" }
 derivative = "2"
-discortp = { features = ["discord-full"], optional = true, version = "0.5" }
+discortp = { default-features = false, features = ["discord", "pnet", "rtp"], optional = true, version = "0.5" }
 flume = { optional = true, version = "0.10" }
 futures = "0.3"
 once_cell = { optional = true, version = "1" }
@@ -32,8 +32,9 @@ rubato = { optional = true, version = "0.12" }
 rusty_pool = { optional = true, version = "0.7" }
 serde = { version = "1", features = ["derive"] }
 serde-aux = { default-features = false, optional = true, version = "3"}
-simd-json = { features = ["serde_impl"], optional = true, version = "0.6.0" }
 serde_json = "1"
+simd-json = { features = ["serde_impl"], optional = true, version = "0.6.0" }
+socket2 = { optional = true, version = "0.4" }
 streamcatcher = { optional = true, version = "1" }
 tokio = { default-features = false, optional = true, version = "1.0" }
 tokio-tungstenite = { optional = true, version = "0.17" }
@@ -110,6 +111,7 @@ driver = [
     "dep:rusty_pool",
     "dep:serde-aux",
     "dep:serenity-voice-model",
+    "dep:socket2",
     "dep:streamcatcher",
     "dep:symphonia",
     "dep:symphonia-core",
@@ -145,9 +147,10 @@ twilight = ["dep:twilight-gateway","dep:twilight-model"]
 
 # Behaviour altering features.
 builtin-queue = []
+receive = ["discortp?/demux", "discortp?/rtcp"]
 
 # Used for docgen/testing/benchmarking.
-full-doc = ["default", "twilight", "builtin-queue"]
+full-doc = ["default", "twilight", "builtin-queue", "receive"]
 internals = []
 
 [[bench]]

README.md

@@ -12,11 +12,11 @@ The library offers:
  * A standalone driver for voice calls, via the `"driver"` feature. If you can create
  a `ConnectionInfo` using any other gateway, or language for your bot, then you
  can run the songbird voice driver.
- * And, by default, a fully featured voice system featuring events, queues, RT(C)P packet
- handling, seeking on compatible streams, shared multithreaded audio stream caches,
+ * Voice receive and RT(C)P packet handling via the `"receive"` feature.
+ * SIMD-accelerated JSON decoding via the `"simd-json"` feature.
+ * And, by default, a fully featured voice system featuring events, queues,
+ seeking on compatible streams, shared multithreaded audio stream caches,
  and direct Opus data passthrough from DCA files.
- * To be able to use `simd-json` from serenity, you will need to enable the `simdjson`
- feature on both songbird and serenity.
 
 ## Intents
 Songbird's gateway functionality requires you to specify the `GUILD_VOICE_STATES` intent.

benches/mixing-task.rs

@@ -25,7 +25,7 @@ use songbird::{
     tracks,
     Config,
 };
-use std::io::Cursor;
+use std::{io::Cursor, net::UdpSocket};
 use tokio::runtime::{Handle, Runtime};
 use xsalsa20poly1305::{aead::NewAead, XSalsa20Poly1305 as Cipher, KEY_SIZE};
 
@@ -41,14 +41,12 @@ fn dummied_mixer(
         Receiver<CoreMessage>,
         Receiver<EventMessage>,
         Receiver<UdpRxMessage>,
-        Receiver<UdpTxMessage>,
     ),
 ) {
     let (mix_tx, mix_rx) = flume::unbounded();
     let (core_tx, core_rx) = flume::unbounded();
     let (event_tx, event_rx) = flume::unbounded();
 
-    let (udp_sender_tx, udp_sender_rx) = flume::unbounded();
     let (udp_receiver_tx, udp_receiver_rx) = flume::unbounded();
 
     let ic = Interconnect {
@@ -61,18 +59,23 @@ fn dummied_mixer(
 
     let mut out = Mixer::new(mix_rx, handle, ic, config);
 
+    let udp_tx = UdpSocket::bind("0.0.0.0:0").expect("Failed to create send port.");
+    udp_tx
+        .connect("127.0.0.1:5316")
+        .expect("Failed to connect to local dest port.");
+
     let fake_conn = MixerConnection {
         cipher: Cipher::new_from_slice(&vec![0u8; KEY_SIZE]).unwrap(),
         crypto_state: CryptoState::Normal,
         udp_rx: udp_receiver_tx,
-        udp_tx: udp_sender_tx,
+        udp_tx,
     };
 
     out.conn_active = Some(fake_conn);
 
     out.skip_sleep = true;
 
-    (out, (core_rx, event_rx, udp_receiver_rx, udp_sender_rx))
+    (out, (core_rx, event_rx, udp_receiver_rx))
 }
 
 fn mixer_float(
@@ -85,7 +88,6 @@ fn mixer_float(
         Receiver<CoreMessage>,
         Receiver<EventMessage>,
         Receiver<UdpRxMessage>,
-        Receiver<UdpTxMessage>,
     ),
 ) {
     let mut out = dummied_mixer(handle, softclip);
@@ -115,7 +117,6 @@ fn mixer_float_drop(
         Receiver<CoreMessage>,
         Receiver<EventMessage>,
         Receiver<UdpRxMessage>,
-        Receiver<UdpTxMessage>,
     ),
 ) {
     let mut out = dummied_mixer(handle, true);
@@ -143,7 +144,6 @@ fn mixer_opus(
         Receiver<CoreMessage>,
         Receiver<EventMessage>,
         Receiver<UdpRxMessage>,
-        Receiver<UdpTxMessage>,
     ),
 ) {
     // should add a single opus-based track.

examples/Cargo.toml

@@ -6,3 +6,6 @@ members = [
     "serenity/voice_receive",
     "twilight",
 ]
+
+[profile.release]
+debug = true

examples/serenity/voice_receive/Cargo.toml

@@ -10,6 +10,7 @@ tracing-subscriber = "0.2"
 tracing-futures = "0.2"
 
 [dependencies.songbird]
+features = ["receive"]
 path = "../../../"
 
 [dependencies.serenity]

src/config.rs

@@ -1,6 +1,8 @@
+#[cfg(feature = "receive")]
+use crate::driver::DecodeMode;
 #[cfg(feature = "driver")]
 use crate::{
-    driver::{retry::Retry, CryptoMode, DecodeMode, MixMode},
+    driver::{retry::Retry, CryptoMode, MixMode},
     input::codecs::*,
 };
 
@@ -29,7 +31,8 @@ pub struct Config {
     ///
     /// [`CryptoMode::Normal`]: CryptoMode::Normal
     pub crypto_mode: CryptoMode,
-    #[cfg(feature = "driver")]
+
+    #[cfg(all(feature = "driver", feature = "receive"))]
     /// Configures whether decoding and decryption occur for all received packets.
     ///
     /// If voice receiving voice packets, generally you should choose [`DecodeMode::Decode`].
@@ -45,6 +48,7 @@ pub struct Config {
     /// [`DecodeMode::Pass`]: DecodeMode::Pass
     /// [user speaking events]: crate::events::CoreEvent::SpeakingUpdate
     pub decode_mode: DecodeMode,
+
     #[cfg(feature = "gateway")]
     /// Configures the amount of time to wait for Discord to reply with connection information
     /// if [`Call::join`]/[`join_gateway`] are used.
@@ -58,14 +62,16 @@ pub struct Config {
     /// [`Call::join`]: crate::Call::join
     /// [`join_gateway`]: crate::Call::join_gateway
     pub gateway_timeout: Option<Duration>,
+
     #[cfg(feature = "driver")]
-    /// Configures the maximum amount of time to wait for an attempted voice
-    /// connection to Discord.
+    /// Configures whether the driver will mix and output stereo or mono Opus data
+    /// over a voice channel.
     ///
     /// Defaults to [`Stereo`].
     ///
     /// [`Stereo`]: MixMode::Stereo
     pub mix_mode: MixMode,
+
     #[cfg(feature = "driver")]
     /// Number of concurrently active tracks to allocate memory for.
     ///
@@ -79,6 +85,7 @@ pub struct Config {
     /// Changes to this field in a running driver will only ever increase
     /// the capacity of the track store.
     pub preallocated_tracks: usize,
+
     #[cfg(feature = "driver")]
     /// Connection retry logic for the [`Driver`].
     ///
@@ -87,6 +94,7 @@ pub struct Config {
     ///
     /// [`Driver`]: crate::driver::Driver
     pub driver_retry: Retry,
+
     #[cfg(feature = "driver")]
     /// Configures whether or not each mixed audio packet is [soft-clipped] into the
     /// [-1, 1] audio range.
@@ -101,12 +109,14 @@ pub struct Config {
     ///
     /// [soft-clipped]: https://opus-codec.org/docs/opus_api-1.3.1/group__opus__decoder.html#gaff99598b352e8939dded08d96e125e0b
     pub use_softclip: bool,
+
     #[cfg(feature = "driver")]
     /// Configures the maximum amount of time to wait for an attempted voice
     /// connection to Discord.
     ///
     /// Defaults to 10 seconds. If set to `None`, connections will never time out.
     pub driver_timeout: Option<Duration>,
+
     #[cfg(feature = "driver")]
     #[derivative(Debug = "ignore")]
     /// Registry of the inner codecs supported by the driver, adding audiopus-based
@@ -116,6 +126,7 @@ pub struct Config {
     ///
     /// [`CODEC_REGISTRY`]: static@CODEC_REGISTRY
     pub codec_registry: &'static CodecRegistry,
+
     #[cfg(feature = "driver")]
     #[derivative(Debug = "ignore")]
     /// Registry of the muxers and container formats supported by the driver.
@@ -142,7 +153,7 @@ impl Default for Config {
         Self {
             #[cfg(feature = "driver")]
             crypto_mode: CryptoMode::Normal,
-            #[cfg(feature = "driver")]
+            #[cfg(all(feature = "driver", feature = "receive"))]
             decode_mode: DecodeMode::Decrypt,
             #[cfg(feature = "gateway")]
             gateway_timeout: Some(Duration::from_secs(10)),
@@ -179,6 +190,7 @@ impl Config {
         self
     }
 
+    #[cfg(feature = "receive")]
     /// Sets this `Config`'s received packet decryption/decoding behaviour.
     #[must_use]
     pub fn decode_mode(mut self, decode_mode: DecodeMode) -> Self {

src/driver/connection/mod.rs

@@ -1,7 +1,9 @@
 pub mod error;
 
+#[cfg(feature = "receive")]
+use super::tasks::udp_rx;
 use super::{
-    tasks::{message::*, udp_rx, udp_tx, ws as ws_task},
+    tasks::{message::*, ws as ws_task},
     Config,
     CryptoMode,
 };
@@ -18,7 +20,8 @@ use crate::{
 use discortp::discord::{IpDiscoveryPacket, IpDiscoveryType, MutableIpDiscoveryPacket};
 use error::{Error, Result};
 use flume::Sender;
-use std::{net::IpAddr, str::FromStr, sync::Arc};
+use socket2::Socket;
+use std::{net::IpAddr, str::FromStr};
 use tokio::{net::UdpSocket, spawn, time::timeout};
 use tracing::{debug, info, instrument};
 use url::Url;
@@ -103,6 +106,16 @@ impl Connection {
         }
 
         let udp = UdpSocket::bind("0.0.0.0:0").await?;
+
+        // Optimisation for non-receive case: set rx buffer size to zero.
+        let udp = if cfg!(feature = "receive") {
+            udp
+        } else {
+            let socket = Socket::from(udp.into_std()?);
+            socket.set_recv_buffer_size(0)?;
+            UdpSocket::from_std(socket.into())?
+        };
+
         udp.connect((ready.ip, ready.port)).await?;
 
         // Follow Discord's IP Discovery procedures, in case NAT tunnelling is needed.
@@ -164,22 +177,36 @@ impl Connection {
         info!("WS heartbeat duration {}ms.", hello.heartbeat_interval,);
 
         let (ws_msg_tx, ws_msg_rx) = flume::unbounded();
-        let (udp_sender_msg_tx, udp_sender_msg_rx) = flume::unbounded();
+        #[cfg(feature = "receive")]
         let (udp_receiver_msg_tx, udp_receiver_msg_rx) = flume::unbounded();
 
+        // NOTE: This causes the UDP Socket on "receive" to be non-blocking,
+        // and the standard to be blocking. A UDP send should only WouldBlock if
+        // you're sending more data than the OS can handle (not likely, and
+        // at that point you should scale horizontally).
+        //
+        // If this is a problem for anyone, we can make non-blocking sends
+        // queue up a delayed send up to a limit.
+        #[cfg(feature = "receive")]
         let (udp_rx, udp_tx) = {
-            let udp_rx = Arc::new(udp);
-            let udp_tx = Arc::clone(&udp_rx);
+            let udp_tx = udp.into_std()?;
+            let udp_rx = UdpSocket::from_std(udp_tx.try_clone()?)?;
             (udp_rx, udp_tx)
         };
+        #[cfg(not(feature = "receive"))]
+        let udp_tx = udp.into_std()?;
 
         let ssrc = ready.ssrc;
 
         let mix_conn = MixerConnection {
+            #[cfg(feature = "receive")]
             cipher: cipher.clone(),
+            #[cfg(not(feature = "receive"))]
+            cipher,
             crypto_state: config.crypto_mode.into(),
+            #[cfg(feature = "receive")]
             udp_rx: udp_receiver_msg_tx,
-            udp_tx: udp_sender_msg_tx,
+            udp_tx,
         };
 
         interconnect
@@ -200,14 +227,14 @@ impl Connection {
             info.clone(),
         ));
 
+        #[cfg(feature = "receive")]
         spawn(udp_rx::runner(
             interconnect.clone(),
             udp_receiver_msg_rx,
             cipher,
             config.clone(),
             udp_rx,
         ));
-        spawn(udp_tx::runner(udp_sender_msg_rx, ssrc, udp_tx));
 
         Ok(Connection {
             info,