Binary WebSocket API: Brotli-compress all outgoing messages

Cargo.toml

@@ -106,6 +106,7 @@ base64 = "0.21.2"
 bitflags = "2.3.3"
 bit-vec = "0.6"
 blake3 = "1.5"
+brotli = "3.5"
 byte-unit = "4.0.18"
 bytes = "1.2.1"
 bytestring = { version = "1.2.0", features = ["serde"] }

crates/core/Cargo.toml

@@ -32,6 +32,7 @@ async-trait.workspace = true
 backtrace.workspace = true
 base64.workspace = true
 blake3.workspace = true
+brotli.workspace = true
 bytes.workspace = true
 bytestring.workspace = true
 chrono.workspace = true

crates/core/src/client/messages.rs

@@ -1,6 +1,8 @@
 use base64::Engine;
+use brotli::CompressorReader;
 use prost::Message as _;
 use spacetimedb_lib::identity::RequestId;
+use std::io::Read;
 use std::time::Instant;
 
 use crate::host::module_host::{EventStatus, ModuleEvent, ProtocolDatabaseUpdate};
@@ -22,7 +24,38 @@ pub trait ServerMessage: Sized {
     fn serialize(self, protocol: Protocol) -> DataMessage {
         match protocol {
             Protocol::Text => self.serialize_text().to_json().into(),
-            Protocol::Binary => self.serialize_binary().encode_to_vec().into(),
+            Protocol::Binary => {
+                let msg_bytes = self.serialize_binary().encode_to_vec();
+                let reader = &mut &msg_bytes[..];
+
+                // TODO(perf): Compression should depend on message size and type.
+                //
+                // SubscriptionUpdate messages will typically be quite large,
+                // while TransactionUpdate messages will typically be quite small.
+                //
+                // If we are optimizing for SubscriptionUpdates,
+                // we want a large buffer.
+                // But if we are optimizing for TransactionUpdates,
+                // we probably want to skip compression altogether.
+                //
+                // For now we choose a reasonable middle ground,
+                // which is to compress everything using a 32KB buffer.
+                const BUFFER_SIZE: usize = 32 * 1024;
+                // Again we are optimizing for compression speed,
+                // so we choose the lowest (fastest) level of compression.
+                const COMPRESSION_LEVEL: u32 = 1;
+                // The default value for an internal compression parameter.
+                // See `BrotliEncoderParams` for more details.
+                const LG_WIN: u32 = 22;
+
+                let mut encoder = CompressorReader::new(reader, BUFFER_SIZE, COMPRESSION_LEVEL, LG_WIN);
+
+                let mut out = Vec::new();
+                encoder
+                    .read_to_end(&mut out)
+                    .expect("Failed to Brotli compress `SubscriptionUpdateMessage`");
+                out.into()
+            }
         }
     }
     fn serialize_text(self) -> MessageJson;

crates/sdk/Cargo.toml

@@ -15,6 +15,7 @@ spacetimedb-client-api-messages.workspace = true
 anyhow.workspace = true
 anymap.workspace = true
 base64.workspace = true
+brotli.workspace = true
 futures.workspace = true
 futures-channel.workspace = true
 home.workspace = true

crates/sdk/src/websocket.rs

@@ -1,5 +1,6 @@
 use crate::identity::Credentials;
-use anyhow::{bail, Result};
+use anyhow::{bail, Context, Result};
+use brotli::BrotliDecompress;
 use futures::{SinkExt, StreamExt, TryStreamExt};
 use futures_channel::mpsc;
 use http::uri::{Scheme, Uri};
@@ -151,7 +152,9 @@ impl DbConnection {
     }
 
     pub(crate) fn parse_response(bytes: &[u8]) -> Result<Message> {
-        Ok(Message::decode(bytes)?)
+        let mut decompressed = Vec::new();
+        BrotliDecompress(&mut &bytes[..], &mut decompressed).context("Failed to Brotli decompress message")?;
+        Ok(Message::decode(&decompressed[..])?)
     }
 
     pub(crate) fn encode_message(msg: Message) -> WebSocketMessage {