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Reduce chunk size from 32MB to 256KB for proper TCP backpressure #103

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Merged
twdamhore merged 1 commit into from
Jan 20, 2026
Merged

Reduce chunk size from 32MB to 256KB for proper TCP backpressure #103

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30 changes: 16 additions & 14 deletions src/services/iso.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -13,8 +13,10 @@ use std::path::PathBuf;
use tokio::sync::mpsc;

const ISO_BLOCK_SIZE: u64 = 2048;
/// Chunk size for streaming (32MB)
const CHUNK_SIZE: usize = 32 * 1024 * 1024;
/// Chunk size for streaming (8MB).
const CHUNK_SIZE: usize = 8 * 1024 * 1024;
/// Channel capacity for streaming. With 8MB chunks, this allows up to 16MB in flight.
const CHANNEL_CAPACITY: usize = 2;

/// Stream file contents in chunks to a channel.
///
Expand Down Expand Up @@ -454,8 +456,8 @@ impl IsoService {
})?;
let file_size = metadata.len();

// Create bounded channel for backpressure (2 chunks max in flight)
let (tx, rx) = mpsc::channel(2);
// Create bounded channel for backpressure
let (tx, rx) = mpsc::channel(CHANNEL_CAPACITY);

// Spawn blocking task to read chunks
tokio::task::spawn_blocking(move || {
Expand Down Expand Up @@ -520,8 +522,8 @@ impl IsoService {
let file_size = entry.size;
let extent_lba = entry.extent_lba;

// Create bounded channel for backpressure (2 chunks max in flight)
let (tx, rx) = mpsc::channel(2);
// Create bounded channel for backpressure
let (tx, rx) = mpsc::channel(CHANNEL_CAPACITY);

let iso_path_clone = iso_path.clone();

Expand Down Expand Up @@ -636,8 +638,8 @@ impl IsoService {
total_size
);

// Create bounded channel for backpressure (2 chunks max in flight)
let (tx, rx) = mpsc::channel(2);
// Create bounded channel for backpressure
let (tx, rx) = mpsc::channel(CHANNEL_CAPACITY);

let iso_path_clone = iso_path.clone();
let firmware_path_clone = firmware_path.clone();
Expand Down Expand Up @@ -960,7 +962,7 @@ mod tests {
std::fs::write(&test_file, &test_data).unwrap();

// Create channel and stream
let (tx, mut rx) = mpsc::channel(2);
let (tx, mut rx) = mpsc::channel(CHANNEL_CAPACITY);
let mut file = File::open(&test_file).unwrap();
let file_size = test_data.len() as u64;

Expand All @@ -982,15 +984,15 @@ mod tests {

#[test]
fn test_stream_file_to_channel_multiple_chunks() {
// Create a file larger than CHUNK_SIZE (32MB) to test chunking
// 70MB = 2 full chunks (32MB each) + 1 partial chunk (6MB)
// Create a file larger than CHUNK_SIZE (8MB) to test chunking
// 20MB = 2 full chunks (8MB each) + 1 partial chunk (4MB)
let dir = setup_test_dir();
let test_file = dir.path().join("large.bin");
let file_size = 70 * 1024 * 1024; // 70MB
let file_size = 20 * 1024 * 1024; // 20MB
let test_data: Vec<u8> = (0..file_size).map(|i| (i % 256) as u8).collect();
std::fs::write(&test_file, &test_data).unwrap();

let (tx, mut rx) = mpsc::channel(2);
let (tx, mut rx) = mpsc::channel(CHANNEL_CAPACITY);
let mut file = File::open(&test_file).unwrap();

std::thread::spawn(move || {
Expand All @@ -1006,7 +1008,7 @@ mod tests {
received.extend_from_slice(&bytes);
}

assert_eq!(chunk_count, 3); // 32MB + 32MB + 6MB
assert_eq!(chunk_count, 3); // 8MB + 8MB + 4MB
assert_eq!(received.len(), test_data.len());
assert_eq!(received, test_data);
}
Expand Down