fix(cap-muxer): finish the open fragment when the recorder dies

crates/cap-muxer/Cargo.toml

@@ -18,3 +18,6 @@ tracing-subscriber = { version = "0.3", features = ["env-filter"] }
 
 [lints]
 workspace = true
+
+[dev-dependencies]
+tempfile = "3"

crates/cap-muxer/src/main.rs

@@ -25,37 +25,45 @@ fn main() -> ExitCode {
     match run() {
         Ok(()) => ExitCode::from(EXIT_OK),
         Err(MuxerError::Protocol(err)) => {
-            eprintln!("cap-muxer protocol error: {err}");
+            report(format_args!("cap-muxer protocol error: {err}"));
             ExitCode::from(EXIT_PROTOCOL_ERROR)
         }
         Err(MuxerError::DiskFull(err)) => {
-            eprintln!("cap-muxer disk full: {err:#}");
+            report(format_args!("cap-muxer disk full: {err:#}"));
             ExitCode::from(EXIT_DISK_FULL)
         }
         Err(MuxerError::FFmpeg(err)) => {
-            eprintln!("cap-muxer ffmpeg error: {err:#}");
+            report(format_args!("cap-muxer ffmpeg error: {err:#}"));
             ExitCode::from(EXIT_FFMPEG_ERROR)
         }
         Err(MuxerError::Init(err)) => {
-            eprintln!("cap-muxer init error: {err:#}");
+            report(format_args!("cap-muxer init error: {err:#}"));
             ExitCode::from(EXIT_INIT_ERROR)
         }
         Err(MuxerError::Abort(reason)) => {
-            eprintln!("cap-muxer parent abort: {reason}");
+            report(format_args!("cap-muxer parent abort: {reason}"));
             ExitCode::from(EXIT_ABORT)
         }
         Err(MuxerError::BadState(reason)) => {
-            eprintln!("cap-muxer bad state: {reason}");
+            report(format_args!("cap-muxer bad state: {reason}"));
             ExitCode::from(EXIT_BAD_STATE)
         }
     }
 }
 
+/// Writes to stderr without panicking: when the recorder dies, the pipe it
+/// read our stderr through is closed, and the open fragment must still be
+/// finished after that.
+fn report(message: std::fmt::Arguments) {
+    let _ = writeln!(io::stderr(), "{message}");
+}
+
 fn init_tracing() {
     let filter = std::env::var("CAP_MUXER_LOG").unwrap_or_else(|_| "info".to_string());
     let _ = tracing_subscriber::fmt()
         .with_env_filter(filter)
         .with_writer(std::io::stderr)
+        .log_internal_errors(false)
         .try_init();
 }
 

crates/cap-muxer/tests/orphaned.rs

@@ -0,0 +1,141 @@
+//! The recorder can die while cap-muxer runs. Its stdin then reaches EOF and
+//! the pipe the recorder read cap-muxer's stderr through is closed; cap-muxer
+//! must still finish the fragment it has open.
+
+use std::{
+    io::Write,
+    process::{Command, Stdio},
+};
+
+use cap_muxer_protocol::{
+    Frame, InitVideo, PACKET_FLAG_KEYFRAME, Packet, STREAM_INDEX_VIDEO, StartParams, write_frame,
+    write_packet,
+};
+use ffmpeg::{codec, format, frame};
+
+const WIDTH: u32 = 320;
+const HEIGHT: u32 = 240;
+const FPS: i32 = 30;
+
+type EncodedPacket = (i64, i64, bool, Vec<u8>);
+
+fn encode(count: i64, gop: u32) -> (Vec<u8>, Vec<EncodedPacket>) {
+    ffmpeg::init().unwrap();
+    let codec = codec::encoder::find_by_name("libx264").expect("libx264");
+    let mut context = codec::context::Context::new_with_codec(codec)
+        .encoder()
+        .video()
+        .unwrap();
+    context.set_width(WIDTH);
+    context.set_height(HEIGHT);
+    context.set_format(format::Pixel::YUV420P);
+    context.set_time_base((1, FPS));
+    context.set_frame_rate(Some((FPS, 1)));
+    context.set_gop(gop);
+    context.set_max_b_frames(0);
+    context.set_flags(codec::Flags::GLOBAL_HEADER);
+    let mut options = ffmpeg::Dictionary::new();
+    options.set("preset", "ultrafast");
+    options.set("tune", "zerolatency");
+    let mut encoder = context.open_as_with(codec, options).unwrap();
+    let extradata = unsafe {
+        let ctx = encoder.as_ptr();
+        std::slice::from_raw_parts((*ctx).extradata, (*ctx).extradata_size as usize).to_vec()
+    };
+    let mut packets = Vec::new();
+    let mut packet = ffmpeg::Packet::empty();
+    let mut drain = |encoder: &mut ffmpeg::encoder::Video, packets: &mut Vec<_>| {
+        while encoder.receive_packet(&mut packet).is_ok() {
+            packets.push((
+                packet.pts().unwrap(),
+                packet.dts().unwrap(),
+                packet.is_key(),
+                packet.data().unwrap().to_vec(),
+            ));
+        }
+    };
+    for index in 0..count {
+        let mut picture = frame::Video::new(format::Pixel::YUV420P, WIDTH, HEIGHT);
+        for plane in 0..3 {
+            picture.data_mut(plane).fill((index * 3 % 255) as u8);
+        }
+        picture.set_pts(Some(index));
+        encoder.send_frame(&picture).unwrap();
+        drain(&mut encoder, &mut packets);
+    }
+    encoder.send_eof().unwrap();
+    drain(&mut encoder, &mut packets);
+    (extradata, packets)
+}
+
+#[test]
+fn an_orphaned_muxer_finishes_its_open_fragment() {
+    let (extradata, packets) = encode(75, 30);
+    let directory = tempfile::tempdir().unwrap();
+    let output = directory.path().join("display");
+    let mut child = Command::new(env!("CARGO_BIN_EXE_cap-muxer"))
+        .env("CAP_MUXER_LOG", "warn")
+        .stdin(Stdio::piped())
+        .stdout(Stdio::null())
+        .stderr(Stdio::piped())
+        .spawn()
+        .unwrap();
+    let mut stdin = child.stdin.take().unwrap();
+    write_frame(
+        &mut stdin,
+        &Frame::InitVideo(InitVideo {
+            codec: "libx264".into(),
+            width: WIDTH,
+            height: HEIGHT,
+            frame_rate_num: FPS,
+            frame_rate_den: 1,
+            time_base_num: 1,
+            time_base_den: FPS,
+            extradata,
+            segment_duration_ms: 1000,
+        }),
+    )
+    .unwrap();
+    write_frame(
+        &mut stdin,
+        &Frame::Start(StartParams {
+            output_directory: output.to_string_lossy().into_owned(),
+            init_segment_name: "init.mp4".into(),
+            media_segment_pattern: "segment_$Number%03d$.m4s".into(),
+        }),
+    )
+    .unwrap();
+    for (pts, dts, key, data) in &packets {
+        write_packet(
+            &mut stdin,
+            &Packet {
+                stream_index: STREAM_INDEX_VIDEO,
+                pts: *pts,
+                dts: *dts,
+                duration: 1,
+                flags: if *key { PACKET_FLAG_KEYFRAME } else { 0 },
+                data,
+            },
+        )
+        .unwrap();
+    }
+    stdin.flush().unwrap();
+    // The recorder dies: its end of the stderr pipe closes, then stdin.
+    drop(child.stderr.take());
+    drop(stdin);
+    let status = child.wait().unwrap();
+    assert_eq!(status.code(), Some(0), "cap-muxer must finish, not panic");
+
+    let mut segments: Vec<_> = std::fs::read_dir(&output)
+        .unwrap()
+        .flatten()
+        .map(|entry| entry.file_name().to_string_lossy().into_owned())
+        .filter(|name| name.starts_with("segment_"))
+        .collect();
+    segments.sort();
+    assert_eq!(
+        segments,
+        ["segment_001.m4s", "segment_002.m4s", "segment_003.m4s"],
+        "every fragment, including the one open when the recorder died, is finished"
+    );
+}