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Fix panic when recording apps that output non-UTF-8 bytes #259

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Merged
ibigbug merged 1 commit into from
Jan 26, 2026
Merged

Fix panic when recording apps that output non-UTF-8 bytes #259

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72 changes: 54 additions & 18 deletions src/commands/record.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,12 @@ use std::{
thread,
};

#[cfg(windows)]
use windows::Win32::{
Foundation::HANDLE,
System::Console::{GetStdHandle, WriteConsoleW, STD_OUTPUT_HANDLE},
};

use crate::commands::types::LineItem;
use crate::commands::types::RecordHeader;
use crate::terminal::{Terminal, WindowsTerminal};
Expand Down Expand Up @@ -116,9 +122,16 @@ impl Record {
let filename = self.filename.clone();

thread::spawn(move || {
loop {
let mut stdout = std::io::stdout();
// Use raw Windows handle to write bytes directly, bypassing Rust's UTF-8 validation
// which fails on Windows console mode with non-UTF-8 sequences
#[cfg(windows)]
let stdout_handle: HANDLE =
unsafe { GetStdHandle(STD_OUTPUT_HANDLE).expect("failed to get stdout handle") };

// Buffer for incomplete UTF-8 sequences split across chunk boundaries
let mut pending_bytes: Vec<u8> = Vec::new();

loop {
Comment on lines +127 to +134
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Copilot AI Jan 24, 2026

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The stdout handle is retrieved once outside the loop, but if the handle becomes invalid during execution (e.g., console detachment), subsequent writes will fail. Consider retrieving the handle inside the loop or adding error handling to detect and recover from invalid handle states.

Suggested change
#[cfg(windows)]
let stdout_handle: HANDLE =
unsafe { GetStdHandle(STD_OUTPUT_HANDLE).expect("failed to get stdout handle") };
// Buffer for incomplete UTF-8 sequences split across chunk boundaries
let mut pending_bytes: Vec<u8> = Vec::new();
loop {
// Buffer for incomplete UTF-8 sequences split across chunk boundaries
let mut pending_bytes: Vec<u8> = Vec::new();
loop {
#[cfg(windows)]
let stdout_handle: HANDLE =
unsafe { GetStdHandle(STD_OUTPUT_HANDLE).expect("failed to get stdout handle") };

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@ibigbug ibigbug Jan 24, 2026

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@SteveSandersonMS do you think this comment makes sense? (i'm not a Windows console expert :))

let rv = stdout_rx.recv();
match rv {
Ok((buf, len)) => {
Expand All @@ -134,22 +147,45 @@ impl Record {

let ts = now.as_secs() as f64 + now.subsec_nanos() as f64 * 1e-9
- record_start_time;
// https://github.com/asciinema/asciinema/blob/5a385765f050e04523c9d74fbf98d5afaa2deff0/asciinema/asciicast/v2.py#L119
let chars = String::from_utf8_lossy(&buf[..len]).to_string();
let data = vec![
LineItem::F64(ts),
LineItem::String("o".to_string()),
LineItem::String(chars),
];
let line = serde_json::to_string(&data).unwrap() + "\n";
output_writer
.lock()
.unwrap()
.write(line.as_bytes())
.unwrap();

stdout.write(&buf[..len]).expect("failed to write stdout");
stdout.flush().expect("failed to flush stdout");

// Combine pending bytes with new data
pending_bytes.extend_from_slice(&buf[..len]);

// Find the last valid UTF-8 boundary
let valid_up_to = match std::str::from_utf8(&pending_bytes) {
Ok(_) => pending_bytes.len(),
Err(e) => e.valid_up_to(),
};

// Only process complete UTF-8 sequences
if valid_up_to > 0 {
// Safe: we just validated these bytes are valid UTF-8
let chars = std::str::from_utf8(&pending_bytes[..valid_up_to]).unwrap();

// https://github.com/asciinema/asciinema/blob/5a385765f050e04523c9d74fbf98d5afaa2deff0/asciinema/asciicast/v2.py#L119
let data = vec![
LineItem::F64(ts),
LineItem::String("o".to_string()),
LineItem::String(chars.to_string()),
];
let line = serde_json::to_string(&data).unwrap() + "\n";
output_writer
.lock()
.unwrap()
.write(line.as_bytes())
.unwrap();

// Write to console using WriteConsoleW for proper Unicode support
#[cfg(windows)]
unsafe {
let utf16: Vec<u16> = chars.encode_utf16().collect();
WriteConsoleW(stdout_handle, &utf16, None, None)
.expect("failed to write stdout");
}
}

// Keep incomplete bytes for next iteration
pending_bytes.drain(..valid_up_to);
}

Err(err) => {
Expand Down