facebook/flow · error

failed to read input file

Error message

failed to read input file

What it means

When --input-file points at a real file, get_filenames_from_input slurps it with std::fs::read_to_string. The .expect() panics when the path does not exist (ENOENT), is not readable (EACCES), is a directory (EISDIR), or its content is not valid UTF-8. Notably this missing-file case is not routed through the friendly 'File not found' exit used elsewhere — it crashes instead.

Source

Thrown at rust_port/crates/flow_cli/src/command_utils.rs:142

        if allow_imaginary {
            flow_common::files::imaginary_realpath(filename)
        } else {
            let msg = format!("File not found: {:?}", filename);
            flow_common_exit::exit(FlowExitStatus::NoInput, Some(&msg));
        }
    };
    let input_file_filenames = match input_file {
        Some("-") => {
            let stdin = std::io::stdin();
            let lines: Vec<String> = stdin
                .lock()
                .lines()
                .map(|l| l.expect("failed to read stdin"))
                .collect();
            flow_common::files::canonicalize_filenames(&cwd, &handle_imaginary, &lines)
        }
        Some(input_file) => {
            let content = std::fs::read_to_string(input_file).expect("failed to read input file");
            let lines: Vec<String> = content.lines().map(|l| l.to_string()).collect();
            let file_dir = Path::new(input_file)
                .parent()
                .map(|p| p.to_string_lossy().to_string())
                .unwrap_or_else(|| cwd.clone());
            flow_common::files::canonicalize_filenames(&file_dir, &handle_imaginary, &lines)
        }
        None => vec![],
    };
    let cli_filenames = match filenames {
        Some(filenames) => {
            let names: Vec<String> = filenames.to_vec();
            flow_common::files::canonicalize_filenames(&cwd, &handle_imaginary, &names)
        }
        None => vec![],
    };
    let mut result = cli_filenames;
    result.extend(input_file_filenames);

View on GitHub (pinned to f88ac94bcf)

Solutions

1. Verify the path and permissions before running: `test -r list.txt && flow ... --input-file list.txt`
2. Re-encode the file to UTF-8: `iconv -f UTF-16 -t UTF-8 list.txt > list.utf8.txt`, or in PowerShell use `Out-File -Encoding utf8`
3. Use absolute paths for --input-file in cron/CI so cwd changes cannot break resolution

Example fix

# before (PowerShell wrote UTF-16 with BOM)
flow check-contents --input-file files.txt

# after
iconv -f UTF-16 -t UTF-8 files.txt > files.utf8.txt
flow check-contents --input-file files.utf8.txt

// Validate existence, readability, and UTF-8 before passing --input-file:
let p = std::path::Path::new(list);
let bytes = std::fs::read(p).unwrap_or_else(|e| {
    eprintln!("cannot read {p:?}: {e}");
    std::process::exit(1);
});
if std::str::from_utf8(&bytes).is_err() {
    eprintln!("{p:?} is not UTF-8 (PowerShell `>` writes UTF-16)");
    std::process::exit(1);
}

let content = match std::fs::read_to_string(input_file) {
    Ok(c) => c,
    Err(e) => flow_common_exit::exit(FlowExitStatus::InputError,
        Some(&format!("cannot read input file {input_file:?}: {e}"))),
};

When it happens

Trigger: A typo'd or stale --input-file path (list generated in a previous CI step that was cleaned); permission-restricted file; a list saved as UTF-16 with BOM — common when generated by PowerShell `>` redirection — which read_to_string rejects as invalid UTF-8.

Common situations: PowerShell/Windows-generated file lists (UTF-16LE); cron jobs using relative paths from a different cwd; artifacts deleted between pipeline stages; files with exotic encodings.

Understand the failure class

Background: "File not found" and ENOENT errors: why libraries can't find a file that should exist — this error's family across 50 libraries.

Related errors

• failed to get current directory
• failed to read stdin
• failed to read stdin
• failed to write json errors
• failed to flush json errors

AI-assisted analysis of facebook/flow@f88ac94bcf (2026-08-20). Data as JSON: /api/errors/79d2c02c7ca9d4fa. Report an issue: GitHub.