cloudflare/quiche · error

Error creating file for

Error message

Error creating file for {url}, attempted path was {path}: {e}

What it means

make_resource_writer panics when std::fs::File::create fails for the file that will store the response body of a downloaded URL. The panic includes the URL, the attempted path, and the underlying io::Error. Failure is typically due to filesystem permissions, a missing parent directory, or the path being a directory.

Solutions

1. Create the target directory first (mkdir -p) and verify write permissions.
2. Check the 'attempted path was' message for a wrong or malformed path.
3. Verify the filesystem is not read-only or full.
4. Prefer running the client from a directory you own if relative paths are used.

Example fix

// before (directory does not exist)
quiche-client --dump-dir /out https://example.org
// after
mkdir -p /out && quiche-client --dump-dir /out https://example.org

let dir = std::path::Path::new(&out_dir);
assert!(dir.is_dir(), "output dir missing: {}", out_dir);
assert!(!dir.is_file(), "output path is a file: {}");
let probe = dir.join(".write_test");
std::fs::File::create(&probe).expect("output dir not writable");
let _ = std::fs::remove_file(&probe);

// Since the app panics, isolate it: run in a subprocess and inspect stderr
let out = std::process::Command::new("quiche-client")
    .args(["--dump-dir", &out_dir, url])
    .output()
    .expect("spawn failed");
if !out.status.success() {
    eprintln!("client failed: {}", String::from_utf8_lossy(&out.stderr));
}

When it happens

Trigger: Running quiche-client with a dump/save option where the derived output path (including the '.N' dedup suffix) cannot be created: parent directory missing, read-only filesystem, or permission denied.

Common situations: Saving responses into a directory that doesn't exist or isn't writable; running in a container with a read-only volume; disk full.

Understand the failure class

Background: "failed to write file", "Could not save figure", "Error saving remote file" — file write failed: causes and fixes across languages and libraries — this error's family across 38 libraries.

Related errors

• Error creating qlog file attempted path was
• Error creating qlog file attempted path was
• Unsupported

AI-assisted analysis of cloudflare/quiche@9f96daa2c2 (2026-09-08). Data as JSON: /api/errors/2f9c9269eb3c1fc5. Report an issue: GitHub.

Appendix: source

Thrown at apps/src/common.rs:128

/// any value "N" greater than 1, will cause ".N" to be appended to the
/// filename.
fn make_resource_writer(
    url: &url::Url, target_path: &Option<String>, cardinal: u64,
) -> Option<std::io::BufWriter<std::fs::File>> {
    if let Some(tp) = target_path {
        let resource =
            url.path_segments().map(|c| c.collect::<Vec<_>>()).unwrap();

        let mut path = format!("{}/{}", tp, resource.iter().last().unwrap());

        if cardinal > 1 {
            path = format!("{path}.{cardinal}");
        }

        match std::fs::File::create(&path) {
            Ok(f) => return Some(std::io::BufWriter::new(f)),

            Err(e) => panic!(
                "Error creating file for {url}, attempted path was {path}: {e}"
            ),
        }
    }

    None
}

fn autoindex(path: path::PathBuf, index: &str) -> path::PathBuf {
    if let Some(path_str) = path.to_str() {
        if path_str.ends_with('/') {
            let path_str = format!("{path_str}{index}");
            return path::PathBuf::from(&path_str);
        }
    }

    path
}

View on GitHub (pinned to 9f96daa2c2)