DioxusLabs/dioxus · error

failed to write chunk

Error message

failed to write chunk

What it means

Each split chunk is written as `chunk_<idx>_<module_name>.wasm` in out_dir, and a failed `std::fs::write` panics with "failed to write chunk". Besides ordinary IO problems (disk full, permissions revoked), the filename embeds the chunk's module_name, so a name containing characters invalid in filenames on the target OS - or a combined name exceeding the filesystem's 255-byte component limit - makes exactly this write fail while earlier writes succeeded.

Source

Thrown at packages/wasm-split/wasm-split-cli/src/main.rs:81

        args.out_dir.join("__wasm_split.js"),
        emit_js(&chunks.chunks, &chunks.modules),
    )
    .expect("failed to write js module");

    for (idx, chunk) in chunks.chunks.iter().enumerate() {
        tracing::info!(
            "Writing chunk {} to {}",
            idx,
            args.out_dir
                .join(format!("chunk_{}_{}.wasm", idx, chunk.module_name))
                .display()
        );
        std::fs::write(
            args.out_dir
                .join(format!("chunk_{}_{}.wasm", idx, chunk.module_name)),
            &chunk.bytes,
        )
        .expect("failed to write chunk");
    }

    for (idx, module) in chunks.modules.iter_mut().enumerate() {
        tracing::info!(
            "Writing module {} to {}",
            idx,
            args.out_dir
                .join(format!(
                    "module_{}_{}.wasm",
                    idx,
                    module.component_name.as_ref().unwrap()
                ))
                .display()
        );
        std::fs::write(
            args.out_dir.join(format!(
                "module_{}_{}.wasm",
                idx,

View on GitHub (pinned to 393d190a80)

Solutions

1. Read the tracing line printed just above the panic - it shows the exact target path; check that filename for invalid characters or excessive length
2. Free disk space or restore write permissions on out_dir, then re-run
3. Shorten the out_dir path so the combined generated filename fits within 255 bytes
4. Rename the offending Rust module (or patch/report wasm-split's name sanitization) if the module_name is not filename-safe on the target OS

Example fix

# before: deep out_dir + long module name exceeds NAME_MAX on this filesystem
wasm-split-cli split app.wasm bg.wasm /very/long/build/prefix/dist
# after: shorter output root (and/or rename the deep Rust module)
wasm-split-cli split app.wasm bg.wasm dist

# before invoking, confirm the target filesystem accepts the generated names
name_max=$(stat -f -c %l dist 2>/dev/null || stat -f -l dist 2>/dev/null || echo 255)
find dist -name 'chunk_*' -printf '%f\n' 2>/dev/null | awk -v m="$name_max" 'length($0) >= m { print "filename too long: " $0; exit 1 }'

if ! wasm-split-cli split app.wasm bg.wasm dist; then echo "chunk write failed (exit $?) - check the logged chunk path for invalid characters/length" >&2; exit 1; fi

When it happens

Trigger: A chunk module_name containing `/`, `\`, or characters like `:` that are invalid on Windows; an out_dir path plus generated name exceeding NAME_MAX; ENOSPC or revoked permissions after the earlier main.wasm and JS glue writes consumed the remaining space or the lock changed.

Common situations: Cross-platform builds where a name is legal on Linux but invalid on Windows/macOS; deeply nested Rust module paths producing very long generated filenames; Docker inode exhaustion mid-build.

Related errors

• failed to create output dir
• failed to expand ifunc table
• Could not find export
• failed to read input file
• failed to write js module

AI-assisted analysis of DioxusLabs/dioxus@393d190a80 (2026-08-16). Data as JSON: /api/errors/569f97be6ed3ef82. Report an issue: GitHub.