FuelLabs/fuels-rs · error · anyhow::Error

Failed to download wasm executor: {}

Error message

Failed to download wasm executor: {}

What it means

Thrown by the e2e test build script (e2e/build.rs) when downloading the fuel-core wasm executor from GitHub releases. The HTTP request completed but returned a non-success status code, which is embedded in the message (e.g. 404 or 403). This blocks compilation of the e2e test crate because the executor wasm is needed in OUT_DIR.

Source

Thrown at e2e/build.rs:55

        }

        Ok(false)
    }

    pub fn download(&self) -> anyhow::Result<()> {
        std::fs::create_dir_all(&self.dir)?;

        const LINK_TEMPLATE: &str = "https://github.com/FuelLabs/fuel-core/releases/download/vVERSION/fuel-core-VERSION-x86_64-unknown-linux-gnu.tar.gz";
        let link = LINK_TEMPLATE.replace("VERSION", &SUPPORTED_FUEL_CORE_VERSION.to_string());

        let response = reqwest::blocking::Client::builder()
            .timeout(std::time::Duration::from_secs(60))
            .build()?
            .get(link)
            .send()?;

        if !response.status().is_success() {
            anyhow::bail!("Failed to download wasm executor: {}", response.status());
        }

        let mut content = Cursor::new(response.bytes()?);

        let mut archive = Archive::new(GzDecoder::new(&mut content));

        let mut extracted = false;
        let executor_in_tar = Path::new(&format!(
            "fuel-core-{SUPPORTED_FUEL_CORE_VERSION}-x86_64-unknown-linux-gnu"
        ))
        .join(Self::EXECUTOR_FILE_NAME);

        for entry in archive.entries()? {
            let mut entry = entry?;

            if entry.path()? == executor_in_tar {
                entry.unpack(self.executor_path())?;
                std::fs::write(

View on GitHub (pinned to d9a250a518)

Solutions

1. Check the embedded HTTP status: 404 means the release asset for SUPPORTED_FUEL_CORE_VERSION does not exist (verify the URL in a browser/curl); 403 usually means GitHub rate limiting — wait or change network/IP.
2. Ensure outbound HTTPS to github.com is allowed (proxy/firewall/CI allowlist) and retry the build.
3. If the version asset genuinely does not exist, update the SDK to a version whose SUPPORTED_FUEL_CORE_VERSION has published linux tarballs.
4. As a workaround, manually download the tarball, extract fuel-core-wasm-executor.wasm into the crate's OUT_DIR, and write the matching semver string into the version file next to it so should_download() returns false.

Example fix

# before: build fails with 'Failed to download wasm executor: 404 Not Found'
curl -fL "https://github.com/FuelLabs/fuel-core/releases/download/v0.40.0/fuel-core-0.40.0-x86_64-unknown-linux-gnu.tar.gz" -o /tmp/fc.tar.gz
# after: pre-seed OUT_DIR so the build script skips the download
OUT_DIR=$(cargo metadata --format-version 1 | jq -r '.target_directory')/debug/build/<e2e-hash>/out
tar -xzf /tmp/fc.tar.gz -C /tmp/fc
mkdir -p "$OUT_DIR" && cp /tmp/fc/fuel-core-*/fuel-core-wasm-executor.wasm "$OUT_DIR/"
echo "0.40.0" > "$OUT_DIR/fuel-core-wasm-executor.version"

const URL: &str = format!("https://github.com/FuelLabs/fuel-core/releases/download/v{V}/fuel-core-{V}-x86_64-unknown-linux-gnu.tar.gz");
let status = reqwest::blocking::head(&URL).send().map(|r| r.status());
if let Ok(s) = &status { assert!(s.is_success(), "release asset unreachable: {s}"); }

for attempt in 1..=3 {
    match run_build() {
        Err(e) if e.to_string().contains("Failed to download wasm executor") && attempt < 3 => {
            std::thread::sleep(backoff(attempt)); continue;
        }
        other => break other,
    }
}

When it happens

Trigger: cargo build/test of the e2e crate when OUT_DIR lacks fuel-core-wasm-executor.wasm or the saved version file does not match SUPPORTED_FUEL_CORE_VERSION, and the GET to https://github.com/FuelLabs/fuel-core/releases/download/vVERSION/fuel-core-VERSION-x86_64-unknown-linux-gnu.tar.gz returns 404 (release/asset missing for that version), 403 (GitHub rate limit), or a proxy/gateway error.

Common situations: Building on CI behind a restrictive proxy or offline environment; GitHub API rate limiting shared CI IPs; the fuel-core release for the SDK's pinned SUPPORTED_FUEL_CORE_VERSION not yet published or with renamed assets; a version bump in fuels-account/provider that outpaces the released artifacts.

Related errors

• Failed to extract wasm executor from the archive
• key arn missing from response
• Failed to deploy the contract

AI-assisted analysis of FuelLabs/fuels-rs@d9a250a518 (2026-08-16). Data as JSON: /api/errors/a24563e3a04708cd. Report an issue: GitHub.