BoundaryML/baml · error

Failed to fetch media: {e:?}

Error message

Failed to fetch media: {e:?}

What it means

to_base64_with_inferred_mime_type failed at the network layer while downloading the media URL (fetch_with_proxy returned Err). BAML wraps the underlying reqwest error in this message rather than silently sending empty content.

Source

Thrown at engine/baml-runtime/src/internal/llm_client/traits/mod.rs:783

            Ok(BamlMedia::base64(
                part.media_type,
                media_b64.base64.clone(),
                mime_type,
            ))
        }
    }
}

async fn to_base64_with_inferred_mime_type(
    ctx: &RuntimeContext,
    media_url: &MediaUrl,
) -> Result<(String, String)> {
    if let Some((mime_type, base64)) = as_base64(media_url.url.as_str()) {
        return Ok((base64.to_string(), mime_type.to_string()));
    }
    let response = match fetch_with_proxy(&media_url.url, ctx.proxy_url()).await {
        Ok(response) => response,
        Err(e) => return Err(anyhow::anyhow!("Failed to fetch media: {e:?}")),
    };
    if response.status().is_success() {
        let bytes = match response.bytes().await {
            Ok(bytes) => bytes,
            Err(e) => return Err(anyhow::anyhow!("Failed to fetch media bytes: {e:?}")),
        };
        let base64 = BASE64_STANDARD.encode(&bytes);
        // TODO: infer based on file extension?
        let mime_type = match infer::get(&bytes) {
            Some(t) => t.mime_type(),
            None => "application/octet-stream",
        }
        .to_string();
        Ok((base64, mime_type))
    } else {
        Err(anyhow::anyhow!(
            "Failed to fetch media: {} {}, {}",
            response.status(),

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Verify the URL is reachable (curl it from the same host)
2. Check for expired pre-signed URLs and regenerate them
3. If a proxy is configured, verify BAML's proxy setting is correct and the proxy is up
4. Encode the media as a base64 data URL to skip fetching entirely

const reachable = await fetch(url, { method: 'HEAD' }).then(r => r.ok).catch(() => false);
if (!reachable) throw new Error(`Media URL unreachable: ${url}`);

try {
  await runBamlFn();
} catch (e) {
  if (/Failed to fetch media:/.test(String(e.message)) && attempts < 3) {
    await sleep(2 ** attempts * 500);
    return runBamlFn(attempts + 1);
  }
  throw e;
}

When it happens

Trigger: The media URL is unreachable: DNS failure, connection refused/reset, TLS error, or a configured proxy is down, and the URL is not a base64 data URL.

Common situations: Private/internal URLs not reachable from the runtime host; typos in the domain; expired signed URLs (S3/GCS); no internet access or corporate proxy misconfiguration.

Understand the failure class

Background: 'Something went wrong' / 'Request failed (500)' / 'HTTP error! status: 404' — what failed HTTP requests actually mean and how to find the real cause — this error's family across 28 libraries.

Related errors

• baml.fetch_as: HTTP request failed: HTTP {} Body: {} at {:?}
• baml.fetch_as: HTTP request failed: HTTP {status} Body: {bod
• Failed to fetch media bytes: {e:?}
• Failed to fetch media: {} {}, {}
• Failed to fetch: {url}

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/07adb62253aa5825. Report an issue: GitHub.