BoundaryML/baml · error

failed to create base http client for WASM: {}

Error message

failed to create base http client for WASM: {}

What it means

The WASM variant of the AWS custom HTTP client construction wraps create_client() failures with this message. In browser/WASM builds, reqwest client creation (including proxy handling) failed, so the AWS BAML client cannot be created.

Source

Thrown at engine/baml-runtime/src/internal/llm_client/primitive/aws/custom_http_client.rs:34

// --- WASM specific imports ---
#[cfg(target_arch = "wasm32")]
use {futures::channel::oneshot, wasm_bindgen_futures::spawn_local};

use crate::request::create_client;

/// Returns a wrapper around the global reqwest client.
/// [HttpClient].
#[cfg(not(target_arch = "wasm32"))] // Keep function non-WASM for now
pub fn client() -> anyhow::Result<Client> {
    let client = crate::request::create_client()
        .map_err(|e| anyhow::anyhow!("failed to create base http client: {}", e))?;
    Ok(Client::new(client.clone()))
}

#[cfg(target_arch = "wasm32")] // Define WASM client function
pub fn client() -> anyhow::Result<Client> {
    let client = crate::request::create_client()
        .map_err(|e| anyhow::anyhow!("failed to create base http client for WASM: {}", e))?;
    Ok(Client::new(client.clone()))
}

/// A wrapper around [reqwest::Client] that implements [HttpClient].
///
/// This is required to support using proxy servers with the AWS SDK.
#[derive(Debug, Clone)]
pub struct Client {
    inner: reqwest::Client,
}

impl Client {
    pub fn new(client: reqwest::Client) -> Self {
        Self { inner: client }
    }
}

#[derive(Debug)]

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Remove proxy env vars (HTTP_PROXY/HTTPS_PROXY/ALL_PROXY) in the WASM environment.
2. Verify reqwest WASM-compatible features are enabled in the build.
3. Check the wrapped inner error for the precise reqwest cause.
4. Run the AWS client on a native target if WASM networking limits persist.

Example fix

// before (node/wasm env)
process.env.HTTPS_PROXY = "http://proxy:8080"; // unsupported in wasm client
// after
delete process.env.HTTPS_PROXY;

if (typeof WebSocket === 'undefined' || process.env.HTTPS_PROXY) { /* wasm reqwest cannot honor proxies */ console.warn('Clear proxy env vars for WASM builds'); }

try { initBamlRuntime(); } catch (e) { if (String(e).startsWith('failed to create base http client for WASM')) { console.error('WASM networking init failed; clear proxy settings / check reqwest features'); } throw e; }

When it happens

Trigger: Building/running BAML's AWS client under target_arch = wasm32 while crate::request::create_client() fails — e.g. unsupported proxy settings or reqwest WASM feature misconfiguration.

Common situations: Using BAML in a WebAssembly/browser environment with proxy env vars set that the WASM reqwest client cannot honor, or compiling without required reqwest WASM features.

Related errors

• failed to create base http client: {}
• JS callback error: {name}: {message}
• BAML internal error - credential provider bridges not initia
• network error fetching {url}: {source}
• WASM history boundary {} was not begun

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/847f2cb855d7601d. Report an issue: GitHub.