BoundaryML/baml · error · RuntimeError

{e:?}

Error message

{e:?}

What it means

Ruby FFI generic serialization error: converting the HTTP request's headers into a Ruby hash via serde_magnus failed. The {e:?} is the magnus conversion error (e.g. a header value type that has no Ruby representation). This is the catch-all serialization guard for the headers accessor on the Ruby HTTPRequest wrapper.

Source

Thrown at engine/language_client_ruby/ext/ruby_ffi/src/types/request.rs:45

        )
    }

    pub fn id(&self) -> String {
        self.inner.id().to_string()
    }

    pub fn url(&self) -> String {
        self.inner.url().to_string()
    }

    pub fn method(&self) -> String {
        self.inner.method().to_string()
    }

    pub fn headers(ruby: &Ruby, rb_self: &Self) -> Result<magnus::Value> {
        // Convert headers to Ruby hash
        serde_magnus::serialize(&rb_self.inner.headers())
            .map_err(|e| Error::new(ruby.exception_runtime_error(), format!("{e:?}")))
    }

    pub fn body(&self) -> HTTPBody {
        // TODO: Avoid clone.
        HTTPBody::from(self.inner.body().clone())
    }

    pub fn define_in_ruby(module: &RModule) -> Result<()> {
        let cls = module.define_class("HTTPRequest", class::object())?;

        cls.define_method("to_s", method!(HTTPRequest::to_s, 0))?;
        cls.define_method("id", method!(HTTPRequest::id, 0))?;
        cls.define_method("url", method!(HTTPRequest::url, 0))?;
        cls.define_method("method", method!(HTTPRequest::method, 0))?;
        cls.define_method("headers", method!(HTTPRequest::headers, 0))?;
        cls.define_method("body", method!(HTTPRequest::body, 0))?;

        Ok(())

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Rebuild/reinstall the baml gem so native extension and runtime versions match.
2. Log the debug serde error from the message to find the offending header.
3. Update to the latest baml release where serialization bugs may be fixed.

Example fix

// before
h = request.headers # RuntimeError: {e:?}
// after
begin
  h = request.headers
rescue RuntimeError => e
  h = {}
  logger.warn("headers serialization failed: #{e.message}")
end

begin
  headers = request.headers
rescue RuntimeError => e
  headers = {}
end

When it happens

Trigger: Calling headers on an FFI HTTPRequest object when the internal header map cannot be serialized into a Ruby value.

Common situations: Version mismatch between the Ruby gem and the compiled native extension, or unusual header values (non-UTF8 / non-string-mappable) produced upstream.

Understand the failure class

Background: json.Marshal / "failed to marshal" errors in Go: why "unsupported type" happens and how to fix it — this error's family across 22 libraries.

Related errors

• {e:?}
• failed coercing BAML value to Ruby value: {e:?}
• failed to convert Ruby object to JSON, errors were: {} Ruby
• encoding method arguments: %w
• unsupported map key type: %s

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/b8a382cca0d82d1f. Report an issue: GitHub.