BoundaryML/baml · error · RuntimeError

Failed deserializing HTTP body as JSON: {e:?}

Error message

Failed deserializing HTTP body as JSON:
{e:?}

What it means

HTTPBody#json reads the body and parses it as JSON, then converts it to a Ruby value. If the body is not valid JSON (or cannot be read), a Ruby RuntimeError 'Failed deserializing HTTP body as JSON' with the debug error is raised.

Source

Thrown at engine/language_client_ruby/ext/ruby_ffi/src/types/request.rs:91

        for byte in rb_self.inner.raw() {
            array.push(*byte)?;
        }

        Ok(array)
    }

    pub fn text(ruby: &Ruby, rb_self: &Self) -> Result<String> {
        rb_self.inner.text().map(String::from).map_err(|e| {
            Error::new(
                ruby.exception_runtime_error(),
                format!("Failed to get text from HTTP body:\n{e:?}"),
            )
        })
    }

    pub fn json(ruby: &Ruby, rb_self: &Self) -> Result<magnus::Value> {
        serde_magnus::serialize(&rb_self.inner.json().map_err(|e| {
            Error::new(
                ruby.exception_runtime_error(),
                format!("Failed deserializing HTTP body as JSON:\n{e:?}"),
            )
        })?)
    }

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

        cls.define_method("raw", method!(HTTPBody::raw, 0))?;
        cls.define_method("text", method!(HTTPBody::text, 0))?;
        cls.define_method("json", method!(HTTPBody::json, 0))?;

        Ok(())
    }
}

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Check the response status and content-type before calling json.
2. Read the body once; store the text and parse manually if you need both forms.
3. Inspect the debug error in the message to distinguish read failure vs JSON parse failure.

Example fix

// before
data = response.body.json # fails on HTML error page
// after
body = response.body
if response.status == 200 && body.text.strip.start_with?('{', '[')
  data = JSON.parse(body.text)
else
  data = nil
end

raw = body.text rescue nil
parsed = raw && raw.strip.start_with?('{', '[') ? JSON.parse(raw) : nil

begin
  data = body.json
rescue RuntimeError => e
  data = nil
end

When it happens

Trigger: Calling json on an HTTPBody containing non-JSON content: empty body, HTML error pages, plain-text errors, or an already-consumed body.

Common situations: Hitting an upstream gateway/proxy error page (502 HTML), an endpoint that returns plain text, or parsing the same body after a prior text() call.

Understand the failure class

Background: "Invalid JSON response" and "Failed to parse response" errors: when an API answers 200 but the body isn't the JSON your library expected — this error's family across 28 libraries.

Related errors

• failed to convert Ruby object to JSON, errors were: {} Ruby
• Failed to get text from HTTP body: {e:?}
• failed to get JSON: %w
• failed to get JSON: %w
• No LLM response: {}

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/d401d649f6e48e7e. Report an issue: GitHub.