continuedev/continue · error · Error

Malformed JSON sent from server: ${json}

Error message

Malformed JSON sent from server: ${json}

What it means

parseDataLine caught a JSON.parse failure on an SSE 'data:' line that wasn't already a streaming error, so the raw line is reported as malformed JSON from the server.

Source

Thrown at packages/fetch/src/stream.ts:107

        console.error("Error in streamed response:", data.error);
        throw new Error(`Error streaming response: ${data.error.message}`);
      }
      throw new Error(
        `Error streaming response: ${JSON.stringify(data.error)}`,
      );
    }

    return data;
  } catch (e) {
    // If the error was thrown by our error check, rethrow it
    if (
      e instanceof Error &&
      e.message.startsWith("Error streaming response:")
    ) {
      throw e;
    }
    // Otherwise it's a JSON parsing error
    throw new Error(`Malformed JSON sent from server: ${json}`);
  }
}

function parseSseLine(line: string): { done: boolean; data: any } {
  if (line.startsWith("data:[DONE]") || line.startsWith("data: [DONE]")) {
    return { done: true, data: undefined };
  }
  if (line.startsWith("data:")) {
    return { done: false, data: parseDataLine(line) };
  }
  if (line.startsWith(": ping")) {
    return { done: true, data: undefined };
  }
  return { done: false, data: undefined };
}

export async function* streamSse(response: Response): AsyncGenerator<any> {
  let buffer = "";

View on GitHub (pinned to 5522c6f44c)

Solutions

1. Log the offending line to see what actually arrived (HTML? truncated JSON?)
2. Retry — truncation is often transient
3. Fix server/proxy to emit only valid JSON data lines
4. Handle multi-line SSE 'data:' events per the SSE spec by joining consecutive data lines before parsing

catch (e) { if (/^Malformed JSON sent from server:/.test(e.message)) { console.error('raw line:', e.message.slice(30)); /* retry or switch endpoint */ } }

When it happens

Trigger: A 'data: ...' line whose payload isn't valid JSON — truncated by network issues, HTML error pages injected mid-stream, or multi-line data split incorrectly.

Common situations: Proxies injecting HTML, servers sending non-JSON heartbeats/comments as data, or chunk truncation from connection issues.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• Malformed JSON sent from server: ${line}
• Error streaming response: ${data.error.message}
• Error streaming response: ${JSON.stringify(data.error)}
• Malformed JSON received from Bedrock: ${decoded}
• non-200 response body: ${await response.text()}

AI-assisted analysis of continuedev/continue@5522c6f44c (2026-08-27). Data as JSON: /api/errors/c75cc54f9c098b6b. Report an issue: GitHub.