deepseek-ai/deepseek-harness · error · LlmError

MALFORMED_RESPONSE

MALFORMED_RESPONSE

Error message

malformed SSE payload: ${payload.slice(0, 120)}

What it means

Error "malformed SSE payload: ${payload.slice(0, 120)}" thrown in deepseek-ai/deepseek-harness.

Source

Thrown at packages/llm/llm-deepseek/src/translate.ts:124

      if (pendingUsage) yield { type: 'usage', usage: pendingUsage }
      const reason = pendingFinish ?? { kind: 'stop' as const }
      yield {
        type: 'finish',
        reason: reason.kind === 'stop' && order.length === 0
          ? {
            kind: 'error',
            failure: { message: 'model returned a completed response with no content', code: EMPTY_RESPONSE_CODE },
          }
          : reason,
      }
      return
    }

    let chunk: WireChunk
    try {
      chunk = JSON.parse(payload) as WireChunk
    } catch {
      throw new LlmError(`malformed SSE payload: ${payload.slice(0, 120)}`, 'MALFORMED_RESPONSE')
    }

    for (const choice of chunk.choices ?? []) {
      const delta = choice.delta

      // Reasoning first: thinking mode interleaves it before text. The
      // empty-string first chunk must not open a block.
      const reasoning = delta?.reasoning_content
      if (typeof reasoning === 'string' && reasoning.length > 0) {
        if (!reasoningBlock) {
          reasoningBlock = open('reasoning')
          yield { type: 'block-start', index: reasoningBlock.index, blockType: 'reasoning' }
        }
        reasoningBlock.text += reasoning
        yield { type: 'reasoning-delta', index: reasoningBlock.index, text: reasoning }
      }

      const content = delta?.content

View on GitHub (pinned to b150a551b8)

Solutions

1. Retry; if it persists, the endpoint or an intermediate proxy is emitting malformed SSE — check baseURL and proxies.

When it happens

Trigger: Thrown at packages/llm/llm-deepseek/src/translate.ts:124 when the library encounters an invalid state.

Common situations: See trigger scenarios.

Understand the failure class

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

AI-assisted analysis of deepseek-ai/deepseek-harness@b150a551b8 (2026-08-24). Data as JSON: /api/errors/ef669e4338c44b48. Report an issue: GitHub.