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Empty text blocks ({"type":"text","text":""}) cause Anthropic upstream to
return 400: "text content blocks must be non-empty". This was not caught
by the existing error detection pattern in isThinkingBlockSignatureError,
nor handled by FilterThinkingBlocksForRetry.
- Add empty text block stripping to FilterThinkingBlocksForRetry
- Fix isThinkingBlockSignatureError to match new Anthropic error format
- Add fast-path byte patterns to avoid unnecessary JSON parsing
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Pull request overview
This PR improves the gateway’s retry sanitization for Anthropic-style requests by recognizing a newer upstream error message and stripping invalid empty "text" content blocks to prevent 400s on retry.
Changes:
- Broaden
isThinkingBlockSignatureErrormatching to detect the newer"text content blocks must be non-empty"error phrasing. - Extend
FilterThinkingBlocksForRetryto strip empty text blocks (with a byte-pattern fast-path to avoid JSON parsing when unnecessary). - Add tests covering empty text block stripping and verifying the fast-path preserves non-empty text requests unchanged.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
| backend/internal/service/gateway_service.go | Expands signature/empty-content error detection to cover new upstream wording. |
| backend/internal/service/gateway_request.go | Adds empty-text-block detection and stripping to the retry filter with a fast-path heuristic. |
| backend/internal/service/gateway_request_test.go | Adds regression tests for empty text block stripping and fast-path preservation. |
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| if strings.Contains(msg, "non-empty content") || strings.Contains(msg, "empty content") { | ||
| // "messages: text content blocks must be non-empty" | ||
| if strings.Contains(msg, "non-empty content") || strings.Contains(msg, "empty content") || | ||
| strings.Contains(msg, "must be non-empty") { |
| // Check for empty text blocks: {"type":"text","text":""} | ||
| // These cause upstream 400: "text content blocks must be non-empty" | ||
| hasEmptyTextBlock := bytes.Contains(body, patternEmptyText) || | ||
| bytes.Contains(body, patternEmptyTextSpaced) |
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| hasEmptyTextBlock := bytes.Contains(body, patternEmptyText) || | ||
| bytes.Contains(body, patternEmptyTextSpaced) |
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The new empty-text fast path only checks "text":"" and "text": "", so payloads that are still valid JSON like "text" : "" are missed. In requests without thinking blocks or content: [], hasEmptyTextBlock stays false and the function returns early, which means the retry path resends the same invalid empty text block and still gets a 400. This makes the fix ineffective for pretty-printed clients that include spaces around the colon.
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Summary
isThinkingBlockSignatureErrorpattern matching to cover new Anthropic error format:"text content blocks must be non-empty"(old patterns only matched"non-empty content"/"empty content"){"type":"text","text":""}) stripping toFilterThinkingBlocksForRetry, with fast-path byte patterns to avoid unnecessary JSON parsingContext
Request
02f05f361f7336a01a4ce002c5763959fromclaude-cli/2.1.78hit upstream 400 because of an empty text content block. The platform had no pre-validation for this, and the retry path could not catch it due to:isThinkingBlockSignatureErrorpattern mismatch on the new error formatFilterThinkingBlocksForRetryonly handled emptycontent: []arrays, not individual empty text blocksTest plan
TestFilterThinkingBlocksForRetry_StripsEmptyTextBlocks— verifies empty text blocks are stripped, placeholder inserted when message becomes emptyTestFilterThinkingBlocksForRetry_PreservesNonEmptyTextBlocks— verifies fast path returns body unchangedTestFilterThinking*tests pass (no regression)go build ./cmd/server/succeeds🤖 Generated with Claude Code