OpenAI Responses

codec/openairesponses targets POST /v1/responses, which is an items API, not a messages array. It implements both client and server codec contracts.

Items

System text becomes top-level instructions. User turns become message items with input_text, input_image, and input_file parts. Assistant tool calls become function_call items; tool results become function_call_output. Consecutive assistant text blocks are grouped into one message item. store is always explicitly false, and the neutral Stop sampling field is omitted because this API does not model it.

body, err := openairesponses.EncodeRequest(req, false)
if err != nil {
	return err
}
fmt.Println(string(body)) // inspect the typed items in a test, not in logs for secrets.

Usage and replay

Responses reports gross input_tokens and a cached subset. The decoder subtracts input_tokens_details.cached_tokens and leaves CacheCreationTokens zero because the DTO has no creation field. Reasoning items preserve summary text and an opaque encrypted_content value in ThinkingBlock.ProviderState; only a state tagged for this dialect is replayed. Streaming uses typed SSE events such as response.output_text.delta and response.completed.

Source and proof

• openairesponses/types.go
• openairesponses/encode.go
• openairesponses/decode.go
• openairesponses/stream.go

Run go test ./codec/openairesponses.