fix(logging): add API response timestamp and fix request timestamp timing #1300

sususu98 · 2026-01-29T04:12:18Z

Summary

Fix REQUEST INFO timestamp to capture when request first arrives (not at log write time)
Add API RESPONSE timestamp when upstream response arrives
Enable accurate measurement of backend response latency in error logs

Changes

File	Change
`request_logging.go`	Add `Timestamp` field to `RequestInfo`, set at middleware initialization
`response_writer.go`	Add `extractAPIResponseTimestamp()`, pass timestamps through logging chain
`request_logger.go`	Update `LogRequestWithOptions()` and `writeAPISection()` to accept/output timestamps
`handlers.go`	Set `API_RESPONSE_TIMESTAMP` in `appendAPIResponse()` on first response
`gemini-cli_handlers.go`	Set `API_RESPONSE_TIMESTAMP` in Gemini CLI handler

Example Output

=== REQUEST INFO ===
Timestamp: 2026-01-27T18:18:30.366575728+08:00
...

=== API RESPONSE ===
Timestamp: 2026-01-27T18:19:45.123456789+08:00
{...response...}

gemini-code-assist · 2026-01-29T04:12:34Z

Summary of Changes

Hello @sususu98, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the logging system by introducing more accurate timestamping for both incoming requests and their corresponding API responses. By capturing these events closer to their actual occurrence, the system gains the ability to precisely measure and analyze the latency of backend responses, which is crucial for debugging and performance monitoring, especially in error scenarios.

Highlights

Timestamp Accuracy: The request timestamp is now captured precisely when the request first arrives, rather than at the time of log writing.
API Response Timestamp: A new timestamp is added to record when the upstream API response is received.
Latency Measurement: These changes enable more accurate measurement of backend response latency, particularly useful for error logs.

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Code Review

This pull request effectively adds timestamps to request and API response logs, which is a great step for monitoring backend latency. The implementation correctly captures the request timestamp at the beginning of the middleware chain. However, there are a couple of issues that undermine the feature's accuracy. For streaming responses, the API response timestamp is recorded at the end of the request, not when the first response chunk arrives. Additionally, for some logging paths, the request timestamp falls back to the log write time instead of using the correctly captured arrival time. I've added specific comments with suggestions on how to address these points.

gemini-code-assist · 2026-01-29T04:14:23Z

internal/logging/request_logger.go

+	if requestTimestamp.IsZero() {
+		requestTimestamp = time.Now()
+	}


This fallback to time.Now() for a zero requestTimestamp contradicts one of the main goals of this PR, which is to 'Fix REQUEST INFO timestamp to capture when request first arrives (not at log write time)'. The LogRequest method calls this with a zero timestamp, causing the log to record the log write time instead of the request arrival time. To ensure the request arrival time is always used, you should consider updating the LogRequest method in the RequestLogger interface to accept a requestTimestamp and update its callers accordingly, or deprecate it in favor of LogRequestWithOptions.

gemini-code-assist · 2026-01-29T04:14:23Z

internal/logging/request_logger.go

 		return nil
 	}
 	w.apiResponse = bytes.Clone(apiResponse)
+	w.apiResponseTimestamp = time.Now()


For streaming responses, this sets the apiResponseTimestamp to the time when the entire response has been processed and Finalize is called, not when the first chunk of the upstream API response arrived. This is inconsistent with the non-streaming implementation and the goal of measuring backend latency.

The timestamp is correctly captured for the first chunk in sdk/api/handlers/handlers.go's appendAPIResponse function and stored in the gin.Context. However, it's not being utilized here.

To fix this, you should:

Modify the StreamingLogWriter interface's WriteAPIResponse method to accept a time.Time parameter: WriteAPIResponse(apiResponse []byte, timestamp time.Time) error.

Update this FileStreamingLogWriter.WriteAPIResponse implementation to use the passed timestamp instead of time.Now().

Update NoOpStreamingLogWriter.WriteAPIResponse to match the new interface.

In internal/api/middleware/response_writer.go's Finalize method, extract the timestamp from the context using w.extractAPIResponseTimestamp(c) and pass it when calling w.streamWriter.WriteAPIResponse().

gemini-code-assist · 2026-01-29T04:14:23Z

internal/api/middleware/response_writer.go

+	ts, isExist := c.Get("API_RESPONSE_TIMESTAMP")
+	if !isExist {
+		return time.Time{}
+	}
+	if t, ok := ts.(time.Time); ok {
+		return t
+	}
+	return time.Time{}


This function can be simplified. A type assertion in Go returns the zero value of the type if it fails. You can leverage this to make the code more concise.

ts, _ := c.Get("API_RESPONSE_TIMESTAMP") t, _ := ts.(time.Time) return t

…ming Previously: - REQUEST INFO timestamp was captured at log write time (not request arrival) - API RESPONSE had NO timestamp at all This fix: - Captures REQUEST INFO timestamp when request first arrives - Adds API RESPONSE timestamp when upstream response arrives Changes: - Add Timestamp field to RequestInfo, set at middleware initialization - Set API_RESPONSE_TIMESTAMP in appendAPIResponse() and gemini handler - Pass timestamps through logging chain to writeNonStreamingLog() - Add timestamp output to API RESPONSE section This enables accurate measurement of backend response latency in error logs.

…ps required - Add firstChunkTimestamp field to ResponseWriterWrapper for sync capture - Capture TTFB in Write() and WriteString() before async channel send - Add SetFirstChunkTimestamp() to StreamingLogWriter interface - Make requestTimestamp/apiResponseTimestamp required in LogRequest() - Remove timestamp capture from WriteAPIResponse() (now via setter) - Fix Gemini handler to set API_RESPONSE_TIMESTAMP before writing response This ensures accurate TTFB measurement for all streaming API formats (OpenAI, Gemini, Claude) by capturing timestamp synchronously when the first response chunk arrives, not when the stream finalizes.

sususu98 mentioned this pull request Jan 29, 2026

feat(logging): add timestamp to API RESPONSE section in error logs #1265

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gemini-code-assist bot reviewed Jan 29, 2026

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luispater approved these changes Jan 29, 2026

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sususu98 force-pushed the feat/log-api-response-timestamp branch from 3b0238a to d87c704 Compare January 29, 2026 14:22

sususu98 force-pushed the feat/log-api-response-timestamp branch from d87c704 to 295f34d Compare January 29, 2026 14:32

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fix(logging): add API response timestamp and fix request timestamp timing #1300

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sususu98 commented Jan 29, 2026

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