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marten-seemann merged 5 commits into from
Dec 19, 2025
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http3: explain how to enable qlog for HTTP/3 events #120

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Initial plan
Copilot Dec 19, 2025
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Add HTTP/3 qlogging documentation
Copilot Dec 19, 2025
4060291
Fix missing imports in custom tracer example
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shorten
marten-seemann Dec 19, 2025
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fix draft name
marten-seemann Dec 19, 2025
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1 change: 0 additions & 1 deletion content/docs/http3/client.md
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Expand Up @@ -79,7 +79,6 @@ The code snippet shows all the knobs that need to be turned to send a request in
## 📝 Future Work {#future-work}

* Support for zstd Content Encoding: [#4100](https://github.com/quic-go/quic-go/issues/4100)
* qlog Support: [#4124](https://github.com/quic-go/quic-go/issues/4124)
* Happy Eyeballs Support: [#3755](https://github.com/quic-go/quic-go/issues/3755)
* Support for Extensible Priorities ([RFC 9218](https://www.rfc-editor.org/rfc/rfc9218.html)): [#3470](https://github.com/quic-go/quic-go/issues/3470)
* Use [`Early-Data` header field](https://datatracker.ietf.org/doc/html/rfc8470#section-5.1) for 0-RTT requests, retry on 425 response status: [#4381](https://github.com/quic-go/quic-go/issues/4381)
28 changes: 28 additions & 0 deletions content/docs/http3/qlog.md
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---
title: Event Logging using qlog
toc: true
weight: 90
---

quic-go logs HTTP/3 events defined in [draft-ietf-quic-qlog-h3-events](https://datatracker.ietf.org/doc/draft-ietf-quic-qlog-h3-events/), providing detailed insights into HTTP/3 frame processing and datagram handling. This complements the QUIC-layer events to give a complete picture of HTTP/3 connections.

## Enabling qlog for HTTP/3

HTTP/3 qlogging is enabled by setting the `Tracer` callback on the `quic.Config`, just like for QUIC connections. However, to log HTTP/3 events in addition to QUIC events, the tracer needs to support the HTTP/3 event schema.

The `http3/qlog` package provides `DefaultConnectionTracer`, which automatically includes both QUIC and HTTP/3 event schemas:

```go
import (
"github.com/quic-go/quic-go"
h3qlog "github.com/quic-go/quic-go/http3/qlog"
)

quic.Config{
Tracer: h3qlog.DefaultConnectionTracer,
}
```

This tracer writes qlog files to a directory specified by the `QLOGDIR` environment variable, if set. Each connection will produce a separate qlog file containing both QUIC and HTTP/3 events.

As described in the [qlog documentation]({{< relref "../quic/qlog.md" >}}), applications can implement the `quic.Config.Tracer` callback to add custom logic to the qlog tracing.
3 changes: 0 additions & 3 deletions content/docs/quic/qlog.md
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Expand Up @@ -57,6 +57,3 @@ quic.Transport{
}
```

## 📝 Future Work

* qlog support for HTTP/3: [#4124](https://github.com/quic-go/quic-go/issues/4124)