net/http: TestServerContentTypeSniff/h3 failures

[gopherbot]

#!watchflakes
default <- pkg == "net/http" && test == "TestServerContentTypeSniff/h3"

Issue created automatically to collect these failures.

Example (log):

=== RUN   TestServerContentTypeSniff/h3
=== PAUSE TestServerContentTypeSniff/h3
=== CONT  TestServerContentTypeSniff/h3
    sniff_test.go:106: RAR v5+: Get "https://127.0.0.1:46313/?i=35": connection closed
    sniff_test.go:106: Incorrect RAR v1.5-v4.0: Get "https://127.0.0.1:46313/?i=36": connection closed
    sniff_test.go:106: Incorrect RAR v5+: Get "https://127.0.0.1:46313/?i=37": connection closed
--- FAIL: TestServerContentTypeSniff/h3 (0.62s)

— watchflakes

[gopherbot]

Found new dashboard test flakes for:

#!watchflakes
default <- pkg == "net/http" && test == "TestServerContentTypeSniff/h3"

2026-04-29 00:53 gotip-freebsd-amd64-race go@a63b23ff net/http.TestServerContentTypeSniff/h3 (log)

=== RUN   TestServerContentTypeSniff/h3
=== PAUSE TestServerContentTypeSniff/h3
=== CONT  TestServerContentTypeSniff/h3
    sniff_test.go:106: RAR v5+: Get "https://127.0.0.1:46313/?i=35": connection closed
    sniff_test.go:106: Incorrect RAR v1.5-v4.0: Get "https://127.0.0.1:46313/?i=36": connection closed
    sniff_test.go:106: Incorrect RAR v5+: Get "https://127.0.0.1:46313/?i=37": connection closed
--- FAIL: TestServerContentTypeSniff/h3 (0.62s)

2026-04-29 19:15 gotip-netbsd-arm64 go@cbaecb28 net/http.TestServerContentTypeSniff/h3 (log)

=== RUN   TestServerContentTypeSniff/h3
=== PAUSE TestServerContentTypeSniff/h3
=== CONT  TestServerContentTypeSniff/h3
    sniff_test.go:106: AVI video #1: Get "https://127.0.0.1:55203/?i=26": peer closed connection: FINAL_SIZE_ERROR: "end of stream occurs before prior data"
    sniff_test.go:106: AVI video #2: Get "https://127.0.0.1:55203/?i=27": connection closed
    sniff_test.go:106: TTF sample  I: Get "https://127.0.0.1:55203/?i=28": connection closed
    sniff_test.go:106: TTF sample II: Get "https://127.0.0.1:55203/?i=29": connection closed
    sniff_test.go:106: OTTO sample  I: Get "https://127.0.0.1:55203/?i=30": connection closed
    sniff_test.go:106: woff sample  I: Get "https://127.0.0.1:55203/?i=31": connection closed
    sniff_test.go:106: woff2 sample: Get "https://127.0.0.1:55203/?i=32": connection closed
    sniff_test.go:106: wasm sample: Get "https://127.0.0.1:55203/?i=33": connection closed
    sniff_test.go:106: RAR v1.5-v4.0: Get "https://127.0.0.1:55203/?i=34": connection closed
    sniff_test.go:106: RAR v5+: Get "https://127.0.0.1:55203/?i=35": connection closed
    sniff_test.go:106: Incorrect RAR v1.5-v4.0: Get "https://127.0.0.1:55203/?i=36": connection closed
    sniff_test.go:106: Incorrect RAR v5+: Get "https://127.0.0.1:55203/?i=37": connection closed
--- FAIL: TestServerContentTypeSniff/h3 (0.41s)

— watchflakes

[gopherbot]

Found new dashboard test flakes for:

#!watchflakes
default <- pkg == "net/http" && test == "TestServerContentTypeSniff/h3"

2026-05-01 14:51 gotip-freebsd-amd64-race go@6baecf31 net/http.TestServerContentTypeSniff/h3 (log)

=== RUN   TestServerContentTypeSniff/h3
=== PAUSE TestServerContentTypeSniff/h3
=== CONT  TestServerContentTypeSniff/h3
    sniff_test.go:106: Plain text: Get "https://127.0.0.1:34896/?i=6": peer closed connection: FINAL_SIZE_ERROR: "end of stream occurs before prior data"
    sniff_test.go:106: XML: Get "https://127.0.0.1:34896/?i=7": connection closed
    sniff_test.go:106: Windows icon: Get "https://127.0.0.1:34896/?i=8": connection closed
    sniff_test.go:106: Windows cursor: Get "https://127.0.0.1:34896/?i=9": connection closed
    sniff_test.go:106: BMP image: Get "https://127.0.0.1:34896/?i=10": connection closed
    sniff_test.go:106: GIF 87a: Get "https://127.0.0.1:34896/?i=11": connection closed
    sniff_test.go:106: GIF 89a: Get "https://127.0.0.1:34896/?i=12": connection closed
...
    sniff_test.go:106: TTF sample II: Get "https://127.0.0.1:34896/?i=29": connection closed
    sniff_test.go:106: OTTO sample  I: Get "https://127.0.0.1:34896/?i=30": connection closed
    sniff_test.go:106: woff sample  I: Get "https://127.0.0.1:34896/?i=31": connection closed
    sniff_test.go:106: woff2 sample: Get "https://127.0.0.1:34896/?i=32": connection closed
    sniff_test.go:106: wasm sample: Get "https://127.0.0.1:34896/?i=33": connection closed
    sniff_test.go:106: RAR v1.5-v4.0: Get "https://127.0.0.1:34896/?i=34": connection closed
    sniff_test.go:106: RAR v5+: Get "https://127.0.0.1:34896/?i=35": connection closed
    sniff_test.go:106: Incorrect RAR v1.5-v4.0: Get "https://127.0.0.1:34896/?i=36": connection closed
    sniff_test.go:106: Incorrect RAR v5+: Get "https://127.0.0.1:34896/?i=37": connection closed
--- FAIL: TestServerContentTypeSniff/h3 (0.25s)

— watchflakes

[gopherbot]

Found new dashboard test flakes for:

#!watchflakes
default <- pkg == "net/http" && test == "TestServerContentTypeSniff/h3"

2026-05-01 20:40 gotip-windows-amd64-race go@7bb9bc64 net/http.TestServerContentTypeSniff/h3 (log)

=== RUN   TestServerContentTypeSniff/h3
=== PAUSE TestServerContentTypeSniff/h3
=== CONT  TestServerContentTypeSniff/h3
    sniff_test.go:106: Incorrect RAR v5+: Get "https://127.0.0.1:65119/?i=37": connection closed
--- FAIL: TestServerContentTypeSniff/h3 (0.40s)

— watchflakes

[gopherbot]

Found new dashboard test flakes for:

#!watchflakes
default <- pkg == "net/http" && test == "TestServerContentTypeSniff/h3"

2026-05-01 20:33 gotip-linux-amd64-longtest-race go@10b5baca net/http.TestServerContentTypeSniff/h3 (log)

=== RUN   TestServerContentTypeSniff/h3
==================
WARNING: DATA RACE
Read at 0x00c000022ff0 by goroutine 24048:
  vendor/golang.org/x/net/quic.(*Conn).streamForFrame()
      /home/swarming/.swarming/w/ir/x/w/goroot/src/vendor/golang.org/x/net/quic/conn_streams.go:166 +0x2c7
  vendor/golang.org/x/net/quic.(*Conn).handleStreamFrame()
      /home/swarming/.swarming/w/ir/x/w/goroot/src/vendor/golang.org/x/net/quic/conn_recv.go:540 +0xbd
  vendor/golang.org/x/net/quic.(*Conn).handleFrames()
      /home/swarming/.swarming/w/ir/x/w/goroot/src/vendor/golang.org/x/net/quic/conn_recv.go:339 +0x34a
...
      /home/swarming/.swarming/w/ir/x/w/goroot/src/net/http/clientserver_test.go:118 +0x382
  net/http_test.TestServerContentTypeSniff()
      /home/swarming/.swarming/w/ir/x/w/goroot/src/net/http/sniff_test.go:91 +0x3b
  testing.tRunner()
      /home/swarming/.swarming/w/ir/x/w/goroot/src/testing/testing.go:2190 +0x21c
  testing.(*T).Run.gowrap1()
      /home/swarming/.swarming/w/ir/x/w/goroot/src/testing/testing.go:2255 +0x38
==================
    testing.go:1865: race detected during execution of test
--- FAIL: TestServerContentTypeSniff/h3 (0.27s)

2026-05-01 20:52 gotip-linux-amd64-longtest-race go@4e078336 net/http.TestServerContentTypeSniff/h3 (log)

=== RUN   TestServerContentTypeSniff/h3
==================
WARNING: DATA RACE
Read at 0x00c000443a70 by goroutine 23981:
  vendor/golang.org/x/net/quic.(*Conn).streamForFrame()
      /home/swarming/.swarming/w/ir/x/w/goroot/src/vendor/golang.org/x/net/quic/conn_streams.go:166 +0x2c7
  vendor/golang.org/x/net/quic.(*Conn).handleStreamFrame()
      /home/swarming/.swarming/w/ir/x/w/goroot/src/vendor/golang.org/x/net/quic/conn_recv.go:540 +0xbd
  vendor/golang.org/x/net/quic.(*Conn).handleFrames()
      /home/swarming/.swarming/w/ir/x/w/goroot/src/vendor/golang.org/x/net/quic/conn_recv.go:339 +0x34a
...
      /home/swarming/.swarming/w/ir/x/w/goroot/src/net/http/clientserver_test.go:118 +0x382
  net/http_test.TestServerContentTypeSniff()
      /home/swarming/.swarming/w/ir/x/w/goroot/src/net/http/sniff_test.go:91 +0x3b
  testing.tRunner()
      /home/swarming/.swarming/w/ir/x/w/goroot/src/testing/testing.go:2190 +0x21c
  testing.(*T).Run.gowrap1()
      /home/swarming/.swarming/w/ir/x/w/goroot/src/testing/testing.go:2255 +0x38
==================
    testing.go:1865: race detected during execution of test
--- FAIL: TestServerContentTypeSniff/h3 (0.28s)

— watchflakes

[gopherbot]

Found new dashboard test flakes for:

#!watchflakes
default <- pkg == "net/http" && test == "TestServerContentTypeSniff/h3"

2026-05-01 21:02 gotip-darwin-amd64-race go@891f4a87 net/http.TestServerContentTypeSniff/h3 (log)

=== RUN   TestServerContentTypeSniff/h3
=== PAUSE TestServerContentTypeSniff/h3
=== CONT  TestServerContentTypeSniff/h3
    sniff_test.go:106: Plain text: Get "https://127.0.0.1:56544/?i=6": peer closed connection: FINAL_SIZE_ERROR: "end of stream occurs before prior data"
    sniff_test.go:106: XML: Get "https://127.0.0.1:56544/?i=7": connection closed
    sniff_test.go:106: Windows icon: Get "https://127.0.0.1:56544/?i=8": connection closed
    sniff_test.go:106: Windows cursor: Get "https://127.0.0.1:56544/?i=9": connection closed
    sniff_test.go:106: BMP image: Get "https://127.0.0.1:56544/?i=10": connection closed
    sniff_test.go:106: GIF 87a: Get "https://127.0.0.1:56544/?i=11": connection closed
    sniff_test.go:106: GIF 89a: Get "https://127.0.0.1:56544/?i=12": connection closed
...
    sniff_test.go:106: TTF sample II: Get "https://127.0.0.1:56544/?i=29": connection closed
    sniff_test.go:106: OTTO sample  I: Get "https://127.0.0.1:56544/?i=30": connection closed
    sniff_test.go:106: woff sample  I: Get "https://127.0.0.1:56544/?i=31": connection closed
    sniff_test.go:106: woff2 sample: Get "https://127.0.0.1:56544/?i=32": connection closed
    sniff_test.go:106: wasm sample: Get "https://127.0.0.1:56544/?i=33": connection closed
    sniff_test.go:106: RAR v1.5-v4.0: Get "https://127.0.0.1:56544/?i=34": connection closed
    sniff_test.go:106: RAR v5+: Get "https://127.0.0.1:56544/?i=35": connection closed
    sniff_test.go:106: Incorrect RAR v1.5-v4.0: Get "https://127.0.0.1:56544/?i=36": connection closed
    sniff_test.go:106: Incorrect RAR v5+: Get "https://127.0.0.1:56544/?i=37": connection closed
--- FAIL: TestServerContentTypeSniff/h3 (0.16s)

2026-05-01 21:02 gotip-freebsd-amd64-race go@891f4a87 net/http.TestServerContentTypeSniff/h3 (log)

=== RUN   TestServerContentTypeSniff/h3
=== PAUSE TestServerContentTypeSniff/h3
=== CONT  TestServerContentTypeSniff/h3
    sniff_test.go:106: RAR v1.5-v4.0: Get "https://127.0.0.1:15337/?i=34": peer closed connection: FINAL_SIZE_ERROR: "end of stream occurs before prior data"
    sniff_test.go:106: RAR v5+: Get "https://127.0.0.1:15337/?i=35": connection closed
    sniff_test.go:106: Incorrect RAR v1.5-v4.0: Get "https://127.0.0.1:15337/?i=36": connection closed
    sniff_test.go:106: Incorrect RAR v5+: Get "https://127.0.0.1:15337/?i=37": connection closed
--- FAIL: TestServerContentTypeSniff/h3 (0.75s)

— watchflakes

[gopherbot]

Found new dashboard test flakes for:

#!watchflakes
default <- pkg == "net/http" && test == "TestServerContentTypeSniff/h3"

2026-05-02 00:09 gotip-netbsd-arm64 go@464dc3f3 net/http.TestServerContentTypeSniff/h3 (log)

=== RUN   TestServerContentTypeSniff/h3
=== PAUSE TestServerContentTypeSniff/h3
=== CONT  TestServerContentTypeSniff/h3
    sniff_test.go:106: OGG audio: Get "https://127.0.0.1:51054/?i=21": peer closed connection: FINAL_SIZE_ERROR: "end of stream occurs before prior data"
    sniff_test.go:106: Must not match OGG: Get "https://127.0.0.1:51054/?i=22": connection closed
    sniff_test.go:106: Must not match OGG: Get "https://127.0.0.1:51054/?i=23": connection closed
    sniff_test.go:106: Must not match OGG: Get "https://127.0.0.1:51054/?i=24": connection closed
    sniff_test.go:106: MP4 video: Get "https://127.0.0.1:51054/?i=25": connection closed
    sniff_test.go:106: AVI video #1: Get "https://127.0.0.1:51054/?i=26": connection closed
    sniff_test.go:106: AVI video #2: Get "https://127.0.0.1:51054/?i=27": connection closed
    sniff_test.go:106: TTF sample  I: Get "https://127.0.0.1:51054/?i=28": connection closed
    sniff_test.go:106: TTF sample II: Get "https://127.0.0.1:51054/?i=29": connection closed
    sniff_test.go:106: OTTO sample  I: Get "https://127.0.0.1:51054/?i=30": connection closed
    sniff_test.go:106: woff sample  I: Get "https://127.0.0.1:51054/?i=31": connection closed
    sniff_test.go:106: woff2 sample: Get "https://127.0.0.1:51054/?i=32": connection closed
    sniff_test.go:106: wasm sample: Get "https://127.0.0.1:51054/?i=33": connection closed
    sniff_test.go:106: RAR v1.5-v4.0: Get "https://127.0.0.1:51054/?i=34": connection closed
    sniff_test.go:106: RAR v5+: Get "https://127.0.0.1:51054/?i=35": connection closed
    sniff_test.go:106: Incorrect RAR v1.5-v4.0: Get "https://127.0.0.1:51054/?i=36": connection closed
    sniff_test.go:106: Incorrect RAR v5+: Get "https://127.0.0.1:51054/?i=37": connection closed
--- FAIL: TestServerContentTypeSniff/h3 (0.62s)

— watchflakes

[prattmic]

Marking as a release blocker, as #79104 (comment) shows actual race reports.

cc @nicholashusin @neild

[nicholashusin]

(Discussed this in person, but posting here posterity.)

This is not user-accessible code, so not necessarily a release blocker.
I'll get it fixed ASAP though so it stops causing presubmit failures.

[gopherbot]

Change https://go.dev/cl/773940 mentions this issue: quic: fix data race in streamForFrame

[gopherbot]

Found new dashboard test flakes for:

#!watchflakes
default <- pkg == "net/http" && test == "TestServerContentTypeSniff/h3"

2026-05-04 21:27 gotip-windows-amd64 go@20982797 net/http.TestServerContentTypeSniff/h3 (log)

=== RUN   TestServerContentTypeSniff/h3
=== PAUSE TestServerContentTypeSniff/h3
=== CONT  TestServerContentTypeSniff/h3
    sniff_test.go:106: AVI video #1: Get "https://127.0.0.1:56645/?i=26": peer closed connection: FINAL_SIZE_ERROR: "end of stream occurs before prior data"
    sniff_test.go:106: AVI video #2: Get "https://127.0.0.1:56645/?i=27": connection closed
    sniff_test.go:106: TTF sample  I: Get "https://127.0.0.1:56645/?i=28": connection closed
    sniff_test.go:106: TTF sample II: Get "https://127.0.0.1:56645/?i=29": connection closed
    sniff_test.go:106: OTTO sample  I: Get "https://127.0.0.1:56645/?i=30": connection closed
    sniff_test.go:106: woff sample  I: Get "https://127.0.0.1:56645/?i=31": connection closed
    sniff_test.go:106: woff2 sample: Get "https://127.0.0.1:56645/?i=32": connection closed
    sniff_test.go:106: wasm sample: Get "https://127.0.0.1:56645/?i=33": connection closed
    sniff_test.go:106: RAR v1.5-v4.0: Get "https://127.0.0.1:56645/?i=34": connection closed
    sniff_test.go:106: RAR v5+: Get "https://127.0.0.1:56645/?i=35": connection closed
    sniff_test.go:106: Incorrect RAR v1.5-v4.0: Get "https://127.0.0.1:56645/?i=36": connection closed
    sniff_test.go:106: Incorrect RAR v5+: Get "https://127.0.0.1:56645/?i=37": connection closed
--- FAIL: TestServerContentTypeSniff/h3 (0.12s)

— watchflakes

[gopherbot]

Found new dashboard test flakes for:

#!watchflakes
default <- pkg == "net/http" && test == "TestServerContentTypeSniff/h3"

2026-05-01 20:24 gotip-netbsd-arm64 go@bb1dde27 net/http.TestServerContentTypeSniff/h3 (log)

=== RUN   TestServerContentTypeSniff/h3
=== PAUSE TestServerContentTypeSniff/h3
=== CONT  TestServerContentTypeSniff/h3
    sniff_test.go:106: PNG image: Get "https://127.0.0.1:60562/?i=14": peer closed connection: FINAL_SIZE_ERROR: "end of stream occurs before prior data"
    sniff_test.go:106: JPEG image: Get "https://127.0.0.1:60562/?i=15": connection closed
    sniff_test.go:106: MIDI audio: Get "https://127.0.0.1:60562/?i=16": connection closed
    sniff_test.go:106: MP3 audio/MPEG audio: Get "https://127.0.0.1:60562/?i=17": connection closed
    sniff_test.go:106: WAV audio #1: Get "https://127.0.0.1:60562/?i=18": connection closed
    sniff_test.go:106: WAV audio #2: Get "https://127.0.0.1:60562/?i=19": connection closed
    sniff_test.go:106: AIFF audio #1: Get "https://127.0.0.1:60562/?i=20": connection closed
    sniff_test.go:106: OGG audio: Get "https://127.0.0.1:60562/?i=21": connection closed
    sniff_test.go:106: Must not match OGG: Get "https://127.0.0.1:60562/?i=22": connection closed
    sniff_test.go:106: Must not match OGG: Get "https://127.0.0.1:60562/?i=23": connection closed
    sniff_test.go:106: Must not match OGG: Get "https://127.0.0.1:60562/?i=24": connection closed
    sniff_test.go:106: MP4 video: Get "https://127.0.0.1:60562/?i=25": connection closed
    sniff_test.go:106: AVI video #1: Get "https://127.0.0.1:60562/?i=26": connection closed
    sniff_test.go:106: AVI video #2: Get "https://127.0.0.1:60562/?i=27": connection closed
    sniff_test.go:106: TTF sample  I: Get "https://127.0.0.1:60562/?i=28": connection closed
    sniff_test.go:106: TTF sample II: Get "https://127.0.0.1:60562/?i=29": connection closed
    sniff_test.go:106: OTTO sample  I: Get "https://127.0.0.1:60562/?i=30": connection closed
    sniff_test.go:106: woff sample  I: Get "https://127.0.0.1:60562/?i=31": connection closed
    sniff_test.go:106: woff2 sample: Get "https://127.0.0.1:60562/?i=32": connection closed
    sniff_test.go:106: wasm sample: Get "https://127.0.0.1:60562/?i=33": connection closed
    sniff_test.go:106: RAR v1.5-v4.0: Get "https://127.0.0.1:60562/?i=34": connection closed
    sniff_test.go:106: RAR v5+: Get "https://127.0.0.1:60562/?i=35": connection closed
    sniff_test.go:106: Incorrect RAR v1.5-v4.0: Get "https://127.0.0.1:60562/?i=36": connection closed
    sniff_test.go:106: Incorrect RAR v5+: Get "https://127.0.0.1:60562/?i=37": connection closed
--- FAIL: TestServerContentTypeSniff/h3 (0.68s)

— watchflakes