net/http: synchronize "100 Continue" write and Handler writes

The expectContinueReader writes to the connection on the first
Request.Body read. Since a Handler might be doing a read in parallel or
before a write, expectContinueReader needs to synchronize with the
ResponseWriter, and abort if a response already went out.

The tests will land in a separate CL.

Fixes #34902
Fixes CVE-2020-15586

Change-Id: Icdd8dd539f45e8863762bd378194bb4741e875fc
Reviewed-by: Filippo Valsorda <>
Run-TryBot: Katie Hockman <>
Reviewed-by: Filippo Valsorda <>
TryBot-Result: Gobot Gobot <>
1 file changed
tree: 3d149d87dad36dcb3bb29f0386a8f3182b693c4b
  1. .gitattributes
  2. .github/
  3. .gitignore
  11. api/
  12. doc/
  13. favicon.ico
  14. lib/
  15. misc/
  16. robots.txt
  17. src/
  18. test/

The Go Programming Language

Go is an open source programming language that makes it easy to build simple, reliable, and efficient software.

Gopher image Gopher image by Renee French, licensed under Creative Commons 3.0 Attributions license.

Our canonical Git repository is located at There is a mirror of the repository at

Unless otherwise noted, the Go source files are distributed under the BSD-style license found in the LICENSE file.

Download and Install

Binary Distributions

Official binary distributions are available at

After downloading a binary release, visit or load doc/install.html in your web browser for installation instructions.

Install From Source

If a binary distribution is not available for your combination of operating system and architecture, visit or load doc/install-source.html in your web browser for source installation instructions.


Go is the work of thousands of contributors. We appreciate your help!

To contribute, please read the contribution guidelines:

Note that the Go project uses the issue tracker for bug reports and proposals only. See for a list of places to ask questions about the Go language.