net/http: avoid panic when writing 100-continue after handler done

When a request contains an "Expect: 100-continue" header,
the first read from the request body causes the server to
write a 100-continue status.

This write caused a panic when performed after the server handler
has exited. Disable the write when cleaning up after a handler
exits.

This also fixes a bug where an implicit 100-continue could be
sent after a call to WriteHeader has sent a non-1xx header.

This change drops tracking of whether we've written a
100-continue or not in response.wroteContinue. This tracking
was used to determine whether we should consume the remaining
request body in chunkWriter.writeHeader, but the discard-the-body
path was only taken when the body was already consumed.
(If the body is not consumed, we set closeAfterReply, and we
don't consume the remaining body when closeAfterReply is set.
If the body is consumed, then we may attempt to discard the
remaining body, but there is obviously no body remaining.)

Fixes #53808

Change-Id: I3542df26ad6cdfe93b50a45ae2d6e7ef031e46fa
Reviewed-on: https://go-review.googlesource.com/c/go/+/585395
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Jonathan Amsterdam <jba@google.com>

0 files changed, 0 insertions, 0 deletions