x/net/http2: The starting streamid for client should be 3 instead of 1 when AllowHTTP is set.

[snowie2000]

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

1.10

Does this issue reproduce with the latest release?

yes

What operating system and processor architecture are you using (go env)?

W64

transport.go line 537:
nextStreamID: 1,
as http2-spec stated in https://http2.github.io/http2-spec/#discover-http

Stream 1 is implicitly "half-closed" from the client toward the server (see Section 5.1), since the request is completed as an HTTP/1.1 request. After commencing the HTTP/2 connection, stream 1 is used for the response.

and https://http2.github.io/http2-spec/#StreamIdentifiers

HTTP/1.1 requests that are upgraded to HTTP/2 (see Section 3.2) are responded to with a stream identifier of one (0x1). After the upgrade completes, stream 0x1 is "half-closed (local)" to the client. Therefore, stream 0x1 cannot be selected as a new stream identifier by a client that upgrades from HTTP/1.1.

The next stream ID for h2c should therefore starts from 3

[bradfitz]

Sounds fine to start at 3 instead of 1 iff AllowHTTP is true. Somebody want to send a change?

[wingyplus]

I can do this.

[gopherbot]

Change https://golang.org/cl/111835 mentions this issue: x/net/http2: set nextStreamID to 3 when AlloHTTP is set

[neild]

Returning here, because this change inadvertently broke requests with a Connection: close header sent over a Transport with AllowHTTP set.

The cited parts of the HTTP/2 specification are referring to HTTP/1.1 requests which are upgraded to HTTP/2. We don't support request protocol upgrading; configuring a Transport with AllowHTTP permits sending unencrypted HTTP/2, but the connection is HTTP/2 from the start. As such, there is no HTTP/1.1 request to consume stream ID 1 and no reason not to use it.