net/http: add Protocols field to Server and Transport

Support configuring which HTTP version(s) a server or client use
via an explicit set of protocols. The Protocols field takes
precedence over TLSNextProto and ForceAttemptHTTP2.

Fixes #67814

Change-Id: I09ece88f78ad4d98ca1f213157b5f62ae11e063f
Reviewed-on: https://go-review.googlesource.com/c/go/+/607496
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

1 files changed, 48 insertions, 0 deletions

diff --git a/src/net/http/http.go b/src/net/http/http.go
index 9dfc36c791..55f518607d 100644
--- a/src/net/http/http.go
+++ b/src/net/http/http.go
@@ -16,6 +16,54 @@ import (
 	"golang.org/x/net/http/httpguts"
 )
 
+// Protocols is a set of HTTP protocols.
+//
+// The supported protocols are:
+//
+//   - HTTP1 is the HTTP/1.0 and HTTP/1.1 protocols.
+//     HTTP1 is supported on both unsecured TCP and secured TLS connections.
+//
+//   - HTTP2 is the HTTP/2 protcol over a TLS connection.
+type Protocols struct {
+	bits uint8
+}
+
+const (
+	protoHTTP1 = 1 << iota
+	protoHTTP2
+)
+
+// HTTP1 reports whether p includes HTTP/1.
+func (p Protocols) HTTP1() bool { return p.bits&protoHTTP1 != 0 }
+
+// SetHTTP1 adds or removes HTTP/1 from p.
+func (p *Protocols) SetHTTP1(ok bool) { p.setBit(protoHTTP1, ok) }
+
+// HTTP2 reports whether p includes HTTP/2.
+func (p Protocols) HTTP2() bool { return p.bits&protoHTTP2 != 0 }
+
+// SetHTTP2 adds or removes HTTP/2 from p.
+func (p *Protocols) SetHTTP2(ok bool) { p.setBit(protoHTTP2, ok) }
+
+func (p *Protocols) setBit(bit uint8, ok bool) {
+	if ok {
+		p.bits |= bit
+	} else {
+		p.bits &^= bit
+	}
+}
+
+func (p Protocols) String() string {
+	var s []string
+	if p.HTTP1() {
+		s = append(s, "HTTP1")
+	}
+	if p.HTTP2() {
+		s = append(s, "HTTP2")
+	}
+	return "{" + strings.Join(s, ",") + "}"
+}
+
 // incomparable is a zero-width, non-comparable type. Adding it to a struct
 // makes that struct also non-comparable, and generally doesn't add
 // any size (as long as it's first).