http2: avoid API changes when built with go1.27

The wrapping implementation accidentally dropped some symbols.
Preserve them.

Move errors into common locations:
  - ErrNoCachedConn
  - ErrPushLimitReached
  - ErrRecursivePush
  - GoAwayError

Move one constant into a common location:
  - TrailerPrefix

Preserve methods of FrameWriteRequest as no-ops.
These are not a user-serviceable part and there is no way
for users to construct FrameWriteRequests.
  - FrameWriteRequest.Consume
  - FrameWriteRequest.DataSize
  - FrameWriteRequest.StreamID
  - FrameWriteRequest.String

Preserve functions which create write schedulers,
returning a no-op implementation of WriteScheduler:
- NewPriorityWriteScheduler
- NewRandomWriteScheduler
- PriorityWriteSchedulerConfig

For golang/go#78508

Change-Id: I327603137cf69d93bb405d9a95e038886a6a6964
Reviewed-on: https://go-review.googlesource.com/c/net/+/776180
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

Author: neild

http2/server.go

@@ -2657,21 +2657,6 @@ func (rws *responseWriterState) writeChunk(p []byte) (n int, err error) {
 	return len(p), nil
 }
 
-// TrailerPrefix is a magic prefix for ResponseWriter.Header map keys
-// that, if present, signals that the map entry is actually for
-// the response trailers, and not the response headers. The prefix
-// is stripped after the ServeHTTP call finishes and the values are
-// sent in the trailers.
-//
-// This mechanism is intended only for trailers that are not known
-// prior to the headers being written. If the set of trailers is fixed
-// or known before the header is written, the normal Go trailers mechanism
-// is preferred:
-//
-//	https://golang.org/pkg/net/http/#ResponseWriter
-//	https://golang.org/pkg/net/http/#example_ResponseWriter_trailers
-const TrailerPrefix = "Trailer:"
-
 // promoteUndeclaredTrailers permits http.Handlers to set trailers
 // after the header has already been flushed. Because the Go
 // ResponseWriter interface has no way to set Trailers (only the
@@ -2948,12 +2933,6 @@ func (w *responseWriter) handlerDone() {
 	responseWriterStatePool.Put(rws)
 }
 
-// Push errors.
-var (
-	ErrRecursivePush    = errors.New("http2: recursive push not allowed")
-	ErrPushLimitReached = errors.New("http2: push would exceed peer's SETTINGS_MAX_CONCURRENT_STREAMS")
-)
-
 var _ http.Pusher = (*responseWriter)(nil)
 
 func (w *responseWriter) Push(target string, opts *http.PushOptions) error {

http2/server_common.go

@@ -6,11 +6,33 @@ package http2
 
 import (
 	"context"
+	"errors"
 	"net"
 	"net/http"
 	"time"
 )
 
+// TrailerPrefix is a magic prefix for ResponseWriter.Header map keys
+// that, if present, signals that the map entry is actually for
+// the response trailers, and not the response headers. The prefix
+// is stripped after the ServeHTTP call finishes and the values are
+// sent in the trailers.
+//
+// This mechanism is intended only for trailers that are not known
+// prior to the headers being written. If the set of trailers is fixed
+// or known before the header is written, the normal Go trailers mechanism
+// is preferred:
+//
+//	https://golang.org/pkg/net/http/#ResponseWriter
+//	https://golang.org/pkg/net/http/#example_ResponseWriter_trailers
+const TrailerPrefix = "Trailer:"
+
+// Push errors.
+var (
+	ErrRecursivePush    = errors.New("http2: recursive push not allowed")
+	ErrPushLimitReached = errors.New("http2: push would exceed peer's SETTINGS_MAX_CONCURRENT_STREAMS")
+)
+
 // ConfigureServer adds HTTP/2 support to a net/http Server.
 //
 // The configuration conf may be nil.

http2/server_wrap.go

@@ -159,3 +159,43 @@ type FrameWriteRequest struct {
 	// to avoid duplicating an exported symbol across two files,
 	// but the changes required to make this work are fairly large.
 }
+
+func (wr FrameWriteRequest) StreamID() uint32 {
+	return 0
+}
+
+func (wr FrameWriteRequest) DataSize() int {
+	return 0
+}
+
+func (wr FrameWriteRequest) Consume(n int32) (FrameWriteRequest, FrameWriteRequest, int) {
+	return FrameWriteRequest{}, FrameWriteRequest{}, 0
+}
+
+func (wr FrameWriteRequest) String() string {
+	return ""
+}
+
+// NewPriorityWriteScheduler is deprecated.
+//
+// Deprecated: User-provided write schedulers are deprecated.
+func NewPriorityWriteScheduler(cfg *PriorityWriteSchedulerConfig) WriteScheduler {
+	return unsupportedWriteScheduler{}
+}
+
+// NewRandomWriteScheduler is deprecated.
+//
+// Deprecated: User-provided write schedulers are deprecated.
+func NewRandomWriteScheduler() WriteScheduler {
+	return unsupportedWriteScheduler{}
+}
+
+type unsupportedWriteScheduler struct{}
+
+func (unsupportedWriteScheduler) OpenStream(streamID uint32, options OpenStreamOptions) {}
+func (unsupportedWriteScheduler) CloseStream(streamID uint32)                           {}
+func (unsupportedWriteScheduler) AdjustStream(streamID uint32, priority PriorityParam)  {}
+func (unsupportedWriteScheduler) Push(wr FrameWriteRequest)                             {}
+func (unsupportedWriteScheduler) Pop() (wr FrameWriteRequest, ok bool) {
+	return FrameWriteRequest{}, false
+}

http2/transport.go

@@ -399,27 +399,6 @@ func (sew stickyErrWriter) Write(p []byte) (n int, err error) {
 	return n, err
 }
 
-// noCachedConnError is the concrete type of ErrNoCachedConn, which
-// needs to be detected by net/http regardless of whether it's its
-// bundled version (in h2_bundle.go with a rewritten type name) or
-// from a user's x/net/http2. As such, as it has a unique method name
-// (IsHTTP2NoCachedConnError) that net/http sniffs for via func
-// isNoCachedConnError.
-type noCachedConnError struct{}
-
-func (noCachedConnError) IsHTTP2NoCachedConnError() {}
-func (noCachedConnError) Error() string             { return "http2: no cached connection was available" }
-
-// isNoCachedConnError reports whether err is of type noCachedConnError
-// or its equivalent renamed type in net/http2's h2_bundle.go. Both types
-// may coexist in the same running program.
-func isNoCachedConnError(err error) bool {
-	_, ok := err.(interface{ IsHTTP2NoCachedConnError() })
-	return ok
-}
-
-var ErrNoCachedConn error = noCachedConnError{}
-
 func (t *Transport) roundTripOpt(req *http.Request, opt RoundTripOpt) (*http.Response, error) {
 	switch req.URL.Scheme {
 	case "https":
@@ -1786,19 +1765,6 @@ func (cc *ClientConn) readLoop() {
 	}
 }
 
-// GoAwayError is returned by the Transport when the server closes the
-// TCP connection after sending a GOAWAY frame.
-type GoAwayError struct {
-	LastStreamID uint32
-	ErrCode      ErrCode
-	DebugData    string
-}
-
-func (e GoAwayError) Error() string {
-	return fmt.Sprintf("http2: server sent GOAWAY and closed the connection; LastStreamID=%v, ErrCode=%v, debug=%q",
-		e.LastStreamID, e.ErrCode, e.DebugData)
-}
-
 func isEOFOrNetReadError(err error) bool {
 	if err == io.EOF {
 		return true

http2/transport_common.go

@@ -411,3 +411,37 @@ func (t *Transport) dialTLSWithContext(ctx context.Context, network, addr string
 	tlsCn := cn.(*tls.Conn) // DialContext comment promises this will always succeed
 	return tlsCn, nil
 }
+
+// GoAwayError is returned by the Transport when the server closes the
+// TCP connection after sending a GOAWAY frame.
+type GoAwayError struct {
+	LastStreamID uint32
+	ErrCode      ErrCode
+	DebugData    string
+}
+
+func (e GoAwayError) Error() string {
+	return fmt.Sprintf("http2: server sent GOAWAY and closed the connection; LastStreamID=%v, ErrCode=%v, debug=%q",
+		e.LastStreamID, e.ErrCode, e.DebugData)
+}
+
+// noCachedConnError is the concrete type of ErrNoCachedConn, which
+// needs to be detected by net/http regardless of whether it's its
+// bundled version (in h2_bundle.go with a rewritten type name) or
+// from a user's x/net/http2. As such, as it has a unique method name
+// (IsHTTP2NoCachedConnError) that net/http sniffs for via func
+// isNoCachedConnError.
+type noCachedConnError struct{}
+
+func (noCachedConnError) IsHTTP2NoCachedConnError() {}
+func (noCachedConnError) Error() string             { return "http2: no cached connection was available" }
+
+// isNoCachedConnError reports whether err is of type noCachedConnError
+// or its equivalent renamed type in net/http2's h2_bundle.go. Both types
+// may coexist in the same running program.
+func isNoCachedConnError(err error) bool {
+	_, ok := err.(interface{ IsHTTP2NoCachedConnError() })
+	return ok
+}
+
+var ErrNoCachedConn error = noCachedConnError{}

http2/writesched_common.go

@@ -47,3 +47,44 @@ type OpenStreamOptions struct {
 	// priority is used to set the priority of the newly opened stream.
 	priority PriorityParam
 }
+
+// PriorityWriteSchedulerConfig configures a priorityWriteScheduler.
+//
+// Deprecated: User-provided write schedulers are deprecated.
+type PriorityWriteSchedulerConfig struct {
+	// MaxClosedNodesInTree controls the maximum number of closed streams to
+	// retain in the priority tree. Setting this to zero saves a small amount
+	// of memory at the cost of performance.
+	//
+	// See RFC 7540, Section 5.3.4:
+	//   "It is possible for a stream to become closed while prioritization
+	//   information ... is in transit. ... This potentially creates suboptimal
+	//   prioritization, since the stream could be given a priority that is
+	//   different from what is intended. To avoid these problems, an endpoint
+	//   SHOULD retain stream prioritization state for a period after streams
+	//   become closed. The longer state is retained, the lower the chance that
+	//   streams are assigned incorrect or default priority values."
+	MaxClosedNodesInTree int
+
+	// MaxIdleNodesInTree controls the maximum number of idle streams to
+	// retain in the priority tree. Setting this to zero saves a small amount
+	// of memory at the cost of performance.
+	//
+	// See RFC 7540, Section 5.3.4:
+	//   Similarly, streams that are in the "idle" state can be assigned
+	//   priority or become a parent of other streams. This allows for the
+	//   creation of a grouping node in the dependency tree, which enables
+	//   more flexible expressions of priority. Idle streams begin with a
+	//   default priority (Section 5.3.5).
+	MaxIdleNodesInTree int
+
+	// ThrottleOutOfOrderWrites enables write throttling to help ensure that
+	// data is delivered in priority order. This works around a race where
+	// stream B depends on stream A and both streams are about to call Write
+	// to queue DATA frames. If B wins the race, a naive scheduler would eagerly
+	// write as much data from B as possible, but this is suboptimal because A
+	// is a higher-priority stream. With throttling enabled, we write a small
+	// amount of data from B to minimize the amount of bandwidth that B can
+	// steal from A.
+	ThrottleOutOfOrderWrites bool
+}

http2/writesched_priority_rfc7540.go

@@ -15,47 +15,6 @@ import (
 // RFC 7540, Section 5.3.5: the default weight is 16.
 const priorityDefaultWeightRFC7540 = 15 // 16 = 15 + 1
 
-// PriorityWriteSchedulerConfig configures a priorityWriteScheduler.
-//
-// Deprecated: User-provided write schedulers are deprecated.
-type PriorityWriteSchedulerConfig struct {
-	// MaxClosedNodesInTree controls the maximum number of closed streams to
-	// retain in the priority tree. Setting this to zero saves a small amount
-	// of memory at the cost of performance.
-	//
-	// See RFC 7540, Section 5.3.4:
-	//   "It is possible for a stream to become closed while prioritization
-	//   information ... is in transit. ... This potentially creates suboptimal
-	//   prioritization, since the stream could be given a priority that is
-	//   different from what is intended. To avoid these problems, an endpoint
-	//   SHOULD retain stream prioritization state for a period after streams
-	//   become closed. The longer state is retained, the lower the chance that
-	//   streams are assigned incorrect or default priority values."
-	MaxClosedNodesInTree int
-
-	// MaxIdleNodesInTree controls the maximum number of idle streams to
-	// retain in the priority tree. Setting this to zero saves a small amount
-	// of memory at the cost of performance.
-	//
-	// See RFC 7540, Section 5.3.4:
-	//   Similarly, streams that are in the "idle" state can be assigned
-	//   priority or become a parent of other streams. This allows for the
-	//   creation of a grouping node in the dependency tree, which enables
-	//   more flexible expressions of priority. Idle streams begin with a
-	//   default priority (Section 5.3.5).
-	MaxIdleNodesInTree int
-
-	// ThrottleOutOfOrderWrites enables write throttling to help ensure that
-	// data is delivered in priority order. This works around a race where
-	// stream B depends on stream A and both streams are about to call Write
-	// to queue DATA frames. If B wins the race, a naive scheduler would eagerly
-	// write as much data from B as possible, but this is suboptimal because A
-	// is a higher-priority stream. With throttling enabled, we write a small
-	// amount of data from B to minimize the amount of bandwidth that B can
-	// steal from A.
-	ThrottleOutOfOrderWrites bool
-}
-
 // NewPriorityWriteScheduler constructs a WriteScheduler that schedules
 // frames by following HTTP/2 priorities as described in RFC 7540 Section 5.3.
 // If cfg is nil, default options are used.