Explicity write http headers on streaming endpoints

This works around issues with the otel http handler wrapper causing
multiple calls to `WriteHeader` when a `Flush` is called before `Write`.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>
(cherry picked from commit 707ab48)
Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>

api/server/httputils/write_log_stream.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"io"
+	"net/http"
 	"net/url"
 	"sort"
 
@@ -16,7 +17,11 @@ import (
 
 // WriteLogStream writes an encoded byte stream of log messages from the
 // messages channel, multiplexing them with a stdcopy.Writer if mux is true
-func WriteLogStream(_ context.Context, w io.Writer, msgs <-chan *backend.LogMessage, config *container.LogsOptions, mux bool) {
+func WriteLogStream(_ context.Context, w http.ResponseWriter, msgs <-chan *backend.LogMessage, config *container.LogsOptions, mux bool) {
+	// See https://github.com/moby/moby/issues/47448
+	// Trigger headers to be written immediately.
+	w.WriteHeader(http.StatusOK)
+
 	wf := ioutils.NewWriteFlusher(w)
 	defer wf.Close()
 

api/server/router/container/container_routes.go

@@ -112,9 +112,18 @@ func (s *containerRouter) getContainersStats(ctx context.Context, w http.Respons
 	}
 
 	return s.backend.ContainerStats(ctx, vars["name"], &backend.ContainerStatsConfig{
-		Stream:    stream,
-		OneShot:   oneShot,
-		OutStream: w,
+		Stream:  stream,
+		OneShot: oneShot,
+		OutStream: func() io.Writer {
+			// Assume that when this is called the request is OK.
+			w.WriteHeader(http.StatusOK)
+			if !stream {
+				return w
+			}
+			wf := ioutils.NewWriteFlusher(w)
+			wf.Flush()
+			return wf
+		},
 	})
 }
 

api/server/router/system/system_routes.go

@@ -263,6 +263,7 @@ func (s *systemRouter) getEvents(ctx context.Context, w http.ResponseWriter, r *
 	}
 
 	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(http.StatusOK)
 	output := ioutils.NewWriteFlusher(w)
 	defer output.Close()
 	output.Flush()

api/types/backend/backend.go

@@ -89,7 +89,7 @@ type LogSelector struct {
 type ContainerStatsConfig struct {
 	Stream    bool
 	OneShot   bool
-	OutStream io.Writer
+	OutStream func() io.Writer
 }
 
 // ExecInspect holds information about a running process started

daemon/stats.go

@@ -12,7 +12,6 @@ import (
 	"github.com/docker/docker/api/types/backend"
 	"github.com/docker/docker/container"
 	"github.com/docker/docker/errdefs"
-	"github.com/docker/docker/pkg/ioutils"
 )
 
 // ContainerStats writes information about the container to the stream
@@ -27,9 +26,11 @@ func (daemon *Daemon) ContainerStats(ctx context.Context, prefixOrName string, c
 		return errdefs.InvalidParameter(errors.New("cannot have stream=true and one-shot=true"))
 	}
 
+	enc := json.NewEncoder(config.OutStream())
+
 	// If the container is either not running or restarting and requires no stream, return an empty stats.
 	if (!ctr.IsRunning() || ctr.IsRestarting()) && !config.Stream {
-		return json.NewEncoder(config.OutStream).Encode(&types.StatsJSON{
+		return enc.Encode(&types.StatsJSON{
 			Name: ctr.Name,
 			ID:   ctr.ID,
 		})
@@ -41,15 +42,7 @@ func (daemon *Daemon) ContainerStats(ctx context.Context, prefixOrName string, c
 		if err != nil {
 			return err
 		}
-		return json.NewEncoder(config.OutStream).Encode(stats)
-	}
-
-	outStream := config.OutStream
-	if config.Stream {
-		wf := ioutils.NewWriteFlusher(outStream)
-		defer wf.Close()
-		wf.Flush()
-		outStream = wf
+		return enc.Encode(stats)
 	}
 
 	var preCPUStats types.CPUStats
@@ -65,12 +58,11 @@ func (daemon *Daemon) ContainerStats(ctx context.Context, prefixOrName string, c
 		return &ss
 	}
 
-	enc := json.NewEncoder(outStream)
-
 	updates := daemon.subscribeToContainerStats(ctr)
 	defer daemon.unsubscribeToContainerStats(ctr, updates)
 
 	noStreamFirstFrame := !config.OneShot
+
 	for {
 		select {
 		case v, ok := <-updates: