Fix 19575: Docker events doesn't work with authorization plugin

To support the requirement of blocking the request after the daemon
responded the authorization plugin use a `response recorder` that replay
the response after the flow ends.

This commit adds support for commands that hijack the connection and
flushes data via the http.Flusher interface. This resolves the error
with the event endpoint.

Signed-off-by: Liron Levin <liron@twistlock.com>

authorization/authz.go

@@ -116,7 +116,7 @@ func (ctx *Ctx) AuthZResponse(rm ResponseModifier, r *http.Request) error {
 		}
 	}
 
-	rm.Flush()
+	rm.FlushAll()
 
 	return nil
 }

authorization/authz_test.go

@@ -118,7 +118,7 @@ func TestResponseModifier(t *testing.T) {
 	m.Write([]byte("body"))
 	m.WriteHeader(500)
 
-	m.Flush()
+	m.FlushAll()
 	if r.Header().Get("h1") != "v1" {
 		t.Fatalf("Header value must exists %s", r.Header().Get("h1"))
 	}
@@ -147,7 +147,7 @@ func TestResponseModifierOverride(t *testing.T) {
 	m.OverrideHeader(overrideHeaderBytes)
 	m.OverrideBody([]byte("override body"))
 	m.OverrideStatusCode(404)
-	m.Flush()
+	m.FlushAll()
 	if r.Header().Get("h1") != "v2" {
 		t.Fatalf("Header value must exists %s", r.Header().Get("h1"))
 	}

authorization/response.go

@@ -5,6 +5,7 @@ import (
 	"bytes"
 	"encoding/json"
 	"fmt"
+	"github.com/Sirupsen/logrus"
 	"net"
 	"net/http"
 )
@@ -12,6 +13,8 @@ import (
 // ResponseModifier allows authorization plugins to read and modify the content of the http.response
 type ResponseModifier interface {
 	http.ResponseWriter
+	http.Flusher
+	http.CloseNotifier
 
 	// RawBody returns the current http content
 	RawBody() []byte
@@ -32,7 +35,10 @@ type ResponseModifier interface {
 	OverrideStatusCode(statusCode int)
 
 	// Flush flushes all data to the HTTP response
-	Flush() error
+	FlushAll() error
+
+	// Hijacked indicates the response has been hijacked by the Docker daemon
+	Hijacked() bool
 }
 
 // NewResponseModifier creates a wrapper to an http.ResponseWriter to allow inspecting and modifying the content
@@ -44,7 +50,10 @@ func NewResponseModifier(rw http.ResponseWriter) ResponseModifier {
 // the http request/response from docker daemon
 type responseModifier struct {
 	// The original response writer
-	rw     http.ResponseWriter
+	rw http.ResponseWriter
+
+	r *http.Request
+
 	status int
 	// body holds the response body
 	body []byte
@@ -52,15 +61,34 @@ type responseModifier struct {
 	header http.Header
 	// statusCode holds the response status code
 	statusCode int
+	// hijacked indicates the request has been hijacked
+	hijacked bool
+}
+
+func (rm *responseModifier) Hijacked() bool {
+	return rm.hijacked
 }
 
 // WriterHeader stores the http status code
 func (rm *responseModifier) WriteHeader(s int) {
+
+	// Use original request if hijacked
+	if rm.hijacked {
+		rm.rw.WriteHeader(s)
+		return
+	}
+
 	rm.statusCode = s
 }
 
 // Header returns the internal http header
 func (rm *responseModifier) Header() http.Header {
+
+	// Use original header if hijacked
+	if rm.hijacked {
+		return rm.rw.Header()
+	}
+
 	return rm.header
 }
 
@@ -90,6 +118,11 @@ func (rm *responseModifier) OverrideHeader(b []byte) error {
 
 // Write stores the byte array inside content
 func (rm *responseModifier) Write(b []byte) (int, error) {
+
+	if rm.hijacked {
+		return rm.rw.Write(b)
+	}
+
 	rm.body = append(rm.body, b...)
 	return len(b), nil
 }
@@ -109,6 +142,10 @@ func (rm *responseModifier) RawHeaders() ([]byte, error) {
 
 // Hijack returns the internal connection of the wrapped http.ResponseWriter
 func (rm *responseModifier) Hijack() (net.Conn, *bufio.ReadWriter, error) {
+
+	rm.hijacked = true
+	rm.FlushAll()
+
 	hijacker, ok := rm.rw.(http.Hijacker)
 	if !ok {
 		return nil, nil, fmt.Errorf("Internal reponse writer doesn't support the Hijacker interface")
@@ -116,8 +153,30 @@ func (rm *responseModifier) Hijack() (net.Conn, *bufio.ReadWriter, error) {
 	return hijacker.Hijack()
 }
 
-// Flush flushes all data to the HTTP response
-func (rm *responseModifier) Flush() error {
+// CloseNotify uses the internal close notify API of the wrapped http.ResponseWriter
+func (rm *responseModifier) CloseNotify() <-chan bool {
+	closeNotifier, ok := rm.rw.(http.CloseNotifier)
+	if !ok {
+		logrus.Errorf("Internal reponse writer doesn't support the CloseNotifier interface")
+		return nil
+	}
+	return closeNotifier.CloseNotify()
+}
+
+// Flush uses the internal flush API of the wrapped http.ResponseWriter
+func (rm *responseModifier) Flush() {
+	flusher, ok := rm.rw.(http.Flusher)
+	if !ok {
+		logrus.Errorf("Internal reponse writer doesn't support the Flusher interface")
+		return
+	}
+
+	rm.FlushAll()
+	flusher.Flush()
+}
+
+// FlushAll flushes all data to the HTTP response
+func (rm *responseModifier) FlushAll() error {
 	// Copy the status code
 	if rm.statusCode > 0 {
 		rm.rw.WriteHeader(rm.statusCode)
@@ -130,7 +189,15 @@ func (rm *responseModifier) Flush() error {
 		}
 	}
 
-	// Write body
-	_, err := rm.rw.Write(rm.body)
+	var err error
+	if len(rm.body) > 0 {
+		// Write body
+		_, err = rm.rw.Write(rm.body)
+	}
+
+	// Clean previous data
+	rm.body = nil
+	rm.statusCode = 0
+	rm.header = http.Header{}
 	return err
 }