feature: filter fifoWithBody (#2685)

* feature: filter fifoWithBody that works similar to fifo(), but release deferred until body streaming to client was finished
* fix: fifo() and fifoWithBody() with canceled requests

Both filters did not check for canceled context from request before semaphore.Acquire, see golang/go#63615

Signed-off-by: Sandor Szücs <sandor.szuecs@zalando.de>

docs/reference/filters.md

@@ -2819,6 +2819,31 @@ Example:
 fifo(100, 150, "10s")
 ```
 
+### fifoWithBody
+
+This Filter is similar to the [lifo](#lifo) filter in regards to
+parameters and status codes.
+Performance considerations are similar to [fifo](#fifo).
+
+The difference between fifo and fifoWithBody is that fifo will decrement
+the concurrency as soon as the backend sent response headers and
+fifoWithBody will decrement the concurrency if the response body was
+served. Normally both are very similar, but if you have a fully async
+component that serves multiple website fragments, this would decrement
+concurrency too early.
+
+Parameters:
+
+* MaxConcurrency specifies how many goroutines are allowed to work on this queue (int)
+* MaxQueueSize sets the queue size (int)
+* Timeout sets the timeout to get request scheduled (time)
+
+Example:
+
+```
+fifoWithBody(100, 150, "10s")
+```
+
 ### lifo
 
 This Filter changes skipper to handle the route with a bounded last in

filters/builtin/builtin.go

@@ -216,6 +216,7 @@ func Filters() []filters.Spec {
 		auth.NewForwardToken(),
 		auth.NewForwardTokenField(),
 		scheduler.NewFifo(),
+		scheduler.NewFifoWithBody(),
 		scheduler.NewLIFO(),
 		scheduler.NewLIFOGroup(),
 		rfc.NewPath(),

filters/filters.go

@@ -327,6 +327,7 @@ const (
 	SetDynamicBackendUrl                       = "setDynamicBackendUrl"
 	ApiUsageMonitoringName                     = "apiUsageMonitoring"
 	FifoName                                   = "fifo"
+	FifoWithBodyName                           = "fifoWithBody"
 	LifoName                                   = "lifo"
 	LifoGroupName                              = "lifoGroup"
 	RfcPathName                                = "rfcPath"

filters/scheduler/fifo.go

@@ -11,24 +11,31 @@ import (
 	"github.com/zalando/skipper/scheduler"
 )
 
-const (
-	fifoKey string = "fifo"
-)
-
 type (
-	fifoSpec   struct{}
+	fifoSpec struct {
+		typ string
+	}
 	fifoFilter struct {
 		config scheduler.Config
 		queue  *scheduler.FifoQueue
+		typ    string
 	}
 )
 
 func NewFifo() filters.Spec {
-	return &fifoSpec{}
+	return &fifoSpec{
+		typ: filters.FifoName,
+	}
+}
+
+func NewFifoWithBody() filters.Spec {
+	return &fifoSpec{
+		typ: filters.FifoWithBodyName,
+	}
 }
 
-func (*fifoSpec) Name() string {
-	return filters.FifoName
+func (s *fifoSpec) Name() string {
+	return s.typ
 }
 
 // CreateFilter creates a fifoFilter, that will use a semaphore based
@@ -65,6 +72,7 @@ func (s *fifoSpec) CreateFilter(args []interface{}) (filters.Filter, error) {
 	}
 
 	return &fifoFilter{
+		typ: s.typ,
 		config: scheduler.Config{
 			MaxConcurrency: cc,
 			MaxQueueSize:   qs,
@@ -132,23 +140,29 @@ func (f *fifoFilter) Request(ctx filters.FilterContext) {
 	}
 
 	// ok
-	pending, _ := ctx.StateBag()[fifoKey].([]func())
-	ctx.StateBag()[fifoKey] = append(pending, done)
+	pending, _ := ctx.StateBag()[f.typ].([]func())
+	ctx.StateBag()[f.typ] = append(pending, done)
 }
 
 // Response will decrease the number of inflight requests to release
 // the concurrency reservation for the request.
 func (f *fifoFilter) Response(ctx filters.FilterContext) {
-	pending, ok := ctx.StateBag()[fifoKey].([]func())
-	if !ok {
-		return
-	}
-	last := len(pending) - 1
-	if last < 0 {
-		return
+	switch f.typ {
+	case filters.FifoName:
+		pending, ok := ctx.StateBag()[f.typ].([]func())
+		if !ok {
+			return
+		}
+		last := len(pending) - 1
+		if last < 0 {
+			return
+		}
+		pending[last]()
+		ctx.StateBag()[f.typ] = pending[:last]
+
+	case filters.FifoWithBodyName:
+		// nothing to do here, handled in the proxy after copyStream()
 	}
-	pending[last]()
-	ctx.StateBag()[fifoKey] = pending[:last]
 }
 
 // HandleErrorResponse is to opt-in for filters to get called