Limit number of running transformation threads

Author: striker2000

imageproxy.go

@@ -20,6 +20,7 @@ import (
 	"net/http"
 	"net/url"
 	"path"
+	"runtime"
 	"strings"
 	"time"
 
@@ -125,6 +126,7 @@ func NewProxy(transport http.RoundTripper, cache Cache) *Proxy {
 		Transport: &TransformingTransport{
 			Transport:     transport,
 			CachingClient: client,
+			limiter:       make(chan struct{}, runtime.NumCPU()),
 			log: func(format string, v ...any) {
 				if proxy.Verbose {
 					proxy.logf(format, v...)
@@ -557,6 +559,8 @@ type TransformingTransport struct {
 	// responses are properly cached.
 	CachingClient *http.Client
 
+	limiter chan struct{}
+
 	log func(format string, v ...any)
 
 	updateCacheHeaders func(hdr http.Header)
@@ -576,6 +580,13 @@ func (t *TransformingTransport) RoundTrip(req *http.Request) (*http.Response, er
 		return resp, err
 	}
 
+	if t.limiter != nil {
+		t.limiter <- struct{}{}
+		defer func() {
+			<-t.limiter
+		}()
+	}
+
 	f := req.URL.Fragment
 	req.URL.Fragment = ""
 	resp, err := t.CachingClient.Do(req)

imageproxy_test.go

@@ -735,6 +735,7 @@ func TestTransformingTransport(t *testing.T) {
 	tr := &TransformingTransport{
 		Transport:     &testTransport{},
 		CachingClient: client,
+		limiter:       make(chan struct{}, 1),
 	}
 	client.Transport = tr