allow overriding the Logger used by Proxy

imageproxy.go

@@ -61,6 +61,9 @@ type Proxy struct {
 	// absolute.
 	DefaultBaseURL *url.URL
 
+	// The Logger used by the image proxy
+	Logger *log.Logger
+
 	// SignatureKey is the HMAC key used to verify signed requests.
 	SignatureKey []byte
 
@@ -105,7 +108,7 @@ func NewProxy(transport http.RoundTripper, cache Cache) *Proxy {
 			CachingClient: client,
 			log: func(format string, v ...interface{}) {
 				if proxy.Verbose {
-					log.Printf(format, v...)
+					proxy.logf(format, v...)
 				}
 			},
 		},
@@ -141,13 +144,13 @@ func (p *Proxy) serveImage(w http.ResponseWriter, r *http.Request) {
 	req, err := NewRequest(r, p.DefaultBaseURL)
 	if err != nil {
 		msg := fmt.Sprintf("invalid request URL: %v", err)
-		log.Print(msg)
+		p.log(msg)
 		http.Error(w, msg, http.StatusBadRequest)
 		return
 	}
 
 	if err := p.allowed(req); err != nil {
-		log.Printf("%s: %v", err, req)
+		p.logf("%s: %v", err, req)
 		http.Error(w, msgNotAllowed, http.StatusForbidden)
 		return
 	}
@@ -166,7 +169,7 @@ func (p *Proxy) serveImage(w http.ResponseWriter, r *http.Request) {
 
 	if err != nil {
 		msg := fmt.Sprintf("error fetching remote image: %v", err)
-		log.Print(msg)
+		p.log(msg)
 		http.Error(w, msg, http.StatusInternalServerError)
 		return
 	}
@@ -175,7 +178,7 @@ func (p *Proxy) serveImage(w http.ResponseWriter, r *http.Request) {
 
 	cached := resp.Header.Get(httpcache.XFromCache)
 	if p.Verbose {
-		log.Printf("request: %+v (served from cache: %t)", *actualReq, cached == "1")
+		p.logf("request: %+v (served from cache: %t)", *actualReq, cached == "1")
 	}
 
 	copyHeader(w.Header(), resp.Header, "Cache-Control", "Last-Modified", "Expires", "Etag", "Link")
@@ -193,7 +196,7 @@ func (p *Proxy) serveImage(w http.ResponseWriter, r *http.Request) {
 		contentType = peekContentType(b)
 	}
 	if resp.ContentLength != 0 && !contentTypeMatches(p.ContentTypes, contentType) {
-		log.Printf("content-type not allowed: %q", contentType)
+		p.logf("content-type not allowed: %q", contentType)
 		http.Error(w, msgNotAllowed, http.StatusForbidden)
 		return
 	}
@@ -368,6 +371,22 @@ func should304(req *http.Request, resp *http.Response) bool {
 	return false
 }
 
+func (p *Proxy) log(v ...interface{}) {
+	if p.Logger != nil {
+		p.Logger.Print(v...)
+	} else {
+		log.Print(v...)
+	}
+}
+
+func (p *Proxy) logf(format string, v ...interface{}) {
+	if p.Logger != nil {
+		p.Logger.Printf(format, v...)
+	} else {
+		log.Printf(format, v...)
+	}
+}
+
 // TransformingTransport is an implementation of http.RoundTripper that
 // optionally transforms images using the options specified in the request URL
 // fragment.

imageproxy_test.go

@@ -21,9 +21,11 @@ import (
 	"fmt"
 	"image"
 	"image/png"
+	"log"
 	"net/http"
 	"net/http/httptest"
 	"net/url"
+	"os"
 	"reflect"
 	"strings"
 	"testing"
@@ -412,6 +414,52 @@ func TestProxy_ServeHTTP_is304(t *testing.T) {
 	}
 }
 
+func TestProxy_log(t *testing.T) {
+	var b strings.Builder
+
+	p := &Proxy{
+		Logger: log.New(&b, "", 0),
+	}
+	p.log("Test")
+
+	if got, want := b.String(), "Test\n"; got != want {
+		t.Errorf("log wrote %s, want %s", got, want)
+	}
+
+	b.Reset()
+	p.logf("Test %v", 123)
+
+	if got, want := b.String(), "Test 123\n"; got != want {
+		t.Errorf("logf wrote %s, want %s", got, want)
+	}
+}
+
+func TestProxy_log_default(t *testing.T) {
+	var b strings.Builder
+
+	defer func(flags int) {
+		log.SetOutput(os.Stderr)
+		log.SetFlags(flags)
+	}(log.Flags())
+
+	log.SetOutput(&b)
+	log.SetFlags(0)
+
+	p := &Proxy{}
+	p.log("Test")
+
+	if got, want := b.String(), "Test\n"; got != want {
+		t.Errorf("log wrote %s, want %s", got, want)
+	}
+
+	b.Reset()
+	p.logf("Test %v", 123)
+
+	if got, want := b.String(), "Test 123\n"; got != want {
+		t.Errorf("logf wrote %s, want %s", got, want)
+	}
+}
+
 func TestTransformingTransport(t *testing.T) {
 	client := new(http.Client)
 	tr := &TransformingTransport{