alfonmga · August 12, 2022 16:53 · Aug 12, 2022 · Aug 12, 2022
diff --git a/gcs_reverse_proxy.go b/gcs_reverse_proxy.go
@@ -0,0 +1,155 @@
+package main
+
+import (
+	"context"
+	"flag"
+	"io"
+	"log"
+	"net/http"
+	"strconv"
+	"time"
+
+	"cloud.google.com/go/storage"
+	"github.com/gorilla/mux"
+	"google.golang.org/api/option"
+)
+
+var (
+	bind        = flag.String("b", "127.0.0.1:8080", "Bind address")
+	verbose     = flag.Bool("v", false, "Show access log")
+	credentials = flag.String("c", "", "The path to the keyfile. If not present, client will use your default application credentials.")
+)
+
+var (
+	client *storage.Client
+	ctx    = context.Background()
+)
+
+func handleError(w http.ResponseWriter, err error) {
+	if err != nil {
+		if err == storage.ErrObjectNotExist {
+			http.Error(w, err.Error(), http.StatusNotFound)
+		} else {
+			http.Error(w, err.Error(), http.StatusInternalServerError)
+		}
+		return
+	}
+}
+
+func header(r *http.Request, key string) (string, bool) {
+	if r.Header == nil {
+		return "", false
+	}
+	if candidate := r.Header[key]; len(candidate) > 0 {
+		return candidate[0], true
+	}
+	return "", false
+}
+
+func setStrHeader(w http.ResponseWriter, key string, value string) {
+	if value != "" {
+		w.Header().Add(key, value)
+	}
+}
+
+func setIntHeader(w http.ResponseWriter, key string, value int64) {
+	if value > 0 {
+		w.Header().Add(key, strconv.FormatInt(value, 10))
+	}
+}
+
+func setTimeHeader(w http.ResponseWriter, key string, value time.Time) {
+	if !value.IsZero() {
+		w.Header().Add(key, value.UTC().Format(http.TimeFormat))
+	}
+}
+
+type wrapResponseWriter struct {
+	http.ResponseWriter
+	status int
+}
+
+func (w *wrapResponseWriter) WriteHeader(status int) {
+	w.ResponseWriter.WriteHeader(status)
+	w.status = status
+}
+
+func wrapper(fn func(w http.ResponseWriter, r *http.Request)) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		proc := time.Now()
+		writer := &wrapResponseWriter{
+			ResponseWriter: w,
+			status:         http.StatusOK,
+		}
+		fn(writer, r)
+		addr := r.RemoteAddr
+		if ip, found := header(r, "X-Forwarded-For"); found {
+			addr = ip
+		}
+		if *verbose {
+			log.Printf("[%s] %.3f %d %s %s",
+				addr,
+				time.Now().Sub(proc).Seconds(),
+				writer.status,
+				r.Method,
+				r.URL,
+			)
+		}
+	}
+}
+
+func proxy(w http.ResponseWriter, r *http.Request) {
+	params := mux.Vars(r)
+	obj := client.Bucket(params["bucket"]).Object(params["object"]).ReadCompressed(false)
+	attr, err := obj.Attrs(ctx)
+	if err != nil {
+		handleError(w, err)
+		return
+	}
+	if lastStrs, ok := r.Header["If-Modified-Since"]; ok && len(lastStrs) > 0 {
+		last, err := http.ParseTime(lastStrs[0])
+		if *verbose && err != nil {
+			log.Printf("could not parse If-Modified-Since: %v", err)
+		}
+		if !attr.Updated.Truncate(time.Second).After(last) {
+			w.WriteHeader(304)
+			return
+		}
+	}
+	objr, err := obj.NewReader(ctx)
+	if err != nil {
+		handleError(w, err)
+		return
+	}
+	attrC := objr.Attrs.ContentEncoding
+	setTimeHeader(w, "Last-Modified", attr.Updated)
+	setStrHeader(w, "Content-Type", attr.ContentType)
+	setStrHeader(w, "Content-Language", attr.ContentLanguage)
+	setStrHeader(w, "Cache-Control", attr.CacheControl)
+	setStrHeader(w, "Content-Encoding", attrC)
+	setStrHeader(w, "Content-Disposition", attr.ContentDisposition)
+	setIntHeader(w, "Content-Length", attr.Size)
+	io.Copy(w, objr)
+}
+
+func main() {
+	flag.Parse()
+
+	var err error
+	if *credentials != "" {
+		client, err = storage.NewClient(ctx, option.WithCredentialsFile(*credentials))
+	} else {
+		client, err = storage.NewClient(ctx)
+	}
+	if err != nil {
+		log.Fatalf("Failed to create client: %v", err)
+	}
+
+	r := mux.NewRouter()
+	r.HandleFunc("/{bucket:[0-9a-zA-Z-_.]+}/{object:.*}", wrapper(proxy)).Methods("GET", "HEAD")
+
+	log.Printf("[service] listening on %s", *bind)
+	if err := http.ListenAndServe(*bind, r); err != nil {
+		log.Fatal(err)
+	}
+}