bundle-server: serve with 'ServeContent()'

Use 'OpenFile()' + 'ServeContent()', rather than 'ReadFile()' + 'Write()' to
serve bundle and bundle list content. There are a few (fairly minor)
benefits to 'ServeContent()': it does not buffer the full file contents
before writing to the response writer, and it automatically derives the
'Content-Type' and other headers from the file content.

Signed-off-by: Victoria Dye <vdye@github.com>

Author: vdye

cmd/git-bundle-web-server/bundle-server.go

@@ -6,9 +6,11 @@ import (
 	"net/http"
 	"os"
 	"os/signal"
+	"path/filepath"
 	"strings"
 	"sync"
 	"syscall"
+	"time"
 
 	"github.com/github/git-bundle-server/internal/common"
 	"github.com/github/git-bundle-server/internal/core"
@@ -70,7 +72,7 @@ func (b *bundleWebServer) serve(w http.ResponseWriter, r *http.Request) {
 	defer exitRegion()
 
 	path := r.URL.Path
-	owner, repo, file, err := b.parseRoute(ctx, path)
+	owner, repo, filename, err := b.parseRoute(ctx, path)
 	if err != nil {
 		w.WriteHeader(http.StatusNotFound)
 		fmt.Printf("Failed to parse route: %s\n", err)
@@ -97,20 +99,22 @@ func (b *bundleWebServer) serve(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	if file == "" {
-		file = "bundle-list"
+	var fileToServe string
+	if filename == "" {
+		fileToServe = filepath.Join(repository.WebDir, "bundle-list")
+	} else {
+		fileToServe = filepath.Join(repository.WebDir, filename)
 	}
 
-	fileToServe := repository.WebDir + "/" + file
-	data, err := os.ReadFile(fileToServe)
+	file, err := os.OpenFile(fileToServe, os.O_RDONLY, 0)
 	if err != nil {
 		w.WriteHeader(http.StatusNotFound)
-		fmt.Printf("Failed to read file\n")
+		fmt.Printf("Failed to open file\n")
 		return
 	}
 
-	fmt.Printf("Successfully serving content for %s/%s\n", route, file)
-	w.Write(data)
+	fmt.Printf("Successfully serving content for %s/%s\n", route, filename)
+	http.ServeContent(w, r, filename, time.UnixMicro(0), file)
 }
 
 func (b *bundleWebServer) StartServerAsync(ctx context.Context) {