server: use http.ServeContent and use cache headers in download handler

Change-Id: I5c24f39c86f6308b32167cf0d92ee68f801b9181

pkg/magic/magic.go

@@ -67,3 +67,11 @@ func MimeTypeFromReader(r io.Reader) (mime string, reader io.Reader) {
 	mime = MimeType(buf.Bytes())
 	return mime, io.MultiReader(&buf, r)
 }
+
+// MimeTypeFromReader takes a ReaderAt, sniffs the beginning of it,
+// and returns the MIME type if sniffed, else the empty string.
+func MIMETypeFromReaderAt(ra io.ReaderAt) (mime string) {
+	var buf [1024]byte
+	n, _ := ra.ReadAt(buf[:], 0)
+	return MimeType(buf[:n])
+}

pkg/server/download.go

@@ -19,8 +19,8 @@ package server
 import (
 	"fmt"
 	"io"
-	"log"
 	"net/http"
+	"time"
 
 	"camlistore.org/pkg/blobref"
 	"camlistore.org/pkg/blobserver"
@@ -28,6 +28,8 @@ import (
 	"camlistore.org/pkg/schema"
 )
 
+const oneYear = 365 * 86400 * time.Second
+
 type DownloadHandler struct {
 	Fetcher   blobref.StreamingFetcher
 	Cache     blobserver.Storage
@@ -43,6 +45,11 @@ func (dh *DownloadHandler) ServeHTTP(rw http.ResponseWriter, req *http.Request,
 		http.Error(rw, "Invalid download method", 400)
 		return
 	}
+	if req.Header.Get("If-Modified-Since") != "" {
+		// Immutable, so any copy's a good copy.
+		rw.WriteHeader(http.StatusNotModified)
+		return
+	}
 
 	fr, err := schema.NewFileReader(dh.storageSeekFetcher(), file)
 	if err != nil {
@@ -52,16 +59,18 @@ func (dh *DownloadHandler) ServeHTTP(rw http.ResponseWriter, req *http.Request,
 	defer fr.Close()
 
 	schema := fr.FileSchema()
-	rw.Header().Set("Content-Length", fmt.Sprintf("%d", schema.SumPartsSize()))
+	h := rw.Header()
+	h.Set("Content-Length", fmt.Sprintf("%d", schema.SumPartsSize()))
+	h.Set("Expires", time.Now().Add(oneYear).Format(http.TimeFormat))
 
-	mimeType, reader := magic.MimeTypeFromReader(fr)
+	mimeType := magic.MIMETypeFromReaderAt(fr)
 	if dh.ForceMime != "" {
 		mimeType = dh.ForceMime
 	}
 	if mimeType == "" {
 		mimeType = "application/octet-stream"
 	}
-	rw.Header().Set("Content-Type", mimeType)
+	h.Set("Content-Type", mimeType)
 	if mimeType == "application/octet-stream" {
 		// Chrome seems to silently do nothing on
 		// application/octet-stream unless this is set.
@@ -70,7 +79,7 @@ func (dh *DownloadHandler) ServeHTTP(rw http.ResponseWriter, req *http.Request,
 		rw.Header().Set("Content-Disposition", "attachment; filename=file-"+file.String()+".dat")
 	}
 
-	if req.Method == "HEAD" {
+	if req.Method == "HEAD" && req.FormValue("verifycontents") != "" {
 		vbr := blobref.Parse(req.FormValue("verifycontents"))
 		if vbr == nil {
 			return
@@ -79,22 +88,12 @@ func (dh *DownloadHandler) ServeHTTP(rw http.ResponseWriter, req *http.Request,
 		if hash == nil {
 			return
 		}
-		io.Copy(hash, reader) // ignore errors, caught later
+		io.Copy(hash, fr) // ignore errors, caught later
 		if vbr.HashMatches(hash) {
 			rw.Header().Set("X-Camli-Contents", vbr.String())
 		}
 		return
 	}
 
-	n, err := io.Copy(rw, reader)
-	if err != nil {
-		log.Printf("error serving download of file schema %s: %v", file, err)
-		return
-	}
-	if size := schema.SumPartsSize(); n != int64(size) {
-		log.Printf("error serving download of file schema %s: sent %d, expected size of %d",
-			file, n, size)
-		return
-	}
-
+	http.ServeContent(rw, req, "", time.Now(), fr)
 }

pkg/server/image.go

@@ -265,8 +265,7 @@ func (ih *ImageHandler) ServeHTTP(rw http.ResponseWriter, req *http.Request, fil
 	}
 
 	h := rw.Header()
-	const oneYearish = 365 * 86400 * time.Second
-	h.Set("Expires", time.Now().Add(oneYearish).Format(http.TimeFormat))
+	h.Set("Expires", time.Now().Add(oneYear).Format(http.TimeFormat))
 	h.Set("Last-Modified", time.Now().Format(http.TimeFormat))
 	h.Set("Content-Type", imageContentTypeOfFormat(format))
 	size := buf.Len()