From 3c6c4207bebd07320b431ce201be3ef1970acf62 Mon Sep 17 00:00:00 2001
From: Brad Fitzpatrick <brad@danga.com>
Date: Thu, 9 Jun 2011 18:33:26 -0700
Subject: [PATCH] download handler: support for verifying a digest in a HEAD
 request

for use in javascript uploads.
---
 lib/go/camli/blobref/blobref.go |  2 +-
 server/go/camlistored/ui.go     | 33 ++++++++++++++++++++++++++++-----
 2 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/lib/go/camli/blobref/blobref.go b/lib/go/camli/blobref/blobref.go
index 3cbca2429..e11108178 100644
--- a/lib/go/camli/blobref/blobref.go
+++ b/lib/go/camli/blobref/blobref.go
@@ -85,7 +85,7 @@ func (o *BlobRef) Equals(other *BlobRef) bool {
 func (o *BlobRef) Hash() hash.Hash {
 	fn, ok := supportedDigests[o.hashName]
 	if !ok {
-		return nil
+		return nil // TODO: return an error here, not nil
 	}
 	return fn()
 }
diff --git a/server/go/camlistored/ui.go b/server/go/camlistored/ui.go
index 75d4064d2..a1b7d61d7 100644
--- a/server/go/camlistored/ui.go
+++ b/server/go/camlistored/ui.go
@@ -211,6 +211,10 @@ func (ui *UIHandler) storageSeekFetcher() (blobref.SeekFetcher, os.Error) {
 }
 
 func (ui *UIHandler) serveDownload(rw http.ResponseWriter, req *http.Request) {
+	if req.Method != "GET" && req.Method != "HEAD" {
+		http.Error(rw, "Invalid download method", 400)
+		return
+	}
 	if ui.Storage == nil {
 		http.Error(rw, "No BlobRoot configured", 500)
 		return
@@ -230,8 +234,8 @@ func (ui *UIHandler) serveDownload(rw http.ResponseWriter, req *http.Request) {
 		return
 	}
 
-	blobref := blobref.Parse(m[1])
-	if blobref == nil {
+	fbr := blobref.Parse(m[1])
+	if fbr == nil {
 		http.Error(rw, "Invalid blobref", 400)
 		return
 	}
@@ -241,24 +245,43 @@ func (ui *UIHandler) serveDownload(rw http.ResponseWriter, req *http.Request) {
 		filename = filename[1:] // remove leading slash
 	}
 
-	fr, err := schema.NewFileReader(fetchSeeker, blobref)
+	fr, err := schema.NewFileReader(fetchSeeker, fbr)
 	if err != nil {
 		http.Error(rw, "Can't serve file: "+err.String(), 500)
 		return
 	}
+	defer fr.Close()
 
 	// TODO: fr.FileSchema() and guess a mime type?  For now:
 	schema := fr.FileSchema()
 	rw.Header().Set("Content-Type", "application/octet-stream")
 	rw.Header().Set("Content-Length", fmt.Sprintf("%d", schema.Size))
+
+	if req.Method == "HEAD" {
+		vbr := blobref.Parse(req.FormValue("verifycontents"))
+		if vbr == nil {
+			return
+		}
+		hash := vbr.Hash()
+		if hash == nil {
+			return
+		}
+		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, fr)
+	log.Printf("For %q request of %s: copied %d, %v", req.Method, req.URL.RawPath, n, err)
 	if err != nil {
-		log.Printf("error serving download of file schema %s: %v", blobref, err)
+		log.Printf("error serving download of file schema %s: %v", fbr, err)
 		return
 	}
 	if n != int64(schema.Size) {
 		log.Printf("error serving download of file schema %s: sent %d, expected size of %d",
-			blobref, n, schema.Size)
+			fbr, n, schema.Size)
 		return
 	}
 }