Added retry to download-blob if MD5 checksums don't match.

blobstore/src/main/clojure/org/jclouds/blobstore.clj

@@ -25,6 +25,7 @@ See http://code.google.com/p/jclouds for details."
             AsyncBlobStore BlobStore BlobStoreContext BlobStoreContextFactory
             domain.BlobMetadata domain.StorageMetadata domain.Blob
             options.ListContainerOptions]
+           [java.security DigestOutputStream MessageDigest]
            [com.google.common.collect ImmutableSet]))
 
 (defn blobstore
@@ -67,6 +68,8 @@ Options can also be specified for extension modules
 
 (def *blobstore*)
 
+(def *max-retries* 3)
+
 (defmacro with-blobstore [[& blobstore-or-args] & body]
   `(binding [*blobstore* (as-blobstore ~@blobstore-or-args)]
      ~@body))
@@ -256,9 +259,19 @@ container, name, string -> etag
   [container-name name target]
   (download-blob *blobstore* container-name name target))
 
-(defmethod download-blob OutputStream [blobstore container-name name target]
-  (let [blob (get-blob blobstore container-name name)]
-    (copy (.getContent blob) target)))
+(defmethod download-blob OutputStream [blobstore container-name name target
+                                       & [retries]]
+  (let [blob (get-blob blobstore container-name name)
+        digest-stream (DigestOutputStream. ;; TODO: not all clouds use MD5
+                       target (MessageDigest/getInstance "MD5"))]
+    (copy (.getContent blob) digest-stream)
+    (let [digest (.digest (.getMessageDigest digest-stream))
+          metadata-digest (.getContentMD5 (.getMetadata blob))]
+      (when-not (MessageDigest/isEqual digest metadata-digest)
+        (if (<= (or retries 0) *max-retries*)
+          (recur blobstore container-name name target [(inc (or retries 1))])
+          (throw (Exception. (format "Download failed for %s/%s"
+                                     container-name name))))))))
 
 (defmethod download-blob File [blobstore container-name name target]
   (download-blob blobstore container-name name (FileOutputStream. target)))

blobstore/src/test/clojure/org/jclouds/blobstore_test.clj

@@ -72,5 +72,22 @@
          (is (= data (slurp (.getAbsolutePath data-file))))
          (finally (.delete data-file)))))
 
+(deftest download-checksum-test
+  (binding [get-blob (fn [blobstore c-name name]
+                       (let [blob (.newBlob blobstore name)
+                             md (.getMetadata blob)]
+                         (.setPayload blob "bogus payload")
+                         (.setContentMD5 md (.getBytes "bogus MD5"))
+                         blob))]
+    (let [name "test"
+          container-name "test-container"
+          data "test content"
+          data-file (java.io.File/createTempFile "jclouds" "data")]
+      (try (create-container container-name)
+           (create-blob container-name name data)
+           (is (thrown? Exception
+                        (download-blob container-name name data-file)))
+           (finally (.delete data-file))))))
+
 ;; TODO: more tests involving blob-specific functions