[blimp] Change to use SHA-256 instead of SHA-1 for unique ids

blimp/common/blob_cache/id_util.h

Index: blimp/common/blob_cache/id_util.h
diff --git a/blimp/common/blob_cache/id_util.h b/blimp/common/blob_cache/id_util.h
index 902d48a3bd4a4af85a5cae5d880fb3aeb6888d6f..cdfa4f6c2c611bbb8130a4ad23c70ad411c7c048 100644
--- a/blimp/common/blob_cache/id_util.h
+++ b/blimp/common/blob_cache/id_util.h
@@ -13,14 +13,17 @@
 
 namespace blimp {
 
-// Returns the bytes of a SHA1 hash of the input. The string is guaranteed
-// to have length base::kSHA1Length.
+// Returns the bytes of a SHA-256 hash of the input. The string is guaranteed
+// to have length crypto::kSHA256Length.

[Wez, 2016/04/23 00:08:52]

The length of the string is only interesting in terms of it being "valid" as per
the comments below; suggest changing this entire comment to "Returns a unique Id
for the Blob, based on its content." - the caller doesn't need to know the
scheme in-use, nor the length of the Ids, though the fact that they're all the
same length might be worthwhile mentioning.

[nyquist, 2016/04/25 08:11:17]

Agreed! Done.

 BLIMP_COMMON_EXPORT const BlobId CalculateBlobId(const void* data,
                                                  size_t data_size);
 
-// Returns a hexadecimal string representation of a SHA1 hash. The input is
-// required to have length base::kSHA1Length.
-BLIMP_COMMON_EXPORT const std::string FormatBlobId(const BlobId& data);
+// Returns a hexadecimal string representation of a SHA-256 hash. The input is

[Wez, 2016/04/23 00:08:52]

"... of a BlobId."

[nyquist, 2016/04/25 08:11:17]

Done.

+// required to have length crypto::kSHA256Length.
+BLIMP_COMMON_EXPORT const std::string FormatBlobId(const BlobId& id);

[Wez, 2016/04/23 00:08:52]

Suggest BlobIdToString rather than "format"; format doesn't specify what it's
formatted to, per-se.

[nyquist, 2016/04/25 08:11:17]

Done.

+
+// Returns whether the BlobId has the required length crypto::kSHA256Length.
+BLIMP_COMMON_EXPORT bool BlobIdHasCorrectLength(const BlobId& id);

[Wez, 2016/04/23 00:08:52]

Suggest naming this IsValidBlobId - then the FormatBlobId function can say
"input must be a valid BlobId" rather than specifying the length.

[nyquist, 2016/04/25 08:11:17]

Awesome suggestion! Done.

 
 }  // namespace blimp