Blob HEAD and GET return 412 instead of 404 for a missing blob with If-Match

[Xuanwo]

Description

Azurite returns 412 ConditionNotMet when HEAD or GET targets a missing blob with If-Match set to a valid ETag obtained from another blob. Azure Blob Storage returns 404 BlobNotFound for the same requests.

This prevents clients and compatibility tests from distinguishing a missing blob from an existing blob whose ETag does not match.

Reproduction

Tested with:

• mcr.microsoft.com/azure-storage/azurite:3.37.0
• Also reproduced with Azurite 3.35.0
• x-ms-version: 2022-11-02
• Raw Shared Key REST requests

Steps:

1. Create a container.
2. Create blob A and save the ETag returned by Azurite.
3. Choose a different blob name B that does not exist in the same container.
4. Send HEAD for blob B with If-Match: <etag-from-blob-A>.
5. Send GET for blob B with the same If-Match value.

The ETag must be a valid value returned by the service. A synthetic malformed ETag is not an equivalent reproduction because Azure Storage can reject it as a failed condition.

Actual behavior

Service	HEAD missing blob	GET missing blob
Azurite 3.37.0	412 ConditionNotMet	412 ConditionNotMet
Azurite 3.35.0	412 ConditionNotMet	412 ConditionNotMet

Azurite 3.37.0 request IDs from one reproduction:

• HEAD: 5d0c1796-dce8-44a9-a8cc-d531185ac35b
• GET: c51e7848-072a-4405-9307-aaced86f9b70

Expected behavior

Match Azure Blob Storage and return 404 BlobNotFound for both requests because blob B does not exist.

The same raw requests against the live Azure Blob Storage service returned:

Service	HEAD missing blob	GET missing blob
Azure Blob Storage	404 BlobNotFound	404 BlobNotFound

Azure request IDs from the control reproduction:

• HEAD: b7fcf34d-c01e-000d-26ff-35582f000000
• GET: 067d7966-601e-0014-38ff-35d894000000

Impact

Clients that expose missing-target and conditional-mismatch results separately cannot run the same conditional read tests against Azurite and Azure Storage. A client-side existence check is not a suitable compatibility workaround because it adds another request and introduces a race.

AI assisted with the live-service comparison and drafting. The submitter directed the scope and conclusion.