How it works

blobmetadb uses hints from HTTP responses received from Azure Blob Storage service to interpret various metadata about blobs and containers.

Those metadata could be:

• blob/container exists
• size of blob
• (planned: last modified, permission, meta headers x-meta-…)

Here is an example request made to download the blob, tracked with blobmetadb:

————> Request 
GET /mycontainer/myblob.txt HTTP/1.1
Host: ahmet.blob.core.windows.net

<———— Response
HTTP/1.1 200 OK
Content-Length: 42
Content-Type: application/octet-stream Charset=UTF-8
Last-Modified: Mon, 10 Mar 2014 17:00:05 GMT
...

Hello world!\r\nThis is the blob contents.\r\n

This request is successful (2xx HTTP response code). Now blobmetadb understands that this blob reference exists.

Here are some other requests you can make to storage service that would hint blobmetadb about this blob:

• Put blob (upload)
• Set blob metadata
• Get blob properties
• Copy blob
• Download blob contents

Same applies for container. Based on DiscoveryMode set on BlobMetaTracker instance, the library can understand that "container exists" using requests like

• Create container
• Get/Set container metadata
• Get container properties
• Set container ACL (permissions)
• List blobs in container