[BUG] Put Blob from URL: Content-MD5 response header is absent despite documentation stating it is always returned

API Spec link

https://github.com/Azure/azure-rest-api-specs/blob/main/specification/storage/data-plane/Microsoft.BlobStorage/stable/2024-11-04/blob.json

API Spec version

2024-11-04

Describe the bug

The Put Blob from URL documentation states:

Content-MD5 — Returned for a block blob so that the client can check the integrity of message content. The Content-MD5 returned value is computed by Blob Storage. This header is returned even when the request doesn't include Content-MD5 or x-ms-blob-content-md5 headers.

In practice, when the source URL is a non-Azure HTTP endpoint that does not itself provide a Content-MD5 response header, the Content-MD5 header is absent from the Put Blob from URL response. Only x-ms-content-crc64 is returned.

However, Azure does silently compute and persist the MD5 as the x-ms-blob-content-md5 blob property — a subsequent Get Blob Properties call returns the correct hash. This storage-side behavior is not documented.

So in summary, there are two issues:

1. Documentation inaccuracy: Content-MD5 is documented as always present in the Put Blob from URL response, but is absent when the source is a non-Azure HTTP URL that does not provide Content-MD5.
2. Undocumented behavior: Azure computes and persists x-ms-blob-content-md5 as a blob property during the Put Blob from URL operation, which is not documented anywhere.

Expected behavior

When a block blob is created using the Put Blob from URL operation, the Content-MD5 response header should be present and contain the MD5 hash computed by Blob Storage, regardless of whether the source URL provides a Content-MD5 header. This is consistent with what the documentation states.

Actual behavior

When the source URL is a non-Azure HTTP endpoint that does not provide Content-MD5 in its response, the Content-MD5 header is absent from the Put Blob from URL response. Only x-ms-content-crc64 is returned.

However, Azure does compute the MD5 and persists it as the x-ms-blob-content-md5 blob property — a subsequent Get Blob Properties call returns the correct hash. This silent persistence is not documented.

Reproduction Steps

using Azure.Storage.Blobs;
using Azure.Storage.Blobs.Models;
using Azure.Storage.Blobs.Specialized;

// --- Configuration ---
// Use a publicly accessible URL that does NOT send Content-MD5 in its response.
var sourceUrl = new Uri(args.Length > 0 ? args[0] : "https://httpbin.org/bytes/1024");
var connectionString = args.Length > 1 ? args[1] : Environment.GetEnvironmentVariable("AZURE_STORAGE_CONNECTION_STRING")
    ?? throw new InvalidOperationException("Set AZURE_STORAGE_CONNECTION_STRING");

var containerName = $"md5-verify-{Guid.NewGuid():N}";
var containerClient = new BlobContainerClient(connectionString, containerName);
await containerClient.CreateIfNotExistsAsync();

try
{
    var blobName = $"test-{Guid.NewGuid():N}";
    var blockBlobClient = containerClient.GetBlockBlobClient(blobName);

    Console.WriteLine($"Source URL : {sourceUrl}");
    Console.WriteLine($"Blob       : {containerName}/{blobName}");
    Console.WriteLine();

    // 1. Upload from URL
    var options = new BlobSyncUploadFromUriOptions { CopySourceBlobProperties = true };
    var response = await blockBlobClient.SyncUploadFromUriAsync(sourceUrl, options);

    // 2. Check SDK typed property
    Console.WriteLine($"BlobContentInfo.ContentHash : {Format(response.Value.ContentHash)}");

    // 3. Check raw response headers
    var raw = response.GetRawResponse();
    Console.WriteLine();
    Console.WriteLine("Raw response headers (hash-related):");

    foreach (var header in raw.Headers)
    {
        if (header.Name.Contains("md5", StringComparison.OrdinalIgnoreCase) ||
            header.Name.Contains("crc", StringComparison.OrdinalIgnoreCase))
        {
            Console.WriteLine($"  {header.Name}: {header.Value}");
        }
    }

    // 4. Check stored blob property
    var props = await blockBlobClient.GetPropertiesAsync();
    Console.WriteLine();
    Console.WriteLine($"BlobProperties.ContentHash  : {Format(props.Value.ContentHash)}");

    // 5. Verdict
    Console.WriteLine();
    var sdkHash = response.Value.ContentHash;
    raw.Headers.TryGetValue("Content-MD5", out string? rawMd5);

    if (sdkHash is { Length: > 0 })
        Console.WriteLine("✓ SDK surfaces Content-MD5 — no bug.");
    else if (rawMd5 != null)
        Console.WriteLine("✗ REST API returns Content-MD5 but SDK does not surface it — file a bug.");
    else
        Console.WriteLine("✗ REST API does not return Content-MD5 — docs are inaccurate.");

    await blockBlobClient.DeleteIfExistsAsync();
}
finally
{
    await containerClient.DeleteIfExistsAsync();
}

static string Format(byte[]? hash) => hash is { Length: > 0 }
    ? Convert.ToBase64String(hash)
    : "(null or empty)";

Environment

No response

Start with the linked specification/blob.json and locate the Put Blob from URL operation and its response headers. Run the supplied C# reproduction against a non-Azure source URL, then compare the response with a subsequent Get Blob Properties result. Done means the specification and related documentation accurately describe Content-MD5 and x-ms-blob-content-md5 behavior.