ReferenceExpression in DaprComponentResource.WithMetadata

[tomboon]

I'm a bit stuck using Dotnet Aspire and Dapr.

First I define Azurite (Azure Blob Storage emulator) using aspire like so:

var blobstorage = builder
    .AddAzureStorage("mystorage")
    .RunAsEmulator(azurite =>
         azurite.WithLifetime(supportingResourceContainerLifetime)
        .WithBlobPort(10000)        // should be dynamically assigned by aspire, but hardcoded for sake of this discussion
        .WithDataVolume());

I define my dapr binding component like so:

var daprBlobStorageBindingComponent = builder
    .AddDaprComponent("myblobstoragebinding", "bindings.azure.blobstorage", new DaprComponentOptions { })
    .WithMetadata("accountName", "<azurite account>")
    .WithMetadata("accountKey", "<azurite key>")
    .WithMetadata("containerName", "mycontainer")
    .WithMetadata("endpoint", "http://127.0.0.1:10000")  // works with hardcoded string
    // .WithMetadata("endpoint", ReferenceExpression.Create($"http://127.0.0.1:10000"))  // doesn't work !?!
    // .WithMetadata("endpoint",  blobstorage.Resource.BlobUriExpression)  // what I really want
    .WithMetadata("decodeBase64", "false")
    .WithMetadata("disableEntityManagement", "true")
    .WaitFor(blobstorage);

The problem
When defining the Dapr component I pass the Azurite endpoint via metadata, however:

• Passing a hardcoded string works (eg http://127.0.0.1:10000)
• Passing a ReferenceExpression in .WithMetadata does not seem to work.
  Even when my ReferenceExpression is nothing more than eg $"http://127.0.0.1:10000", it still doesn't work.

The Dapr binding does not recognize the passed ReferenceExpression as a valid URL and falls back to 'https://devstoreaccount1.blob.core.windows.net' which is of course not my local azurite anymore.

[shreyanshjain1]

This looks like a difference between plain metadata values and Aspire resource expressions.

From what you described:

• a literal string works
• even a ReferenceExpression.Create("http://127.0.0.1:10000") does not
• BlobUriExpression also does not

That makes me think WithMetadata(...) for the Dapr component is expecting a resolved scalar value, not an unresolved ReferenceExpression.

So even if the expression text represents a valid URL, it may still be getting passed through as an expression object/template rather than as the final concrete string that the Dapr component expects.

That would also explain why Dapr falls back to the default blob endpoint instead of using Azurite.

So I’d treat this as:

• hardcoded string → already concrete, works
• ReferenceExpression → not being resolved in this metadata path, so Dapr never receives the final endpoint value

If that is correct, then WithMetadata("endpoint", ...) likely does not currently support ReferenceExpression the way other Aspire resource properties do.

Practical takeaway:

• if you need it working right now, use a concrete string value for the Dapr metadata

• if you need the Aspire-generated blob URI dynamically, this may require either:

  • a different API/path that resolves the expression before writing metadata, or
  • a toolkit fix/enhancement so WithMetadata can consume ReferenceExpression properly

Since even ReferenceExpression.Create($"http://127.0.0.1:10000") fails, I think the issue is probly not your blob URI specifically, but that ReferenceExpression itself is not supported in this metadata pipeline.

If this helps, feel free to mark it as the answer so others can find it faster.