Alanxtl commented on PR #3364:
URL: https://github.com/apache/dubbo-go/pull/3364#issuecomment-4601531507
Thanks for working on this, but I think we should not fix this by improving
the error message.
The issue is not that the error is unclear. The issue is that REST
application-level service discovery leaks an internal metadata transport
dependency to user code.
For a REST consumer, users configure and import REST-related components:
```go
_ "dubbo.apache.org/dubbo-go/v3/protocol/rest"
_ "dubbo.apache.org/dubbo-go/v3/registry/servicediscovery"
```
But application-level discovery internally fetches metadata through:
```text
dubbo://.../org.apache.dubbo.metadata.MetadataService
```
So today the consumer also has to manually import:
```go
_ "dubbo.apache.org/dubbo-go/v3/protocol/dubbo"
```
That should not be required. The Dubbo protocol here is an internal
metadata-service transport detail.
I suggest changing the fix direction:
1. Revert the new `GetProtocolWithError` / metadata-specific import hint
change.
2. Make application-level service discovery register its internal metadata
transport dependency automatically.
3. Add a test proving that a REST consumer using service discovery works
without importing `protocol/dubbo`.
A minimal fix may be to add a side-effect import in the service discovery
package:
```go
import (
_ "dubbo.apache.org/dubbo-go/v3/protocol/dubbo"
)
```
Probably `registry/servicediscovery` is a reasonable place, because that is
the feature path that calls `metadata.GetMetadataFromRpc(...)` and requires the
default Dubbo metadata protocol.
The expected test should cover:
- provider protocol: REST;
- registry type: application-level service discovery;
- consumer imports REST protocol and service discovery packages;
- consumer does **not** import `dubbo.apache.org/dubbo-go/v3/protocol/dubbo`;
- metadata is still fetched and the REST provider URL is reconstructed
successfully.
So I would prefer fixing the dependency registration instead of returning a
clearer error that still asks REST users to import Dubbo manually.
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