core: Make MetadataApplier an interface again

Swapping MetadataApplier to an abstract class is not ABI-safe for
callers. So I revert back to the previous interface definition and
introduce a CallCredentials2.MetadataApplier which is an abstract class.
Once everyone is on CallCredentials2 then we can swap it to an abstract
class again.

Fixes #5002

6 files changed, 40 insertions, 22 deletions

diff --git a/core/src/main/java/io/grpc/CallCredentials.java b/core/src/main/java/io/grpc/CallCredentials.java
index 2bc4b2876..03be65310 100644
--- a/core/src/main/java/io/grpc/CallCredentials.java
+++ b/core/src/main/java/io/grpc/CallCredentials.java
@@ -99,18 +99,19 @@ public interface CallCredentials {
    *
    * <p>Exactly one of its methods must be called to make the RPC proceed.
    */
+  @Deprecated
   @ExperimentalApi("https://github.com/grpc/grpc-java/issues/1914")
-  public abstract static class MetadataApplier {
+  public interface MetadataApplier {
     /**
      * Called when headers are successfully generated. They will be merged into the original
      * headers.
      */
-    public abstract void apply(Metadata headers);
+    void apply(Metadata headers);
 
     /**
      * Called when there has been an error when preparing the headers. This will fail the RPC.
      */
-    public abstract void fail(Status status);
+    void fail(Status status);
   }
 
   /**
diff --git a/core/src/main/java/io/grpc/CallCredentials2.java b/core/src/main/java/io/grpc/CallCredentials2.java
index 458a04c9f..998df42db 100644
--- a/core/src/main/java/io/grpc/CallCredentials2.java
+++ b/core/src/main/java/io/grpc/CallCredentials2.java
@@ -54,7 +54,7 @@ public abstract class CallCredentials2 implements CallCredentials {
   @SuppressWarnings("deprecation")
   public final void applyRequestMetadata(
       final MethodDescriptor<?, ?> method, final Attributes attrs,
-      Executor appExecutor, CallCredentials.MetadataApplier applier) {
+      Executor appExecutor, final CallCredentials.MetadataApplier applier) {
     final String authority = checkNotNull(attrs.get(ATTR_AUTHORITY), "authority");
     final SecurityLevel securityLevel =
         firstNonNull(attrs.get(ATTR_SECURITY_LEVEL), SecurityLevel.NONE);
@@ -79,6 +79,21 @@ public abstract class CallCredentials2 implements CallCredentials {
           return attrs;
         }
       };
-    applyRequestMetadata(requestInfo, appExecutor, applier);
+    MetadataApplier applierAdapter = new MetadataApplier() {
+        @Override
+        public void apply(Metadata headers) {
+          applier.apply(headers);
+        }
+
+        @Override
+        public void fail(Status status) {
+          applier.fail(status);
+        }
+      };
+    applyRequestMetadata(requestInfo, appExecutor, applierAdapter);
   }
+
+  @ExperimentalApi("https://github.com/grpc/grpc-java/issues/1914")
+  @SuppressWarnings("deprecation")
+  public abstract static class MetadataApplier implements CallCredentials.MetadataApplier {}
 }
diff --git a/core/src/main/java/io/grpc/internal/MetadataApplierImpl.java b/core/src/main/java/io/grpc/internal/MetadataApplierImpl.java
index c3196ddd1..56548b282 100644
--- a/core/src/main/java/io/grpc/internal/MetadataApplierImpl.java
+++ b/core/src/main/java/io/grpc/internal/MetadataApplierImpl.java
@@ -20,7 +20,7 @@ import static com.google.common.base.Preconditions.checkArgument;
 import static com.google.common.base.Preconditions.checkNotNull;
 import static com.google.common.base.Preconditions.checkState;
 
-import io.grpc.CallCredentials.MetadataApplier;
+import io.grpc.CallCredentials2.MetadataApplier;
 import io.grpc.CallOptions;
 import io.grpc.Context;
 import io.grpc.Metadata;
diff --git a/core/src/test/java/io/grpc/internal/CallCredentials2ApplyingTest.java b/core/src/test/java/io/grpc/internal/CallCredentials2ApplyingTest.java
index f87e22810..fd2b2c18f 100644
--- a/core/src/test/java/io/grpc/internal/CallCredentials2ApplyingTest.java
+++ b/core/src/test/java/io/grpc/internal/CallCredentials2ApplyingTest.java
@@ -29,9 +29,9 @@ import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
 import io.grpc.Attributes;
-import io.grpc.CallCredentials.MetadataApplier;
 import io.grpc.CallCredentials.RequestInfo;
 import io.grpc.CallCredentials2;
+import io.grpc.CallCredentials2.MetadataApplier;
 import io.grpc.CallOptions;
 import io.grpc.IntegerMarshaller;
 import io.grpc.Metadata;
diff --git a/core/src/test/java/io/grpc/internal/CallCredentialsApplyingTest.java b/core/src/test/java/io/grpc/internal/CallCredentialsApplyingTest.java
index 51df406b5..a8ca1219b 100644
--- a/core/src/test/java/io/grpc/internal/CallCredentialsApplyingTest.java
+++ b/core/src/test/java/io/grpc/internal/CallCredentialsApplyingTest.java
@@ -30,7 +30,6 @@ import static org.mockito.Mockito.when;
 
 import io.grpc.Attributes;
 import io.grpc.CallCredentials;
-import io.grpc.CallCredentials.MetadataApplier;
 import io.grpc.CallOptions;
 import io.grpc.IntegerMarshaller;
 import io.grpc.Metadata;
@@ -128,7 +127,7 @@ public class CallCredentialsApplyingTest {
 
     ArgumentCaptor<Attributes> attrsCaptor = ArgumentCaptor.forClass(null);
     verify(mockCreds).applyRequestMetadata(same(method), attrsCaptor.capture(), same(mockExecutor),
-        any(MetadataApplier.class));
+        any(CallCredentials.MetadataApplier.class));
     Attributes attrs = attrsCaptor.getValue();
     assertSame(ATTR_VALUE, attrs.get(ATTR_KEY));
     assertSame(AUTHORITY, attrs.get(CallCredentials.ATTR_AUTHORITY));
@@ -148,7 +147,7 @@ public class CallCredentialsApplyingTest {
 
     ArgumentCaptor<Attributes> attrsCaptor = ArgumentCaptor.forClass(null);
     verify(mockCreds).applyRequestMetadata(same(method), attrsCaptor.capture(), same(mockExecutor),
-        any(MetadataApplier.class));
+        any(CallCredentials.MetadataApplier.class));
     Attributes attrs = attrsCaptor.getValue();
     assertSame(ATTR_VALUE, attrs.get(ATTR_KEY));
     assertEquals("transport-override-authority", attrs.get(CallCredentials.ATTR_AUTHORITY));
@@ -170,7 +169,7 @@ public class CallCredentialsApplyingTest {
 
     ArgumentCaptor<Attributes> attrsCaptor = ArgumentCaptor.forClass(null);
     verify(mockCreds).applyRequestMetadata(same(method), attrsCaptor.capture(),
-        same(anotherExecutor), any(MetadataApplier.class));
+        same(anotherExecutor), any(CallCredentials.MetadataApplier.class));
     Attributes attrs = attrsCaptor.getValue();
     assertSame(ATTR_VALUE, attrs.get(ATTR_KEY));
     assertEquals("calloptions-authority", attrs.get(CallCredentials.ATTR_AUTHORITY));
@@ -182,7 +181,8 @@ public class CallCredentialsApplyingTest {
     final RuntimeException ex = new RuntimeException();
     when(mockTransport.getAttributes()).thenReturn(Attributes.EMPTY);
     doThrow(ex).when(mockCreds).applyRequestMetadata(
-        same(method), any(Attributes.class), same(mockExecutor), any(MetadataApplier.class));
+        same(method), any(Attributes.class), same(mockExecutor),
+        any(CallCredentials.MetadataApplier.class));
 
     FailingClientStream stream =
         (FailingClientStream) transport.newStream(method, origHeaders, callOptions);
@@ -198,14 +198,15 @@ public class CallCredentialsApplyingTest {
     doAnswer(new Answer<Void>() {
         @Override
         public Void answer(InvocationOnMock invocation) throws Throwable {
-          MetadataApplier applier = (MetadataApplier) invocation.getArguments()[3];
+          CallCredentials.MetadataApplier applier =
+              (CallCredentials.MetadataApplier) invocation.getArguments()[3];
           Metadata headers = new Metadata();
           headers.put(CREDS_KEY, CREDS_VALUE);
           applier.apply(headers);
           return null;
         }
       }).when(mockCreds).applyRequestMetadata(same(method), any(Attributes.class),
-          same(mockExecutor), any(MetadataApplier.class));
+          same(mockExecutor), any(CallCredentials.MetadataApplier.class));
 
     ClientStream stream = transport.newStream(method, origHeaders, callOptions);
 
@@ -222,12 +223,13 @@ public class CallCredentialsApplyingTest {
     doAnswer(new Answer<Void>() {
         @Override
         public Void answer(InvocationOnMock invocation) throws Throwable {
-          MetadataApplier applier = (MetadataApplier) invocation.getArguments()[3];
+          CallCredentials.MetadataApplier applier =
+              (CallCredentials.MetadataApplier) invocation.getArguments()[3];
           applier.fail(error);
           return null;
         }
       }).when(mockCreds).applyRequestMetadata(same(method), any(Attributes.class),
-          same(mockExecutor), any(MetadataApplier.class));
+          same(mockExecutor), any(CallCredentials.MetadataApplier.class));
 
     FailingClientStream stream =
         (FailingClientStream) transport.newStream(method, origHeaders, callOptions);
@@ -243,7 +245,7 @@ public class CallCredentialsApplyingTest {
     // Will call applyRequestMetadata(), which is no-op.
     DelayedStream stream = (DelayedStream) transport.newStream(method, origHeaders, callOptions);
 
-    ArgumentCaptor<MetadataApplier> applierCaptor = ArgumentCaptor.forClass(null);
+    ArgumentCaptor<CallCredentials.MetadataApplier> applierCaptor = ArgumentCaptor.forClass(null);
     verify(mockCreds).applyRequestMetadata(same(method), any(Attributes.class),
         same(mockExecutor), applierCaptor.capture());
     verify(mockTransport, never()).newStream(method, origHeaders, callOptions);
@@ -265,7 +267,7 @@ public class CallCredentialsApplyingTest {
     // Will call applyRequestMetadata(), which is no-op.
     DelayedStream stream = (DelayedStream) transport.newStream(method, origHeaders, callOptions);
 
-    ArgumentCaptor<MetadataApplier> applierCaptor = ArgumentCaptor.forClass(null);
+    ArgumentCaptor<CallCredentials.MetadataApplier> applierCaptor = ArgumentCaptor.forClass(null);
     verify(mockCreds).applyRequestMetadata(same(method), any(Attributes.class),
         same(mockExecutor), applierCaptor.capture());
 
diff --git a/core/src/test/java/io/grpc/internal/ManagedChannelImplTest.java b/core/src/test/java/io/grpc/internal/ManagedChannelImplTest.java
index 863834a0f..c5fdf713e 100644
--- a/core/src/test/java/io/grpc/internal/ManagedChannelImplTest.java
+++ b/core/src/test/java/io/grpc/internal/ManagedChannelImplTest.java
@@ -57,7 +57,6 @@ import com.google.common.util.concurrent.SettableFuture;
 import io.grpc.Attributes;
 import io.grpc.BinaryLog;
 import io.grpc.CallCredentials;
-import io.grpc.CallCredentials.MetadataApplier;
 import io.grpc.CallOptions;
 import io.grpc.Channel;
 import io.grpc.ClientCall;
@@ -1404,7 +1403,7 @@ public class ManagedChannelImplTest {
         }
       }).when(creds).applyRequestMetadata(  // TODO(zhangkun83): remove suppression of deprecations
           any(MethodDescriptor.class), any(Attributes.class), any(Executor.class),
-          any(MetadataApplier.class));
+          any(CallCredentials.MetadataApplier.class));
 
     // First call will be on delayed transport.  Only newCall() is run within the expected context,
     // so that we can verify that the context is explicitly attached before calling newStream() and
@@ -1436,7 +1435,7 @@ public class ManagedChannelImplTest {
 
     verify(creds, never()).applyRequestMetadata(
         any(MethodDescriptor.class), any(Attributes.class), any(Executor.class),
-        any(MetadataApplier.class));
+        any(CallCredentials.MetadataApplier.class));
 
     // applyRequestMetadata() is called after the transport becomes ready.
     transportInfo.listener.transportReady();
@@ -1445,7 +1444,8 @@ public class ManagedChannelImplTest {
     helper.updateBalancingState(READY, mockPicker);
     executor.runDueTasks();
     ArgumentCaptor<Attributes> attrsCaptor = ArgumentCaptor.forClass(Attributes.class);
-    ArgumentCaptor<MetadataApplier> applierCaptor = ArgumentCaptor.forClass(MetadataApplier.class);
+    ArgumentCaptor<CallCredentials.MetadataApplier> applierCaptor
+        = ArgumentCaptor.forClass(CallCredentials.MetadataApplier.class);
     verify(creds).applyRequestMetadata(same(method), attrsCaptor.capture(),
         same(executor.getScheduledExecutorService()), applierCaptor.capture());
     assertEquals("testValue", testKey.get(credsApplyContexts.poll()));