chore(x-goog-spanner-request-id): add SessionImpl.getChannel() and Options.RequestIdOption.(equals, hashCode)

Implements channelId retrieval that'll then be used to
plumb into x-goog-spanner-request-id's channel. Also implements
Options.RequestIdOption.(equals, hashCode)

Fixes #3899

Implement Options.RequestIdOption.(equals, hashCode)

Author: odeke-em

google-cloud-spanner/src/main/java/com/google/cloud/spanner/Options.java

@@ -1088,12 +1088,20 @@ void appendToOptions(Options options) {
 
     @Override
     public int hashCode() {
-      return RequestIdOption.class.hashCode();
+      return this.reqId.hashCode();
     }
 
     @Override
     public boolean equals(Object o) {
-      return o instanceof RequestIdOption;
+      // instanceof for a null object returns false.
+      if (!(o instanceof RequestIdOption)) {
+        return false;
+      }
+      RequestIdOption other = (RequestIdOption) o;
+      if (this.reqId == null || other.reqId == null) {
+        return this.reqId == null && other.reqId == null;
+      }
+      return this.reqId.equals(other.reqId);
     }
   }
 }

google-cloud-spanner/src/main/java/com/google/cloud/spanner/SessionImpl.java

@@ -319,7 +319,7 @@ public CommitResponse writeAtLeastOnceWithOptions(
   private XGoogSpannerRequestId reqIdOrFresh(Options options) {
     XGoogSpannerRequestId reqId = options.reqId();
     if (reqId == null) {
-      reqId = this.getRequestIdCreator().nextRequestId(1 /* TODO: channelId */, 1);
+      reqId = this.getRequestIdCreator().nextRequestId(this.getChannel(), 1);
     }
     return reqId;
   }
@@ -464,17 +464,15 @@ public AsyncTransactionManagerImpl transactionManagerAsync(TransactionOption...
 
   @Override
   public ApiFuture<Empty> asyncClose() {
-    XGoogSpannerRequestId reqId =
-        this.getRequestIdCreator().nextRequestId(1 /* TODO: channelId */, 0);
+    XGoogSpannerRequestId reqId = this.getRequestIdCreator().nextRequestId(this.getChannel(), 0);
     return spanner.getRpc().asyncDeleteSession(getName(), reqId.withOptions(getOptions()));
   }
 
   @Override
   public void close() {
     ISpan span = tracer.spanBuilder(SpannerImpl.DELETE_SESSION);
     try (IScope s = tracer.withSpan(span)) {
-      XGoogSpannerRequestId reqId =
-          this.getRequestIdCreator().nextRequestId(1 /* TODO: channelId */, 0);
+      XGoogSpannerRequestId reqId = this.getRequestIdCreator().nextRequestId(this.getChannel(), 0);
       spanner.getRpc().deleteSession(getName(), reqId.withOptions(getOptions()));
     } catch (RuntimeException e) {
       span.setStatus(e);
@@ -505,8 +503,7 @@ ApiFuture<Transaction> beginTransactionAsync(
     }
     final BeginTransactionRequest request = requestBuilder.build();
     final ApiFuture<Transaction> requestFuture;
-    XGoogSpannerRequestId reqId =
-        this.getRequestIdCreator().nextRequestId(1 /* TODO: channelId */, 1);
+    XGoogSpannerRequestId reqId = this.getRequestIdCreator().nextRequestId(this.getChannel(), 1);
     try (IScope ignore = tracer.withSpan(span)) {
       requestFuture =
           spanner
@@ -597,4 +594,9 @@ public void setRequestIdCreator(XGoogSpannerRequestId.RequestIdCreator creator)
   public XGoogSpannerRequestId.RequestIdCreator getRequestIdCreator() {
     return this.requestIdCreator;
   }
+
+  int getChannel() {
+    Long channelHint = (Long) this.getOptions().get(SpannerRpc.Option.CHANNEL_HINT);
+    return (int) (channelHint % this.spanner.getOptions().getNumChannels());
+  }
 }

google-cloud-spanner/src/test/java/com/google/cloud/spanner/OptionsTest.java

@@ -900,6 +900,22 @@ public void testRequestId() {
     assertThat(option3.toString()).doesNotContain("requestId");
   }
 
+  @Test
+  public void testRequestIdOptionEqualsAndHashCode() {
+    XGoogSpannerRequestId reqId1 = XGoogSpannerRequestId.of(1, 2, 3, 4);
+    XGoogSpannerRequestId reqId2 = XGoogSpannerRequestId.of(2, 3, 4, 5);
+    Options.RequestIdOption opt1 = Options.requestId(reqId1);
+    Options.RequestIdOption opt1Prime = Options.requestId(reqId1);
+    Options.RequestIdOption opt2 = Options.requestId(reqId2);
+
+    assertTrue(opt1.equals(opt1));
+    assertTrue(opt1.equals(opt1Prime));
+    assertEquals(opt1.hashCode(), opt1Prime.hashCode());
+    assertFalse(opt1.equals(opt2));
+    assertNotEquals(opt1, opt2);
+    assertNotEquals(opt1.hashCode(), opt2.hashCode());
+  }
+
   @Test
   public void testOptions_WithMultipleDifferentRequestIds() {
     XGoogSpannerRequestId reqId1 = XGoogSpannerRequestId.of(1, 1, 1, 1);