api: Summarize EquivalentAddressGroup toString

api/src/main/java/io/grpc/EquivalentAddressGroup.java

@@ -34,6 +34,7 @@
  */
 @ExperimentalApi("https://github.com/grpc/grpc-java/issues/1770")
 public final class EquivalentAddressGroup {
+  static final int MAX_ADDRESSES_TO_STRING = 100;
 
   /**
    * The authority to be used when constructing Subchannels for this EquivalentAddressGroup.
@@ -113,8 +114,24 @@ public Attributes getAttributes() {
 
   @Override
   public String toString() {
-    // TODO(zpencer): Summarize return value if addr is very large
-    return "[" + addrs + "/" + attrs + "]";
+    StringBuilder sb = new StringBuilder();
+    sb.append('[');
+    if (addrs.size() <= MAX_ADDRESSES_TO_STRING) {
+      sb.append(addrs);
+    } else {
+      sb.append('[');
+      for (int i = 0; i < MAX_ADDRESSES_TO_STRING; i++) {
+        if (i > 0) {
+          sb.append(", ");
+        }
+        sb.append(addrs.get(i));
+      }
+      sb.append(", ... ");
+      sb.append(addrs.size() - MAX_ADDRESSES_TO_STRING);
+      sb.append(" more]");
+    }
+    sb.append('/').append(attrs).append(']');
+    return sb.toString();
   }
 
   @Override

api/src/test/java/io/grpc/EquivalentAddressGroupTest.java

@@ -0,0 +1,81 @@
+/*
+ * Copyright 2026 The gRPC Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.grpc;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import java.net.SocketAddress;
+import java.util.ArrayList;
+import java.util.List;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+/**
+ * Unit tests for {@link EquivalentAddressGroup}.
+ */
+@RunWith(JUnit4.class)
+public class EquivalentAddressGroupTest {
+
+  @Test
+  public void toString_summarizesLargeAddressList() {
+    int maxAddressesToString = EquivalentAddressGroup.MAX_ADDRESSES_TO_STRING;
+    List<SocketAddress> addrs = new ArrayList<>();
+    for (int i = 0; i <= maxAddressesToString; i++) {
+      addrs.add(new FakeSocketAddress("addr" + i));
+    }
+    EquivalentAddressGroup eag = new EquivalentAddressGroup(addrs);
+
+    StringBuilder expected = new StringBuilder();
+    expected.append('[').append('[');
+    for (int i = 0; i < maxAddressesToString; i++) {
+      if (i > 0) {
+        expected.append(", ");
+      }
+      expected.append(addrs.get(i));
+    }
+    expected.append(", ... 1 more]/{}]");
+    assertThat(eag.toString()).isEqualTo(expected.toString());
+  }
+
+  @Test
+  public void toString_doesNotSummarizeAtMaxAddressCount() {
+    int maxAddressesToString = EquivalentAddressGroup.MAX_ADDRESSES_TO_STRING;
+    List<SocketAddress> addrs = new ArrayList<>();
+    for (int i = 0; i < maxAddressesToString; i++) {
+      addrs.add(new FakeSocketAddress("addr" + i));
+    }
+    EquivalentAddressGroup eag = new EquivalentAddressGroup(addrs);
+
+    String expected = "[" + addrs + "/{}]";
+    assertThat(eag.toString()).isEqualTo(expected);
+  }
+
+  private static final class FakeSocketAddress extends SocketAddress {
+
+    private final String name;
+
+    FakeSocketAddress(String name) {
+      this.name = name;
+    }
+
+    @Override
+    public String toString() {
+      return name;
+    }
+  }
+}

grpclb/src/test/java/io/grpc/grpclb/GrpclbNameResolverTest.java

@@ -46,6 +46,7 @@
 import java.net.InetAddress;
 import java.net.InetSocketAddress;
 import java.net.UnknownHostException;
+import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 import java.util.concurrent.Executor;
@@ -211,6 +212,40 @@ public ConfigOrError answer(InvocationOnMock invocation) {
     verify(mockResourceResolver).resolveSrv("_grpclb._tcp." + hostName);
   }
 
+  @Test
+  public void resolve_presentResourceResolver_manyBalancerAddressesSummarizedInToString()
+      throws Exception {
+    int addressCount = 1000;
+    InetAddress backendAddr = InetAddress.getByAddress(new byte[] {127, 0, 0, 0});
+    String lbName = "foo.example.com.";  // original name in SRV record
+    SrvRecord srvRecord = new SrvRecord(lbName, 8080);
+    List<InetAddress> lbAddrs = new ArrayList<>();
+    for (int i = 0; i < addressCount; i++) {
+      lbAddrs.add(InetAddress.getByAddress(new byte[] {10, 1, 0, (byte) (i + 1)}));
+    }
+    AddressResolver mockAddressResolver = mock(AddressResolver.class);
+    when(mockAddressResolver.resolveAddress(hostName))
+        .thenReturn(Collections.singletonList(backendAddr));
+    when(mockAddressResolver.resolveAddress(lbName))
+        .thenReturn(lbAddrs);
+    ResourceResolver mockResourceResolver = mock(ResourceResolver.class);
+    when(mockResourceResolver.resolveTxt(anyString())).thenReturn(Collections.<String>emptyList());
+    when(mockResourceResolver.resolveSrv(anyString()))
+        .thenReturn(Collections.singletonList(srvRecord));
+
+    resolver.setAddressResolver(mockAddressResolver);
+    resolver.setResourceResolver(mockResourceResolver);
+
+    resolver.start(mockListener);
+    assertThat(fakeClock.runDueTasks()).isEqualTo(1);
+    verify(mockListener).onResult2(resultCaptor.capture());
+    ResolutionResult result = resultCaptor.getValue();
+    EquivalentAddressGroup resolvedBalancerAddr =
+        Iterables.getOnlyElement(result.getAttributes().get(GrpclbConstants.ATTR_LB_ADDRS));
+    assertThat(resolvedBalancerAddr.getAddresses().size()).isEqualTo(addressCount);
+    assertThat(resolvedBalancerAddr.toString()).contains("... ");
+  }
+
   @Test
   public void resolve_nullResourceResolver() throws Exception {
     InetAddress backendAddr = InetAddress.getByAddress(new byte[] {127, 0, 0, 0});
@@ -341,4 +376,5 @@ public void resolve_addressAndBalancersLookupFail_neverLookupServiceConfig() thr
     verify(mockResourceResolver, never()).resolveTxt("_grpc_config." + hostName);
     verify(mockResourceResolver).resolveSrv("_grpclb._tcp." + hostName);
   }
+
 }