fix: respect SPANNER_EMULATOR_HOST env var when autoConfigEmulator=true

README.md

@@ -50,20 +50,20 @@ If you are using Maven without the BOM, add this to your dependencies:
 If you are using Gradle 5.x or later, add this to your dependencies:
 
 ```Groovy
-implementation platform('com.google.cloud:libraries-bom:26.26.0')
+implementation platform('com.google.cloud:libraries-bom:26.27.0')
 
 implementation 'com.google.cloud:google-cloud-spanner'
 ```
 If you are using Gradle without BOM, add this to your dependencies:
 
 ```Groovy
-implementation 'com.google.cloud:google-cloud-spanner:6.52.1'
+implementation 'com.google.cloud:google-cloud-spanner:6.53.0'
 ```
 
 If you are using SBT, add this to your dependencies:
 
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-spanner" % "6.52.1"
+libraryDependencies += "com.google.cloud" % "google-cloud-spanner" % "6.53.0"
 ```
 <!-- {x-version-update-end} -->
 
@@ -432,7 +432,7 @@ Java is a registered trademark of Oracle and/or its affiliates.
 [kokoro-badge-link-5]: http://storage.googleapis.com/cloud-devrel-public/java/badges/java-spanner/java11.html
 [stability-image]: https://img.shields.io/badge/stability-stable-green
 [maven-version-image]: https://img.shields.io/maven-central/v/com.google.cloud/google-cloud-spanner.svg
-[maven-version-link]: https://central.sonatype.com/artifact/com.google.cloud/google-cloud-spanner/6.52.1
+[maven-version-link]: https://central.sonatype.com/artifact/com.google.cloud/google-cloud-spanner/6.53.0
 [authentication]: https://github.com/googleapis/google-cloud-java#authentication
 [auth-scopes]: https://developers.google.com/identity/protocols/oauth2/scopes
 [predefined-iam-roles]: https://cloud.google.com/iam/docs/understanding-roles#predefined_roles

google-cloud-spanner/src/main/java/com/google/cloud/spanner/connection/ConnectionOptions.java

@@ -48,6 +48,7 @@
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Map;
 import java.util.Objects;
 import java.util.Set;
 import java.util.regex.Matcher;
@@ -191,6 +192,7 @@ public String[] getValidValues() {
   private static final String PLAIN_TEXT_PROTOCOL = "http:";
   private static final String HOST_PROTOCOL = "https:";
   private static final String DEFAULT_HOST = "https://spanner.googleapis.com";
+  private static final String SPANNER_EMULATOR_HOST_ENV_VAR = "SPANNER_EMULATOR_HOST";
   private static final String DEFAULT_EMULATOR_HOST = "http://localhost:9010";
   /** Use plain text is only for local testing purposes. */
   private static final String USE_PLAIN_TEXT_PROPERTY_NAME = "usePlainText";
@@ -473,7 +475,10 @@ private Builder() {}
         "(?:cloudspanner:)(?<HOSTGROUP>//[\\w.-]+(?:\\.[\\w\\.-]+)*[\\w\\-\\._~:/?#\\[\\]@!\\$&'\\(\\)\\*\\+,;=.]+)?/projects/(?<PROJECTGROUP>(([a-z]|[-.:]|[0-9])+|(DEFAULT_PROJECT_ID)))(/instances/(?<INSTANCEGROUP>([a-z]|[-]|[0-9])+)(/databases/(?<DATABASEGROUP>([a-z]|[-]|[_]|[0-9])+))?)?(?:[?|;].*)?";
 
     private static final String SPANNER_URI_REGEX = "(?is)^" + SPANNER_URI_FORMAT + "$";
-    private static final Pattern SPANNER_URI_PATTERN = Pattern.compile(SPANNER_URI_REGEX);
+
+    @VisibleForTesting
+    static final Pattern SPANNER_URI_PATTERN = Pattern.compile(SPANNER_URI_REGEX);
+
     private static final String HOST_GROUP = "HOSTGROUP";
     private static final String PROJECT_GROUP = "PROJECTGROUP";
     private static final String INSTANCE_GROUP = "INSTANCEGROUP";
@@ -706,7 +711,7 @@ private ConnectionOptions(Builder builder) {
     this.autoConfigEmulator = parseAutoConfigEmulator(this.uri);
     this.dialect = parseDialect(this.uri);
     this.usePlainText = this.autoConfigEmulator || parseUsePlainText(this.uri);
-    this.host = determineHost(matcher, autoConfigEmulator, usePlainText);
+    this.host = determineHost(matcher, autoConfigEmulator, usePlainText, System.getenv());
     this.rpcPriority = parseRPCPriority(this.uri);
     this.delayTransactionStartUntilFirstWrite = parseDelayTransactionStartUntilFirstWrite(this.uri);
     this.trackSessionLeaks = parseTrackSessionLeaks(this.uri);
@@ -791,11 +796,19 @@ private ConnectionOptions(Builder builder) {
     }
   }
 
-  private static String determineHost(
-      Matcher matcher, boolean autoConfigEmulator, boolean usePlainText) {
+  @VisibleForTesting
+  static String determineHost(
+      Matcher matcher,
+      boolean autoConfigEmulator,
+      boolean usePlainText,
+      Map<String, String> environment) {
     if (matcher.group(Builder.HOST_GROUP) == null) {
       if (autoConfigEmulator) {
-        return DEFAULT_EMULATOR_HOST;
+        if (Strings.isNullOrEmpty(environment.get(SPANNER_EMULATOR_HOST_ENV_VAR))) {
+          return DEFAULT_EMULATOR_HOST;
+        } else {
+          return PLAIN_TEXT_PROTOCOL + "//" + environment.get(SPANNER_EMULATOR_HOST_ENV_VAR);
+        }
       } else {
         return DEFAULT_HOST;
       }

google-cloud-spanner/src/test/java/com/google/cloud/spanner/connection/ConnectionOptionsTest.java

@@ -16,6 +16,8 @@
 
 package com.google.cloud.spanner.connection;
 
+import static com.google.cloud.spanner.connection.ConnectionOptions.Builder.SPANNER_URI_PATTERN;
+import static com.google.cloud.spanner.connection.ConnectionOptions.determineHost;
 import static com.google.common.truth.Truth.assertThat;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
@@ -33,13 +35,15 @@
 import com.google.cloud.spanner.ErrorCode;
 import com.google.cloud.spanner.SpannerException;
 import com.google.cloud.spanner.SpannerOptions;
+import com.google.common.collect.ImmutableMap;
 import com.google.common.io.BaseEncoding;
 import com.google.common.io.Files;
 import java.io.File;
 import java.nio.charset.StandardCharsets;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.Objects;
+import java.util.regex.Matcher;
 import org.junit.Test;
 import org.junit.function.ThrowingRunnable;
 import org.junit.runner.RunWith;
@@ -153,6 +157,105 @@ public void testBuildWithAutoConfigEmulator() {
     assertTrue(options.isUsePlainText());
   }
 
+  @Test
+  public void testDetermineHost() {
+    final String uriWithoutHost =
+        "cloudspanner:/projects/test-project-123/instances/test-instance-123/databases/test-database-123";
+    Matcher matcherWithoutHost = SPANNER_URI_PATTERN.matcher(uriWithoutHost);
+    assertTrue(matcherWithoutHost.find());
+    final String uriWithHost =
+        "cloudspanner://custom.host.domain:1234/projects/test-project-123/instances/test-instance-123/databases/test-database-123";
+    Matcher matcherWithHost = SPANNER_URI_PATTERN.matcher(uriWithHost);
+    assertTrue(matcherWithHost.find());
+
+    assertEquals(
+        DEFAULT_HOST,
+        determineHost(
+            matcherWithoutHost,
+            /* autoConfigEmulator= */ false,
+            /* usePlainText= */ false,
+            ImmutableMap.of()));
+    assertEquals(
+        DEFAULT_HOST,
+        determineHost(
+            matcherWithoutHost,
+            /* autoConfigEmulator= */ false,
+            /* usePlainText= */ false,
+            ImmutableMap.of("FOO", "bar")));
+    assertEquals(
+        "http://localhost:9010",
+        determineHost(
+            matcherWithoutHost,
+            /* autoConfigEmulator= */ true,
+            /* usePlainText= */ false,
+            ImmutableMap.of()));
+    assertEquals(
+        "http://localhost:9011",
+        determineHost(
+            matcherWithoutHost,
+            /* autoConfigEmulator= */ true,
+            /* usePlainText= */ false,
+            ImmutableMap.of("SPANNER_EMULATOR_HOST", "localhost:9011")));
+    assertEquals(
+        "http://localhost:9010",
+        determineHost(
+            matcherWithoutHost,
+            /* autoConfigEmulator= */ true,
+            /* usePlainText= */ true,
+            ImmutableMap.of()));
+    assertEquals(
+        "http://localhost:9011",
+        determineHost(
+            matcherWithoutHost,
+            /* autoConfigEmulator= */ true,
+            /* usePlainText= */ true,
+            ImmutableMap.of("SPANNER_EMULATOR_HOST", "localhost:9011")));
+
+    // A host in the connection string has precedence over all other options.
+    assertEquals(
+        "https://custom.host.domain:1234",
+        determineHost(
+            matcherWithHost,
+            /* autoConfigEmulator= */ false,
+            /* usePlainText= */ false,
+            ImmutableMap.of()));
+    assertEquals(
+        "http://custom.host.domain:1234",
+        determineHost(
+            matcherWithHost,
+            /* autoConfigEmulator= */ false,
+            /* usePlainText= */ true,
+            ImmutableMap.of()));
+    assertEquals(
+        "http://custom.host.domain:1234",
+        determineHost(
+            matcherWithHost,
+            /* autoConfigEmulator= */ false,
+            /* usePlainText= */ true,
+            ImmutableMap.of()));
+    assertEquals(
+        "https://custom.host.domain:1234",
+        determineHost(
+            matcherWithHost,
+            /* autoConfigEmulator= */ true,
+            /* usePlainText= */ false,
+            ImmutableMap.of()));
+    assertEquals(
+        "http://custom.host.domain:1234",
+        determineHost(
+            matcherWithHost,
+            /* autoConfigEmulator= */ false,
+            /* usePlainText= */ true,
+            ImmutableMap.of("SPANNER_EMULATOR_HOST", "localhost:9011")));
+    assertEquals(
+        "https://custom.host.domain:1234",
+        determineHost(
+            matcherWithHost,
+            /* autoConfigEmulator= */ true,
+            /* usePlainText= */ false,
+            ImmutableMap.of("SPANNER_EMULATOR_HOST", "localhost:9011")));
+  }
+
   @Test
   public void testBuildWithRouteToLeader() {
     final String BASE_URI =