feat: add method to set emulator host programmatically (#319)

google-cloud-firestore/src/main/java/com/google/cloud/firestore/FirestoreOptions.java

@@ -60,6 +60,7 @@ public final class FirestoreOptions extends ServiceOptions<Firestore, FirestoreO
  private final String databaseId;
  private final TransportChannelProvider channelProvider;
  private final CredentialsProvider credentialsProvider;
+ private final String emulatorHost;
 
  public static class DefaultFirestoreFactory implements FirestoreFactory {
 
@@ -114,11 +115,16 @@ public TransportChannelProvider getTransportChannelProvider() {
  return channelProvider;
  }
 
+ public String getEmulatorHost() {
+ return emulatorHost;
+ }
+
  public static class Builder extends ServiceOptions.Builder<Firestore, FirestoreOptions, Builder> {
 
  @Nullable private String databaseId = null;
  @Nullable private TransportChannelProvider channelProvider = null;
  @Nullable private CredentialsProvider credentialsProvider = null;
+ @Nullable private String emulatorHost = null;
 
  private Builder() {}
 
@@ -127,6 +133,7 @@ private Builder(FirestoreOptions options) {
  this.databaseId = options.databaseId;
  this.channelProvider = options.channelProvider;
  this.credentialsProvider = options.credentialsProvider;
+ this.emulatorHost = options.emulatorHost;
  }
 
  /**
@@ -174,6 +181,17 @@ public Builder setCredentialsProvider(@Nonnull CredentialsProvider credentialsPr
  return this;
  }
 
+ /**
+ * Sets the emulator host to use with this Firestore client. The value passed to this method
+ * will take precedent if the {@code FIRESTORE_EMULATOR_HOST} environment variable is also set.
+ *
+ * @param emulatorHost The Firestore emulator host to use with this client.
+ */
+ public Builder setEmulatorHost(@Nonnull String emulatorHost) {
+ this.emulatorHost = emulatorHost;
+ return this;
+ }
+
  /**
  * Sets the database ID to use with this Firestore client.
  *
@@ -196,7 +214,9 @@ public FirestoreOptions build() {
  }
 
  // Override credentials and channel provider if we are using the emulator.
- String emulatorHost = System.getenv(FIRESTORE_EMULATOR_SYSTEM_VARIABLE);
+ if (emulatorHost == null) {
+ emulatorHost = System.getenv(FIRESTORE_EMULATOR_SYSTEM_VARIABLE);
+ }
  if (emulatorHost != null) {
  // Try creating a host in order to validate that the host name is valid.
  try {
@@ -280,6 +300,8 @@ protected FirestoreOptions(Builder builder) {
  builder.credentialsProvider != null
  ? builder.credentialsProvider
  : GrpcTransportOptions.setUpCredentialsProvider(this);
+
+ this.emulatorHost = builder.emulatorHost;
  }
 
  private static class FirestoreDefaults implements ServiceDefaults<Firestore, FirestoreOptions> {