xds: Change how xDS filters are created by introducing Filter.Provider

xds/src/main/java/io/grpc/xds/FaultFilter.java

@@ -45,7 +45,6 @@
 import io.grpc.internal.GrpcUtil;
 import io.grpc.xds.FaultConfig.FaultAbort;
 import io.grpc.xds.FaultConfig.FaultDelay;
-import io.grpc.xds.Filter.ClientInterceptorBuilder;
 import io.grpc.xds.ThreadSafeRandom.ThreadSafeRandomImpl;
 import java.util.Locale;
 import java.util.concurrent.Executor;
@@ -56,10 +55,11 @@
 import javax.annotation.Nullable;
 
 /** HttpFault filter implementation. */
-final class FaultFilter implements Filter, ClientInterceptorBuilder {
+final class FaultFilter implements Filter {
 
-  static final FaultFilter INSTANCE =
+  private static final FaultFilter INSTANCE =
       new FaultFilter(ThreadSafeRandomImpl.instance, new AtomicLong());
+
   @VisibleForTesting
   static final Metadata.Key<String> HEADER_DELAY_KEY =
       Metadata.Key.of("x-envoy-fault-delay-request", Metadata.ASCII_STRING_MARSHALLER);
@@ -87,96 +87,108 @@
     this.activeFaultCounter = activeFaultCounter;
   }
 
-  @Override
-  public String[] typeUrls() {
-    return new String[] { TYPE_URL };
-  }
-
-  @Override
-  public ConfigOrError<FaultConfig> parseFilterConfig(Message rawProtoMessage) {
-    HTTPFault httpFaultProto;
-    if (!(rawProtoMessage instanceof Any)) {
-      return ConfigOrError.fromError("Invalid config type: " + rawProtoMessage.getClass());
+  static final class Provider implements Filter.Provider {
+    @Override
+    public String[] typeUrls() {
+      return new String[]{TYPE_URL};
     }
-    Any anyMessage = (Any) rawProtoMessage;
-    try {
-      httpFaultProto = anyMessage.unpack(HTTPFault.class);
-    } catch (InvalidProtocolBufferException e) {
-      return ConfigOrError.fromError("Invalid proto: " + e);
+
+    @Override
+    public boolean isClientFilter() {
+      return true;
     }
-    return parseHttpFault(httpFaultProto);
-  }
 
-  private static ConfigOrError<FaultConfig> parseHttpFault(HTTPFault httpFault) {
-    FaultDelay faultDelay = null;
-    FaultAbort faultAbort = null;
-    if (httpFault.hasDelay()) {
-      faultDelay = parseFaultDelay(httpFault.getDelay());
+    @Override
+    public FaultFilter newInstance() {
+      return INSTANCE;
     }
-    if (httpFault.hasAbort()) {
-      ConfigOrError<FaultAbort> faultAbortOrError = parseFaultAbort(httpFault.getAbort());
-      if (faultAbortOrError.errorDetail != null) {
-        return ConfigOrError.fromError(
-            "HttpFault contains invalid FaultAbort: " + faultAbortOrError.errorDetail);
+
+    @Override
+    public ConfigOrError<FaultConfig> parseFilterConfig(Message rawProtoMessage) {
+      HTTPFault httpFaultProto;
+      if (!(rawProtoMessage instanceof Any)) {
+        return ConfigOrError.fromError("Invalid config type: " + rawProtoMessage.getClass());
       }
-      faultAbort = faultAbortOrError.config;
-    }
-    Integer maxActiveFaults = null;
-    if (httpFault.hasMaxActiveFaults()) {
-      maxActiveFaults = httpFault.getMaxActiveFaults().getValue();
-      if (maxActiveFaults < 0) {
-        maxActiveFaults = Integer.MAX_VALUE;
+      Any anyMessage = (Any) rawProtoMessage;
+      try {
+        httpFaultProto = anyMessage.unpack(HTTPFault.class);
+      } catch (InvalidProtocolBufferException e) {
+        return ConfigOrError.fromError("Invalid proto: " + e);
       }
+      return parseHttpFault(httpFaultProto);
     }
-    return ConfigOrError.fromConfig(FaultConfig.create(faultDelay, faultAbort, maxActiveFaults));
-  }
 
-  private static FaultDelay parseFaultDelay(
-      io.envoyproxy.envoy.extensions.filters.common.fault.v3.FaultDelay faultDelay) {
-    FaultConfig.FractionalPercent percent = parsePercent(faultDelay.getPercentage());
-    if (faultDelay.hasHeaderDelay()) {
-      return FaultDelay.forHeader(percent);
+    @Override
+    public ConfigOrError<FaultConfig> parseFilterConfigOverride(Message rawProtoMessage) {
+      return parseFilterConfig(rawProtoMessage);
     }
-    return FaultDelay.forFixedDelay(Durations.toNanos(faultDelay.getFixedDelay()), percent);
-  }
 
-  @VisibleForTesting
-  static ConfigOrError<FaultAbort> parseFaultAbort(
-      io.envoyproxy.envoy.extensions.filters.http.fault.v3.FaultAbort faultAbort) {
-    FaultConfig.FractionalPercent percent = parsePercent(faultAbort.getPercentage());
-    switch (faultAbort.getErrorTypeCase()) {
-      case HEADER_ABORT:
-        return ConfigOrError.fromConfig(FaultAbort.forHeader(percent));
-      case HTTP_STATUS:
-        return ConfigOrError.fromConfig(FaultAbort.forStatus(
-            GrpcUtil.httpStatusToGrpcStatus(faultAbort.getHttpStatus()), percent));
-      case GRPC_STATUS:
-        return ConfigOrError.fromConfig(FaultAbort.forStatus(
-            Status.fromCodeValue(faultAbort.getGrpcStatus()), percent));
-      case ERRORTYPE_NOT_SET:
-      default:
-        return ConfigOrError.fromError(
-            "Unknown error type case: " + faultAbort.getErrorTypeCase());
+    private static ConfigOrError<FaultConfig> parseHttpFault(HTTPFault httpFault) {
+      FaultDelay faultDelay = null;
+      FaultAbort faultAbort = null;
+      if (httpFault.hasDelay()) {
+        faultDelay = parseFaultDelay(httpFault.getDelay());
+      }
+      if (httpFault.hasAbort()) {
+        ConfigOrError<FaultAbort> faultAbortOrError = parseFaultAbort(httpFault.getAbort());
+        if (faultAbortOrError.errorDetail != null) {
+          return ConfigOrError.fromError(
+              "HttpFault contains invalid FaultAbort: " + faultAbortOrError.errorDetail);
+        }
+        faultAbort = faultAbortOrError.config;
+      }
+      Integer maxActiveFaults = null;
+      if (httpFault.hasMaxActiveFaults()) {
+        maxActiveFaults = httpFault.getMaxActiveFaults().getValue();
+        if (maxActiveFaults < 0) {
+          maxActiveFaults = Integer.MAX_VALUE;
+        }
+      }
+      return ConfigOrError.fromConfig(FaultConfig.create(faultDelay, faultAbort, maxActiveFaults));
     }
-  }
 
-  private static FaultConfig.FractionalPercent parsePercent(FractionalPercent proto) {
-    switch (proto.getDenominator()) {
-      case HUNDRED:
-        return FaultConfig.FractionalPercent.perHundred(proto.getNumerator());
-      case TEN_THOUSAND:
-        return FaultConfig.FractionalPercent.perTenThousand(proto.getNumerator());
-      case MILLION:
-        return FaultConfig.FractionalPercent.perMillion(proto.getNumerator());
-      case UNRECOGNIZED:
-      default:
-        throw new IllegalArgumentException("Unknown denominator type: " + proto.getDenominator());
+    private static FaultDelay parseFaultDelay(
+        io.envoyproxy.envoy.extensions.filters.common.fault.v3.FaultDelay faultDelay) {
+      FaultConfig.FractionalPercent percent = parsePercent(faultDelay.getPercentage());
+      if (faultDelay.hasHeaderDelay()) {
+        return FaultDelay.forHeader(percent);
+      }
+      return FaultDelay.forFixedDelay(Durations.toNanos(faultDelay.getFixedDelay()), percent);
     }
-  }
 
-  @Override
-  public ConfigOrError<FaultConfig> parseFilterConfigOverride(Message rawProtoMessage) {
-    return parseFilterConfig(rawProtoMessage);
+    @VisibleForTesting
+    static ConfigOrError<FaultAbort> parseFaultAbort(
+        io.envoyproxy.envoy.extensions.filters.http.fault.v3.FaultAbort faultAbort) {
+      FaultConfig.FractionalPercent percent = parsePercent(faultAbort.getPercentage());
+      switch (faultAbort.getErrorTypeCase()) {
+        case HEADER_ABORT:
+          return ConfigOrError.fromConfig(FaultAbort.forHeader(percent));
+        case HTTP_STATUS:
+          return ConfigOrError.fromConfig(FaultAbort.forStatus(
+              GrpcUtil.httpStatusToGrpcStatus(faultAbort.getHttpStatus()), percent));
+        case GRPC_STATUS:
+          return ConfigOrError.fromConfig(FaultAbort.forStatus(
+              Status.fromCodeValue(faultAbort.getGrpcStatus()), percent));
+        case ERRORTYPE_NOT_SET:
+        default:
+          return ConfigOrError.fromError(
+              "Unknown error type case: " + faultAbort.getErrorTypeCase());
+      }
+    }
+
+    private static FaultConfig.FractionalPercent parsePercent(FractionalPercent proto) {
+      switch (proto.getDenominator()) {
+        case HUNDRED:
+          return FaultConfig.FractionalPercent.perHundred(proto.getNumerator());
+        case TEN_THOUSAND:
+          return FaultConfig.FractionalPercent.perTenThousand(proto.getNumerator());
+        case MILLION:
+          return FaultConfig.FractionalPercent.perMillion(proto.getNumerator());
+        case UNRECOGNIZED:
+        default:
+          throw new IllegalArgumentException("Unknown denominator type: " + proto.getDenominator());
+      }
+    }
   }
 
   @Nullable

xds/src/main/java/io/grpc/xds/Filter.java

@@ -25,48 +25,82 @@
 import javax.annotation.Nullable;
 
 /**
- * Defines the parsing functionality of an HTTP filter. A Filter may optionally implement either
- * {@link ClientInterceptorBuilder} or {@link ServerInterceptorBuilder} or both, indicating it is
- * capable of working on the client side or server side or both, respectively.
+ * Defines the parsing functionality of an HTTP filter.
+ *
+ * <p>A Filter may optionally implement either {@link Filter#buildClientInterceptor} or
+ * {@link Filter#buildServerInterceptor} or both, and return true from corresponding
+ * {@link Provider#isClientFilter()}, {@link Provider#isServerFilter()} to indicate that the filter
+ * is capable of working on the client side or server side or both, respectively.
  */
 interface Filter {
 
-  /**
-   * The proto message types supported by this filter. A filter will be registered by each of its
-   * supported message types.
-   */
-  String[] typeUrls();
+  /** Represents an opaque data structure holding configuration for a filter. */
+  interface FilterConfig {
+    String typeUrl();
+  }
 
   /**
-   * Parses the top-level filter config from raw proto message. The message may be either a {@link
-   * com.google.protobuf.Any} or a {@link com.google.protobuf.Struct}.
+   * Common interface for filter providers.
    */
-  ConfigOrError<? extends FilterConfig> parseFilterConfig(Message rawProtoMessage);
+  interface Provider {
+    /**
+     * The proto message types supported by this filter. A filter will be registered by each of its
+     * supported message types.
+     */
+    String[] typeUrls();
 
-  /**
-   * Parses the per-filter override filter config from raw proto message. The message may be either
-   * a {@link com.google.protobuf.Any} or a {@link com.google.protobuf.Struct}.
-   */
-  ConfigOrError<? extends FilterConfig> parseFilterConfigOverride(Message rawProtoMessage);
+    /**
+     * Whether the filter can be installed on the client side.
+     *
+     * <p>Returns true if the filter implements {@link Filter#buildClientInterceptor}.
+     */
+    default boolean isClientFilter() {
+      return false;
+    }
 
-  /** Represents an opaque data structure holding configuration for a filter. */
-  interface FilterConfig {
-    String typeUrl();
+    /**
+     * Whether the filter can be installed into xDS-enabled servers.
+     *
+     * <p>Returns true if the filter implements {@link Filter#buildServerInterceptor}.
+     */
+    default boolean isServerFilter() {
+      return false;
+    }
+
+    /**
+     * Creates a new instance of the filter.
+     *
+     * <p>Returns a filter instance registered with the same typeUrls as the provider,
+     * capable of working with the same FilterConfig type returned by provider's parse functions.
+     */
+    Filter newInstance();
+
+    /**
+     * Parses the top-level filter config from raw proto message. The message may be either a {@link
+     * com.google.protobuf.Any} or a {@link com.google.protobuf.Struct}.
+     */
+    ConfigOrError<? extends FilterConfig> parseFilterConfig(Message rawProtoMessage);
+
+    /**
+     * Parses the per-filter override filter config from raw proto message. The message may be
+     * either a {@link com.google.protobuf.Any} or a {@link com.google.protobuf.Struct}.
+     */
+    ConfigOrError<? extends FilterConfig> parseFilterConfigOverride(Message rawProtoMessage);
   }
 
   /** Uses the FilterConfigs produced above to produce an HTTP filter interceptor for clients. */
-  interface ClientInterceptorBuilder {
-    @Nullable
-    ClientInterceptor buildClientInterceptor(
-        FilterConfig config, @Nullable FilterConfig overrideConfig,
-        ScheduledExecutorService scheduler);
+  @Nullable
+  default ClientInterceptor buildClientInterceptor(
+      FilterConfig config, @Nullable FilterConfig overrideConfig,
+      ScheduledExecutorService scheduler) {
+    return null;
   }
 
   /** Uses the FilterConfigs produced above to produce an HTTP filter interceptor for the server. */
-  interface ServerInterceptorBuilder {
-    @Nullable
-    ServerInterceptor buildServerInterceptor(
-        FilterConfig config, @Nullable FilterConfig overrideConfig);
+  @Nullable
+  default ServerInterceptor buildServerInterceptor(
+      FilterConfig config, @Nullable FilterConfig overrideConfig) {
+    return null;
   }
 
   /** Filter config with instance name. */

xds/src/main/java/io/grpc/xds/FilterRegistry.java

@@ -23,21 +23,21 @@
 
 /**
  * A registry for all supported {@link Filter}s. Filters can be queried from the registry
- * by any of the {@link Filter#typeUrls() type URLs}.
+ * by any of the {@link Filter.Provider#typeUrls() type URLs}.
  */
 final class FilterRegistry {
   private static FilterRegistry instance;
 
-  private final Map<String, Filter> supportedFilters = new HashMap<>();
+  private final Map<String, Filter.Provider> supportedFilters = new HashMap<>();
 
   private FilterRegistry() {}
 
   static synchronized FilterRegistry getDefaultRegistry() {
     if (instance == null) {
       instance = newRegistry().register(
-              FaultFilter.INSTANCE,
-              RouterFilter.INSTANCE,
-              RbacFilter.INSTANCE);
+              new FaultFilter.Provider(),
+              new RouterFilter.Provider(),
+              new RbacFilter.Provider());
     }
     return instance;
   }
@@ -48,8 +48,8 @@ static FilterRegistry newRegistry() {
   }
 
   @VisibleForTesting
-  FilterRegistry register(Filter... filters) {
-    for (Filter filter : filters) {
+  FilterRegistry register(Filter.Provider... filters) {
+    for (Filter.Provider filter : filters) {
       for (String typeUrl : filter.typeUrls()) {
         supportedFilters.put(typeUrl, filter);
       }
@@ -58,7 +58,7 @@ FilterRegistry register(Filter... filters) {
   }
 
   @Nullable
-  Filter get(String typeUrl) {
+  Filter.Provider get(String typeUrl) {
     return supportedFilters.get(typeUrl);
   }
 }