Clarify guarantees around remote channnel/request attribute presence

service/src/main/java/org/whispersystems/textsecuregcm/auth/grpc/AbstractAuthenticationInterceptor.java

@@ -1,34 +1,22 @@
 package org.whispersystems.textsecuregcm.auth.grpc;
 
-import io.grpc.Grpc;
-import io.grpc.Metadata;
 import io.grpc.ServerCall;
 import io.grpc.ServerInterceptor;
-import io.grpc.Status;
-import io.netty.channel.local.LocalAddress;
-import org.whispersystems.textsecuregcm.grpc.net.GrpcClientConnectionManager;
 import java.util.Optional;
+import org.whispersystems.textsecuregcm.grpc.ChannelNotFoundException;
+import org.whispersystems.textsecuregcm.grpc.net.GrpcClientConnectionManager;
 
 abstract class AbstractAuthenticationInterceptor implements ServerInterceptor {
 
   private final GrpcClientConnectionManager grpcClientConnectionManager;
 
-  private static final Metadata EMPTY_TRAILERS = new Metadata();
-
   AbstractAuthenticationInterceptor(final GrpcClientConnectionManager grpcClientConnectionManager) {
     this.grpcClientConnectionManager = grpcClientConnectionManager;
   }
 
-  protected Optional<AuthenticatedDevice> getAuthenticatedDevice(final ServerCall<?, ?> call) {
-    if (call.getAttributes().get(Grpc.TRANSPORT_ATTR_REMOTE_ADDR) instanceof LocalAddress localAddress) {
-      return grpcClientConnectionManager.getAuthenticatedDevice(localAddress);
-    } else {
-      throw new AssertionError("Unexpected channel type: " + call.getAttributes().get(Grpc.TRANSPORT_ATTR_REMOTE_ADDR));
-    }
-  }
+  protected Optional<AuthenticatedDevice> getAuthenticatedDevice(final ServerCall<?, ?> call)
+      throws ChannelNotFoundException {
 
-  protected <ReqT, RespT> ServerCall.Listener<ReqT> closeAsUnauthenticated(final ServerCall<ReqT, RespT> call) {
-    call.close(Status.UNAUTHENTICATED, EMPTY_TRAILERS);
-    return new ServerCall.Listener<>() {};
+    return grpcClientConnectionManager.getAuthenticatedDevice(call);
   }
 }

service/src/main/java/org/whispersystems/textsecuregcm/auth/grpc/ProhibitAuthenticationInterceptor.java

@@ -3,12 +3,17 @@ package org.whispersystems.textsecuregcm.auth.grpc;
 import io.grpc.Metadata;
 import io.grpc.ServerCall;
 import io.grpc.ServerCallHandler;
+import io.grpc.Status;
+import org.whispersystems.textsecuregcm.grpc.ChannelNotFoundException;
+import org.whispersystems.textsecuregcm.grpc.ServerInterceptorUtil;
 import org.whispersystems.textsecuregcm.grpc.net.GrpcClientConnectionManager;
 
 /**
  * A "prohibit authentication" interceptor ensures that requests to endpoints that should be invoked anonymously do not
  * originate from a channel that is associated with an authenticated device. Calls with an associated authenticated
- * device are closed with an {@code UNAUTHENTICATED} status.
+ * device are closed with an {@code UNAUTHENTICATED} status. If a call's authentication status cannot be determined
+ * (i.e. because the underlying remote channel closed before the {@code ServerCall} started), the interceptor will
+ * reject the call with a status of {@code UNAVAILABLE}.
  */
 public class ProhibitAuthenticationInterceptor extends AbstractAuthenticationInterceptor {
 
@@ -21,8 +26,15 @@ public class ProhibitAuthenticationInterceptor extends AbstractAuthenticationInt
       final Metadata headers,
       final ServerCallHandler<ReqT, RespT> next) {
 
-    return getAuthenticatedDevice(call)
-        .map(ignored -> closeAsUnauthenticated(call))
-        .orElseGet(() -> next.startCall(call, headers));
+    try {
+      return getAuthenticatedDevice(call)
+          // Status.INTERNAL may seem a little surprising here, but if a caller is reaching an authentication-prohibited
+          // service via an authenticated connection, then that's actually a server configuration issue and not a
+          // problem with the client's request.
+          .map(ignored -> ServerInterceptorUtil.closeWithStatus(call, Status.INTERNAL))
+          .orElseGet(() -> next.startCall(call, headers));
+    } catch (final ChannelNotFoundException e) {
+      return ServerInterceptorUtil.closeWithStatus(call, Status.UNAVAILABLE);
+    }
   }
 }

service/src/main/java/org/whispersystems/textsecuregcm/auth/grpc/RequireAuthenticationInterceptor.java

@@ -5,12 +5,16 @@ import io.grpc.Contexts;
 import io.grpc.Metadata;
 import io.grpc.ServerCall;
 import io.grpc.ServerCallHandler;
+import io.grpc.Status;
+import org.whispersystems.textsecuregcm.grpc.ChannelNotFoundException;
+import org.whispersystems.textsecuregcm.grpc.ServerInterceptorUtil;
 import org.whispersystems.textsecuregcm.grpc.net.GrpcClientConnectionManager;
 
 /**
  * A "require authentication" interceptor requires that requests be issued from a connection that is associated with an
  * authenticated device. Calls without an associated authenticated device are closed with an {@code UNAUTHENTICATED}
- * status.
+ * status. If a call's authentication status cannot be determined (i.e. because the underlying remote channel closed
+ * before the {@code ServerCall} started), the interceptor will reject the call with a status of {@code UNAVAILABLE}.
  */
 public class RequireAuthenticationInterceptor extends AbstractAuthenticationInterceptor {
 
@@ -23,10 +27,17 @@ public class RequireAuthenticationInterceptor extends AbstractAuthenticationInte
       final Metadata headers,
       final ServerCallHandler<ReqT, RespT> next) {
 
-    return getAuthenticatedDevice(call)
-        .map(authenticatedDevice -> Contexts.interceptCall(Context.current()
-                .withValue(AuthenticationUtil.CONTEXT_AUTHENTICATED_DEVICE, authenticatedDevice),
-            call, headers, next))
-        .orElseGet(() -> closeAsUnauthenticated(call));
+    try {
+      return getAuthenticatedDevice(call)
+          .map(authenticatedDevice -> Contexts.interceptCall(Context.current()
+                  .withValue(AuthenticationUtil.CONTEXT_AUTHENTICATED_DEVICE, authenticatedDevice),
+              call, headers, next))
+          // Status.INTERNAL may seem a little surprising here, but if a caller is reaching an authentication-required
+          // service via an unauthenticated connection, then that's actually a server configuration issue and not a
+          // problem with the client's request.
+          .orElseGet(() -> ServerInterceptorUtil.closeWithStatus(call, Status.INTERNAL));
+    } catch (final ChannelNotFoundException e) {
+      return ServerInterceptorUtil.closeWithStatus(call, Status.UNAVAILABLE);
+    }
   }
 }

service/src/main/java/org/whispersystems/textsecuregcm/filters/RemoteDeprecationFilter.java

@@ -81,7 +81,16 @@ public class RemoteDeprecationFilter implements Filter, ServerInterceptor {
       final Metadata headers,
       final ServerCallHandler<ReqT, RespT> next) {
 
-    if (shouldBlock(RequestAttributesUtil.getUserAgent().orElse(null))) {
+    @Nullable final UserAgent userAgent = RequestAttributesUtil.getUserAgent()
+        .map(userAgentString -> {
+          try {
+            return UserAgentUtil.parseUserAgentString(userAgentString);
+          } catch (final UnrecognizedUserAgentException e) {
+            return null;
+          }
+        }).orElse(null);
+
+    if (shouldBlock(userAgent)) {
       call.close(StatusConstants.UPGRADE_NEEDED_STATUS, new Metadata());
       return new ServerCall.Listener<>() {};
     } else {

service/src/main/java/org/whispersystems/textsecuregcm/grpc/ChannelNotFoundException.java

@@ -0,0 +1,12 @@
+/*
+ * Copyright 2025 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.whispersystems.textsecuregcm.grpc;
+
+/**
+ * Indicates that a remote channel was not found for a given server call or remote address.
+ */
+public class ChannelNotFoundException extends Exception {
+}

service/src/main/java/org/whispersystems/textsecuregcm/grpc/MessagesAnonymousGrpcService.java

@@ -253,7 +253,7 @@ public class MessagesAnonymousGrpcService extends SimpleMessagesAnonymousGrpc.Me
           story,
           ephemeral,
           urgent,
-          RequestAttributesUtil.getRawUserAgent().orElse(null));
+          RequestAttributesUtil.getUserAgent().orElse(null));
 
       final SendMultiRecipientMessageResponse.Builder responseBuilder = SendMultiRecipientMessageResponse.newBuilder();
 

service/src/main/java/org/whispersystems/textsecuregcm/grpc/MessagesGrpcHelper.java

@@ -55,7 +55,7 @@ public class MessagesGrpcHelper {
           messagesByDeviceId,
           registrationIdsByDeviceId,
           syncMessageSenderDeviceId,
-          RequestAttributesUtil.getRawUserAgent().orElse(null));
+          RequestAttributesUtil.getUserAgent().orElse(null));
 
       return SEND_MESSAGE_SUCCESS_RESPONSE;
     } catch (final MismatchedDevicesException e) {

service/src/main/java/org/whispersystems/textsecuregcm/grpc/RequestAttributes.java

@@ -0,0 +1,16 @@
+/*
+ * Copyright 2025 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.whispersystems.textsecuregcm.grpc;
+
+import java.net.InetAddress;
+import java.util.List;
+import java.util.Locale;
+import javax.annotation.Nullable;
+
+public record RequestAttributes(InetAddress remoteAddress,
+                                @Nullable String userAgent,
+                                List<Locale.LanguageRange> acceptLanguage) {
+}

service/src/main/java/org/whispersystems/textsecuregcm/grpc/RequestAttributesInterceptor.java

@@ -2,28 +2,25 @@ package org.whispersystems.textsecuregcm.grpc;
 
 import io.grpc.Context;
 import io.grpc.Contexts;
-import io.grpc.Grpc;
 import io.grpc.Metadata;
 import io.grpc.ServerCall;
 import io.grpc.ServerCallHandler;
 import io.grpc.ServerInterceptor;
 import io.grpc.Status;
-import io.netty.channel.local.LocalAddress;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
 import org.whispersystems.textsecuregcm.grpc.net.GrpcClientConnectionManager;
-import org.whispersystems.textsecuregcm.util.ua.UserAgent;
-import java.net.InetAddress;
-import java.util.List;
-import java.util.Locale;
-import java.util.Optional;
 
+/**
+ * The request attributes interceptor makes request attributes from the underlying remote channel available to service
+ * implementations by attaching them to a {@link Context} attribute that can be read via {@link RequestAttributesUtil}.
+ * All server calls should have request attributes, and calls will be rejected with a status of {@code UNAVAILABLE} if
+ * request attributes are unavailable (i.e. the underlying channel closed before the {@code ServerCall} started).
+ *
+ * @see RequestAttributesUtil
+ */
 public class RequestAttributesInterceptor implements ServerInterceptor {
 
   private final GrpcClientConnectionManager grpcClientConnectionManager;
 
-  private static final Logger log = LoggerFactory.getLogger(RequestAttributesInterceptor.class);
-
   public RequestAttributesInterceptor(final GrpcClientConnectionManager grpcClientConnectionManager) {
     this.grpcClientConnectionManager = grpcClientConnectionManager;
   }
@@ -33,52 +30,12 @@ public class RequestAttributesInterceptor implements ServerInterceptor {
       final Metadata headers,
       final ServerCallHandler<ReqT, RespT> next) {
 
-    if (call.getAttributes().get(Grpc.TRANSPORT_ATTR_REMOTE_ADDR) instanceof LocalAddress localAddress) {
-      Context context = Context.current();
-
-      {
-        final Optional<InetAddress> maybeRemoteAddress = grpcClientConnectionManager.getRemoteAddress(localAddress);
-
-        if (maybeRemoteAddress.isEmpty()) {
-          // We should never have a call from a party whose remote address we can't identify
-          log.warn("No remote address available");
-
-          call.close(Status.INTERNAL, new Metadata());
-          return new ServerCall.Listener<>() {};
-        }
-
-        context = context.withValue(RequestAttributesUtil.REMOTE_ADDRESS_CONTEXT_KEY, maybeRemoteAddress.get());
-      }
-
-      {
-        final Optional<List<Locale.LanguageRange>> maybeAcceptLanguage =
-            grpcClientConnectionManager.getAcceptableLanguages(localAddress);
-
-        if (maybeAcceptLanguage.isPresent()) {
-          context = context.withValue(RequestAttributesUtil.ACCEPT_LANGUAGE_CONTEXT_KEY, maybeAcceptLanguage.get());
-        }
-      }
-
-      {
-        final Optional<String> maybeRawUserAgent =
-            grpcClientConnectionManager.getRawUserAgent(localAddress);
-
-        if (maybeRawUserAgent.isPresent()) {
-          context = context.withValue(RequestAttributesUtil.RAW_USER_AGENT_CONTEXT_KEY, maybeRawUserAgent.get());
-        }
-      }
-
-      {
-        final Optional<UserAgent> maybeUserAgent = grpcClientConnectionManager.getUserAgent(localAddress);
-
-        if (maybeUserAgent.isPresent()) {
-          context = context.withValue(RequestAttributesUtil.USER_AGENT_CONTEXT_KEY, maybeUserAgent.get());
-        }
-      }
-
-      return Contexts.interceptCall(context, call, headers, next);
-    } else {
-      throw new AssertionError("Unexpected channel type: " + call.getAttributes().get(Grpc.TRANSPORT_ATTR_REMOTE_ADDR));
+    try {
+      return Contexts.interceptCall(Context.current()
+              .withValue(RequestAttributesUtil.REQUEST_ATTRIBUTES_CONTEXT_KEY,
+                  grpcClientConnectionManager.getRequestAttributes(call)), call, headers, next);
+    } catch (final ChannelNotFoundException e) {
+      return ServerInterceptorUtil.closeWithStatus(call, Status.UNAVAILABLE);
     }
   }
 }

service/src/main/java/org/whispersystems/textsecuregcm/grpc/RequestAttributesUtil.java

@@ -3,18 +3,13 @@ package org.whispersystems.textsecuregcm.grpc;
 import io.grpc.Context;
 import java.net.InetAddress;
 import java.util.Arrays;
-import java.util.Collections;
 import java.util.List;
 import java.util.Locale;
 import java.util.Optional;
-import org.whispersystems.textsecuregcm.util.ua.UserAgent;
 
 public class RequestAttributesUtil {
 
-  static final Context.Key<List<Locale.LanguageRange>> ACCEPT_LANGUAGE_CONTEXT_KEY = Context.key("accept-language");
-  static final Context.Key<InetAddress> REMOTE_ADDRESS_CONTEXT_KEY = Context.key("remote-address");
-  static final Context.Key<String> RAW_USER_AGENT_CONTEXT_KEY = Context.key("unparsed-user-agent");
-  static final Context.Key<UserAgent> USER_AGENT_CONTEXT_KEY = Context.key("parsed-user-agent");
+  static final Context.Key<RequestAttributes> REQUEST_ATTRIBUTES_CONTEXT_KEY = Context.key("request-attributes");
 
   private static final List<Locale> AVAILABLE_LOCALES = Arrays.asList(Locale.getAvailableLocales());
 
@@ -23,8 +18,8 @@ public class RequestAttributesUtil {
    *
    * @return the acceptable languages listed by the remote client; may be empty if unparseable or not specified
    */
-  public static Optional<List<Locale.LanguageRange>> getAcceptableLanguages() {
-    return Optional.ofNullable(ACCEPT_LANGUAGE_CONTEXT_KEY.get());
+  public static List<Locale.LanguageRange> getAcceptableLanguages() {
+    return REQUEST_ATTRIBUTES_CONTEXT_KEY.get().acceptLanguage();
   }
 
   /**
@@ -35,9 +30,7 @@ public class RequestAttributesUtil {
    * @return a list of distinct locales acceptable to the remote client and available in this JVM
    */
   public static List<Locale> getAvailableAcceptedLocales() {
-    return getAcceptableLanguages()
-        .map(languageRanges -> Locale.filter(languageRanges, AVAILABLE_LOCALES))
-        .orElseGet(Collections::emptyList);
+    return Locale.filter(getAcceptableLanguages(), AVAILABLE_LOCALES);
   }
 
   /**
@@ -46,16 +39,7 @@ public class RequestAttributesUtil {
    * @return the remote address of the remote client
    */
   public static InetAddress getRemoteAddress() {
-    return REMOTE_ADDRESS_CONTEXT_KEY.get();
-  }
-
-  /**
-   * Returns the parsed user-agent of the remote client in the current gRPC request context.
-   *
-   * @return the parsed user-agent of the remote client; may be empty if unparseable or not specified
-   */
-  public static Optional<UserAgent> getUserAgent() {
-    return Optional.ofNullable(USER_AGENT_CONTEXT_KEY.get());
+    return REQUEST_ATTRIBUTES_CONTEXT_KEY.get().remoteAddress();
   }
 
   /**
@@ -63,7 +47,7 @@ public class RequestAttributesUtil {
    *
    * @return the unparsed user-agent of the remote client; may be empty if not specified
    */
-  public static Optional<String> getRawUserAgent() {
-    return Optional.ofNullable(RAW_USER_AGENT_CONTEXT_KEY.get());
+  public static Optional<String> getUserAgent() {
+    return Optional.ofNullable(REQUEST_ATTRIBUTES_CONTEXT_KEY.get().userAgent());
   }
 }

service/src/main/java/org/whispersystems/textsecuregcm/grpc/ServerInterceptorUtil.java

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2025 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.whispersystems.textsecuregcm.grpc;
+
+import io.grpc.Metadata;
+import io.grpc.ServerCall;
+import io.grpc.Status;
+
+public class ServerInterceptorUtil {
+
+  @SuppressWarnings("rawtypes")
+  private static final ServerCall.Listener NO_OP_LISTENER = new ServerCall.Listener<>() {};
+
+  private static final Metadata EMPTY_TRAILERS = new Metadata();
+
+  private ServerInterceptorUtil() {
+  }
+
+  /**
+   * Closes the given server call with the given status, returning a no-op listener.
+   *
+   * @param call the server call to close
+   * @param status the status with which to close the call
+   *
+   * @return a no-op server call listener
+   *
+   * @param <ReqT> the type of request object handled by the server call
+   * @param <RespT> the type of response object returned by the server call
+   */
+  public static <ReqT, RespT> ServerCall.Listener<ReqT> closeWithStatus(final ServerCall<ReqT, RespT> call, final Status status) {
+    call.close(status, EMPTY_TRAILERS);
+
+    //noinspection unchecked
+    return NO_OP_LISTENER;
+  }
+}

service/src/main/java/org/whispersystems/textsecuregcm/grpc/net/EstablishLocalGrpcConnectionHandler.java

@@ -12,8 +12,10 @@ import io.netty.handler.codec.http.websocketx.WebSocketCloseStatus;
 import io.netty.util.ReferenceCountUtil;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Optional;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
+import org.whispersystems.textsecuregcm.auth.grpc.AuthenticatedDevice;
 
 /**
  * An "establish local connection" handler waits for a Noise handshake to complete upstream in the pipeline, buffering
@@ -48,12 +50,12 @@ class EstablishLocalGrpcConnectionHandler extends ChannelInboundHandlerAdapter {
 
   @Override
   public void userEventTriggered(final ChannelHandlerContext remoteChannelContext, final Object event) {
-    if (event instanceof NoiseIdentityDeterminedEvent noiseIdentityDeterminedEvent) {
+    if (event instanceof NoiseIdentityDeterminedEvent(final Optional<AuthenticatedDevice> authenticatedDevice)) {
       // We assume that we'll only get a completed handshake event if the handshake met all authentication requirements
       // for the requested service. If the handshake doesn't have an authenticated device, we assume we're trying to
       // connect to the anonymous service. If it does have an authenticated device, we assume we're aiming for the
       // authenticated service.
-      final LocalAddress grpcServerAddress = noiseIdentityDeterminedEvent.authenticatedDevice().isPresent()
+      final LocalAddress grpcServerAddress = authenticatedDevice.isPresent()
           ? authenticatedGrpcServerAddress
           : anonymousGrpcServerAddress;
 
@@ -72,7 +74,7 @@ class EstablishLocalGrpcConnectionHandler extends ChannelInboundHandlerAdapter {
             if (localChannelFuture.isSuccess()) {
               grpcClientConnectionManager.handleConnectionEstablished((LocalChannel) localChannelFuture.channel(),
                   remoteChannelContext.channel(),
-                  noiseIdentityDeterminedEvent.authenticatedDevice());
+                  authenticatedDevice);
 
               // Close the local connection if the remote channel closes and vice versa
               remoteChannelContext.channel().closeFuture().addListener(closeFuture -> localChannelFuture.channel().close());

service/src/main/java/org/whispersystems/textsecuregcm/grpc/net/GrpcClientConnectionManager.java

@@ -1,6 +1,8 @@
 package org.whispersystems.textsecuregcm.grpc.net;
 
 import com.google.common.annotations.VisibleForTesting;
+import io.grpc.Grpc;
+import io.grpc.ServerCall;
 import io.netty.channel.Channel;
 import io.netty.channel.ChannelFutureListener;
 import io.netty.channel.local.LocalAddress;
@@ -23,15 +25,25 @@ import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.whispersystems.textsecuregcm.auth.DisconnectionRequestListener;
 import org.whispersystems.textsecuregcm.auth.grpc.AuthenticatedDevice;
-import org.whispersystems.textsecuregcm.util.ua.UnrecognizedUserAgentException;
-import org.whispersystems.textsecuregcm.util.ua.UserAgent;
-import org.whispersystems.textsecuregcm.util.ua.UserAgentUtil;
+import org.whispersystems.textsecuregcm.grpc.ChannelNotFoundException;
+import org.whispersystems.textsecuregcm.grpc.RequestAttributes;
 
 /**
  * A client connection manager associates a local connection to a local gRPC server with a remote connection through a
- * Noise-over-WebSocket tunnel. It provides access to metadata associated with the remote connection, including the
- * authenticated identity of the device that opened the connection (for non-anonymous connections). It can also close
- * connections associated with a given device if that device's credentials have changed and clients must reauthenticate.
+ * Noise tunnel. It provides access to metadata associated with the remote connection, including the authenticated
+ * identity of the device that opened the connection (for non-anonymous connections). It can also close connections
+ * associated with a given device if that device's credentials have changed and clients must reauthenticate.
+ * <p>
+ * In general, all {@link ServerCall}s <em>must</em> have a local address that in turn <em>should</em> be resolvable to
+ * a remote channel, which <em>must</em> have associated request attributes and authentication status. It is possible
+ * that a server call's local address may not be resolvable to a remote channel if the remote channel closed in the
+ * narrow window between a server call being created and the start of call execution, in which case accessor methods
+ * in this class will throw a {@link ChannelNotFoundException}.
+ * <p>
+ * A gRPC client connection manager's methods for getting request attributes accept {@link ServerCall} entities to
+ * identify connections. In general, these methods should only be called from {@link io.grpc.ServerInterceptor}s.
+ * Methods for requesting connection closure accept an {@link AuthenticatedDevice} to identify the connection and may
+ * be called from any application code.
  */
 public class GrpcClientConnectionManager implements DisconnectionRequestListener {
 
@@ -43,94 +55,56 @@ public class GrpcClientConnectionManager implements DisconnectionRequestListener
       AttributeKey.valueOf(GrpcClientConnectionManager.class, "authenticatedDevice");
 
   @VisibleForTesting
-  static final AttributeKey<InetAddress> REMOTE_ADDRESS_ATTRIBUTE_KEY =
-      AttributeKey.valueOf(WebsocketHandshakeCompleteHandler.class, "remoteAddress");
-
-  @VisibleForTesting
-  static final AttributeKey<String> RAW_USER_AGENT_ATTRIBUTE_KEY =
-      AttributeKey.valueOf(WebsocketHandshakeCompleteHandler.class, "rawUserAgent");
-
-  @VisibleForTesting
-  static final AttributeKey<UserAgent> PARSED_USER_AGENT_ATTRIBUTE_KEY =
-      AttributeKey.valueOf(WebsocketHandshakeCompleteHandler.class, "userAgent");
-
-  @VisibleForTesting
-  static final AttributeKey<List<Locale.LanguageRange>> ACCEPT_LANGUAGE_ATTRIBUTE_KEY =
-      AttributeKey.valueOf(WebsocketHandshakeCompleteHandler.class, "acceptLanguage");
+  public static final AttributeKey<RequestAttributes> REQUEST_ATTRIBUTES_KEY =
+      AttributeKey.valueOf(GrpcClientConnectionManager.class, "requestAttributes");
 
   private static final Logger log = LoggerFactory.getLogger(GrpcClientConnectionManager.class);
 
   /**
-   * Returns the authenticated device associated with the given local address, if any. An authenticated device is
-   * available if and only if the given local address maps to an active local connection and that connection is
-   * authenticated (i.e. not anonymous).
+   * Returns the authenticated device associated with the given server call, if any. If the connection is anonymous
+   * (i.e. unauthenticated), the returned value will be empty.
    *
-   * @param localAddress the local address for which to find an authenticated device
+   * @param serverCall the gRPC server call for which to find an authenticated device
    *
    * @return the authenticated device associated with the given local address, if any
+   *
+   * @throws ChannelNotFoundException if the server call is not associated with a known channel; in practice, this
+   * generally indicates that the channel has closed while request processing is still in progress
    */
-  public Optional<AuthenticatedDevice> getAuthenticatedDevice(final LocalAddress localAddress) {
-    return getAuthenticatedDevice(remoteChannelsByLocalAddress.get(localAddress));
+  public Optional<AuthenticatedDevice> getAuthenticatedDevice(final ServerCall<?, ?> serverCall)
+      throws ChannelNotFoundException {
+
+    return getAuthenticatedDevice(getRemoteChannel(serverCall));
   }
 
-  private Optional<AuthenticatedDevice> getAuthenticatedDevice(@Nullable final Channel remoteChannel) {
-    return Optional.ofNullable(remoteChannel)
-        .map(channel -> channel.attr(AUTHENTICATED_DEVICE_ATTRIBUTE_KEY).get());
+  @VisibleForTesting
+  Optional<AuthenticatedDevice> getAuthenticatedDevice(final Channel remoteChannel) {
+    return Optional.ofNullable(remoteChannel.attr(AUTHENTICATED_DEVICE_ATTRIBUTE_KEY).get());
   }
 
   /**
-   * Returns the parsed acceptable languages associated with the given local address, if any. Acceptable languages may
-   * be unavailable if the local connection associated with the given local address has already closed, if the client
-   * did not provide a list of acceptable languages, or the list provided by the client could not be parsed.
+   * Returns the request attributes associated with the given server call.
    *
-   * @param localAddress the local address for which to find acceptable languages
+   * @param serverCall the gRPC server call for which to retrieve request attributes
    *
-   * @return the acceptable languages associated with the given local address, if any
+   * @return the request attributes associated with the given server call
+   *
+   * @throws ChannelNotFoundException if the server call is not associated with a known channel; in practice, this
+   * generally indicates that the channel has closed while request processing is still in progress
    */
-  public Optional<List<Locale.LanguageRange>> getAcceptableLanguages(final LocalAddress localAddress) {
-    return Optional.ofNullable(remoteChannelsByLocalAddress.get(localAddress))
-        .map(remoteChannel -> remoteChannel.attr(ACCEPT_LANGUAGE_ATTRIBUTE_KEY).get());
+  public RequestAttributes getRequestAttributes(final ServerCall<?, ?> serverCall) throws ChannelNotFoundException {
+    return getRequestAttributes(getRemoteChannel(serverCall));
   }
 
-  /**
-   * Returns the remote address associated with the given local address, if any. A remote address may be unavailable if
-   * the local connection associated with the given local address has already closed.
-   *
-   * @param localAddress the local address for which to find a remote address
-   *
-   * @return the remote address associated with the given local address, if any
-   */
-  public Optional<InetAddress> getRemoteAddress(final LocalAddress localAddress) {
-    return Optional.ofNullable(remoteChannelsByLocalAddress.get(localAddress))
-        .map(remoteChannel -> remoteChannel.attr(REMOTE_ADDRESS_ATTRIBUTE_KEY).get());
-  }
+  @VisibleForTesting
+  RequestAttributes getRequestAttributes(final Channel remoteChannel) {
+    final RequestAttributes requestAttributes = remoteChannel.attr(REQUEST_ATTRIBUTES_KEY).get();
 
-  /**
-   * Returns the unparsed user agent provided by the client that opened the connection associated with the given local
-   * address. This method may return an empty value if no active local connection is associated with the given local
-   * address.
-   *
-   * @param localAddress the local address for which to find a User-Agent string
-   *
-   * @return the user agent string associated with the given local address
-   */
-  public Optional<String> getRawUserAgent(final LocalAddress localAddress) {
-    return Optional.ofNullable(remoteChannelsByLocalAddress.get(localAddress))
-        .map(remoteChannel -> remoteChannel.attr(RAW_USER_AGENT_ATTRIBUTE_KEY).get());
-  }
+    if (requestAttributes == null) {
+      throw new IllegalStateException("Channel does not have request attributes");
+    }
 
-  /**
-   * Returns the parsed user agent provided by the client that opened the connection associated with the given local
-   * address. This method may return an empty value if no active local connection is associated with the given local
-   * address or if the client's user-agent string was not recognized.
-   *
-   * @param localAddress the local address for which to find a User-Agent string
-   *
-   * @return the user agent associated with the given local address
-   */
-  public Optional<UserAgent> getUserAgent(final LocalAddress localAddress) {
-    return Optional.ofNullable(remoteChannelsByLocalAddress.get(localAddress))
-        .map(remoteChannel -> remoteChannel.attr(PARSED_USER_AGENT_ATTRIBUTE_KEY).get());
+    return requestAttributes;
   }
 
   /**
@@ -156,11 +130,32 @@ public class GrpcClientConnectionManager implements DisconnectionRequestListener
     return remoteChannelsByAuthenticatedDevice.get(authenticatedDevice);
   }
 
+  private Channel getRemoteChannel(final ServerCall<?, ?> serverCall) throws ChannelNotFoundException {
+    return getRemoteChannel(getLocalAddress(serverCall));
+  }
+
   @VisibleForTesting
-  Channel getRemoteChannelByLocalAddress(final LocalAddress localAddress) {
+  Channel getRemoteChannel(final LocalAddress localAddress) throws ChannelNotFoundException {
+    final Channel remoteChannel = remoteChannelsByLocalAddress.get(localAddress);
+
+    if (remoteChannel == null) {
+      throw new ChannelNotFoundException();
+    }
+
     return remoteChannelsByLocalAddress.get(localAddress);
   }
 
+  private static LocalAddress getLocalAddress(final ServerCall<?, ?> serverCall) {
+    // In this server, gRPC's "remote" channel is actually a local channel that proxies to a distinct Noise channel.
+    // The gRPC "remote" address is the "local address" for the proxy connection, and the local address uniquely maps to
+    // a proxied Noise channel.
+    if (!(serverCall.getAttributes().get(Grpc.TRANSPORT_ATTR_REMOTE_ADDR) instanceof LocalAddress localAddress)) {
+      throw new IllegalArgumentException("Unexpected channel type: " + serverCall.getAttributes().get(Grpc.TRANSPORT_ATTR_REMOTE_ADDR));
+    }
+
+    return localAddress;
+  }
+
   /**
    * Handles successful completion of a WebSocket handshake and associates attributes and headers from the handshake
    * request with the channel via which the handshake took place.
@@ -171,30 +166,23 @@ public class GrpcClientConnectionManager implements DisconnectionRequestListener
    * @param acceptLanguageHeader the value of the Accept-Language header provided in the handshake request; may be
    * {@code null}
    */
-  static void handleWebSocketHandshakeComplete(final Channel channel,
+  static void handleHandshakeComplete(final Channel channel,
       final InetAddress preferredRemoteAddress,
       @Nullable final String userAgentHeader,
       @Nullable final String acceptLanguageHeader) {
 
-    channel.attr(GrpcClientConnectionManager.REMOTE_ADDRESS_ATTRIBUTE_KEY).set(preferredRemoteAddress);
-
-    if (StringUtils.isNotBlank(userAgentHeader)) {
-      channel.attr(GrpcClientConnectionManager.RAW_USER_AGENT_ATTRIBUTE_KEY).set(userAgentHeader);
-
-      try {
-        channel.attr(GrpcClientConnectionManager.PARSED_USER_AGENT_ATTRIBUTE_KEY)
-            .set(UserAgentUtil.parseUserAgentString(userAgentHeader));
-      } catch (final UnrecognizedUserAgentException ignored) {
-      }
-    }
+    @Nullable List<Locale.LanguageRange> acceptLanguages = Collections.emptyList();
 
     if (StringUtils.isNotBlank(acceptLanguageHeader)) {
       try {
-        channel.attr(GrpcClientConnectionManager.ACCEPT_LANGUAGE_ATTRIBUTE_KEY).set(Locale.LanguageRange.parse(acceptLanguageHeader));
+        acceptLanguages = Locale.LanguageRange.parse(acceptLanguageHeader);
       } catch (final IllegalArgumentException e) {
         log.debug("Invalid Accept-Language header from User-Agent {}: {}", userAgentHeader, acceptLanguageHeader, e);
       }
     }
+
+    channel.attr(REQUEST_ATTRIBUTES_KEY)
+        .set(new RequestAttributes(preferredRemoteAddress, userAgentHeader, acceptLanguages));
   }
 
   /**

service/src/main/java/org/whispersystems/textsecuregcm/grpc/net/WebsocketHandshakeCompleteHandler.java

@@ -74,7 +74,7 @@ class WebsocketHandshakeCompleteHandler extends ChannelInboundHandlerAdapter {
         preferredRemoteAddress = maybePreferredRemoteAddress.get();
       }
 
-      GrpcClientConnectionManager.handleWebSocketHandshakeComplete(context.channel(),
+      GrpcClientConnectionManager.handleHandshakeComplete(context.channel(),
           preferredRemoteAddress,
           handshakeCompleteEvent.requestHeaders().getAsString(HttpHeaderNames.USER_AGENT),
           handshakeCompleteEvent.requestHeaders().getAsString(HttpHeaderNames.ACCEPT_LANGUAGE));