Chapter 37. gRPC Since Camel 2.19 Both producer and consumer are supported The gRPC component allows you to call or expose Remote Procedure Call (RPC) services using Protocol Buffers (protobuf) exchange format over HTTP/2 transport. 37.1. Dependencies When using grpc with Red Hat build of Camel Spring Boot make sure to use the following Maven dependency to have support for auto configuration: <dependency> <groupId>org.apache.camel.springboot</groupId> <artifactId>camel-grpc-starter</artifactId> </dependency> 37.2. URI format 37.3. Configuring Options Camel components are configured on two separate levels: component level endpoint level 37.3.1. Configuring component options The component level is the highest level which holds general and common configurations that are inherited by the endpoints. For example a component may have security settings, credentials for authentication, urls for network connection and so forth. Some components only have a few options, and others may have many. Because components typically have pre configured defaults that are commonly used, then you may often only need to configure a few options on a component; or none at all. Configuring components can be done with the Component DSL , in a configuration file (application.properties|yaml), or directly with Java code. 37.3.2. Configuring endpoint options Where you find yourself configuring the most is on endpoints, as endpoints often have many options, which allows you to configure what you need the endpoint to do. The options are also categorized into whether the endpoint is used as consumer (from) or as a producer (to), or used for both. Configuring endpoints is most often done directly in the endpoint URI as path and query parameters. You can also use the Endpoint DSL and DataFormat DSL as a type safe way of configuring endpoints and data formats in Java. A good practice when configuring options is to use Property Placeholders , which allows to not hardcode urls, port numbers, sensitive information, and other settings. In other words placeholders allows to externalize the configuration from your code, and gives more flexibility and reuse. The following two sections lists all the options, firstly for the component followed by the endpoint. 37.4. Component Options The gRPC component supports 3 options, which are listed below. Name Description Default Type bridgeErrorHandler (consumer) Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions occurred while the consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. By default the consumer will use the org.apache.camel.spi.ExceptionHandler to deal with exceptions, that will be logged at WARN or ERROR level and ignored. false boolean lazyStartProducer (producer) Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel's routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing. false boolean autowiredEnabled (advanced) Whether autowiring is enabled. This is used for automatic autowiring options (the option must be marked as autowired) by looking up in the registry to find if there is a single instance of matching type, which then gets configured on the component. This can be used for automatic configuring JDBC data sources, JMS connection factories, AWS Clients, etc. true boolean 37.5. Endpoint Options The gRPC endpoint is configured using URI syntax: with the following path and query parameters: 37.5.1. Path Parameters (3 parameters) Name Description Default Type host (common) Required The gRPC server host name. This is localhost or 0.0.0.0 when being a consumer or remote server host name when using producer. String port (common) Required The gRPC local or remote server port. int service (common) Required Fully qualified service name from the protocol buffer descriptor file (package dot service definition name). String 37.5.2. Query Parameters (29 parameters) Name Description Default Type flowControlWindow (common) The HTTP/2 flow control window size (MiB). 1048576 int maxMessageSize (common) The maximum message size allowed to be received/sent (MiB). 4194304 int autoDiscoverServerInterceptors (consumer) Setting the autoDiscoverServerInterceptors mechanism, if true, the component will look for a ServerInterceptor instance in the registry automatically otherwise it will skip that checking. true boolean consumerStrategy (consumer) This option specifies the top-level strategy for processing service requests and responses in streaming mode. If an aggregation strategy is selected, all requests will be accumulated in the list, then transferred to the flow, and the accumulated responses will be sent to the sender. If a propagation strategy is selected, request is sent to the stream, and the response will be immediately sent back to the sender. Enum values: AGGREGATION PROPAGATION PROPAGATION GrpcConsumerStrategy forwardOnCompleted (consumer) Determines if onCompleted events should be pushed to the Camel route. false boolean forwardOnError (consumer) Determines if onError events should be pushed to the Camel route. Exceptions will be set as message body. false boolean maxConcurrentCallsPerConnection (consumer) The maximum number of concurrent calls permitted for each incoming server connection. 2147483647 int routeControlledStreamObserver (consumer) Lets the route to take control over stream observer. If this value is set to true, then the response observer of gRPC call will be set with the name GrpcConstants.GRPC_RESPONSE_OBSERVER in the Exchange object. Please note that the stream observer's onNext(), onError(), onCompleted() methods should be called in the route. false boolean bridgeErrorHandler (consumer (advanced)) Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions occurred while the consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. By default the consumer will use the org.apache.camel.spi.ExceptionHandler to deal with exceptions, that will be logged at WARN or ERROR level and ignored. false boolean exceptionHandler (consumer (advanced)) To let the consumer use a custom ExceptionHandler. Notice if the option bridgeErrorHandler is enabled then this option is not in use. By default the consumer will deal with exceptions, that will be logged at WARN or ERROR level and ignored. ExceptionHandler exchangePattern (consumer (advanced)) Sets the exchange pattern when the consumer creates an exchange. Enum values: InOnly InOut ExchangePattern autoDiscoverClientInterceptors (producer) Setting the autoDiscoverClientInterceptors mechanism, if true, the component will look for a ClientInterceptor instance in the registry automatically otherwise it will skip that checking. true boolean method (producer) gRPC method name. String producerStrategy (producer) The mode used to communicate with a remote gRPC server. In SIMPLE mode a single exchange is translated into a remote procedure call. In STREAMING mode all exchanges will be sent within the same request (input and output of the recipient gRPC service must be of type 'stream'). Enum values: SIMPLE STREAMING SIMPLE GrpcProducerStrategy streamRepliesTo (producer) When using STREAMING client mode, it indicates the endpoint where responses should be forwarded. String userAgent (producer) The user agent header passed to the server. String lazyStartProducer (producer (advanced)) Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel's routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing. false boolean synchronous (advanced) Sets whether synchronous processing should be strictly used. false boolean authenticationType (security) Authentication method type in advance to the SSL/TLS negotiation. Enum values: NONE GOOGLE JWT NONE GrpcAuthType jwtAlgorithm (security) JSON Web Token sign algorithm. Enum values: HMAC256 HMAC384 HMAC512 HMAC256 JwtAlgorithm jwtIssuer (security) JSON Web Token issuer. String jwtSecret (security) JSON Web Token secret. String jwtSubject (security) JSON Web Token subject. String keyCertChainResource (security) The X.509 certificate chain file resource in PEM format link. String keyPassword (security) The PKCS#8 private key file password. String keyResource (security) The PKCS#8 private key file resource in PEM format link. String negotiationType (security) Identifies the security negotiation type used for HTTP/2 communication. Enum values: TLS PLAINTEXT_UPGRADE PLAINTEXT PLAINTEXT NegotiationType serviceAccountResource (security) Service Account key file in JSON format resource link supported by the Google Cloud SDK. String trustCertCollectionResource (security) The trusted certificates collection file resource in PEM format for verifying the remote endpoint's certificate. String 37.6. Message Headers The gRPC component supports 3 message header(s), which is/are listed below: Name Description Default Type CamelGrpcMethodName (consumer) Constant: GRPC_METHOD_NAME_HEADER Method name handled by the consumer service. String CamelGrpcUserAgent (consumer) Constant: GRPC_USER_AGENT_HEADER If provided, the given agent will prepend the gRPC library's user agent information. String CamelGrpcEventType (consumer) Constant: GRPC_EVENT_TYPE_HEADER Received event type from the sent request. Possible values: onNext onCompleted onError. String 37.7. Transport security and authentication support The following authentication mechanisms are built-in to gRPC and available in this component: SSL/TLS: gRPC has SSL/TLS integration and promotes the use of SSL/TLS to authenticate the server, and to encrypt all the data exchanged between the client and the server. Optional mechanisms are available for clients to provide certificates for mutual authentication. Token-based authentication with Google: gRPC provides a generic mechanism to attach metadata based credentials to requests and responses. Additional support for acquiring access tokens while accessing Google APIs through gRPC is provided. In general this mechanism must be used as well as SSL/TLS on the channel. To enable these features the following component properties combinations must be configured: Num. Option Parameter Value Required/Optional 1 SSL/TLS negotiationType TLS Required keyCertChainResource Required keyResource Required keyPassword Optional trustCertCollectionResource Optional 2 Token-based authentication with Google API authenticationType GOOGLE Required negotiationType TLS Required serviceAccountResource Required 3 Custom JSON Web Token implementation authentication authenticationType JWT Required negotiationType NONE or TLS Optional. The TLS/SSL not checking for this type, but strongly recommended. jwtAlgorithm HMAC256(default) or (HMAC384,HMAC512) Optional jwtSecret Required jwtIssuer Optional jwtSubject Optional 37.8. gRPC producer resource type mapping The table below shows the types of objects in the message body, depending on the types (simple or stream) of incoming and outgoing parameters, as well as the invocation style (synchronous or asynchronous). Please note, that invocation of the procedures with incoming stream parameter in asynchronous style are not allowed. Invocation style Request type Response type Request Body Type Result Body Type synchronous simple simple Object Object synchronous simple stream Object List<Object> synchronous stream simple not allowed not allowed synchronous stream stream not allowed not allowed asynchronous simple simple Object List<Object> asynchronous simple stream Object List<Object> asynchronous stream simple Object or List<Object> List<Object> asynchronous stream stream Object or List<Object> List<Object> 37.9. Examples Below is a simple synchronous method invoke with host and port parameters: from("direct:grpc-sync") .to("grpc://remotehost:1101/org.apache.camel.component.grpc.PingPong?method=sendPing&synchronous=true"); <route> <from uri="direct:grpc-sync" /> <to uri="grpc://remotehost:1101/org.apache.camel.component.grpc.PingPong?method=sendPing&synchronous=true"/> </route> An asynchronous method invokes from("direct:grpc-async") .to("grpc://remotehost:1101/org.apache.camel.component.grpc.PingPong?method=pingAsyncResponse"); a gRPC service consumer with propagation consumer strategy: from("grpc://localhost:1101/org.apache.camel.component.grpc.PingPong?consumerStrategy=PROPAGATION") .to("direct:grpc-service"); gRPC service producer with streaming producer strategy (requires a service that uses "stream" mode as input and output): from("direct:grpc-request-stream") .to("grpc://remotehost:1101/org.apache.camel.component.grpc.PingPong?method=PingAsyncAsync&producerStrategy=STREAMING&streamRepliesTo=direct:grpc-response-stream"); from("direct:grpc-response-stream") .log("Response received: USD{body}"); gRPC service consumer TLS/SSL security negotiation enabled: from("grpc://localhost:1101/org.apache.camel.component.grpc.PingPong?consumerStrategy=PROPAGATION&negotiationType=TLS&keyCertChainResource=file:src/test/resources/certs/server.pem&keyResource=file:src/test/resources/certs/server.key&trustCertCollectionResource=file:src/test/resources/certs/ca.pem") .to("direct:tls-enable") gRPC service producer with custom JSON Web Token (JWT) implementation authentication: from("direct:grpc-jwt") .to("grpc://localhost:1101/org.apache.camel.component.grpc.PingPong?method=pingSyncSync&synchronous=true&authenticationType=JWT&jwtSecret=supersecuredsecret"); 37.10. Configuration Use the protobuf-maven-plugin , which calls the Protocol Buffer Compiler (protoc) to generate Java source files from .proto (protocol buffer definition) files. This plugin will generate procedures request and response classes, their builders and gRPC procedures stubs classes as well. Following steps are required: Insert operating system and CPU architecture detection extension inside <build> tag of the project pom.xml or set USD\{os.detected.classifier} parameter manually <extensions> <extension> <groupId>kr.motd.maven</groupId> <artifactId>os-maven-plugin</artifactId> <version>1.7.1</version> </extension> </extensions> Insert the gRPC and protobuf Java code generator plugins into the <plugins> tag of the project's pom.xml . <plugin> <groupId>org.xolstice.maven.plugins</groupId> <artifactId>protobuf-maven-plugin</artifactId> <version>0.6.1</version> <configuration> <protocArtifact>com.google.protobuf:protoc:USD{protobuf-version}:exe:USD{os.detected.classifier}</protocArtifact> <pluginId>grpc-java</pluginId> <pluginArtifact>io.grpc:protoc-gen-grpc-java:USD{grpc-version}:exe:USD{os.detected.classifier}</pluginArtifact> </configuration> <executions> <execution> <goals> <goal>compile</goal> <goal>compile-custom</goal> <goal>test-compile</goal> <goal>test-compile-custom</goal> </goals> </execution> </executions> </plugin> 37.11. Additional resources See these resources: gRPC project site Maven Protocol Buffers Plugin 37.12. Spring Boot Auto-Configuration The component supports 4 options, which are listed below. Name Description Default Type camel.component.grpc.autowired-enabled Whether autowiring is enabled. This is used for automatic autowiring options (the option must be marked as autowired) by looking up in the registry to find if there is a single instance of matching type, which then gets configured on the component. This can be used for automatic configuring JDBC data sources, JMS connection factories, AWS Clients, etc. true Boolean camel.component.grpc.bridge-error-handler Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions occurred while the consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. By default the consumer will use the org.apache.camel.spi.ExceptionHandler to deal with exceptions, that will be logged at WARN or ERROR level and ignored. false Boolean camel.component.grpc.enabled Whether to enable auto configuration of the grpc component. This is enabled by default. Boolean camel.component.grpc.lazy-start-producer Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel's routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing. false Boolean

Commands:
<dependency> <groupId>org.apache.camel.springboot</groupId> <artifactId>camel-grpc-starter</artifactId> </dependency>
grpc:host:port/service[?options]
grpc:host:port/service
from("direct:grpc-sync") .to("grpc://remotehost:1101/org.apache.camel.component.grpc.PingPong?method=sendPing&synchronous=true");
<route> <from uri="direct:grpc-sync" /> <to uri="grpc://remotehost:1101/org.apache.camel.component.grpc.PingPong?method=sendPing&synchronous=true"/> </route>
from("direct:grpc-async") .to("grpc://remotehost:1101/org.apache.camel.component.grpc.PingPong?method=pingAsyncResponse");
from("grpc://localhost:1101/org.apache.camel.component.grpc.PingPong?consumerStrategy=PROPAGATION") .to("direct:grpc-service");
from("direct:grpc-request-stream") .to("grpc://remotehost:1101/org.apache.camel.component.grpc.PingPong?method=PingAsyncAsync&producerStrategy=STREAMING&streamRepliesTo=direct:grpc-response-stream"); from("direct:grpc-response-stream") .log("Response received: USD{body}");
from("grpc://localhost:1101/org.apache.camel.component.grpc.PingPong?consumerStrategy=PROPAGATION&negotiationType=TLS&keyCertChainResource=file:src/test/resources/certs/server.pem&keyResource=file:src/test/resources/certs/server.key&trustCertCollectionResource=file:src/test/resources/certs/ca.pem") .to("direct:tls-enable")
from("direct:grpc-jwt") .to("grpc://localhost:1101/org.apache.camel.component.grpc.PingPong?method=pingSyncSync&synchronous=true&authenticationType=JWT&jwtSecret=supersecuredsecret");
<extensions> <extension> <groupId>kr.motd.maven</groupId> <artifactId>os-maven-plugin</artifactId> <version>1.7.1</version> </extension> </extensions>
<plugin> <groupId>org.xolstice.maven.plugins</groupId> <artifactId>protobuf-maven-plugin</artifactId> <version>0.6.1</version> <configuration> <protocArtifact>com.google.protobuf:protoc:USD{protobuf-version}:exe:USD{os.detected.classifier}</protocArtifact> <pluginId>grpc-java</pluginId> <pluginArtifact>io.grpc:protoc-gen-grpc-java:USD{grpc-version}:exe:USD{os.detected.classifier}</pluginArtifact> </configuration> <executions> <execution> <goals> <goal>compile</goal> <goal>compile-custom</goal> <goal>test-compile</goal> <goal>test-compile-custom</goal> </goals> </execution> </executions> </plugin>