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Chapter 120. gRPC Component

Available as of Camel version 2.19

The gRPC component allows you to call or expose Remote Procedure Call (RPC) services using Protocol Buffers (protobuf) exchange format over HTTP/2 transport.

Maven users will need to add the following dependency to their pom.xml for this component:

<dependency>
    <groupId>org.apache.camel</groupId>
    <artifactId>camel-grpc</artifactId>
    <version>x.x.x</version>
    <!-- use the same version as your Camel core version -->
</dependency>

120.1. URI format

grpc://service[?options]

120.2. Endpoint Options

The gRPC component has no options.

The gRPC endpoint is configured using URI syntax:

grpc:host:port/service

with the following path and query parameters:

120.2.1. Path Parameters (3 parameters):

Name	Description	Type
host	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	Required The gRPC local or remote server port	int
service	Required Fully qualified service name from the protocol buffer descriptor file (package dot service definition name)	String

120.2.2. Query Parameters (25 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
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
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.	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
maxConcurrentCallsPer Connection (consumer)	The maximum number of concurrent calls permitted for each incoming server connection	2147483647	int
exceptionHandler (consumer)	To let the consumer use a custom ExceptionHandler. Notice if the option bridgeErrorHandler is enabled then this options 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)	Sets the exchange pattern when the consumer creates an exchange.		ExchangePattern
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').	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
synchronous (advanced)	Sets whether synchronous processing should be strictly used, or Camel is allowed to use asynchronous processing (if supported).	false	boolean
authenticationType (security)	Authentication method type in advance to the SSL/TLS negotiation	NONE	GrpcAuthType
jwtAlgorithm (security)	JSON Web Token sign algorithm	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 PKCS8 private key file password		String
keyResource (security)	The PKCS8 private key file resource in PEM format link		String
negotiationType (security)	Identifies the security negotiation type used for HTTP/2 communication	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

120.3. Transport security and authentication support (available from Camel 2.20)

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

TLS with OpenSSL is currently the recommended approach for using gRPC over TLS component. Using the JDK for ALPN is generally much slower and may not support the necessary ciphers for HTTP2. This function is not implemented in the component.

120.4. 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>

120.5. gRPC consumer headers (will be installed after the consumer invocation)

Header name	Description	Possible values
CamelGrpcMethodName	Method name handled by the consumer service
CamelGrpcEventType	Received event type from the sent request	onNext, onCompleted or onError
CamelGrpcUserAgent	If provided, the given agent will prepend the gRPC library’s user agent information

120.6. 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 invoke

from("direct:grpc-async")
.to("grpc://remotehost:1101/org.apache.camel.component.grpc.PingPong?method=pingAsyncResponse");

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: ${body}");

gRPC service consumer TLS/SLL security negotiation enable

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 implementation authentication

from("direct:grpc-jwt")
.to("grpc://localhost:1101/org.apache.camel.component.grpc.PingPong?method=pingSyncSync&synchronous=true&authenticationType=JWT&jwtSecret=supersecuredsecret");

120.7. Configuration

It’s it is recommended to use Maven Protocol Buffers Plugin which calls Protocol Buffer Compiler (protoc) tool to generate Java source files from .proto (protocol buffer definition) files for the custom project. 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 ${os.detected.classifier} parameter manually

<extensions>
  <extension>
    <groupId>kr.motd.maven</groupId>
    <artifactId>os-maven-plugin</artifactId>
    <version>1.4.1.Final</version>
  </extension>
</extensions>

Insert gRPC and protobuf Java code generator plugin <plugins> tag of the project pom.xml

<plugin>
  <groupId>org.xolstice.maven.plugins</groupId>
  <artifactId>protobuf-maven-plugin</artifactId>
  <version>0.5.0</version>
  <configuration>
    <protocArtifact>com.google.protobuf:protoc:${protobuf-version}:exe:${os.detected.classifier}</protocArtifact>
    <pluginId>grpc-java</pluginId>
    <pluginArtifact>io.grpc:protoc-gen-grpc-java:${grpc-version}:exe:${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>

120.8. For more information, see these resources

gRPC project site

Maven Protocol Buffers Plugin

120.9. See Also

Getting Started
Configuring Camel
Component
Endpoint
Protocol Buffers Data Format