Chapter 127. 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>

127.1. URI format

grpc://service[?options]

127.2. 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:

127.2.1. Path Parameters (3 parameters):

NameDescriptionDefaultType

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

127.2.2. Query Parameters (25 parameters):

NameDescriptionDefaultType

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

127.3. 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.OptionParameterValueRequired/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.

127.4. 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 styleRequest typeResponse typeRequest Body TypeResult 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>

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

Header nameDescriptionPossible 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

 

127.6. 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");

127.7. 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>

127.8. For more information, see these resources

gRPC project site

Maven Protocol Buffers Plugin

127.9. See Also