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Modern frameworks such as gRPC and Apache Thrift provide a very [1] provide flexible API for implementing request interceptors, with which you can solve almost any middleware task.
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ServiceCallContext - immutable map of custom parameters to user parameter map that can be implicitly passed to the service (and interceptor) on every method call.
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public interface ServiceCallContext { public String attribute(String name); public byte[] binaryAttribute(String name); } |
ServiceCallInterceptor - intercepts service method calls.
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public interface ServiceCallInterceptor extends Serializable { public/** default void onInvoke(ServiceInterceptorContext ctx) throws* ServiceInterceptExceptionIntercepts { a call to a // No-opservice method. }* public default* void@param onComplete(@Nullablemtd Object res, ServiceInterceptorContext ctx) throws ServiceInterceptException {Method name. * @param args // No-opMethod arguments. } * @param ctx public default void onError(Throwable err, ServiceInterceptorContext ctx) {Service context. * @param call // No-opDelegated call. } } |
ServiceInterceptorContext - extended mutable version of caller context (interceptor obtains method call parameters from it and can use it to update the caller context).
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public interface ServiceInterceptorContext extends ServiceCallContext { public String method(); * @return Service method call result. */ public @Nullable Object[] arguments(); public void attribute(String name, String val); public void binaryAttribute(String name, byte[] val); } |
invoke(String mtd, Object[] args, ServiceContext ctx, Callable<Object> call) throws Exception;
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ServiceCallInterceptor security = new ServiceCallInterceptor() { @Override public void onInvoke(ServiceInterceptorContext ctx) throws ServiceInterceptException { mtd, args, ctx, svcCall) -> { // Check permission before execution of the method. if (!CustomSecurityProvider.get().access(mtd, ctx.methodcurrentCallContext(), ctx.attribute("sessionId"))) throw new SecurityException("Method invocation is not permitted"); // Execute remaining interceptors and service }method. } return svcCall.call(); }; ServiceCallInterceptor audit = new ServiceCallInterceptor() { mtd, args, ctx, svcCall) -> { @OverrideString publicsessionId void onInvoke(ServiceInterceptorContext ctx) { = ctx.currentCallContext().attribute("sessionId"); AuditProvider prov = AuditProvider.get(); // Record an event before execution of the method. AuditProvider.get().prov.recordStartEvent(ctx.methodname(), mtd, ctx.attribute("sessionId")); try }{ @Override// publicExecute void onComplete(@Nullable Object res, ServiceInterceptorContext ctx) {service method. AuditProvider.get().recordFinishEvent(ctx.method(), ctx.attribute("sessionId"))svcCall.call(); } } catch (Exception e) { @Override public void onError(Throwable err, ServiceInterceptorContext ctx) { // Record error. AuditProvider.get()prov.recordError(ctx.methodname(), mtd, ctx.attribute("sessionId"), erre.getMessage()); // Re-throw exception to }initiator. throw e; } finally { // Set context parameters for Record finish event after execution of the service proxymethod. ServiceCallContext ctx = ServiceCallContextprov.builderrecordFinishEvent()ctx.put("sessionId"name(), mtd, sessionId).build(); } } ServiceConfiguration svcCfg = new ServiceConfiguration() .setName("service") .setService(new MyServiceImpl()) .setMaxPerNodeCount(1) .setInterceptors(security, audit); // Deploy service. ignite.services().deploy(svcCfg); // Deploy Set context parameters for the service proxy. ServiceCallContext callCtx ignite.services().deploy(svcCfg= ServiceCallContext.builder().put("sessionId", sessionId).build(); // Make service proxy. MyService proxy = ignite.services().serviceProxy("service", MyService.class, false, ctxcallCtx, 0); // A business method call to be intercepted. proxy.placeOrder(order1); proxy.placeOrder(order2); |
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Interceptor can modify ServiceCallContext, but Service methods can only read it.
If an interceptor has been specified, but the user has not passed the caller context through the proxy, it will be created dynamically.
One service can have several interceptors. They are defined using the service configuration and deployed with the service.
To add/remove interceptor service should be redeployed.
Interceptor is located and executed where the service is implemented (for Java service - on Java side, for .NET-service on .NET side without any ). Its execution should not cause additional serialization).
To add/remove interceptor - service should be redeployed.
Interceptor must support ignite instance resource injection.
Interceptor should be LifeCycleAware
// todo ServiceInterceptException
If an interceptor throws an exception, then processing is aborted, but the exception is passed to all listed interceptors (onError)
// todo explain forwardCallerContext
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The user can specify multiple interceptors.Each interceptor invokes the next interceptor in the chain using a delegated call, the last interceptor will call the service method.
So the interceptor specified first in the configuration will process the result of the service method execution last.
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Interceptor must support the injection of generic resources.
Interceptor does not apply to service lifecycle methods - init, execute andcancel,
The user can create context (map with custom parameters) and bind it to the service proxy. After that, each call to the proxy method will also implicitly pass context parameters to the service.
Service method can read current context parameters using ServiceContext#currentCallContext method. It is only accessible from the current thread during the execution of a service method.
If one service calls another, then by default the current call context will not be bound to the created proxy - the user must explicitly bind it. But Java service has a special ServiceResource annotation to inject another service proxy into the current service. If the user wants to redirect the current call context to this (injected) proxy, he can set the forwardCallerContext option of this annotation.
Exception thrown by the interceptor will be wrapped into unchecked IgniteException and passed to the initiator.
The interceptor gives the user full control over the invocation of the service methods, so in case of implementation errors, the user may get unexpected behavior of the service.
[1] https://pkg.go.dev/github.com/grpc-ecosystem/go-grpc-middleware
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