I'm working on a Spring Boot (2.2) project using Kotlin, with CouchDB as (reactive) database, and in consequence, async DAO (either suspend functions, or functions returning a Flow). I'm trying to setup WebFlux in order to have async controllers too (again, I want to return Flows, not Flux). But I'm having troubles retrieving my security context from ReactiveSecurityContextHolder.
From what I've read, unlike SecurityContextHolder which is using ThreadLocal to store it, ReactiveSecurityContextHolder relies on the fact that Spring, while making a subscription to my reactive chain, also stored that context inside this chain, thus allowing me to call ReactiveSecurityContextHolder.getContext() from within the chain.
The problem is that I have to transform my Mono<SecurityContext> into a Flow at some point, which makes me loose my SecurityContext. So my question is: is there a way to have a Spring Boot controller returning a Flow while retrieving the security context from ReactiveSecurityContextHolder inside my logic? Basically, after simplification, it should look like this:
#GetMapping
fun getArticles(): Flow<String> {
return ReactiveSecurityContextHolder.getContext().flux().asFlow() // returns nothing
}
Note that if I return the Flux directly (skipping the .asFlow()), or add a .single() or .toList() in the end (hence using a suspend fun), then it works fine and my security context is returned, but again that's not what I want. I guess the solution would be to transfer the context from the Flux (initial reactive chain from ReactiveSecurityContextHolder) to the Flow, but it doesn't seem to be done by default.
Edit: here is a sample project showcasing the problem: https://github.com/Simon3/webflux-kotlin-sample
What you really try to achieve is accessing your ReactorContext from inside a Flow.
One way to do this is to relax the need for returning a Flow and return a Flux instead. This allows you to recover the ReactorContext and pass it to the Flow you are going to use to generate your data.
#ExperimentalCoroutinesApi
#GetMapping("/flow")
fun flow(): Flux<Map<String, String>> = Mono.subscriberContext().flatMapMany { reactorCtx ->
flow {
val ctx = coroutineContext[ReactorContext.Key]?.context?.get<Mono<SecurityContext>>(SecurityContext::class.java)?.asFlow()?.single()
emit(mapOf("user" to ((ctx?.authentication?.principal as? User)?.username ?: "<NONE>")))
}.flowOn(reactorCtx.asCoroutineContext()).asFlux()
}
In the case when you need to access the ReactorContext from a suspend method, you can simply get it back from the coroutineContext with no further artifice:
#ExperimentalCoroutinesApi
#GetMapping("/suspend")
suspend fun suspend(): Map<String,String> {
val ctx = coroutineContext[ReactorContext.Key]?.context?.get<Mono<SecurityContext>>(SecurityContext::class.java)?.asFlow()?.single()
return mapOf("user" to ((ctx?.authentication?.principal as? User)?.username ?: "<NONE>"))
}
Related
I have a Spring Boot web application that takes a string as a GET request. The application then generates a list of text from the keyword in their own thread then returns a CompletableFuture.
Some threads may take 30 seconds to complete, other maybe less than a second.
Is it possible for the controller to return the result of each thread as they get completed to the calling client?
Yes, you can return CompletableFuture<> or a List<CompletableFuture<>> as they are finished.
Spring delivers a starter project 'org.springframework.boot:spring-boot-starter-webflux' that allows you to write non-blocking, reactive controllers.
So, provided that you have a list of CompletableFuture<> as the result of texts generations, your controller should look like this:
#GetMapping(path = "/test")
public Flux<String> getListReactively2(#RequestParam String keyword) {
List<CompletableFuture<String>> completableFutures = getCompletableFutures(keyword);
List<Mono<String>> monos = completableFutures.stream().map(Mono::fromFuture).toList();
return Flux.fromIterable(monos).flatMap(Function.identity());
}
The List of CompletableFuture<> is mapped to Flux<String which is the spring-webflux type that represents a Stream of objects that will be returned as the objects are delivered in the stream.
For more information, refer to spring webflux documentation https://docs.spring.io/spring-framework/docs/current/reference/html/web-reactive.html
I'm using kotlin exposed and spring acl: JdbcMutableAclService.
The dummy code looks like:
transaction {
//operation 1
dao.updateSomething(resourceId)
val sids = dao.getUserIdsByResourceId(resourceId)
//operation 2
val pObjectIdentity = ObjectIdentityImpl(PROJECT, resourceId)
val pMutableAcl = aclService.readAclById(pObjectIdentity) as MutableAcl
var i = pMutableAcl.entries.size
sids.forEach {
pMutableAcl.insertAce(i++, BasePermission.READ, PrincipalSid(it), true)
}
aclService.updateAcl(pMutableAcl)
//operation 3
val rObjectIdentity = ObjectIdentityImpl(RESOURCE, resourceId)
val rMutableAcl = aclService.readAclById(rObjectIdentity) as MutableAcl
var i = rMutableAcl.entries.size
sids.forEach {
rMutableAcl.insertAce(i++, BasePermission.READ, PrincipalSid(it), true)
}
aclService.updateAcl(rMutableAcl)
}
If something happens in operation 3 - it won't write nothing to db, the outer transaction will also rolled back, and operation 1 won't be committed as well.
Unfortunately operation 2 won't be rolled back.
So my assumption every time of using updateAcl it creates its own isolated transaction.
I don't know how it work in case of Spring Jpa, and #Transactional annotation (is JdbcMutableAclService take into consideration outer transaction or not), but in case of Exposed it is not.
Is it correct behaviour at all? Should every acl update be an isolated transaction?
Is there a way to integrate Exposed and JdbcMutableAclService without implementing my own MutableAclService?
UPD for #Tapac
I'm using org.jetbrains.exposed:exposed-spring-boot-starter without any additional configuration, so based on ExposedAutoConfiguration it is org.jetbrains.exposed.spring.SpringTransactionManager.
But during the debugging i saw in stacktrace some refs to ThreadLocalTransactionManager.
And don't know is it useful information, but i don't use spring transaction annotation and instead of that i use exposed transaction{} block.
I'm having some trouble wrapping my head around a supposedly simple RESTful WS response handling scenario when using Spring WebFlux in combination with Kotlin coroutines. Suppose we have a simple WS method in our REST controller that is supposed to return a possibly huge number (millions) of response "things":
#GetMapping
suspend fun findAllThings(): Flow<Thing> {
//Reactive DB query, return a flow of things
}
This works as one would expect: the result is streamed to the client as long as a streaming media type (e.g. "application/x-ndjson") is used. In more complex service calls that also accounts for the possibility of errors/warnings I would like to return a response object of the following form:
class Response<T> {
val errors: Flow<String>
val things: Flow<T>
}
The idea here being that a response either is successful (returning an empty error Flow and a Flow of things), or failed (errors contained in the corresponding Flow while the things Flow being empty). In blocking programming this is a quite common response idiom. My question now is how can I adapt this idiom to the reactive approach in Kotlin/Spring WebFlux?
I know its possible to just return the Response as described (or Mono<Response> for Java users), but this somewhat defeats the purpose of being reactive as the entire Mono has to exist in memory at serialization time. Is there any way to solve this? The only possible solution I can think of right now is a custom Spring Encoder that is smart enough to stream both errors or things (whatever is present).
How about returning Success/Error per Thing?
class Result<T> private constructor(val result: T?, val error: String?) {
constructor(data: T) : this(data, null)
constructor(error: String) : this(null, error)
val isError = error != null
}
#GetMapping
suspend fun findAllThings(): Flow<Result<Thing>> {
//Reactive DB query, return a flow of things
}
I have an endpoint that accepts as well as returns a reactive type. What I'm trying to achieve is to somehow verify that the complete reactive request (that is actually an array of resources) is valid before persisting the changes to the database (read Full-Update of a ressource). The question is not so much concerned with how to actually verify the request but more with how to chain the steps together using which of springs reactive handler methods (map, flatMap and the likes) in the desired order which is basically:
verify correctness of request (the Ressource is properly annotated with JSR-303 annotations)
clear the current resource in case of valid request
persist new resources in the database after clearing the database
Let's assume the following scenario:
val service : ResourceService
#PostMapping("/resource/")
fun replaceResources(#Valid #RequestBody resources:
Flux<RessourceDto>): Flux<RessourceDto> {
var deleteWrapper = Mono.fromCallable {
service.deleteAllRessources()
}
deleteWrapper = deleteWrapper.subscribeOn(Schedulers.elastic())
return deleteWrapper.thenMany<RessourceDto> {
resources
.map(mapper::map) // map to model object
.flatMap(service::createResource)
.map(mapper::map) // map to dto object
.subscribeOn(Schedulers.parallel())
}
}
//alternative try
#PostMapping("/resourceAlternative/")
override fun replaceResourcesAlternative2(#RequestBody resources:
Flux<ResourceDto>): Flux<ResourceDto> {
return service.deleteAllResources()
.thenMany<ResourceDto> {
resources
.map(mapper::map)
.flatMap(service::createResource)
.map(mapper::map)
}
}
Whats the idiomatic way of doing this in a reactive fashion?
Is there a way to pass data to dependencies registered with either Execution Context Scope or Lifetime Scope in Simple Injector?
One of my dependencies requires a piece of data in order to be constructed in the dependency chain. During HTTP and WCF requests, this data is easy to get to. For HTTP requests, the data is always present in either the query string or as a Request.Form parameter (and thus is available from HttpContext.Current). For WCF requests, the data is always present in the OperationContext.Current.RequestContext.RequestMessage XML, and can be parsed out. I have many command handler implementations that depend on an interface implementation that needs this piece of data, and they work great during HTTP and WCF scoped lifestyles.
Now I would like to be able to execute one or more of these commands using the Task Parallel Library so that it will execute in a separate thread. It is not feasible to move the piece of data out into a configuration file, class, or any other static artifact. It must initially be passed to the application either via HTTP or WCF.
I know how to create a hybrid lifestyle using Simple Injector, and already have one set up as hybrid HTTP / WCF / Execution Context Scope (command interfaces are async, and return Task instead of void). I also know how to create a command handler decorator that will start a new Execution Context Scope when needed. The problem is, I don't know how or where (or if I can) "save" this piece of data so that is is available when the dependency chain needs it to construct one of the dependencies.
Is it possible? If so, how?
Update
Currently, I have an interface called IProvideHostWebUri with two implementations: HttpHostWebUriProvider and WcfHostWebUriProvider. The interface and registration look like this:
public interface IProvideHostWebUri
{
Uri HostWebUri { get; }
}
container.Register<IProvideHostWebUri>(() =>
{
if (HttpContext.Current != null)
return container.GetInstance<HttpHostWebUriProvider>();
if (OperationContext.Current != null)
return container.GetInstance<WcfHostWebUriProvider>();
throw new NotSupportedException(
"The IProvideHostWebUri service is currently only supported for HTTP and WCF requests.");
}, scopedLifestyle); // scopedLifestyle is the hybrid mentioned previously
So ultimately unless I gut this approach, my goal would be to create a third implementation of this interface which would then depend on some kind of context to obtain the Uri (which is just constructed from a string in the other 2 implementations).
#Steven's answer seems to be what I am looking for, but I am not sure how to make the ITenantContext implementation immutable and thread-safe. I don't think it will need to be made disposable, since it just contains a Uri value.
So what you are basically saying is that:
You have an initial request that contains some contextual information captured in the request 'header'.
During this request you want to kick off a background operation (on a different thread).
The contextual information from the initial request should stay available when running in the background thread.
The short answer is that Simple Injector does not contain anything that allows you to do so. The solution is in creating a piece of infrastructure that allows moving this contextual information along.
Say for instance you are processing command handlers (wild guess here ;-)), you can specify a decorator as follows:
public class BackgroundProcessingCommandHandlerDecorator<T> : ICommandHandler<T>
{
private readonly ITenantContext tenantContext;
private readonly Container container;
private readonly Func<ICommandHandler<T>> decorateeFactory;
public BackgroundProcessingCommandHandlerDecorator(ITenantContext tenantContext,
Container container, Func<ICommandHandler<T>> decorateeFactory) {
this.tenantContext = tenantContext;
this.container = container;
this.decorateeFactory = decorateeFactory;
}
public void Handle(T command) {
// Capture the contextual info in a local variable
// NOTE: This object must be immutable and thread-safe.
var tenant = this.tenantContext.CurrentTenant;
// Kick off a new background operation
Task.Factory.StartNew(() => {
using (container.BeginExecutionContextScope()) {
// Load a service that allows setting contextual information
var context = this.container.GetInstance<ITenantContextApplier>();
// Set the context for this thread, before resolving the handler
context.SetCurrentTenant(tenant);
// Resolve the handler
var decoratee = this.decorateeFactory.Invoke();
// And execute it.
decoratee.Handle(command);
}
});
}
}
Note that in the example I make use of an imaginary ITenantContext abstraction, assuming that you need to supply the commands with information about the current tenant, but any other sort of contextual information will obviously do as well.
The decorator is a small piece of infrastructure that allows you to process commands in the background and it is its responsibility to make sure all the required contextual information is moved to the background thread as well.
To be able to do this, the contextual information is captured and used as a closure in the background thread. I created an extra abstraction for this, namely ITenantContextApplier. Do note that the tenant context implementation can implement both the ITenantContext and the ITenantContextApplier interface. If however you define the ITenantContextApplier in your composition root, it will be impossible for the application to change the context, since it does not have a dependency on ITenantContextApplier.
Here's an example:
// Base library
public interface ITenantContext { }
// Business Layer
public class SomeCommandHandler : ICommandHandler<Some> {
public SomeCommandHandler(ITenantContext context) { ... }
}
// Composition Root
public static class CompositionRoot {
// Make the ITenantContextApplier private so nobody can see it.
// Do note that this is optional; there's no harm in making it public.
private interface ITenantContextApplier {
void SetCurrentTenant(Tenant tenant);
}
private class AspNetTenantContext : ITenantContextApplier, ITenantContext {
// Implement both interfaces
}
private class BackgroundProcessingCommandHandlerDecorator<T> { ... }
public static Container Bootstrap(Container container) {
container.RegisterPerWebRequest<ITenantContext, AspNetTenantContext>();
container.Register<ITenantContextApplier>(() =>
container.GetInstance<ITenantContext>() as ITenantContextApplier);
container.RegisterDecorator(typeof(ICommandHandler<>),
typeof(BackgroundProcessingCommandHandlerDecorator<>));
}
}
A different approach would be to just make the complete ITenantContext available to the background thread, but to be able to pull this off, you need to make sure that:
The implementation is immutable and thus thread-safe.
The implementation doesn't require disposing, because it will typically be disposed when the original request ends.