Spring Cloud Custom GatewayFilter - Modify Response POST filter with results from another client request inside filter - kotlin

Question

I have a POST Gateway filter that I want to modify the response body with the response of a separate webclient request within the gateway filter. I am able to get as far as sending the WebClient().create().post().exchange() within my custom filter. I can see this in my logs
onStateChange(POST{uri=/test, connection=PooledConnection{channel=[id: 0x38eb2b4f, L:/127.0.0.1:51643 - R:localhost/127.0.0.1:9000]}}, [request_prepared])
and
onStateChange(POST{uri=/test, connection=PooledConnection{channel=[id: 0x38eb2b4f, L:/127.0.0.1:51643 - R:localhost/127.0.0.1:9000]}}, [request_sent])
the connection hangs here and doesn't complete.
here is my custom filter code
class PostProxyGatewayFilterFactory : AbstractGatewayFilterFactory<PostProxyGatewayFilterFactory.Params>(Params::class.java) {
override fun apply(params: Params): GatewayFilter {
val cachedBody = StringBuilder()
return GatewayFilter { exchange: ServerWebExchange, chain: GatewayFilterChain ->
chain.filter(exchange).then(
executeRequest(cachedBody,exchange, params)
.map {
val mr = ResponseHandler(exchange)
mr.mutateResponse(it.body.toString())
}.flatMap{
it
}
) }
}
data class Params(
val urlPath: String = "",
)
private fun cache(cachedBody: StringBuilder, buffer: DataBuffer) {
cachedBody.append(Charsets.UTF_8.decode(buffer.asByteBuffer())
.toString())
}
private fun executeRequest(cachedBody: StringBuilder, exchange: ServerWebExchange, params: PostProxyGatewayFilterFactory.Params): Mono<ResponseEntity<JsonNode>>{
val request = when(exchange.request.method){
HttpMethod.PUT -> WebClient.create().put().uri(params.urlPath).body(BodyInserters.fromDataBuffers(exchange.request.body.doOnNext{ cache(cachedBody, it)}))
HttpMethod.POST -> WebClient.create().post().uri(params.urlPath).body(BodyInserters.fromDataBuffers(exchange.request.body.doOnNext{ cache(cachedBody, it)}))
HttpMethod.GET -> WebClient.create().get().uri(params.urlPath)
HttpMethod.DELETE -> WebClient.create().delete().uri(params.urlPath)
else -> throw Exception("Invalid request method passed in to the proxy filter")
}
return request.headers { it.addAll(exchange.request.headers) }
.exchange()
.flatMap{
it.toEntity(JsonNode::class.java)
}
}
}
here is my ResponseHandler class
class ResponseHandler(val delegate: ServerWebExchange) {
fun mutateResponse(body: String): Mono<Void> {
val bytes: ByteArray = body.toByteArray(StandardCharsets.UTF_8)
val buffer: DataBuffer = delegate.response.bufferFactory().wrap(bytes)
return delegate.response.writeWith(Flux.just(buffer))
}
}
here is application.yml
- id: proxy
uri: http://${HOST:localhost}:${PORT:9000}
predicates:
- Path=/proxy/**
filters:
- RewritePath=/test(?<segment>/?.*), $\{segment}
- name: PostProxy
args:
proxyBasePath: http://localhost:9000/thisSecond
So the idea is to send request to localhost:9001/test/thisFirst (proxied to localhost:9000/thisFirst which does happen successfully),get this response back and do nothing with this response, make WebClient request to localhost:9000/thisSecond via executeRequest() ,return this response, and then use that response as the new exchange.response body. I am also not sure if ResponseHandler is correct as executeRequest() never finishes. This would be part 2 of the question once I can resolve why executeRequest() never finishes.