Spring WebFlux Webclient receiving an application/octet-stream file as a Mono - kotlin

Question

I'm prototyping a small Spring WebFlux application in Kotlin. This application needs to GET a tar archive from a remote REST endpoint and store it locally on disk. Sounds simple.
I first created an integration test that starts the spring server and one other WebFlux server with a mock REST endpoint that serves the tar archive.
The test should go like:
1) app: GET mock-server/archive
2) mock-server: response with status 200 and tar archive in body as type attachment
3) app: block until all bytes received, then untar and use files
The problem I'm having is that when I try and collect the bytes into a ByteArray on the app, it blocks forever.
My mock-server/archive routes to the following function:
fun serveArchive(request: ServerRequest): Mono<ServerResponse> {
val tarFile = FileSystemResource(ARCHIVE_PATH)
assert(tarFile.exists() && tarFile.isFile && tarFile.contentLength() != 0L)
return ServerResponse
.ok()
.contentType(MediaType.APPLICATION_OCTET_STREAM)
.contentLength(tarFile.contentLength())
.header("Content-Disposition", "attachment; filename=\"$ARCHIVE_FNAME\"")
.body(fromResource(tarFile))
}
Then my app calls that with the following:
private fun retrieveArchive {
client.get().uri(ARCHIVE_URL).accept(MediaType.APPLICATION_OCTET_STREAM)
.exchange()
.flatMap { response ->
storeArchive(response.bodyToMono())
}.subscribe()
}
private fun storeArchive(archive: Mono<ByteArrayResource>): Mono<Void> {
val archiveContentBytes = archive.block() // <- this blocks forever
val archiveContents = TarArchiveInputStream(archiveContentBytes.inputStream)
// read archive
}
I've see How to best get a byte array from a ClientResponse from Spring WebClient? and that's why I'm trying to use the ByteArrayResource.
When I step through everything, I see that serveArchive seems to be working (the assert statement says the file I'm passing exists and there are some bytes in it). In retrieveArchive I get a 200 and can see all the appropriate information in the .headers (content-type, content-length all look good). When I get down to storeArchive and try to retrieve the bytes from the Mono using block, it simply blocks forever.
I'm at a complete loss of how to debug something like this.

Answer 1

You just have to return the converted body from the flatMap so it transforms from Mono<T> to T:
client.get().uri(ARCHIVE_URL).accept(MediaType.APPLICATION_OCTET_STREAM)
.exchange()
.flatMap { response ->
response.bodyToMono(ByteArrayResource::class.java)
}
.map { archiveContentBytes ->
archiveContentBytes.inputStream
}
.doOnSuccess { inputStream ->
//here is you code to do anything with the inputStream
val archiveContents = TarArchiveInputStream(inputStream)
}
.subscribe()