Vert.x Write Buffer to WriteStream?

Question

At a Vert.x verticle I'm implementing I have a Buffer that was previously loaded into memory and now I want to dump it into disk.

As far as I understood we should use a Pump to make sure not to overload the WriteStream.

But I'm not finding a way to get a ReadStream child instance from a Buffer. Shouldn't there be an easy / standard way to do this?

Regards

Answer 1

Generally, vert.x does not warn on any issues writing directly into AsyncFiles. Furthermore, they provide the corresponding example of using AsyncFile.write directly here and state that you can use those to write directly: http://vertx.io/docs/vertx-core/java/#_asynchronous_files

However, if you want the pump with Buffer you need an instance of ReadStream<Buffer> along with an AsyncFile to pump into. You can make use of the implementation by PitchPoint Solutions (Copyright 2016 The Simple File Server Authors):

https://github.com/pitchpoint-solutions/sfs/blob/master/sfs-server/src/main/java/org/sfs/io/BufferReadStream.java

Putting it all together:

CompletableFuture<Void> done = new CompletableFuture<>();

Buffer buffer = Buffer.buffer(new byte[100]);

Vertx.vertx().fileSystem.open("myfile.txt", new OpenOptions(), res -> {
    if (res.succeeded()) {
        AsyncFile outputFile = res.result();

        BufferReadStream reader = new BufferReadStream(buffer)
        Pump pump = Pump.pump(reader, outputFile);
        pump.start();
        reader.endHandler((r) -> {
            pump.stop(); // not sure this is required
            done.complete(null);
        });

    } else {
        // Something went wrong!
    }
});

// wait elsewhere
done.get();