streaming write to gcs using apache beam per element

Question

Current beam pipeline is reading files as stream using FileIO.matchAll().continuously() . This returns PCollection . I want to write these files back with the same names to another gcs bucket ie each PCollection is one file metadata/readableFile which should be written back to another bucket after some processing. Is there any sink that i should use to achieve writing each PCollection item back to GCS or are there any ways to do it ? Is it possible to create a window per element and then use some GCS sink IO to be able to do this. When operating on a window (even if it has multiple elements) , does beam guarantees that either a window is fully processed or not processed at all , in other words are write operations to GCS or bigquery for a given window atomic and not partial in case of any failures ?

Answer 1

Can you simply write a DoFn<ReadableFile, Void> that takes the file and copies it to the desired location using the FileSystems API? You don't need any "sink" to do that - and, in any case, this is what all "sinks" ( TextIO.write() , AvroIO.write() etc.) are under the hood anyway: they are simply Beam transforms made of ParDo 's and GroupByKey 's.