Note that the play link isn't a self-contained test, so the issue isn't reproducible. Perhaps use something like an io.Reader that just gives 3GB of garbage?

The code was given for reference. I don't think it is possible to upload/create files in playground

You don't need to use files. All you need are readers.

I suspect _, err = buffer.Read(rawbytes) is the issue. Read() is not guaranteed to fill rawbytes.

The bytes are taken from at most one Read on the underlying Reader, hence n may be less than len(p).

https://golang.org/pkg/bufio/#Reader.Read

You could use ioutil.ReadAll to get the bytes from the source file, but it would be more efficient and idiomatic to use the io.Reader/io.Writer interfaces to stream the gzip operation. Example: https://play.golang.org/p/u6eAphPRrk

I'm going to close this issue as it does not appear to be a bug, but please feel free to reopen if I've assessed this incorrectly. For any questions on how to use io.Reader/io.Writer, please refer to https://github.com/golang/go/wiki/Questions, where you'll find a number of venues to ask questions.