Read twice from the same io.Reader

[michalis...@gmail.com]

How can I do that? If I was reading from a file instead, I would probably run file.Seek(0,0) in between the reads, but how can this be done with io.Readers?

[Dave Cheney]

Type asset the value to see if it implements interface { Seek(int,int) error}. If it does not you will have to buffer the results from reading from the reader.

[alessio....@gmail.com]

Can you provide sample code? 

Thanks

[alexm]

I coded up a simple example: http://play.golang.org/p/UA1wuGyCr3

You can see in the first part r implements the io.Seeker interface and so can be asserted as a Seeker in the function readAndPrint. On the other hand the buf doesn't implement the io.Seeker interface and will fail the condition check and you can see will only print just once. 

I hope this helped.

[Alessio Cavaleri]

This solution works if you can assert that the io.Reader is also an io.Seeker, which is not always true. I've ended up to use a TeeReader, check this:https://gist.github.com/miku/293f253b706c4de1b75c

--

Alessio

[Nick Craig-Wood]

You are buffering the entire body in memory....

If you make the tee reader first, then run readFirst and readSecond as
go routines so they run at the same time you can get rid of the buffer.

> --
> You received this message because you are subscribed to the Google
> Groups "golang-nuts" group.
> To unsubscribe from this group and stop receiving emails from it, send
> an email to golang-nuts...@googlegroups.com
> <mailto:golang-nuts...@googlegroups.com>.
> For more options, visit https://groups.google.com/d/optout.


--
Nick Craig-Wood <ni...@craig-wood.com> -- http://www.craig-wood.com/nick