Reading from and writing to a file without passing around filename

Question

I was looking for a way to write to and then read from a file in different parts of my code, without passing the filename around and without consumers needing to know it was coming from a file.

I came up with this FilePipe based on io.Pipe:

package pipe
import (
 "io"
 "os"
)
func FilePipe(name string) (*io.PipeReader, *io.PipeWriter) {
 inr, inw := io.Pipe()
 outr, outw := io.Pipe()
 go func() {
 // Open the file for writing
 f, err := os.Create(name)
 if err != nil {
 outw.CloseWithError(err)
 return
 }
 // Copy the input to the file
 _, err = io.Copy(f, inr)
 f.Close()
 if err != nil {
 outw.CloseWithError(err)
 return
 }
 // Open the file for reading
 f, err = os.Open(name)
 if err != nil {
 outw.CloseWithError(err)
 return
 }
 // Copy the file to the output
 _, err = io.Copy(outw, f)
 f.Close()
 if err != nil {
 outw.CloseWithError(err)
 return
 }
 outw.Close()
 }()
 return outr, inw
}

What do you think? Is there a better way to do this?

• Rafael: Is the file an important side-effect? If so you could do an io.Copy(io.MultiWriter(thefile, otheroutput), input).
• Alex Zylman: Yeah, in this case it is an important side-effect. We don't want to start processing the results until we've finished writing everything to the file successfully.
• metakeule: Please provide a full example with a caller of FilePipe and explain what exactly your code should do and how you want to avoid races. I see no mutex or channel, so I can't see how this could work nor how you want it to work.
• Dave C: You should always check the error return by os.File.Close if the file was written to. An error writing a file may not get reported until the file gets closed.

Answer 1

you could use a teereader:

inr, inw := io.Pipe()
f, _ := os.Create(name)
tr := io.TeeReader(inr, f)
return tr, inw

use this code in go routine and handle errors

• Vogel612: For a go noob like me: how does this work, why is it better than the solution in the question?