Copy file using io.Pipe

[Archos]

I wanted to use io.Pipe to avoid to use a variable with all content of a file into memory.
I've tried this:

    pr, pw := io.Pipe()

    content, err := ioutil.ReadFile(FILE)
    _, err = pr.Read(content)

but the problem is that Read needs a []byte so I would have to use an intermediate variable to get it, avoiding the advantage that I was looking for.


Is possible copy a file using Pipe but without to use an intermediate variable with the content of the file?

[Rémy Oudompheng]

Why not:

src, err := os.Open("source")
frobnicate(err)
dest, err := os.Create("destination")
frobnicate(err)
err := io.Copy(dest, src)
frobnicate(err)

Rémy

[Archos]

perfect!

Or to copy it into a temporary file:

    dest, err := ioutil.TempFile("", "destination")

[Kyle Lemons]

I'll point out that this isn't equivalent to something like the "cp" command, which attempts to also copy the permissions, owner, timestamps, etc.  Those are also doable with relative ease if you require them.

[Archos]

I've forgotten that I've built a function to copy preserving permissions:

srcFile, err := os.Open("source")
handle(err)

srcInfo, err := os.Stat("source")
handle(err)

dstFile, err := os.OpenFile("dest", os.O_WRONLY|os.O_CREATE|os.O_TRUNC, srcInfo.Mode().Perm())
handle(err)

_, err = io.Copy(dstFile, srcFile)
handle(err)

[Kyle Lemons]

On Thu, Aug 2, 2012 at 2:42 PM, Archos <raul...@sent.com> wrote:

I've forgotten that I've built a function to copy preserving permissions:

srcFile, err := os.Open("source")
handle(err)

srcInfo, err := os.Stat("source")
handle(err)

dstFile, err := os.OpenFile("dest", os.O_WRONLY|os.O_CREATE|os.O_TRUNC, srcInfo.Mode().Perm())
handle(err)

Opening a file with those permissions makes them subject to your process's umask.  Using syscall.Chmod seems like a more likely way to actually get the correct permissions.

[Archos]

El jueves, 2 de agosto de 2012 23:12:01 UTC+1, Kyle Lemons escribió:

On Thu, Aug 2, 2012 at 2:42 PM, Archos <raul...@sent.com> wrote:

I've forgotten that I've built a function to copy preserving permissions:

srcFile, err := os.Open("source")
handle(err)

srcInfo, err := os.Stat("source")
handle(err)

dstFile, err := os.OpenFile("dest", os.O_WRONLY|os.O_CREATE|os.O_TRUNC, srcInfo.Mode().Perm())
handle(err)

Opening a file with those permissions makes them subject to your process's umask.  Using syscall.Chmod seems like a more likely way to actually get the correct permissions.

Right. Anyway, I could be wrong but I believe that syscall.Chmod also is affected by the user mask so the safest would be to use `syscall.Umask(0)` before of the function that depends of umask.
 

[Kyle Lemons]

The umask only affects the file creation mode.  See man 2 umask. 

 

[Archos]

Ok, but it could be used before of the function that opens the file:

syscall.Umask(0)

dstFile, err := os.OpenFile("dest", os.O_WRONLY|os.O_CREATE|os.O_TRUNC, srcInfo.Mode().Perm())

The bad point is that I'm supposed that to use syscall.Umask would be invalid in windows system, would not be?