Encoding/Decoding a Gif - go

Question

I will be working on a project connected with GIF images and I tried to do some basic operations on them in Go (such as retrieving frames or creating GIF from a bunch of images). But for now let's do a simple example in which I am only trying to decode a GIF and then to encode it again. I tried to use "image/gif" package, but I am unable to get it to do what I want.
Here is the code :
package main
import (
"os"
"image/gif"
)
func main() {
inputFile , err := os.Open("travolta.gif")
defer inputFile.Close()
if err != nil {
panic(err)
}
g, err := gif.DecodeAll(inputFile)
if err != nil {
panic(err)
}
outputFile, err := os.OpenFile("travolta2.gif", os.O_WRONLY|os.O_CREATE, 0777)
defer outputFile.Close()
if err != nil {
panic(err)
}
err = gif.EncodeAll(outputFile, g)
if err != nil {
panic(err)
}
}
When I run the code it does not panic and another gif is indeed created. Unfortunetely it is corrupted. Moreover the gif's size changes from 3,4MB to 4,4MB. Is it not a way to save/read a gif? What mistake do I make?
EDIT:
By corrupted I mean that when I try to open it an error occurs- screnshot here : http://www.filedropper.com/obrazekpociety.
GIF:
http://vader.joemonster.org/upload/rwu/1539970c1d48acceLw7m.gif
Go version 1.7.4

Answer 1

The problem is you are passing a File* to DecodeAll rather than something that supports the io.Reader interface.
I have adapted your code so that it creates a bufio.Reader from the file and then hands that to DecodeAll as below:
import (
"bufio"
"os"
"image/gif"
)
func main() {
inputFile , err := os.Open("travolta.gif")
defer inputFile.Close()
if err != nil {
panic(err)
}
r := bufio.NewReader(inputFile)
g, err := gif.DecodeAll(r)
if err != nil {
panic(err)
}
// ... remaining code
}