What I want is something like this:
r := strings.NewReader("fee fi fo fum")
fmt.Printf("%r\n", r)
where the %r would be a format specifier that reads from an io.Reader. I didn't see anything like that in the fmt documentation https://pkg.go.dev/fmt, but it's possible I missed it.
CodePudding user response：
Does Go have a format specifier for io.Readers?
No.
CodePudding user response：
An io.Reader may be a stream which never ends, as such a fmt.Printf rendering may never complete.
If you know there will be a discrete payload and it's not excessively large, you can load the contents to memory:
r := strings.NewReader("fee fi fo fum")
b, _ := io.ReadAll(r)
fmt.Printf("%q\n", b)
https://go.dev/play/p/DZybA_f6Ole
This will however move the reader current position to the end, so if you need to "replay" the reader to a future call, you need to use another io.Reader (e.g. bytes Buffer) to hold the original content e.g.
r := strings.NewReader("fee fi fo fum")
if debug {
var b bytes.Buffer
_, err = io.Copy(&b, r) // handle err
log.Printf("io.Reader content: %q\n", b.String())
r = &b // replay
}
// r io.Reader content and position perserved