What version of Go are you using (go version)?

Go 1.10

What operating system and processor architecture are you using (go env)?

Linux and OSX (not that it matters).

What did you do?

What did you see instead?

I'll paste my post from #16791 instead of answering the above questions separately. This issue was fixed for csv.Reader in https://golang.org/cl/72150. Thanks go to @dsnet. The issue number was #19410.

The problem is, however, still present for csv.Writer. Specifically for the writer, in csv/writer.go:

		for _, r1 := range field {
			var err error
			switch r1 {
			case '"':
				_, err = w.w.WriteString(`""`)
			case '\r':
				if !w.UseCRLF {
					err = w.w.WriteByte('\r')
				}
			case '\n':
				if w.UseCRLF {
					_, err = w.w.WriteString("\r\n")
				} else {
					err = w.w.WriteByte('\n')
				}
			default:
				_, err = w.w.WriteRune(r1)
			}
			if err != nil {
				return err
			}
		}

The call to w.w.WriteRune(r1) mangles the character.

What did you expect to see?

I expect it to not mangle my bytes if they don't contain special characters. Namely the delimiter (usually a comma), a newline (or carriage return) and double quotes. In my specific case, those characters are not present in the field that gets altered.