pkg/util: add CopyDetachable from podman

conmon-rs currently depends on podmans utils.CopyDetachable(). Since podman
wants to import conmon-rs go code this can cause many problems.

To fix this we move the shared code to c/common so both projects can use
it without trouble.

see containers/conmon-rs#504

Signed-off-by: Paul Holzinger <[email protected]>

pkg/util/copy.go

@@ -0,0 +1,57 @@
+package util
+
+import (
+	"errors"
+	"io"
+)
+
+// ErrDetach indicates that an attach session was manually detached by
+// the user.
+var ErrDetach = errors.New("detached from container")
+
+// CopyDetachable is similar to io.Copy but support a detach key sequence to break out.
+func CopyDetachable(dst io.Writer, src io.Reader, keys []byte) (written int64, err error) {
+	buf := make([]byte, 32*1024)
+	for {
+		nr, er := src.Read(buf)
+		if nr > 0 {
+			preservBuf := []byte{}
+			for i, key := range keys {
+				preservBuf = append(preservBuf, buf[0:nr]...)
+				if nr != 1 || buf[0] != key {
+					break
+				}
+				if i == len(keys)-1 {
+					return 0, ErrDetach
+				}
+				nr, er = src.Read(buf)
+			}
+			var nw int
+			var ew error
+			if len(preservBuf) > 0 {
+				nw, ew = dst.Write(preservBuf)
+				nr = len(preservBuf)
+			} else {
+				nw, ew = dst.Write(buf[0:nr])
+			}
+			if nw > 0 {
+				written += int64(nw)
+			}
+			if ew != nil {
+				err = ew
+				break
+			}
+			if nr != nw {
+				err = io.ErrShortWrite
+				break
+			}
+		}
+		if er != nil {
+			if er != io.EOF {
+				err = er
+			}
+			break
+		}
+	}
+	return written, err
+}