pkg/copy: add parsing API

Add an API for parsing user input into a possibly specified container
and path.  This allows for sharing the parsing code between the local
and the remote client (and bindings) in the future.

Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

pkg/copy/parse.go

@@ -0,0 +1,61 @@
+package copy
+
+import (
+	"strings"
+
+	"github.com/pkg/errors"
+)
+
+// ParseSourceAndDestination parses the source and destination input into a
+// possibly specified container and path.  The input format is described in
+// podman-cp(1) as "[nameOrID:]path".  Colons in paths are supported as long
+// they start with a dot or slash.
+//
+// It returns, in order, the source container and path, followed by the
+// destination container and path, and an error.  Note that exactly one
+// container must be specified.
+func ParseSourceAndDestination(source, destination string) (string, string, string, string, error) {
+	sourceContainer, sourcePath := parseUserInput(source)
+	destContainer, destPath := parseUserInput(destination)
+
+	numContainers := 0
+	if len(sourceContainer) > 0 {
+		numContainers++
+	}
+	if len(destContainer) > 0 {
+		numContainers++
+	}
+
+	if numContainers != 1 {
+		return "", "", "", "", errors.Errorf("invalid arguments %q, %q: exactly 1 container expected but %d specified", source, destination, numContainers)
+	}
+
+	if len(sourcePath) == 0 || len(destPath) == 0 {
+		return "", "", "", "", errors.Errorf("invalid arguments %q, %q: you must specify paths", source, destination)
+	}
+
+	return sourceContainer, sourcePath, destContainer, destPath, nil
+}
+
+// parseUserInput parses the input string and returns, if specified, the name
+// or ID of the container and the path.  The input format is described in
+// podman-cp(1) as "[nameOrID:]path".  Colons in paths are supported as long
+// they start with a dot or slash.
+func parseUserInput(input string) (container string, path string) {
+	if len(input) == 0 {
+		return
+	}
+	path = input
+
+	// If the input starts with a dot or slash, it cannot refer to a
+	// container.
+	if input[0] == '.' || input[0] == '/' {
+		return
+	}
+
+	if spl := strings.SplitN(path, ":", 2); len(spl) == 2 {
+		container = spl[0]
+		path = spl[1]
+	}
+	return
+}