Add input checker

This should allow things like gateway urls to be passed in and turned into proper references

main.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"os"
 	"os/signal"
+	"regexp"
 	"strings"
 	"syscall"
 
@@ -37,6 +38,7 @@ func main() {
 
 		outfile := c.String("output")
 		arg := c.Args().First()
+		arg = cleanIPFSPath(arg)
 
 		// Use the final segment of the object's path if no path was given.
 		if outfile == "" {
@@ -132,3 +134,13 @@ func movePostfixOptions(args []string) []string {
 	// append extracted arguments to the real args
 	return append(args, the_args...)
 }
+
+// cleanIPFSPath attempts to extract an IPFS reference from a string
+// if it can't find one it returns the input string
+func cleanIPFSPath(path string) string {
+	matches := regexp.MustCompile(`^.*(/ip(f|n)s/.+)$`).FindStringSubmatch(path)
+	if len(matches) > 1 {
+		return matches[1]
+	}
+	return path
+}