Add reserved keys

handlers.go

@@ -5,6 +5,7 @@ package main
 //go:generate go-bindata -pkg $GOPACKAGE assets/
 
 import (
+	"bytes"
 	"crypto/rand"
 	"crypto/subtle"
 	"encoding/base64"
@@ -47,6 +48,9 @@ const (
 
 const CookieOwnerToken = "owner_token"
 
+// These keys are designated reserved, and will not be randomly chosen
+var ReservedPasteKeys [][]byte = [][]byte{[]byte("xd42"), []byte("example")}
+
 // Base64 encoding and decoding
 var base64Alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_"
 var base64Encoder = base64.NewEncoding(base64Alphabet).WithPadding(base64.NoPadding)
@@ -286,10 +290,23 @@ func shortenURL(tx *bolt.Tx, userURL *url.URL, ownerKey [16]byte) (*StoredPaste,
 		if err != nil {
 			return nil, errors.Wrap(err, "url-key generation failed")
 		}
+
 		found := shortenBucket.Get(urlKey)
 		if found == nil {
 			break
 		}
+
+		isReserved := false
+		for _, reservedKey := range ReservedPasteKeys {
+			if bytes.HasPrefix(urlKey, reservedKey) {
+				isReserved = true
+				break
+			}
+		}
+		if !isReserved {
+			break
+		}
+
 		epoch++
 	}