[gnome-games] utils: Add FingerprintUid.for_chunk()

[Adrien Plazas <aplazas src gnome org>]

commit 59fc041668a118e2686ad0a5c959bfb63dc21c16
Author: Adrien Plazas <kekun plazas laposte net>
Date:   Thu Aug 4 09:36:30 2016 +0200

    utils: Add FingerprintUid.for_chunk()
    
    This will be used in the next commit to create an UID by hashing only
    the header of a Mega-CD disc.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=769474

 src/utils/fingerprint.vala |   30 +++++++++++++++++++++++-------
 1 files changed, 23 insertions(+), 7 deletions(-)
---
diff --git a/src/utils/fingerprint.vala b/src/utils/fingerprint.vala
index 0c28482..ecea389 100644
--- a/src/utils/fingerprint.vala
+++ b/src/utils/fingerprint.vala
@@ -1,18 +1,23 @@
 // This file is part of GNOME Games. License: GPLv3
 
 namespace Games.Fingerprint {
-       private string get_for_file_uri (string uri) throws Error {
+       private string get_for_file_uri (string uri, size_t start, size_t? length) throws Error {
                var file = File.new_for_uri (uri);
                var istream = file.read ();
 
-               return get_for_file_input_stream (istream);
+               return get_for_file_input_stream (istream, start, length);
        }
 
-       private string get_for_file_input_stream (FileInputStream file_stream) throws Error {
-               file_stream.seek (0, SeekType.END);
-               var size = (size_t) file_stream.tell ();
+       private string get_for_file_input_stream (FileInputStream file_stream, size_t start, size_t? length) 
throws Error {
+               size_t size;
+               if (length == null) {
+                       file_stream.seek (0, SeekType.END);
+                       size = (size_t) file_stream.tell ();
+               }
+               else
+                       size = length;
 
-               file_stream.seek (0, SeekType.SET);
+               file_stream.seek (start, SeekType.SET);
                var bytes = file_stream.read_bytes (size);
 
                return Checksum.compute_for_bytes (ChecksumType.MD5, bytes);
@@ -22,18 +27,29 @@ namespace Games.Fingerprint {
 public class Games.FingerprintUid: Object, Uid {
        private string uri;
        private string prefix;
+       private size_t start;
+       private size_t? length;
        private string uid;
 
        public FingerprintUid (string uri, string prefix) {
                this.uri = uri;
                this.prefix = prefix;
+               start = 0;
+               length = null;
+       }
+
+       public FingerprintUid.for_chunk (string uri, string prefix, size_t start, size_t length) {
+               this.uri = uri;
+               this.prefix = prefix;
+               this.start = start;
+               this.length = length;
        }
 
        public string get_uid () throws Error {
                if (uid != null)
                        return uid;
 
-               var fingerprint = Fingerprint.get_for_file_uri (uri);
+               var fingerprint = Fingerprint.get_for_file_uri (uri, start, length);
                uid = @"$prefix-$fingerprint";
 
                return uid;