fix: correct fileOffset to file.Length when Info.GetFileByOffset reaches the last file

metainfo/info.go

@@ -139,8 +139,9 @@ func (info Info) GetFileByOffset(offset int64) (file File, fileOffset int64) {
 	}
 
 	fileOffset = offset
-	for _, file = range info.Files {
-		if fileOffset < file.Length {
+	for i, _len := 0, len(info.Files)-1; i <= _len; i++ {
+		file = info.Files[i]
+		if i == _len || fileOffset < file.Length {
 			return
 		}
 		fileOffset -= file.Length

metainfo/info_test.go

@@ -0,0 +1,75 @@
+// Copyright 2020 xgfone
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package metainfo
+
+import "testing"
+
+func TestInfo_GetFileByOffset(t *testing.T) {
+	FileInfo := Info{
+		Name:        "test_rw",
+		PieceLength: 64,
+		Length:      600,
+	}
+	file, fileOffset := FileInfo.GetFileByOffset(0)
+	if file.Offset(FileInfo) != 0 || fileOffset != 0 {
+		t.Errorf("expect fileOffset='%d', but got '%d'", 0, fileOffset)
+	}
+	file, fileOffset = FileInfo.GetFileByOffset(100)
+	if file.Offset(FileInfo) != 0 || fileOffset != 100 {
+		t.Errorf("expect fileOffset='%d', but got '%d'", 100, fileOffset)
+	}
+	file, fileOffset = FileInfo.GetFileByOffset(600)
+	if file.Offset(FileInfo) != 0 || fileOffset != 600 {
+		t.Errorf("expect fileOffset='%d', but got '%d'", 600, fileOffset)
+	}
+
+	DirInfo := Info{
+		Name:        "test_rw",
+		PieceLength: 64,
+		Files: []File{
+			{Length: 100, Paths: []string{"file1"}},
+			{Length: 200, Paths: []string{"file2"}},
+			{Length: 300, Paths: []string{"file3"}},
+		},
+	}
+	file, fileOffset = DirInfo.GetFileByOffset(0)
+	if file.Offset(DirInfo) != 0 || file.Length != 100 || fileOffset != 0 {
+		t.Errorf("expect fileOffset='%d', but got '%d'", 0, fileOffset)
+	}
+	file, fileOffset = DirInfo.GetFileByOffset(50)
+	if file.Offset(DirInfo) != 0 || file.Length != 100 || fileOffset != 50 {
+		t.Errorf("expect fileOffset='%d', but got '%d'", 50, fileOffset)
+	}
+	file, fileOffset = DirInfo.GetFileByOffset(100)
+	if file.Offset(DirInfo) != 100 || file.Length != 200 || fileOffset != 0 {
+		t.Errorf("expect fileOffset='%d', but got '%d'", 0, fileOffset)
+	}
+	file, fileOffset = DirInfo.GetFileByOffset(200)
+	if file.Offset(DirInfo) != 100 || file.Length != 200 || fileOffset != 100 {
+		t.Errorf("expect fileOffset='%d', but got '%d'", 100, fileOffset)
+	}
+	file, fileOffset = DirInfo.GetFileByOffset(300)
+	if file.Offset(DirInfo) != 300 || file.Length != 300 || fileOffset != 0 {
+		t.Errorf("expect fileOffset='%d', but got '%d'", 0, fileOffset)
+	}
+	file, fileOffset = DirInfo.GetFileByOffset(400)
+	if file.Offset(DirInfo) != 300 || file.Length != 300 || fileOffset != 100 {
+		t.Errorf("expect fileOffset='%d', but got '%d'", 100, fileOffset)
+	}
+	file, fileOffset = DirInfo.GetFileByOffset(600)
+	if file.Offset(DirInfo) != 300 || file.Length != 300 || fileOffset != 300 {
+		t.Errorf("expect fileOffset='%d', but got '%d'", 300, fileOffset)
+	}
+}