Add documentation and example for CutDiffAroundLine

models/git_diff.go

@@ -266,6 +266,9 @@ func isHeader(lof string) bool {
 	return strings.HasPrefix(lof, cmdDiffHead) || strings.HasPrefix(lof, "---") || strings.HasPrefix(lof, "+++")
 }
 
+// CutDiffAroundLine cuts a diff of a file in way that only the given line + numberOfLine above it will be shown
+// it also recalculates hunks and adds the appropriate headers to the new diff.
+// Warning: Only one-file diffs are allowed.
 func CutDiffAroundLine(originalDiff io.Reader, line int64, old bool, numbersOfLine int) string {
 	if line == 0 || numbersOfLine == 0 {
 		// no line or num of lines => no diff
@@ -337,6 +340,11 @@ func CutDiffAroundLine(originalDiff io.Reader, line int64, old bool, numbersOfLi
 		}
 	}
 
+	// No hunk found
+	if currentLine == 0 {
+		return ""
+	}
+
 	if len(hunk)-headerLines < numbersOfLine {
 		// No need to cut the hunk => return existing hunk
 		return strings.Join(hunk, "\n")

models/git_diff_test.go

@@ -71,6 +71,32 @@ func TestCutDiffAroundLine(t *testing.T) {
 
 	emptyResult := CutDiffAroundLine(strings.NewReader(exampleDiff), 6, false, 0)
 	assert.Empty(t, emptyResult)
+
+	// Line is out of scope
+	emptyResult = CutDiffAroundLine(strings.NewReader(exampleDiff), 434, false, 0)
+	assert.Empty(t, emptyResult)
+}
+
+func BenchmarkCutDiffAroundLine(b *testing.B) {
+	for n := 0; n < b.N; n++ {
+		CutDiffAroundLine(strings.NewReader(exampleDiff), 3, true, 3)
+	}
+}
+
+func ExampleCutDiffAroundLine() {
+	const diff = `diff --git a/README.md b/README.md
+--- a/README.md
++++ b/README.md
+@@ -1,3 +1,6 @@
+ # gitea-github-migrator
++
++ Build Status
+- Latest Release
+ Docker Pulls
++ cut off
++ cut off`
+	result := CutDiffAroundLine(strings.NewReader(exampleDiff), 4, false, 3)
+	println(result)
 }
 
 func TestDiff_LoadComments(t *testing.T) {