Handle incomplete diff files properly (#13662)

* Handle incomplete diff files properly

The code for parsing diff hunks has a bug whereby a very long line
in a very long diff would not be completely read leading to an unexpected
character.

This PR ensures that the line is completely cleared

Fix #13602

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Also allow git max line length <4096

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Add test case

Signed-off-by: Andrew Thornton <art27@cantab.net>

Co-authored-by: techknowlogick <techknowlogick@gitea.io>

services/gitdiff/gitdiff.go

@@ -676,6 +676,15 @@ func parseHunks(curFile *DiffFile, maxLines, maxLineCharacters int, input *bufio
 	leftLine, rightLine := 1, 1
 
 	for {
+		for isFragment {
+			curFile.IsIncomplete = true
+			_, isFragment, err = input.ReadLine()
+			if err != nil {
+				// Now by the definition of ReadLine this cannot be io.EOF
+				err = fmt.Errorf("Unable to ReadLine: %v", err)
+				return
+			}
+		}
 		sb.Reset()
 		lineBytes, isFragment, err = input.ReadLine()
 		if err != nil {
@@ -790,6 +799,10 @@ func parseHunks(curFile *DiffFile, maxLines, maxLineCharacters int, input *bufio
 				}
 			}
 		}
+		if len(line) > maxLineCharacters {
+			curFile.IsIncomplete = true
+			line = line[:maxLineCharacters]
+		}
 		curSection.Lines[len(curSection.Lines)-1].Content = line
 
 		// handle LFS

services/gitdiff/gitdiff_test.go

@@ -9,6 +9,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"html/template"
+	"strconv"
 	"strings"
 	"testing"
 
@@ -153,11 +154,11 @@ func TestParsePatch_singlefile(t *testing.T) {
 			name: "really weird filename",
 			gitdiff: `diff --git "\\a/a b/file b/a a/file" "\\b/a b/file b/a a/file"
 index d2186f1..f5c8ed2 100644
---- "\\a/a b/file b/a a/file"	
+--- "\\a/a b/file b/a a/file"	` + `
-+++ "\\b/a b/file b/a a/file"	
++++ "\\b/a b/file b/a a/file"	` + `
 @@ -1,3 +1,2 @@
  Create a weird file.
- 
+ ` + `
 -and what does diff do here?
 \ No newline at end of file`,
 			addition:    0,
@@ -170,7 +171,7 @@ index d2186f1..f5c8ed2 100644
 			gitdiff: `diff --git "\\a/file with blanks" "\\b/file with blanks"
 deleted file mode 100644
 index 898651a..0000000
---- "\\a/file with blanks"	
+--- "\\a/file with blanks" ` + `
 +++ /dev/null
 @@ -1,5 +0,0 @@
 -a blank file
@@ -263,7 +264,83 @@ index 6961180..9ba1a00 100644
 		})
 	}
 
-	var diff = `diff --git "a/README.md" "b/README.md"
+	// Test max lines
+	diffBuilder := &strings.Builder{}
+
+	var diff = `diff --git a/newfile2 b/newfile2
+new file mode 100644
+index 0000000..6bb8f39
+--- /dev/null
++++ b/newfile2
+@@ -0,0 +1,35 @@
+`
+	diffBuilder.WriteString(diff)
+
+	for i := 0; i < 35; i++ {
+		diffBuilder.WriteString("+line" + strconv.Itoa(i) + "\n")
+	}
+	diff = diffBuilder.String()
+	result, err := ParsePatch(20, setting.Git.MaxGitDiffLineCharacters, setting.Git.MaxGitDiffFiles, strings.NewReader(diff))
+	if err != nil {
+		t.Errorf("There should not be an error: %v", err)
+	}
+	if !result.Files[0].IsIncomplete {
+		t.Errorf("Files should be incomplete! %v", result.Files[0])
+	}
+	result, err = ParsePatch(40, setting.Git.MaxGitDiffLineCharacters, setting.Git.MaxGitDiffFiles, strings.NewReader(diff))
+	if err != nil {
+		t.Errorf("There should not be an error: %v", err)
+	}
+	if result.Files[0].IsIncomplete {
+		t.Errorf("Files should not be incomplete! %v", result.Files[0])
+	}
+	result, err = ParsePatch(40, 5, setting.Git.MaxGitDiffFiles, strings.NewReader(diff))
+	if err != nil {
+		t.Errorf("There should not be an error: %v", err)
+	}
+	if !result.Files[0].IsIncomplete {
+		t.Errorf("Files should be incomplete! %v", result.Files[0])
+	}
+
+	// Test max characters
+	diff = `diff --git a/newfile2 b/newfile2
+new file mode 100644
+index 0000000..6bb8f39
+--- /dev/null
++++ b/newfile2
+@@ -0,0 +1,35 @@
+`
+	diffBuilder.Reset()
+	diffBuilder.WriteString(diff)
+
+	for i := 0; i < 33; i++ {
+		diffBuilder.WriteString("+line" + strconv.Itoa(i) + "\n")
+	}
+	diffBuilder.WriteString("+line33")
+	for i := 0; i < 512; i++ {
+		diffBuilder.WriteString("0123456789ABCDEF")
+	}
+	diffBuilder.WriteByte('\n')
+	diffBuilder.WriteString("+line" + strconv.Itoa(34) + "\n")
+	diffBuilder.WriteString("+line" + strconv.Itoa(35) + "\n")
+	diff = diffBuilder.String()
+
+	result, err = ParsePatch(20, 4096, setting.Git.MaxGitDiffFiles, strings.NewReader(diff))
+	if err != nil {
+		t.Errorf("There should not be an error: %v", err)
+	}
+	if !result.Files[0].IsIncomplete {
+		t.Errorf("Files should be incomplete! %v", result.Files[0])
+	}
+	result, err = ParsePatch(40, 4096, setting.Git.MaxGitDiffFiles, strings.NewReader(diff))
+	if err != nil {
+		t.Errorf("There should not be an error: %v", err)
+	}
+	if !result.Files[0].IsIncomplete {
+		t.Errorf("Files should be incomplete! %v", result.Files[0])
+	}
+
+	diff = `diff --git "a/README.md" "b/README.md"
 --- a/README.md
 +++ b/README.md
 @@ -1,3 +1,6 @@
@@ -274,7 +351,7 @@ index 6961180..9ba1a00 100644
  Docker Pulls
 + cut off
 + cut off`
-	result, err := ParsePatch(setting.Git.MaxGitDiffLines, setting.Git.MaxGitDiffLineCharacters, setting.Git.MaxGitDiffFiles, strings.NewReader(diff))
+	result, err = ParsePatch(setting.Git.MaxGitDiffLines, setting.Git.MaxGitDiffLineCharacters, setting.Git.MaxGitDiffFiles, strings.NewReader(diff))
 	if err != nil {
 		t.Errorf("ParsePatch failed: %s", err)
 	}