Limit diff size to prevent out of control memory use. (#1035)

* Limit diff size to prevent out of control memory use.

* Group consts

pkg/gitparse/gitparse.go

@@ -17,8 +17,13 @@ import (
 	"github.com/trufflesecurity/trufflehog/v3/pkg/context"
 )
 
-// DateFormat is the standard date format for git.
-const DateFormat = "Mon Jan 02 15:04:05 2006 -0700"
+const (
+	// DateFormat is the standard date format for git.
+	DateFormat = "Mon Jan 02 15:04:05 2006 -0700"
+
+	// MaxDiffSize is the maximum size for a diff. Larger diffs will be cut off.
+	MaxDiffSize = 1 * 1024 * 1024 * 1024 // 1GB
+)
 
 // Commit contains commit header info and diffs.
 type Commit struct {
@@ -222,7 +227,10 @@ func FromReader(ctx context.Context, stdOut io.Reader, commitChan chan Commit) {
 				}
 			}
 		}
-
+		if currentDiff.Content.Len() > MaxDiffSize {
+			log.Debugf("Diff for %s exceeded MaxDiffSize(%d)", currentDiff.PathB, MaxDiffSize)
+			break
+		}
 	}
 	if currentDiff != nil && currentDiff.Content.Len() > 0 {
 		currentCommit.Diffs = append(currentCommit.Diffs, *currentDiff)

pkg/gitparse/gitparse_test.go

@@ -181,6 +181,30 @@ func TestMultiCommitContextDiff(t *testing.T) {
 	}
 }
 
+func TestMaxDiffSize(t *testing.T) {
+	bigBytes := bytes.Buffer{}
+	bigBytes.WriteString(singleCommitSingleDiff)
+	for i := 0; i <= MaxDiffSize/1024+10; i++ {
+		bigBytes.WriteString("+")
+		for n := 0; n < 1024; n++ {
+			bigBytes.Write([]byte("0"))
+		}
+		bigBytes.WriteString("\n")
+	}
+	bigReader := bytes.NewReader(bigBytes.Bytes())
+
+	commitChan := make(chan Commit)
+	go func() {
+		FromReader(context.TODO(), bigReader, commitChan)
+	}()
+
+	commit := <-commitChan
+	if commit.Diffs[0].Content.Len() > MaxDiffSize+1024 {
+		t.Errorf("diff did not match MaxDiffSize. Got: %d, expected (max): %d", commit.Diffs[0].Content.Len(), MaxDiffSize+1024)
+	}
+
+}
+
 const singleCommitSingleDiff = `commit 70001020fab32b1fcf2f1f0e5c66424eae649826 (HEAD -> master, origin/master, origin/HEAD)
 Author: Dustin Decker <[email protected]>
 Date:   Mon Mar 15 23:27:16 2021 -0700