fix(detect): handle EOF with bytes (#1472)

detect/reader.go

@@ -15,23 +15,28 @@ func (d *Detector) DetectReader(r io.Reader, bufSize int) ([]report.Finding, err
 
 	for {
 		n, err := reader.Read(buf[:cap(buf)])
-		buf = buf[:n]
+
+		// "Callers should always process the n > 0 bytes returned before considering the error err."
+		// https://pkg.go.dev/io#Reader
+		if n > 0 {
+			buf = buf[:n]
+			fragment := Fragment{
+				Raw: string(buf),
+			}
+			for _, finding := range d.Detect(fragment) {
+				findings = append(findings, finding)
+				if d.Verbose {
+					printFinding(finding, d.NoColor)
+				}
+			}
+		}
+
 		if err != nil {
 			if err != io.EOF {
 				return findings, err
 			}
 			break
 		}
-
-		fragment := Fragment{
-			Raw: string(buf),
-		}
-		for _, finding := range d.Detect(fragment) {
-			findings = append(findings, finding)
-			if d.Verbose {
-				printFinding(finding, d.NoColor)
-			}
-		}
 	}
 
 	return findings, nil

detect/reader_test.go

@@ -0,0 +1,61 @@
+package detect
+
+import (
+	"github.com/stretchr/testify/require"
+	"io"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+const secret = "AKIAIRYLJVKMPEXAMPLE"
+
+type mockReader struct {
+	data []byte
+}
+
+func (r *mockReader) Read(p []byte) (n int, err error) {
+	// Copy data to the provided buffer.
+	n = copy(p, r.data)
+
+	// Return io.EOF along with the bytes.
+	return n, io.EOF
+}
+
+// TestDetectReader tests the DetectReader function.
+func TestDetectReader(t *testing.T) {
+	tests := []struct {
+		name          string
+		reader        io.Reader
+		bufSize       int
+		findingsCount int
+	}{
+		{
+			name:          "Test case - Reader returns n > 0 bytes and nil error",
+			bufSize:       10,
+			findingsCount: 1,
+			reader:        strings.NewReader(secret),
+		},
+		{
+			name:          "Test case - Reader returns n > 0 bytes and io.EOF error",
+			bufSize:       10,
+			findingsCount: 1,
+			reader: &mockReader{
+				data: []byte(secret),
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			detector, err := NewDetectorDefaultConfig()
+			require.NoError(t, err)
+
+			findings, err := detector.DetectReader(test.reader, test.bufSize)
+			require.NoError(t, err)
+
+			assert.Equal(t, test.findingsCount, len(findings))
+		})
+	}
+}