feat: implement experimental BackScanner for reading files backward and add tests for various scenarios

internal/net/gphttp/accesslog/back_scanner_test.go

@@ -0,0 +1,127 @@
+package accesslog
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+)
+
+func TestBackScanner(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    string
+		expected []string
+	}{
+		{
+			name:     "empty file",
+			input:    "",
+			expected: []string{},
+		},
+		{
+			name:     "single line without newline",
+			input:    "single line",
+			expected: []string{"single line"},
+		},
+		{
+			name:     "single line with newline",
+			input:    "single line\n",
+			expected: []string{"single line"},
+		},
+		{
+			name:     "multiple lines",
+			input:    "first\nsecond\nthird\n",
+			expected: []string{"third", "second", "first"},
+		},
+		{
+			name:     "multiple lines without final newline",
+			input:    "first\nsecond\nthird",
+			expected: []string{"third", "second", "first"},
+		},
+		{
+			name:     "lines longer than chunk size",
+			input:    "short\n" + strings.Repeat("a", 20) + "\nshort\n",
+			expected: []string{"short", strings.Repeat("a", 20), "short"},
+		},
+		{
+			name:     "empty lines",
+			input:    "first\n\n\nlast\n",
+			expected: []string{"last", "first"},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// Setup mock file
+			mockFile := &MockFile{}
+			_, err := mockFile.Write([]byte(tt.input))
+			if err != nil {
+				t.Fatalf("failed to write to mock file: %v", err)
+			}
+
+			// Create scanner with small chunk size to test chunking
+			scanner := NewBackScanner(mockFile, 10)
+
+			// Collect all lines
+			var lines [][]byte
+			for scanner.Scan() {
+				lines = append(lines, scanner.Bytes())
+			}
+
+			// Check for scanning errors
+			if err := scanner.Err(); err != nil {
+				t.Errorf("scanner error: %v", err)
+			}
+
+			// Compare results
+			if len(lines) != len(tt.expected) {
+				t.Errorf("got %d lines, want %d lines", len(lines), len(tt.expected))
+				return
+			}
+
+			for i, line := range lines {
+				if string(line) != tt.expected[i] {
+					t.Errorf("line %d: got %q, want %q", i, line, tt.expected[i])
+				}
+			}
+		})
+	}
+}
+
+func TestBackScannerWithVaryingChunkSizes(t *testing.T) {
+	input := "first\nsecond\nthird\nfourth\nfifth\n"
+	expected := []string{"fifth", "fourth", "third", "second", "first"}
+	chunkSizes := []int{1, 2, 3, 5, 10, 20, 100}
+
+	for _, chunkSize := range chunkSizes {
+		t.Run(fmt.Sprintf("chunk_size_%d", chunkSize), func(t *testing.T) {
+			mockFile := &MockFile{}
+			_, err := mockFile.Write([]byte(input))
+			if err != nil {
+				t.Fatalf("failed to write to mock file: %v", err)
+			}
+
+			scanner := NewBackScanner(mockFile, chunkSize)
+
+			var lines [][]byte
+			for scanner.Scan() {
+				lines = append(lines, scanner.Bytes())
+			}
+
+			if err := scanner.Err(); err != nil {
+				t.Errorf("scanner error: %v", err)
+			}
+
+			if len(lines) != len(expected) {
+				t.Errorf("got %d lines, want %d lines", len(lines), len(expected))
+				return
+			}
+
+			for i, line := range lines {
+				if string(line) != expected[i] {
+					t.Errorf("chunk size %d, line %d: got %q, want %q",
+						chunkSize, i, line, expected[i])
+				}
+			}
+		})
+	}
+}