refactor(read): make header validation more flexible

read.go

@@ -72,6 +72,7 @@ import (
 	"io"
 	"io/ioutil"
 	"os"
+	"regexp"
 	"sort"
 	"strconv"
 )
@@ -122,14 +123,19 @@ func NewReader(f io.ReaderAt, size int64) (*Reader, error) {
 	return NewReaderEncrypted(f, size, nil)
 }
 
+// headerRegexp is used to check the validity of the header line of a PDF.
+// This should be able to support extra spaces between the version and the
+// newline (as inserted by libtiff/tiff2pdf) as well as supporting CRLF and LF.
+var headerRegexp = regexp.MustCompile(`^%PDF-1\.[0-7]\s*\r?\n`)
+
 // NewReaderEncrypted opens a file for reading, using the data in f with the given total size.
 // If the PDF is encrypted, NewReaderEncrypted calls pw repeatedly to obtain passwords
 // to try. If pw returns the empty string, NewReaderEncrypted stops trying to decrypt
 // the file and returns an error.
 func NewReaderEncrypted(f io.ReaderAt, size int64, pw func() string) (*Reader, error) {
-	buf := make([]byte, 10)
+	buf := make([]byte, 11)
 	f.ReadAt(buf, 0)
-	if !bytes.HasPrefix(buf, []byte("%PDF-1.")) || buf[7] < '0' || buf[7] > '7' || buf[8] != '\r' || buf[8] != '\n' {
+	if !headerRegexp.Match(buf) {
 		return nil, fmt.Errorf("not a PDF file: invalid header")
 	}
 	end := size

read_test.go

@@ -0,0 +1,54 @@
+package pdf
+
+import (
+	"testing"
+)
+
+func TestRead(t *testing.T) {
+	t.Run("HeaderValidation", testHeaderValidation)
+}
+
+func testHeaderValidation(t *testing.T) {
+	tscs := map[string]struct {
+		input         []byte
+		expectedValid bool
+	}{
+		"nil": {
+			input:         nil,
+			expectedValid: false,
+		},
+		"empty": {
+			input:         []byte{},
+			expectedValid: false,
+		},
+		"missing LF": {
+			input:         []byte{37, 80, 68, 70, 45, 49, 46, 55},
+			expectedValid: false,
+		},
+		"ok LF": {
+			input:         []byte{37, 80, 68, 70, 45, 49, 46, 55, 10},
+			expectedValid: true,
+		},
+		"invalid version 1.8": {
+			input:         []byte{37, 80, 68, 70, 45, 49, 46, 58, 10},
+			expectedValid: false,
+		},
+		"ok CRLF": {
+			input:         []byte{37, 80, 68, 70, 45, 49, 46, 55, 13, 10},
+			expectedValid: true,
+		},
+		"ok space + CRLF": {
+			input:         []byte{37, 80, 68, 70, 45, 49, 46, 55, 32, 13, 10},
+			expectedValid: true,
+		},
+	}
+	for name, data := range tscs {
+		data := data
+		t.Run(name, func(t *testing.T) {
+			gotValid := headerRegexp.Match(data.input)
+			if gotValid != data.expectedValid {
+				t.Errorf("expected %t, got %t", data.expectedValid, gotValid)
+			}
+		})
+	}
+}