mostly refinements and some code refactoring (see below)

- Moved some test-related code to separate function to improve code
readability
- renamed and refined testSpecialCharsEncodedAsHex: you don't need an
if-clause in a test if you insist on certain values along the way, just
use assertX to check for expected values ("fail early")
- ElementString: moved the part which handles escaped characters to a
separate function to improve code readability
- added references / comments

src/Smalot/PdfParser/Element/ElementString.php

@@ -51,6 +51,51 @@ public function equals($value): bool
         return $value == $this->value;
     }
 
+    /**
+     * Part of parsing process to handle escaped characters.
+     * Note, most parameters are passed by reference.
+     *
+     * Further information in PDF specification (page 53):
+     * https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandards/pdfreference1.7old.pdf
+     */
+    private static function handleEscapedCharacters(string &$name, int &$position, string &$processedName, string $char): void
+    {
+        // escaped chars
+        $nextChar = substr($name, 0, 1);
+        switch ($nextChar) {
+            // end-of-line markers (CR, LF, CRLF) should be ignored
+            case "\r":
+            case "\n":
+                preg_match('/^\\r?\\n?/', $name, $matches);
+                $name = substr($name, \strlen($matches[0]));
+                $position += \strlen($matches[0]);
+                break;
+                // process LF, CR, HT, BS, FF
+            case 'n':
+            case 't':
+            case 'r':
+            case 'b':
+            case 'f':
+                $processedName .= stripcslashes('\\'.$nextChar);
+                $name = substr($name, 1);
+                ++$position;
+                break;
+                // decode escaped parentheses and backslash
+            case '(':
+            case ')':
+            case '\\':
+            case ' ': // TODO: this should probably be removed - kept for compatibility
+                $processedName .= $nextChar;
+                $name = substr($name, 1);
+                ++$position;
+                break;
+                // TODO: process octal encoding (but it is also processed later)
+                // keep backslash in other cases
+            default:
+                $processedName .= $char;
+        }
+    }
+
     /**
      * @return bool|ElementString
      */
@@ -80,46 +125,13 @@ public static function parse(string $content, ?Document $document = null, int &$
                         $processedName .= $char;
                         --$delimiterCount;
                         break;
-                        // escaped chars
                     case '\\':
-                        $nextChar = substr($name, 0, 1);
-                        switch ($nextChar) {
-                            // end-of-line markers (CR, LF, CRLF) should be ignored
-                            case "\r":
-                            case "\n":
-                                preg_match('/^\\r?\\n?/', $name, $matches);
-                                $name = substr($name, \strlen($matches[0]));
-                                $position += \strlen($matches[0]);
-                                break;
-                                // process LF, CR, HT, BS, FF
-                            case 'n':
-                            case 't':
-                            case 'r':
-                            case 'b':
-                            case 'f':
-                                $processedName .= stripcslashes('\\'.$nextChar);
-                                $name = substr($name, 1);
-                                ++$position;
-                                break;
-                                // decode escaped parentheses and backslash
-                            case '(':
-                            case ')':
-                            case '\\':
-                            case ' ': // TODO: this should probably be removed - kept for compatibility
-                                $processedName .= $nextChar;
-                                $name = substr($name, 1);
-                                ++$position;
-                                break;
-                                // TODO: process octal encoding (but it is also processed later)
-                                // keep backslash in other cases
-                            default:
-                                $processedName .= $char;
-                        }
+                        self::handleEscapedCharacters($name, $position, $processedName, $char);
                         break;
                     default:
                         $processedName .= $char;
                 }
-            } while (\strlen($name));
+            } while ('' !== $name);
 
             $offset += strpos($content, '(') + 1 + $position;
 

tests/PHPUnit/Integration/Element/ElementHexaTest.php

@@ -130,7 +130,16 @@ public function testParse(): void
 007000610  073007100750061002c0020> ');
 
         $this->assertEquals('pasqua, primavera, resurrezione, festa cristiana, gesù, uova di cioccolata, coniglietti, pulcini, pasquale, campane, dina rebucci, uova di pasqua, ', $element);
+    }
 
+    /**
+     * Closing round bracket encoded in hexadecimal format breaks parsing - string is truncated.
+     *
+     * @see https://github.com/smalot/pdfparser/issues/715
+     */
+    public function testIssue715(): void
+    {
+        $offset = 0;
         $testString = '()\\';
         $element = ElementHexa::parse('<'.bin2hex($testString).'>', null, $offset);
         $this->assertEquals($testString, (string) $element);

tests/PHPUnit/Integration/Element/ElementStringTest.php

@@ -131,7 +131,13 @@ public function testParse(): void
         $element = ElementString::parse('(Gutter\\ console\\ assembly)', null, $offset);
         $this->assertEquals('Gutter console assembly', $element->getContent());
         $this->assertEquals(27, $offset);
+    }
 
+    /**
+     * @see https://github.com/smalot/pdfparser/issues/715
+     */
+    public function testParseIssue715(): void
+    {
         $element = ElementString::parse('(())');
         $this->assertEquals('()', $element->getContent());
     }

tests/PHPUnit/Integration/ParserTest.php

@@ -441,19 +441,20 @@ public function testIgnoreEncryption(): void
 
     /**
      * Tests special chars encoded as hex.
+     *
+     * @see https://github.com/smalot/pdfparser/issues/715
      */
-    public function testSpecialCharsEncodedAsHex(): void
+    public function testIssue715SpecialCharsEncodedAsHex(): void
     {
         $filename = $this->rootDir.'/samples/bugs/Issue715.pdf';
 
         $this->fixture = new Parser();
         $document = $this->fixture->parseFile($filename);
         $sigObject = $document->getObjectsByType('Sig');
-        $result = null;
-        if (isset($sigObject['4_0'])) {
-            $result = (string) $sigObject['4_0']->getHeader()->get('Contents');
-        }
-        $this->assertEquals('()\\', $result);
+
+        $this->assertTrue(isset($sigObject['4_0']));
+        $this->assertEquals('()\\', (string) $sigObject['4_0']->getHeader()->get('Contents'));
+
         $details = $document->getDetails();
         $this->assertEquals('x(y)', $details['Producer'] ?? null);
         $this->assertEquals('a(b)', $details['Creator'] ?? null);