Merge pull request #527 from fnatzke/Issue350-PdfPageBuilder.CopyFrom()_creates_invalid_PDF

Issue350 pdf page builder.copy from() creates invalid pdf

src/UglyToad.PdfPig.Tests/Integration/ShowTextEscapeText.cs

@@ -0,0 +1,48 @@
+namespace UglyToad.PdfPig.Tests.Integration
+{
+    using System.Linq;
+    using UglyToad.PdfPig;
+    using UglyToad.PdfPig.Writer;
+    using Xunit;
+
+    public class ShowTextEscapeText
+    {
+        private static string GetFilename()
+        {
+            // On the single page of the source PDF has 3 ShowText operations with unbalanced round brackets in the text.
+            // Unbalanced meaning there is an open bracket without a close bracket or close without open.
+            // 1. line 387   (\() Tj
+            // 2. line 397   (\)) Tj
+            // 3. line 384   ( \(I\222ll try to stay on ) Tj
+            // note in text 3 the 0222 (octal) or (0x92 hex) is similar to an apostople ' so text is similar to " (I'll try to stay on" (with an open bracket).
+            return IntegrationHelpers.GetDocumentPath("ShowTextOpWithUnbalancedRoundBrackets.pdf");
+        }
+
+        [Fact]
+        public void PdfCopyShowTextOpUsesEscapedText()
+        {
+            var filePath = GetFilename();
+            using (var sourceDocument = PdfDocument.Open(filePath))
+            {
+                PdfDocumentBuilder pdfBuilder = new PdfDocumentBuilder();
+                var numberOfPages = sourceDocument.NumberOfPages;
+                int pageNumber = 1; ////for (int pageNumber = 1; pageNumber <= numberOfPages; pageNumber++)
+                {                    
+                    var sourcePage = sourceDocument.GetPage(pageNumber);
+                     
+                    pdfBuilder.AddPage(sourcePage.Width, sourcePage.Height).CopyFrom(sourcePage); 
+                }
+                var pdfBytes = pdfBuilder.Build();
+
+                // Reread (in memory) copied PDF and check example text ("wander") exists in word extract after ShowText operation with unbalanced bracket.
+                using (var document = PdfDocument.Open(pdfBytes))
+                {
+                    var page = document.GetPage(1);
+                    var words = page.GetWords();
+                    var isExpectedTextInCopiedPdf = words.Any(w => w.Text.Contains("wander"));
+                    Assert.True(isExpectedTextInCopiedPdf);
+                }
+            }
+        } 
+    }
+}

src/UglyToad.PdfPig/Graphics/Operations/TextShowing/ShowText.cs

@@ -67,16 +67,40 @@
             operationContext.ShowText(input);
         }
 
+        string EscapeText(string text)
+        {
+            if (text is null) return null;
+            // Fix Issue 350 from PDF Spec 1.7 (page 408) on handling 'special characters' of '(', ')' and '\'.
+
+            // The strings must conform to the syntax for string objects.
+            // When a string is written by enclosing the data in parentheses,
+            // bytes whose values are the same as those 
+            // of the ASCII characters left parenthesis (40), right parenthesis (41), and backslash (92)
+            // must be preceded by a backslash character.
+            // All other byte values between 0 and 255 may be used in a string object.
+            // These rules apply to each individual byte in a string object, whether the string is interpreted by the text-showing operators
+            // as single-byte or multiple-byte character codes. 
+
+            // Note: order of replacing is important. Replace slash first before brackets.
+            text = text.Replace(@"\", @"\\)");  // Escape any slash          '\'  -> '\\'
+            text = text.Replace("(", @"\(");    // Escape any open  brackets '('  -> '\('
+            text = text.Replace(")", @"\)");    // Escape any close brackets ')'  -> '\)'
+
+            return text;
+        }
+
         /// <inheritdoc />
         public void Write(Stream stream)
         {
+             
             if (Bytes != null)
             {
                 stream.WriteHex(Bytes);
             }
             else
             {
-                stream.WriteText($"({Text})");
+                var EscapedText = EscapeText(Text);     // escape '(', ')' or '\'
+                stream.WriteText($"({EscapedText})");
             }
 
             stream.WriteWhiteSpace();