From 36d1093f5f6fbd9bef20872a3ceccdf7abdc8828 Mon Sep 17 00:00:00 2001
From: Jason Nelson <jason@carbonmade.com>
Date: Sun, 14 Apr 2024 19:50:52 -0700
Subject: [PATCH] Update int buffers to exact unsigned max length and eliminate
 additional byte allocation

---
 src/UglyToad.PdfPig.Core/ReadHelper.cs | 35 +++++++++++++++-----------
 1 file changed, 21 insertions(+), 14 deletions(-)

diff --git a/src/UglyToad.PdfPig.Core/ReadHelper.cs b/src/UglyToad.PdfPig.Core/ReadHelper.cs
index b2971ffd6..1ede57fbe 100644
--- a/src/UglyToad.PdfPig.Core/ReadHelper.cs
+++ b/src/UglyToad.PdfPig.Core/ReadHelper.cs
@@ -199,17 +199,21 @@ public static long ReadLong(IInputBytes bytes)
         {
             SkipSpaces(bytes);
 
-            ReadOnlySpan<byte> longBuffer = ReadNumberAsUtf8Bytes(bytes);
+            Span<byte> buffer = stackalloc byte[19]; // max ulong32 length
 
-            if (Utf8Parser.TryParse(longBuffer, out long result, out _))
+            ReadNumberAsUtf8Bytes(bytes, buffer, out int bytesRead);
+
+            ReadOnlySpan<byte> longBytes = buffer.Slice(0, bytesRead);
+
+            if (Utf8Parser.TryParse(longBytes, out long result, out _))
             {
                 return result;
             }
             else
             {
-                bytes.Seek(bytes.CurrentOffset - longBuffer.Length);
+                bytes.Seek(bytes.CurrentOffset - bytesRead);
 
-                throw new InvalidOperationException($"Error: Expected a long type at offset {bytes.CurrentOffset}, instead got \'{OtherEncodings.BytesAsLatin1String(longBuffer)}\'");
+                throw new InvalidOperationException($"Error: Expected a long type at offset {bytes.CurrentOffset}, instead got \'{OtherEncodings.BytesAsLatin1String(longBytes)}\'");
             }
         }
         
@@ -233,17 +237,21 @@ public static int ReadInt(IInputBytes bytes)
 
             SkipSpaces(bytes);
 
-            ReadOnlySpan<byte> intBuffer = ReadNumberAsUtf8Bytes(bytes);
+            Span<byte> buffer = stackalloc byte[10]; // max uint32 length
+
+            ReadNumberAsUtf8Bytes(bytes, buffer, out int bytesRead);
 
-            if (Utf8Parser.TryParse(intBuffer, out int result, out _))
+            var intBytes = buffer.Slice(0, bytesRead);
+
+            if (Utf8Parser.TryParse(intBytes, out int result, out _))
             {
                 return result;
             }
             else
             {
-                bytes.Seek(bytes.CurrentOffset - intBuffer.Length);
+                bytes.Seek(bytes.CurrentOffset - bytesRead);
                 
-                throw new PdfDocumentFormatException($"Error: Expected an integer type at offset {bytes.CurrentOffset}, instead got \'{OtherEncodings.BytesAsLatin1String(intBuffer)}\'");
+                throw new PdfDocumentFormatException($"Error: Expected an integer type at offset {bytes.CurrentOffset}, instead got \'{OtherEncodings.BytesAsLatin1String(intBytes)}\'");
             }
         }
         
@@ -296,9 +304,8 @@ public static bool IsValidUtf8(byte[] input)
 #endif
         }
 
-        private static byte[] ReadNumberAsUtf8Bytes(IInputBytes reader)
+        private static void ReadNumberAsUtf8Bytes(IInputBytes reader, scoped Span<byte> buffer, out int bytesRead)
         {
-            Span<byte> buffer = stackalloc byte[MaximumNumberStringLength]; // 20 bytes
             int position = 0;
 
             byte lastByte;
@@ -311,12 +318,12 @@ private static byte[] ReadNumberAsUtf8Bytes(IInputBytes reader)
                    lastByte != '(' && // PDFBOX-2579
                    lastByte != 0)
             {
-                buffer[position++] = lastByte;
-
-                if (position > MaximumNumberStringLength)
+                if (position >= buffer.Length)
                 {
                     throw new InvalidOperationException($"Number \'{OtherEncodings.BytesAsLatin1String(buffer.Slice(0, position))}\' is getting too long, stop reading at offset {reader.CurrentOffset}");
                 }
+
+                buffer[position++] = lastByte;                
             }
 
             if (!reader.IsAtEnd())
@@ -324,7 +331,7 @@ private static byte[] ReadNumberAsUtf8Bytes(IInputBytes reader)
                 reader.Seek(reader.CurrentOffset - 1);
             }
 
-            return buffer.Slice(0, position).ToArray();
+            bytesRead = position;
         }
     }
 }