public CrossReferencePart ReadPart(PdfStreamReader streamReader, IPdf pdf)
{
if (pdf == null)
{
throw new ArgumentNullException(nameof(pdf));
}
if (pdf.Trailer == null ||
pdf.Trailer.StartCrossReference == 0)
{
return(null);
}
var originalPosition = streamReader.Position;
try
{
streamReader.Seek(pdf.Trailer.StartCrossReference, SeekOrigin.Begin);
var line = streamReader.ReadLine();
if (line != "xref")
{
throw new ArgumentOutOfRangeException(nameof(streamReader), line, "Invalid Cross Reference Header");
}
var subsections = new List <CrossReferencePartSubSection>();
while (line == "xref")
{
subsections.Add(_subSectionReader.ReadPart(streamReader, pdf));
line = streamReader.ReadLine();
}
var result = new CrossReferencePart
{
Sections = subsections.ToArray()
};
return(result);
}
finally
{
streamReader.Seek(originalPosition, SeekOrigin.Begin);
}
}
public TrailerPart ReadPart(PdfStreamReader streamReader, IPdf pdf)
{
var currentPosition = streamReader.Position;
try
{
var trailerBlockSize = 512;
var block = new byte[trailerBlockSize];
int trailerStart;
//we'll read x number of bytes at a time with a 7 byte overlap to account for the word trailer.
//length = 1500
streamReader.Seek(-trailerBlockSize, SeekOrigin.End);
string content;
var foundTrailer = false;
do
{
var loopPosition = streamReader.Position;
streamReader.Read(block, 0, trailerBlockSize);
content = Encoding.ASCII.GetString(block);
if ((trailerStart = content.IndexOf("trailer")) >= 0)
{
streamReader.Seek(loopPosition + trailerStart, SeekOrigin.Begin);
foundTrailer = true;
break;
}
content = null;
if (loopPosition == 0)
{
//we were at the beginning of the stream meaning we can't go back any more
break;
}
if (streamReader.Position > trailerBlockSize)
{
streamReader.Seek((trailerBlockSize * -2) + 7, SeekOrigin.Current); //7 byte overlap
}
else
{
streamReader.Seek(0, SeekOrigin.Begin);
}
} while (streamReader.Position - trailerBlockSize > 0); //make sure we don't go before the beginning of the stream for files that have no trailer
if (foundTrailer)
{
var result = ParseTrailer(streamReader, pdf);
return(result);
}
return(null);
}
finally
{
// go back to where we were.
streamReader.Seek(currentPosition, SeekOrigin.Begin);
}
}