PdfStamper.CreateSignature和空MemoryStream

Question

在使用iTextSharp 5.3.4.0时，我在使用PdfStamper和MemoryStream时遇到了困难。

MemoryStream始终为空。

    PdfReader pdfReader = new PdfReader(Server.MapPath(@"Document.pdf"));

    MemoryStream memoryStream = new MemoryStream();

    PdfStamper pdfStamper = PdfStamper.CreateSignature(pdfReader, memoryStream, '\0');

    //...

    pdfStamper.Writer.CloseStream = false;
    pdfStamper.Close();

    byte[] bt = memoryStream.GetBuffer(); //.ToArray()
    pdfReader.Close();

Download Project (full source code)

我该如何解决这个问题？谢谢!

Answer 1

在Default.aspx.cs中，您可以做一些问题的代码块中遗漏的相关操作：

PdfStamper pdfStamper = PdfStamper.CreateSignature(pdfReader, memoryStream, '\0');

PdfSignatureAppearance pdfSignatureAppearance = pdfStamper.SignatureAppearance;
//...
pdfSignatureAppearance.PreClose(exc);
//...

pdfStamper.Writer.CloseStream = false;
pdfStamper.Close();

无论何时调用PdfSignatureAppearance.PreClose,，都必须使用PdfSignatureAppearance.Close,，而不是PdfStamper.Close, cf。方法文档：

/**
 * This is the first method to be called when using external signatures. The general sequence is:
 * preClose(), getDocumentBytes() and close().
 * <p>
 * If calling preClose() <B>dont't</B> call PdfStamper.close().
 * <p>
 * <CODE>exclusionSizes</CODE> must contain at least
 * the <CODE>PdfName.CONTENTS</CODE> key with the size that it will take in the
 * document. Note that due to the hex string coding this size should be
 * byte_size*2+2.
 * @param exclusionSizes a <CODE>HashMap</CODE> with names and sizes to be excluded in the signature
 * calculation. The key is a <CODE>PdfName</CODE> and the value an
 * <CODE>Integer</CODE>. At least the <CODE>PdfName.CONTENTS</CODE> must be present
 * @throws IOException on error
 * @throws DocumentException on error
 */
public void PreClose(Dictionary<PdfName, int> exclusionSizes) {

(来自)

/**
 * Closes the document. No more content can be written after the
 * document is closed.
 * <p>
 * If closing a signed document with an external signature the closing must be done
 * in the <CODE>PdfSignatureAppearance</CODE> instance.
 * @throws DocumentException on error
 * @throws IOException on error
 */
public void Close() {

(来自)

原因是，当您使用CreateSignature(pdfReader, memoryStream, '\0'),创建PdfStamper时，stamper本身并不写入内存流，而是写入内部ByteBuffer (这对于最终的签名创建和集成是必需的)。在PdfSignatureAppearance.Close期间，该ByteBuffer的内容被写入内存流。

而且我看到你在用

byte[] bt = memoryStream.GetBuffer();

请不要这样！除非您确定您正确地解释了缓冲区内容(可能包含其他垃圾数据)，否则请使用

byte[] bt = memoryStream.ToArray();

而不是。