Why 'Not enough space' exception thrown when applying TSA?

Question

I am trying to apply TSA using code below, Why I got: "Not enough space" exception

Prepare signature container:

        ITSAClient tsaClient = new TSAClientBouncyCastle("https://freetsa.org/tsr", "", "");

        PdfSigner signer = new PdfSigner(new PdfReader("results/example.pdf"), new FileStream("results/prepared1.pdf", FileMode.Create), new StampingProperties().UseAppendMode());
        signer.SetFieldName("Signature1");
        signer.SetCertificationLevel(0);
        signer.Timestamp(tsaClient, "Signature1");   // EXCEPTION THROWN HERE

        PdfSignatureAppearance sigAppearance = signer.GetSignatureAppearance();
        sigAppearance
            .SetPageRect(new Rectangle(144, 144, 200, 100))
            .SetPageNumber(1)
            .SetContact("This is contact1")
            .SetReason("This is reason1")
            .SetLocation("This is location1")
            .SetSignatureCreator("This is signature creator");

        ExternalEmptySignatureContainer container = new ExternalEmptySignatureContainer();
        signer.SignExternalContainer(container, 8192);

        byte[] dataToSign = container.Data;

        return dataToSign;enter code here

Answer 1

You use the TSAClientBouncyCastle constructor without a size estimate:

ITSAClient tsaClient = new TSAClientBouncyCastle("https://freetsa.org/tsr", "", "");

So a default of 4 KB is assumed. Thus, when you apply a document time stamp

signer.Timestamp(tsaClient, "Signature1");

a place holder for a 4 KB time stamp token is reserved, then a time stamp is requested. The error message you receive here now tells you that the actually retrieved time stamp apparently is larger.

You should, therefore, use a TSAClientBouncyCastle constructor which also accepts a size parameter and set it to e.g. 8 KB = 8192.

---

That being said, you seem to misunderstand the Timestamp method: It immediately applies a document time stamp and then closes the document:

    /// <summary>Signs a document with a PAdES-LTV Timestamp.</summary>
    /// <remarks>
    /// Signs a document with a PAdES-LTV Timestamp. The document is closed at the end.
    /// <br /><br />
    /// NOTE: This method closes the underlying pdf document. This means, that current instance
    /// of PdfSigner cannot be used after this method call.
    /// </remarks>
    /// <param name="tsa">the timestamp generator</param>
    /// <param name="signatureName">
    /// the signature name or null to have a name generated
    /// automatically
    /// </param>
    public virtual void Timestamp(ITSAClient tsa, String signatureName)

Thus, you'll run into other errors after fixing the timestamp token size estimate problem!