Downloading Docusign PDF in Grails, file corrupted - grails

Question

Using Groovy 1.8.6 and Grails 2.1.0
Using embedded API, after user signs document, browser is redirected back to my app. Using "Get Envelope Documents and Certificate" API to download document to server. URL format:
"${baseUrl}/envelopes/${envelopeId}/documents/combined"
Code snippet (with minor details removed):
private void getDocument(requestUrl) {
def connection = urlConnect(requestUrl, null, "GET")
if (connection.responseCode == 200) {
savePDF(envelopeId, connection.inputStream)
}
}
private void savePDF(envelopeId, inputStream) {
String filePath = getSavedPDFPath(envelopeId)
def pdfWriter = new File(filePath).newWriter()
pdfWriter << inputStream
pdfWriter.close()
}
What happens is that the resulting file is not 100% correct, Adobe Reader complains that "at least one signature is invalid". Reader at least knows that the file was signed by DocuSign, Inc., and can show details about the certificate.

Answer 1

Per the Question's comment thread, the issue was being caused by the way the file was being saved. Using this code instead, the file saves / opens correctly:
private void savePDF(envelopeId, connection)
{
FileOutputStream fop = null;
File file;
String filePath = getSavedPDFPath(envelopeId);
try {
file = new File(filePath);
fop = new FileOutputStream(file);
byte[] buffer = new byte[1024];
int numRead;
while((numRead = connection.getInputStream().read(buffer)) > 0)
{
fop.write(buffer, 0, numRead);
}
fop.flush();
fop.close();
}
catch (Exception e)
{
throw new RuntimeException(e);
}
}