I'm having trouble writing to an Azure Block Blob from C++ using a SAS (Shared Access Signature). I'm using the Blob REST API and Poco. The HTTP request returns error 404 (resource does not exist), but I can't figure out what I'm doing wrong.
I generate the SAS on the server in C# like this (seems to work fine):
CloudStorageAccount storageAccount = CloudStorageAccount.Parse(CloudConfigurationManager.GetSetting("StorageConnectionString"));
CloudBlobClient blobClient = storageAccount.CreateCloudBlobClient();
CloudBlobContainer container = blobClient.GetContainerReference("my-blob");
container.CreateIfNotExists();
SharedAccessBlobPolicy sasConstraints = new SharedAccessBlobPolicy();
sasConstraints.SharedAccessExpiryTime = DateTime.UtcNow.AddMinutes(40);
sasConstraints.Permissions = SharedAccessBlobPermissions.Write | SharedAccessBlobPermissions.List;
string sasContainerToken = container.GetSharedAccessSignature(sasConstraints);
return Request.CreateResponse(HttpStatusCode.OK, container.Uri + sasContainerToken);
In the Azure portal I can indeed see the Blob container being created as expected. I receive this SAS in C++ using an HTTP request. What I get looks like this (some names and signature replaced for security reasons):
Then I try to create the file using Poco and the Blob REST API. That looks like this:
std::string cloudUrl = sasURI + "&restype=container";
std::string fileName = "fname.ext";
Poco::URI* uri = new Poco::URI(cloudUrl.c_str());
std::string* path = new std::string(uri->getPathAndQuery());
Poco::Net::HTTPSClientSession* session = new Poco::Net::HTTPSClientSession(uri->getHost(), uri->getPort());
std::string method = Poco::Net::HTTPRequest::HTTP_PUT;
Poco::Net::HTTPRequest* request = new Poco::Net::HTTPRequest(method, *path, Poco::Net::HTTPMessage::HTTP_1_1);
request->add("x-ms-blob-content-disposition", "attachment; filename=\"" + fileName + "\"");
request->add("x-ms-blob-type", "BlockBlob");
request->add("x-ms-meta-m1", "v1");
request->add("x-ms-meta-m2", "v2");
Poco::Net::HTTPResponse* httpResponse = new Poco::Net::HTTPResponse();
int fileContent = 42;
request->setContentLength(sizeof(int));
request->setKeepAlive(true);
std::ostream& outputStream = session->sendRequest(*request);
outputStream << fileContent;
std::istream &is = session->receiveResponse(*httpResponse);
Poco::Net::HTTPResponse::HTTPStatus status = httpResponse->getStatus();
std::ostringstream outString;
Poco::StreamCopier::copyStream(is, outString);
if (status != Poco::Net::HTTPResponse::HTTP_OK)
{
Logger::log("Connection failed\nstatus:", status, "\nreason:", httpResponse->getReason(), "\nreasonForStatus:", httpResponse->getReasonForStatus(status), "\nresponseContent:", outString.str());
}
I've looked up here how the REST API works. I found here that when using a SAS I don't need to do regular authentication.
What am I doing wrong here? Why am I getting error 404?
I've finally figured out what was going wrong here. :)
There were two problems in the above code. The first is that the filename needed to be inserted into the URL, as Gaurav Mantri explained. This does the trick:
int indexOfQuestionMark = cloudUrl.find('?');
cloudUrl = cloudUrl.substr(0, indexOfQuestionMark) + "/" + fileName + cloudUrl.substr(indexOfQuestionMark);
The other problem is that I wasn't uploading enough bytes. sizeof(int) is 4 bytes while pushing 42 into a stream turns it into characters, making it only 2 bytes. The server then keeps waiting for the remaining 2 bytes. That makes this the correct line in the example code above:
request->setContentLength(2);
Also, it works without these three lines so I suppose they're not needed:
request->add("x-ms-blob-content-disposition", "attachment; filename=\"" + fileName + "\"");
request->add("x-ms-meta-m1", "v1");
request->add("x-ms-meta-m2", "v2");
Similarly, adding this doesn't seem needed: "&restype=container".
Finally, for writing the SharedAccessBlobPermissions.List rights aren't needed so those can be left out in SAS generation on the server side.