Develop Reference

Windows BLE GattValueChangedEventArgs.Characteristic.Value missing data

I use windows BLE to connect and read from BLE barcode scanner. Everything works fine while the value I receive from the BLE device is only short string. If I scan a barcode which is more than 16 bytes, the GattCharacteristic.ValueChanged event fires multiple times, and each time I receive a chunk from the data. It would not be problem but I don't receive everything and parts are missing. I use identical method on Xamarin.IOS and the event raised once and I receive 1 long string containing the whole data. So it works in Xamarin.IOS but not in winform.net.
It seems windows uses about 16bytes IBuffer for GattCharacteristic.Value and while it raises the event, that buffer gets cleared and replaced with new data.
Is there any way to increase Windows BLE IBuffer size or tell windows to get the whole data together before raise the event?
What I should receive:
Collection: 1000
From: West Midlands
To: Distribution
RaisedBy: holloway
Raised: 29/09/2021
Item: Camargue 572 4m - hometx44cama
SKU: 26479
Identifier: 174435
SubIdentifier: 21642727-6
Qty: 4.27
What I receive:
Collection: 1000
From: West Mid
land To: Distr
edBy: holloway
ised: 29/09/20
21 Item: Camarg
ue 572 4m
Identifier
: 174435
SubIde
ntifier: 21642
4.27
The code:
CurrentConnectedDevice = await BluetoothLEDevice.FromIdAsync(deviceid);
GattDeviceServicesResult result = await CurrentConnectedDevice.GetGattServicesAsync(BluetoothCacheMode.Uncached);
var services = result.Services;
GattDeviceService ScannerService = services.Single(d => d.Uuid == ScannerServiceUUID);
var Characteristics = await ScannerService.GetCharacteristicsAsync(BluetoothCacheMode.Uncached);
ScanCharacteristic = Characteristics.Characteristics.Single(c => c.Uuid == ScannerNotifyUUID);
var status = await ScanCharacteristic.WriteClientCharacteristicConfigurationDescriptorAsync(GattClientCharacteristicConfigurationDescriptorValue.Notify);
ScanCharacteristic.ValueChanged += BarcodeScanned;
private void BarcodeScanned(GattCharacteristic sender, GattValueChangedEventArgs args)
{
byte[] data;
CryptographicBuffer.CopyToByteArray(args.CharacteristicValue, out data);
Console.WriteLine(Encoding.UTF8.GetString(data));
}

In the Buffer constructor (link) you can pass the size of the buffer. In your implementation, you are using args.CharacteristicValue as the buffer. If you can control the value of args.CharacteristicValue then you can increase the buffer size, or you can pass in a new Buffer to the CopyToByteArray method.

AWS S3 .Net List Objects 3rd level only

I'm trying to list objects from my S3 bucket, 3rd level of a certain folder only:
bucket
samples
XXXX
XXXX_XXXXX
XXXX_XXXXX
YYYY
YYYY_YYYYY
YYYY_YYYYY
The XXXX_XXXXX and YYYY_YYYYY folders only.
Using C#, this is my code:
using (IAmazonS3 client = new AmazonS3Client("awsAccessKeyId", "awsSecretAccessKey", RegionEndpoint.GetBySystemName("eu-central-1")))
{
ListObjectsRequest request = new ListObjectsRequest
{
BucketName = bucketName,
Prefix = "samples/",
Delimiter = "/"
};
do
{
ListObjectsResponse response = client.ListObjects(request);
if (response.S3Objects.Count() > 0)
{ // CODE }
The response.S3Objects is empty. If I remove the Delimiter from the Request ALL the objects are returned, and the loading time is too long.
I've been following the AWS S3 docs, but it simply returns nothing. Please help me understand what is wrong. Many thanks.

You need to be looking in CommonPrefixes, not S3Objects. CommonPrefixes gives you all of the prefixes up to the next delimiter, each of which you use to repeat the request, taking you another level deeper each time.

UWP AudioGraph setup not working in all devices, HRESULT: 0x88960001 thrown on AddOutgoingConnection

I'm having trouble with a AudioGraph in a UWP app. My trouble is that when I'm adding adding an Outgoing Connection to my input device node I get a Exception thrown with HRESULT: 0x88960001.
Using trial and error I figured out that the problem is with the MediaEncoding profile I set on both the input and output node... but I have now 2 settings only work on one machine and the other only works on another machine... I needed the audio to be Single Channel, 16bit sample with a 16K sample in PCM.
The code I'm using is fairly simple and was based on samples that exist online, the thing is it works only on some microphones and not others... I needed it to be generic and have always the same output so that I can input that to my service endpoint.
I left the 2 AudioEncodingProperties settings there (one of them commented out)
var result = await AudioGraph.CreateAsync(
new AudioGraphSettings(AudioRenderCategory.Media));
if (result.Status == AudioGraphCreationStatus.Success)
{
this.graph = result.Graph;
var microphone = await DeviceInformation.CreateFromIdAsync(
MediaDevice.GetDefaultAudioCaptureId(AudioDeviceRole.Default));
// Low gives us 1 channel, 16-bits per sample, 16K sample rate.
var outProfile = MediaEncodingProfile.CreateWav(AudioEncodingQuality.Low);
//outProfile.Audio = AudioEncodingProperties.CreatePcm(16000, 1, 16);
outProfile.Audio = AudioEncodingProperties.CreatePcm(44100, 2, 32);
var inProfile = MediaEncodingProfile.CreateWav(AudioEncodingQuality.Low);
//inProfile.Audio = AudioEncodingProperties.CreatePcm(16000, 1, 16);
inProfile.Audio = AudioEncodingProperties.CreatePcm(44100, 2, 32);
var outputResult = await this.graph.CreateFileOutputNodeAsync(file,
outProfile);
if (outputResult.Status == AudioFileNodeCreationStatus.Success)
{
this.outputNode = outputResult.FileOutputNode;
var inputResult = await this.graph.CreateDeviceInputNodeAsync(
MediaCategory.Speech,
inProfile.Audio,
microphone);
if (inputResult.Status == AudioDeviceNodeCreationStatus.Success)
{
//EXEPTION IS THROWN HERE
inputResult.DeviceInputNode.AddOutgoingConnection(
this.outputNode);
this.graph.Start();
}
}
}
else
{
throw new Exception("Could not create AudioGraph");
}
Thank you guys for our help

Instead of constructing the inputResult with the inProfile.Audio object, try using the default encoding properties for the graph:
var enc = graph.EncodingProperties;
CreateAudioDeviceInputNodeResult deviceInputNodeResult = await graph.CreateDeviceInputNodeAsync(MediaCategory.Media, enc, this.outputNode);
I had a similar issue and this cleared things up, and allowed the audio to be input from any device without specifying the encoding profile.

Example of QRCode ZXing

I need to create a qrreader with windows phone.
Xzing examples only print to video the qr string captured,
I need an example of how to understand if this string is a vcard and, consequently, save it in contact, or if it is a link and open it in the browser.
private void ScanPreviewBuffer()
{
try
{
_photoCamera.GetPreviewBufferY(_luminance.PreviewBufferY);
var binarizer = new HybridBinarizer(_luminance);
var binBitmap = new BinaryBitmap(binarizer);
var result = _reader.decode(binBitmap);
Dispatcher.BeginInvoke(() => CheckQr(result.Text));
}
catch { }
}
private void CheckQr(string qrString)
{
VibrateController vibrate = VibrateController.Default;
vibrate.Start(TimeSpan.FromMilliseconds(500));
MessageBox.Show(qrString);
/* CONTROLS HERE */
}

Obviously you have to start by parsing the qrString content to get what you want, i think we'll both agree on that point ;)
So the main issues are :
Determining formats (url or vcard)
Parsing them (if needed)
Using them to trigger wanted actions
1. About vCard
To determine if you qrString holds a vCard, maybe you could just try to match (with string.Contains or string.StartsWith methods) the vCard header which is BEGIN:VCARD and always seems to be the same from one version to another (see wikipedia).
For Windows Phone 7, there's no builtin features to parse vCards, so you have to do it by yourself or you could try to use the vCard library For Windows Phone. It would be used this way :
byte[] byteArray = Encoding.UTF8.GetBytes(qrString);
using (StreamReader reader = new StreamReader(new MemoryStream(byteArray)))
{
vCard card = new vCard(reader);
// access here card.PropertyFromvCard to get the information you need
}
There's not so much documentation about it, but sources are available on codeplex, so you'll probably find all the property names and samples you need.
For Windows Phone 8, the builtin ContactInformation.ParseVcardAsync method could help you to parse your qrString content (here is an official tutorial)
Then you need to finally create your contact :
If you're developping your App on Windows Phone 7, there's no way to create a contact directly from your application. You need to use the "save contact task" and pre-populate the fields you need. Here's an example :
SaveContactTask saveContactTask = new SaveContactTask();
saveContactTask.Completed += new EventHandler<SaveContactResult>(saveContactTask_Completed);
saveContactTask.FirstName = "John"; // card.PropertyFromvCard and so on...
saveContactTask.LastName = "Doe";
saveContactTask.MobilePhone = "2065550123";
saveContactTask.Show();
If you're developping on Windows Phone 8 (and it doesn't seem to be the case given your question tags), you can create a Custom contact store and write directly into it
2. About URLs
To know if you're dealing with an URL or not, i would advice you to follow suggestions coming with this SO answer. To make a long story short, here's the code you could use or at least something similar :
static bool IsValidUrl(string qrString)
{
Uri uri;
return Uri.TryCreate(urlString, UriKind.Absolute, out uri)
&& (uri.Scheme == Uri.UriSchemeHttp
|| uri.Scheme == Uri.UriSchemeHttps
|| uri.Scheme == Uri.UriSchemeFtp
|| uri.Scheme == Uri.UriSchemeMailto
/*...*/);
}
And finally to open your URL into a web browser (if it is a valid one of course), you could use the WebBrowser task or embed a true WebBrowser into your application with the WebBrowser control and make good use of it.

ZXing has a class called ResultParser with a static method parseResult.
The ResultParser supports some common content formats like vCard, vEvent, URL, etc.
It gives you as a result an instance of AddressBookParsedResult for vCard content back.
ParsedResult parsedResult = ResultParser.parseResult(result);

Failed to open file after many attempts

I am using PcapDotNet DLL's in my application, and I am encountering a problem:
My application takes a PCap file (Wireshark file) and sends the packets to the network card. If I send a file or files many times (usually ~500 times), my application crashes with the error Failed opening file C:\file.pcap. I tried to ask in the project forum, but the developer isn't there permanently, so maybe someone else could help me here.
The error cause is here in inputCommunicator, and when the error occurs, this object value is null. Please note that this happens only after a few hundred iterations (approximately 500).
code:
using (PacketCommunicator inputCommunicator = selectedInputDevice.Open(65536, PacketDeviceOpenAttributes.Promiscuous, 1000))
{
using (mOutputCommunicator = selectedOutputDevice.Open(100, PacketDeviceOpenAttributes.Promiscuous, 1000))
{
while (inputCommunicator.ReceivePacket(out packet) == PacketCommunicatorReceiveResult.Ok && _isStop) //fill the buffer with the packets from the file
{
using (PacketSendBuffer mSendBuffer = new PacketSendBuffer((uint)packet.Length * 4))
{
else if (packet != null)
{
lastTime = packet.Timestamp;
mSendBuffer.Enqueue(packet); //put the packet in the buffer
}
mOutputCommunicator.Transmit(mSendBuffer, _isBurst); //send the packet
_numberOfSendPackets++;
}
}
}
}

This is a bug in WinPcap.
For the details, see http://www.winpcap.org/pipermail/winpcap-bugs/2012-December/001547.html