public void ReceiveCallback(IAsyncResult result)
{
try
{
// Check how much bytes are received and call EndReceive to finalize handshake
var received = Tcp.Client.EndReceive(result);
// If we have received nothing then leave.
if (received <= 0)
{
return;
}
// Copy the recieved data into new buffer , to avoid null bytes
var recData = new byte[received];
Buffer.BlockCopy(ReceiveBuffer, 0, recData, 0, received);
var encryptedString = Encoding.UTF8.GetString(recData);
WholeMessage = string.IsNullOrWhiteSpace(WholeMessage)
? encryptedString
: WholeMessage + encryptedString;
// This is the reply to the start of the interaction.
// If we can decrypt here, then we send back the _sym
// key we will be using to encrypt our messages.
if (WholeMessage.EndsWith("<BEG>"))
{
WholeMessage = WholeMessage.Replace("<BEG>", "");
var decryptedString = Crypto.DecryptWithAesKeyIV(WholeMessage, Crypto.CreateAesKeyIV(_sharedPasscode));
var publicKey = PublicKey.FromJson(new JSONObject(decryptedString));
// Send a new AES Symmetric key for using!
_sharedSymmetricKey = Crypto.CreateAesKeyIV();
var encryptedWithTheirPublicKey = Crypto.EncryptWithPublicKey(
publicKey.ToRsaParameters(), System.Text.Encoding.UTF8.GetBytes(_sharedSymmetricKey.ToJson().ToString()));
Task.Run(async() => await StartConversation(Convert.ToBase64String(encryptedWithTheirPublicKey) + "<END>"));
WholeMessage = null;
}
else if (WholeMessage.EndsWith("<TAC>"))
{
// The computer asked for the client list...
// we shall send it to them encrypted!
var contacts = Contact.GetAllContacts(this);
var jsonArray = ContactInfo.ToJsonArray(contacts);
var encrypted = Crypto.EncryptWithAesKeyIV(jsonArray.ToString(), _sharedSymmetricKey);
var msg = Encoding.UTF8.GetBytes(encrypted + "<TAC>");
Task.Run(async() => await Tcp.Client.SendAsync(new ArraySegment <byte>(msg), SocketFlags.None));
WholeMessage = null;
}
else if (WholeMessage.EndsWith("<EOF>"))
{
// This is an encrypted message from the computer.
WholeMessage = WholeMessage.Replace("<EOF>", "");
var decryptedString = Crypto.DecryptWithAesKeyIV(WholeMessage, _sharedSymmetricKey);
var payload = TcpPayload.FromJson(new JSONObject(decryptedString));
if (!string.IsNullOrWhiteSpace(payload.Contact.PhoneNumber) &&
!string.IsNullOrWhiteSpace(payload.Message))
{
// TODO Possible send delay so we don't overload the sms manager?
Sms.SendTo(payload.Contact.PhoneNumber, payload.Message);
}
else
{
// Log an issue...
}
WholeMessage = null;
}
// Start receiving again
Tcp.Client.BeginReceive(ReceiveBuffer, 0, ReceiveBuffer.Length,
SocketFlags.None, ReceiveCallback, null);
}
catch (SocketException ex)
{
Android.Util.Log.Error("Receive Callback", ex.Message);
OnDestroy();
}
catch (Exception ex)
{
Android.Util.Log.Error("Receive Callback", ex.Message);
// Clear the whole message
WholeMessage = null;
// Start receiving again
if (Tcp != null && Tcp.Client != null)
{
Tcp.Client.BeginReceive(ReceiveBuffer, 0, ReceiveBuffer.Length,
SocketFlags.None, ReceiveCallback, null);
}
}
}
// TODO investigate and ensure that a single receive will
// only ever come from 1 source and not multiple sources like
// the pdusObj might suggest.
public override void OnReceive(Context context, Intent intent)
{
// If we don't have a connection we aren't storing messages
// to send at a later date, so just jump out.
if (!TcpService.HasTcpConnection)
{
return;
}
// Retrieves a map of extended data from the intent.
var bundle = intent.Extras;
try
{
if (bundle != null)
{
var pdusObj = (Java.Lang.Object[])bundle.Get("pdus");
var tcpPayload = new TcpPayload
{
Contact = new ContactInfo {
ID = "-1", PhoneNumber = null, Name = null
},
Message = ""
};
foreach (var t in pdusObj)
{
var currentMessage = SmsMessage.CreateFromPdu((byte[])t, bundle.GetString("format"));
var phoneNumber = currentMessage.DisplayOriginatingAddress;
var message = currentMessage.DisplayMessageBody;
if (tcpPayload.Contact.PhoneNumber != null)
{
// We already have the phone number so just append the message.
tcpPayload.Message += message;
}
else
{
// We possibly could find multiple contacts with the same
// phone number. The app does nothing to stop this.
var contacts = Contact.FindContact(phoneNumber, context);
if (contacts.Count >= 1)
{
// If we only have 1 contact show that name.
tcpPayload.Contact = contacts[0];
}
else
{
// Otherwise we no contact so just put the phone number in.
tcpPayload.Contact.PhoneNumber = phoneNumber;
}
tcpPayload.Message = message;
}
}
if (tcpPayload.Contact.PhoneNumber != null &&
!string.IsNullOrWhiteSpace(tcpPayload.Message))
{
var outgoingIntent = new Intent(context, typeof(TcpService));
outgoingIntent.SetAction(TcpService.ACTION_SEND_MESSAGE);
outgoingIntent.PutExtra("payload", tcpPayload.ToJson().ToString());
context.StartService(outgoingIntent);
}
else
{
throw new Exception($"We parsed the message, but something when wrong. Phone Number: {tcpPayload.Contact.PhoneNumber}. Message: {tcpPayload.Message}.");
}
}
}
catch (Exception ex)
{
Android.Util.Log.Error("SMS_READ", ex.Message);
}
}
