Problem
My app needs to send an HTTP-like request over TCP, followed by periodic data and get back a stream of data in the foreground and background in return.
In the background, I need to open and close the socket after receiving a Bluetooth characteristic value, which is an unnecessary overhead that slows the user down and may lead to a lot of lost data.
Currently
In the foreground, it opens an NSSocket (through a framework), sends the initial request and periodically sends and receives data.
While in the background, the app is started when it receives a characteristic value from the bluetooth-central background mode. It then opens the socket to send some initial data, waits for some data in return, and closes the socket.
Considerations
The protocol I need to connect to is HTTP-like (NTRIP), so I considered using a URLSession, which can keep a socket open, even in the background. However, the protocol has some non-standard behaviors. Namely:
- It can return a
SOURCETABLEresponse (interchangeable withHTTP/1.1). - Some implementations have a non-standard second status line (e.g.
HTTP/1.1 OK 200, followed byHTTP/1.1. Not Authorized 401). - Some rare implementations incorrectly fail to separate the status line and message body with CRLF.
- The connection needs to be kept open to periodically send and receive data.
A future revision of NTRIP does enforce HTTP compliance, but is not yet widely used.