Correctly handle partial JSON at the end of a chunk

[PallavAg]

What

Streaming a response occasionally encounters the error "The given data was not valid JSON."
Related Issues: #97 #103

Why

The end of a chunk can have an incomplete JSON.
The rest of the JSON will come through at the beginning of the next chunk.

Affected Areas

StreamingSession.swift

More Info

This change stores the last JSON from the chunk and appends it to the beginning of the next chunk.

A likely partial JSON is stored when:

1. ResultType decoding fails
2. APIErrorResponse decoding fails
3. The JSON is last in the chunk

---

Having an incomplete JSON at the end of a chunk is seemingly random - likely based on OpenAI server load etc.
A request that surfaces this issue more often than not is: "Write 1 to 40 using bullet points"

// Sample incomplete chunk
{"id":"chatcmpl-893wTs9tI87Yt0t6moRbyhXT2xn93","object":"chat.completion.chunk","created":1697170797,"model":"gpt-4-0613","choices":[{"index":0,"delta":{"content":"."},"fi

---

Kudos to @jcmourey for suggesting the fix in #97

[PSchmiedmayer]

Nice, great addition @PallavAg, we run experience the same issue as noted in #103, this looks like a nice and useful fix, makes sense that it is not guaranteed that each streaming package contains a fully contained JSON.

Would be amazing if this can be merged and added in a next release.

[ingvarus-bc]

Neat! 🔥
Amazing addition to the project. What do you think about moving all json handling outside of urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) to a separate method for the sake of testability and more obvious look?

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
1 Code Smell

No Coverage information
0.0% Duplication

[ingvarus-bc]

@PallavAg, hi, I just moved json processing out, what do you think?

[prateekshac1]

It looks like this issue has started to happen again. Have noticed the intensity of this go up in the past 2-3 days. I'm using the latest version of OpenAI 0.2.5 which has this fix. But yet many of my chatsStream(query: query) queries are erroring out with this error

"The data couldn’t be read because it isn’t in the correct format. dataCorrupted(Swift.DecodingError.Context(codingPath: [], debugDescription: "The given data was not valid JSON.", underlyingError: Optional(Error Domain=NSCocoaErrorDomain Code=3840 "Unable to parse empty data." UserInfo={NSDebugDescription=Unable to parse empty data.})))"