Include rate limit headers in response

[JaredShay]

Responses contain a lot of information in headers.

x-ratelimit-limit-requests
x-ratelimit-limit-tokens
x-ratelimit-remaining-requests
x-ratelimit-remaining-tokens
x-ratelimit-reset-requests
x-ratelimit-reset-tokens

These are not accessible as the response objects are json representations of the response body.

Having access to these values would be helpful to implement custom rate limiting without relying on parsing out values from error messages.

There are a few ways to do this:

• To keep backwards compatibility an optional flag: include_headers could be provided to the client interface. The response object could then contain a top level key with the headers (parsed into a usable format). This modifies the payload from the underlying service so it isn't a very clean solution.
• Break backwards compatibility and return response objects. This is a pretty big design change, but it may have other benefits like avoiding code such as response.dig("choices", 0, "message", "function_call", "arguments") when you're trying to fetch values from the payload
• Add, and document, custom errors that are raised that contain all of the rate limiting information in a readable format. This doesn't allow for implementing back-off logic prior to encountering an error, but could be implemented without breaking the api.

[alexrudall]

This PR enables this kinda thing as needed I think. eg. if you set

OpenAI::Client.new do |client|
  client.response :logger, ::Logger.new(STDOUT), bodies: true
end

ya get everything including

openai-version: "2020-10-01"
strict-transport-security: "max-age=15724800; includeSubDomains"
x-ratelimit-limit-requests: "3500"
x-ratelimit-limit-tokens: "90000"
x-ratelimit-remaining-requests: "3499"
x-ratelimit-remaining-tokens: "89980"
x-ratelimit-reset-requests: "17ms"
x-ratelimit-reset-tokens: "12ms"

[JaredShay]

That looks great. Allowing the ability to pass in middleware means anything can be modified. I can access the headers and set them as variables, add them to the response, log them, etc.

Absolutely solves my use case. Thanks for the quick reply.

[alexrudall]

@JaredShay Awesome, that's released in v6.3!