Adds upload_files functionality for request transport

[DENKweit]

@leszekhanusz This PR requires a new package dependency: requests_toolbelt but I'm not sure where to include it. Could you add it for me? Thanks!

[leszekhanusz]

@leszekhanusz This PR requires a new package dependency: requests_toolbelt but I'm not sure where to include it. Could you add it for me? Thanks!

I don't have access to a pc right now but you could add it to the install_requests_requires array in setup.py

[codecov-commenter]

Codecov Report

Merging #244 (3697543) into master (af8f223) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #244   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           16        16           
  Lines         1214      1240   +26     
=========================================
+ Hits          1214      1240   +26     

Impacted Files	Coverage Δ
gql/transport/requests.py	100.00% <100.00%> (ø)

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[DENKweit]

@leszekhanusz Could you have a look and merge this PR if you're satisfied? :)

[leszekhanusz]

For the coverage, you could refactor:

            if self.headers is None:
                post_args["headers"] = {"Content-Type": data.content_type}
            else:
                post_args["headers"]["Content-Type"] = data.content_type

into:

            if post_args["headers"] is None:
                post_args["headers"] = {}

            post_args["headers"]["Content-Type"] = data.content_type

[leszekhanusz]

LGTM 🚀
Just please add a maximum version for the requests_toolbelt dependency.

[leszekhanusz]

Thanks, I'll merge this PR next week.

[maaft]

Hi! I noticed something strange with this PR.. The content-type header gets set correctly to "multipart/form-data" when you do an upload mutation, but when you execute another mutation/query on the same client afterwards, this header is still present.

Looking at the code, I fail to grasp how this can be the case as post_args exists only in the local context and should not have any impact after the mutation was send.. @leszekhanusz @DENKweit do you have any idea how this can happen??

[leszekhanusz]

Indeed, post_args["headers"] is set as a reference to self.headers so if you modify it, you modify self.headers.
This is a bug.

[DENKweit]

Thank you for finding this! So, this is happening:

• post_args["headers"] is initialized to self.headers
• setting post_args["headers"]["Content-Type"] to foo is also modifying self.headers which gets used again during the next request

Writing a fix now.

[leszekhanusz]

Thanks @DENKweit, @maaft !