Fix generated go client cannot upload file

[dhontecillas]

Fixes #8392 with the naive approach of checking if the body type is **os.File , so it can read its content and avoid the bug of not reading the bytes and having content-length 0.

Tested the fixed code on a separate branch in the same repo used to reproduce the issue : https://github.com/dhontecillas/openapi-generator-go-upload-bug/tree/test_fix (the updated line can be found in https://github.com/dhontecillas/openapi-generator-go-upload-bug/blob/test_fix/pkg/bug/client.go#L415 ). When running the go run . command in that branch, the bug is not reproduced anymore. We get an output of :

The request failed for a different reason: Post "http://127.0.0.1:8000/upload": dial tcp 127.0.0.1:8000: connect: connection refused

That is the expected result as we do not have any server running.

Can you have a look @antihax @grokify @kemokemo @jirikuncar please ? thank you

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[dhontecillas]

hi @jirikuncar , I see there is a test failing for this PR, could you help me into fixing that ?

[wing328]

cc @antihax (2017/11) @grokify (2018/07) @kemokemo (2018/09) @jirikuncar (2021/01)

[wing328]

CircleCI failure due to code format change in the sample. Will fix it after merging this in the master.

[wing328]

@dhontecillas thanks for the PR, which has been included in the v5.1.0 release: https://twitter.com/oas_generator/status/1373636654024380423