Fix multipart file readers not being reset when doing a retry

[nikplx]

As mentioned in https://github.com/go-resty/resty/issues/166 by @neganovalexey, when doing a retry on a multipart request the io.Reader is not reset to the start again. This can lead to subtle bugs, as the request will be retried, but the form part of the file will be empty, because the reader was already exhausted. Solving this issue in the caller code is pretty ugly, because Request does not expose access to multipartFiles and so the caller would have to use RetryHooks and recreate the Response.Request and that at each call site (where there is access to the original ReadSeeker).

In the PR, I created a new client options SetRetryResetReaders which adds a retry hook seeking the start of each reader in multipartFiles, if the reader it got also implements io.ReadSeeker. This solved the above issue described above for my usecase and should have minimal implications on existing usages.

[SVilgelm]

What about the readers that cannot be reset?

[nikplx]

@SVilgelm They won't be reset. The code only resets the reader if it implements io.ReadSeeker and that only if you enable it, so as to not break any existing code. Every other reader will be untouched. I don't know if there is a usecase for passing in a reader that should not be reset, but it will not do anything if there is a reader that can not be reset.

[jeevatkm]

@nikplx I'm sorry for the delayed attention on the PR. Thanks for your contribution.

[jeevatkm]

@nikplx I'm sorry for the delayed attention on the PR. Thanks for your contribution. Yes, it make sense to provide the reset readers option for resty users.

[nikplx]

Hey @jeevatkm

I fixed the test stage. There was some mixup in the sum file. It now runs locally. Maybe you can retrigger the pipeline if you have some time.

[codecov[bot]]

Codecov Report

Merging #549 (23e9fef) into master (0451c4c) will decrease coverage by 0.11%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #549      +/-   ##
==========================================
- Coverage   95.94%   95.84%   -0.11%     
==========================================
  Files          10       10              
  Lines        1357     1372      +15     
==========================================
+ Hits         1302     1315      +13     
- Misses         34       36       +2     
  Partials       21       21              

Impacted Files	Coverage Δ
request.go	95.47% <ø> (ø)
client.go	97.78% <100.00%> (+0.01%)	:arrow_up:
retry.go	100.00% <100.00%> (ø)
util.go	94.44% <0.00%> (-1.12%)	:arrow_down:

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[jeevatkm]

@nikplx This time PR validation build executed without any issue.

Do you mind checking this codecov feedback?