Add case-instensitive GetHeader for HookRequest & HookResponse

[sparshev]

Simple implementation for case-insensitive GetHeader. I thought about caching the keys, but it seems too complicated for now with additional not predictable memory consumption. Tests are included.

Fixes#3555

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.24%. Comparing base (6a7684f) to head (2d0b5cc).
Report is 4 commits behind head on master.

Additional details and impacted files

@@ Coverage Diff @@## master #3556 +/- ##
=======================================
Coverage 91.23% 91.24% =======================================
Files 183 183 Lines 16053 16063 +10 =======================================
+ Hits 14646 14656 +10 
Misses 1231 1231 Partials 176 176 

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[gmlewis]

If you add one more test case to each of your tests that covers lines 57 and 78, respectively, then the linter will be happy. 😄

[sparshev]

Oh you right! Completely forgot about negative cases)

[gmlewis]

Thank you, @sparshev!
LGTM.

Awaiting second LGTM+Approval from any other contributor to this repo before merging.

@stevehipwell - might you have time for a code review? Thank you!

[atilsensalduz]

LGTM! Tiny nit: wdyt to abstract the common functionality into a shared helper function aims to reduce code duplication like below?

func getHeader(headers map[string]string, key string) string {
for k, v := range headers {
if strings.EqualFold(k, key) {
return v
}
}
return ""
}
func (r *HookRequest) GetHeader(key string) string {
return getHeader(r.Headers, key)
}
func (r *HookResponse) GetHeader(key string) string {
return getHeader(r.Headers, key)
}

[gmlewis]

Thank you, @atilsensalduz and @sparshev!
Merging after the tests all pass.