changed response type of API to application/JSON

[pgrudra]

PR for issue: #883

// Helper handlers

// Error replies to the request with the specified error message and HTTP code.
// It does not otherwise end the request; the caller should ensure no further
// writes are done to w.
// The error message should be plain text.
func Error(w ResponseWriter, error string, code int) {
	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
	w.Header().Set("X-Content-Type-Options", "nosniff")
	w.WriteHeader(code)
	fmt.Fprintln(w, error)
}

Removed use of inbuilt function http.Error()

Screenshot of response after merging PR attached.

[codecov-commenter]

Codecov Report

Merging #948 (360a47f) into staging (b064087) will not change coverage.
The diff coverage is n/a.

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@@           Coverage Diff            @@
##           staging     #948   +/-   ##
========================================
  Coverage    26.63%   26.63%           
========================================
  Files           76       76           
  Lines         7648     7648           
========================================
  Hits          2037     2037           
  Misses        5345     5345           
  Partials       266      266           

Flag	Coverage Δ
Unit-Tests	26.63% <ø> (ø)

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[service-0chain]

Manual system tests [failure] with the following config

config	value
tests skipped	FALSE
system-tests	master
gosdk	NOT OVERRIDDEN
zboxcli	staging
zwalletcli	staging
0chain	staging
blobber	test_response_for_error
authorizer	staging
0box	staging
0block	staging
0dns	staging
explorer	master
0proxy	staging
0search	staging

[peterlimg]

LGTM

[peterlimg]

@din-mukhammed please fix the system test errors, search re-run 2 in the failed cases, and see what happened.

[dabasov]

@pgrudra @peterlimg please pay attention that appropriate issue is attached to the PR

[peterlimg]

All failed cases in system tests are known cases that are not related to the changes, I'll mark it as pass.

[service-0chain]

Manual system tests [success] with the following config

config	value
tests skipped	TRUE
system-tests	master
gosdk	NOT OVERRIDDEN
zboxcli	staging
zwalletcli	staging
0chain	staging
blobber	test_response_for_error
authorizer	staging
0box	staging
0block	staging
0dns	staging
explorer	master
0proxy	staging
0search	staging