fix: do not pre-bind for BindXXX interface & normalize content-type

[FGYFFFF]

What type of PR is this?

fix

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• The description of this PR title is user-oriented and clear enough for others to understand.
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使用BindXXX()接口时，无需做提前的 pre-bind；并且对 content-type 做归一化处理

(Optional) More detailed description for this PR(en: English/zh: Chinese).

en: do not pre-bind for BindXXX interface & normalize content-type
zh(optional): 使用BindXXX()接口时，无需做提前的 pre-bind；并且对 content-type 做归一化处理

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[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (0619701) 82.52% compared to head (9a6d2f2) 82.54%.

Files	Patch %	Lines
pkg/app/context.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1060      +/-   ##
===========================================
+ Coverage    82.52%   82.54%   +0.02%     
===========================================
  Files           98       98              
  Lines        10025    10026       +1     
===========================================
+ Hits          8273     8276       +3     
+ Misses        1255     1254       -1     
+ Partials       497      496       -1     

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