match HttpRequest app_data behavior in ServiceRequest

[robjtede]

PR Type

Fix

PR Checklist

Check your PR fulfills the following:

• Tests for the changes have been added / updated.
• Documentation comments have been added / updated.
• A changelog entry has been made for the appropriate packages.

Overview

Changes ServiceRequest::app_data to match HttpRequest::app_data's return type since it doesn't make much sense to have different return types given you can just split a ServiceRequest and get at the HttpRequest anyway.

closes #1613

[codecov-commenter]

Codecov Report

Merging #1618 into master will increase coverage by 0.07%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1618      +/-   ##
==========================================
+ Coverage   53.07%   53.15%   +0.07%     
==========================================
  Files         126      126              
  Lines       11757    11770      +13     
==========================================
+ Hits         6240     6256      +16     
+ Misses       5517     5514       -3     

Impacted Files	Coverage Δ
src/service.rs	79.62% <100.00%> (+3.15%)	⬆️
actix-http/src/header/common/accept.rs	0.00% <0.00%> (ø)
actix-http/src/header/common/etag.rs
...ctix-http/src/header/common/if_unmodified_since.rs
actix-http/src/header/common/if_modified_since.rs	0.00% <0.00%> (ø)
actix-http/src/header/common/accept_language.rs	0.00% <0.00%> (ø)

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[fakeshadow]

I like this change. It also fully enabled custom data types where it can be extracted both in handler and requests.