新增request中间件设计

[guonaihong]

see #235

[codecov-commenter]

Codecov Report

Merging #236 into master will decrease coverage by 0.07%.
The diff coverage is 75.00%.

@@            Coverage Diff             @@
##           master     #236      +/-   ##
==========================================
- Coverage   92.61%   92.53%   -0.08%     
==========================================
  Files          41       41              
  Lines        1922     1930       +8     
==========================================
+ Hits         1780     1786       +6     
- Misses         96       97       +1     
- Partials       46       47       +1     

Impacted Files	Coverage Δ
dataflow/req.go	83.77% <50.00%> (-0.61%)	⬇️
dataflow/dataflow.go	94.21% <100.00%> (+0.12%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update d58f429...6dbf348. Read the comment docs.