feat: Add HTTP Probe trace time metrics

[haoel]

the following tracing metrics have been added:

• dns: get the ip address, from dnsStartAt() to dnsDone()
• conn: tcp connection, from connectStart() to connectDone()
• tls: tls connection, from tlsStart() to tlsDone()
• send: send the http header, from wroteHeaderField() to wroteHeaders()
• wait: send the http request, from wroteRequest() to gotFirstResponseByte()
• transfer : wait all of data received, from gotFirstResponseByte() to putIdleConn()
• total: from the beginning to the end. getConn() to putIdleConn()

total >= DNS + conn + tls + send + wait +transfer 

it can be seen in Prometheus and Grafana, the following snapshot is an example.

open the debug log, you will see the following debug information

DEBU[2022-06-28T20:26:33+08:00] [http TRACE MegaEase] - total - start get connection: 1656419193697500000 
DEBU[2022-06-28T20:26:33+08:00] [http TRACE MegaEase] - dns - start resolve megaease.com: 1656419193697806 
DEBU[2022-06-28T20:26:33+08:00] [http TRACE MegaEase] - dns - resolve ip [{172.67.222.231 } {104.21.46.25 } {2606:4700:3033::6815:2e19 } {2606:4700:3033::ac43:dee7 }], time 67.725ms 
DEBU[2022-06-28T20:26:33+08:00] [http TRACE MegaEase] - conn - start tcp connect to 172.67.222.231:443: 1656419193765629 
DEBU[2022-06-28T20:26:33+08:00] [http TRACE MegaEase] - conn - tcp connection created to 172.67.222.231:443. time: 85.463ms 
DEBU[2022-06-28T20:26:33+08:00] [http TRACE MegaEase] - tls - start negotiation: 1656419193851180 
DEBU[2022-06-28T20:26:33+08:00] [http TRACE MegaEase] - tls - negotiated to "megaease.com", time: 96.888ms 
DEBU[2022-06-28T20:26:33+08:00] [http TRACE MegaEase] - connection established. reused: false idle: false idle time: 0ms 
DEBU[2022-06-28T20:26:33+08:00] [http TRACE MegaEase] - send - start write header field :authority [megaease.com] : 1656419193948308 
DEBU[2022-06-28T20:26:33+08:00] [http TRACE MegaEase] - send - start write header field :method [GET] : 1656419193948308 
DEBU[2022-06-28T20:26:33+08:00] [http TRACE MegaEase] - send - start write header field :path [/] : 1656419193948308 
DEBU[2022-06-28T20:26:33+08:00] [http TRACE MegaEase] - send - start write header field :scheme [https] : 1656419193948308 
DEBU[2022-06-28T20:26:33+08:00] [http TRACE MegaEase] - send - start write header field user-agent [MegaEase EaseProbe/v1.7.0] : 1656419193948308 
DEBU[2022-06-28T20:26:33+08:00] [http TRACE MegaEase] - send - start write header field accept-encoding [gzip] : 1656419193948308 
DEBU[2022-06-28T20:26:33+08:00] [http TRACE MegaEase] - send - headers written, time: 0.089ms 
DEBU[2022-06-28T20:26:33+08:00] [http TRACE MegaEase] - wait - start write request: 1656419193948405 
DEBU[2022-06-28T20:26:34+08:00] [http TRACE MegaEase] - transfer - start transfer the response: 1656419194738504 
DEBU[2022-06-28T20:26:34+08:00] [http TRACE MegaEase] - wait - got first response byte, time: 790.082ms 
DEBU[2022-06-28T20:26:34+08:00] [http TRACE MegaEase] - transfer - done, time: 0.085ms 
DEBU[2022-06-28T20:26:34+08:00] [http TRACE MegaEase] - total - done , time: 1041.068ms 
DEBU[2022-06-28T20:26:34+08:00] [http TRACE MegaEase] ======================== Trace Stats ====================== 
DEBU[2022-06-28T20:26:34+08:00] [http TRACE MegaEase] DNS       Connect TLS     Send    Wait    Trans   Total 
DEBU[2022-06-28T20:26:34+08:00] [http TRACE MegaEase] 67.73     85.46   96.89   0.09    790.08  0.09    1041.07 
DEBU[2022-06-28T20:26:34+08:00] [http TRACE MegaEase] =========================================================== 

[codecov-commenter]

Codecov Report

Merging #150 (6df2594) into main (2f049ee) will increase coverage by 1.25%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #150      +/-   ##
==========================================
+ Coverage   90.92%   92.18%   +1.25%     
==========================================
  Files          44       45       +1     
  Lines        3020     3197     +177     
==========================================
+ Hits         2746     2947     +201     
+ Misses        203      185      -18     
+ Partials       71       65       -6     

Impacted Files	Coverage Δ
global/global.go	100.00% <ø> (ø)
metric/prometheus.go	100.00% <ø> (+25.80%)	⬆️
probe/http/http.go	100.00% <100.00%> (ø)
probe/http/metrics.go	100.00% <100.00%> (ø)
probe/http/trace.go	100.00% <100.00%> (ø)
probe/tls/metrics.go	100.00% <100.00%> (ø)

---

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[proditis]

Tested and confirmed working as advertised 😄

LGTM

[zhao-kun]

Please update the README for the new feature.

[haoel]

Please update the README for the new feature.

Done!

[zhao-kun]

LGTM