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http.Client in go
1.15.6
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http.Client가 쓰이는 곳
- RESTful API
- elastic search
- AWS endpoint
http.Client 안씀
- RDBMS connection (postgresql, mysql)
- gRPC
- redis
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http.Client, http.Transport
http.Client: 껍데기
http.Transport: 실제 요청 처리
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http.Transport
실제 http요청이 처리되는 구현체
connection pool을 들고 있어서 goroutine-safe 함
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client.Do(req)
client := &http.Client{} // init 시점에 한번만 생성
req := http.Request { … }
res, err := client.Do(req)
if err != nil { … }
defer res.Body.Close()
…
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Transport shared variables
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getConn()
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tryPutIdleConn()
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default values
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http.ClientTrace
trace := &httptrace.ClientTrace{
GetConn: func(hostPort string) { fmt.Println(“%s”, hostPort) },
}
req.WithContext(httptrace.WithClientTrace(req.Context(), trace))
res, err := client.Do(req)
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httptrace.ClientTrace
Request
1. http.Client.Do(req)
2. RoundTrip()
3. GetConn()
4. idleConn 가져오기 실패
5. idleConnWait에 req 등록
6. go dialConnFor()
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1. DNS Lookup
2. DNSStart()
3. DNSDone()
4. Connect
5. ConnectStart()
6. ConnectDone()
7. TLSHandshake
8. TLSHandshakeStart()
9. TLSHandshakeDone()
10. go readLoop()
11. go writeLoop()
httptrace.ClientTrace
Request dialConnFor()
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httptrace.ClientTrace
Request dialConnFor() pc.readLoop() pc.writeLoop()
1. <- pc.reqch
12. tryDeliver(pc)
7. GotConn()
8. pc.roundTrip()
9. pc.writech <- WriteRequest
10. pc.reqch <- requestAndChan
11. <- WriteErrch, resc
1. <- pc.writech
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httptrace.ClientTrace
Request pc.readLoop() pc.writeLoop()
2. br.peek(1)
3. GotFirstResponseByte()
4. ReadResponse(br)
5. Got100Continue()
6. continueCh <- {}
2. WroteHeaderField()
3. WroteHeaders()
4. Wait100Continue()
5. <- continueCh
6. bw.write(req)
7. WroteRequest()
<- pc.writech
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httptrace.ClientTrace
Request pc.readLoop()
7. ReadResponse(br)
8. requestAndChan.resc <- body
9. <- waitForBodyRead
10. tryPutIdleConn()
11. PutIdleConn()
<- pc.reqch
12. ended roundTrip()
13. ended http.Client.Do()
14. call res.body.Close()
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request가 완료되었을때 trace는??
- 커넥션을 받고 난 뒤 실제 요청을 던지는 시점: GotConn()
- request가 완료되었을때 trace는 RoundTripper interface를 활용해야함
- http.Client에 transport가 interface로 들어가므로,
wrapper를 씌워서 transport.RoundTrip이 끝나는 시점에 trace를 남김
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Datadog에 timespan을 보여주기 적절한 trace 방식
1. Transport Wrapper에서 RoundTrip 시작 전에 Trace
2. Transport.RoundTrip() 호출
3. Transport에서 GetConn() 호출
3. Transport에서 GotConn() 호출
4. Transport Wrapper에서 RoundTrip이 완료되었을때
Trace
connection을 받는데 걸리는 시간
요청을 보내고, 응답을 받는데
걸리는 시간
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요약
1. http.Transport는 한개만 쓸것
2. http.Client.Do()가 끝나고 err가 없으면 res.Body.Close()를 호출할것
3. httptrace.GetConn/GotConn을 활용하여 connect 의 timespan 분리
4. MaxIdleConnsPerHost를 잘 조정하자 (=MaxIdleConns / #hosts)
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끝
컨플루언스 문서
● [Golang] http connection management
● [Golang] http.persistConn, httptrace.ClientTrace