CODEWITHSUNDEEP
go
yatogami jim
yatogami jim

Reputation: 33

First HTTP request always slow

I have following code

package main

import (
    "fmt"
    "net/http"
    "time"
)

func Get(url string, client *http.Client, header []string) (*http.Response, error) {
    start := time.Now()
    req, err := http.NewRequest("GET", url, nil)
    if err != nil {
        return nil, err
    }
    for i := 0; i < len(header)/2; i++ {
        req.Header.Add(header[2*i], header[2*i+1])
    }
    resp, err := client.Do(req)
    fmt.Println(time.Until(start))
    return resp, nil
}

func main() {
    header := []string{"accept-encoding", "gzip, deflate, br"}

    cl := &http.Client{}
    url1 := "https://example1.com"
    url2 := "https://example2.com"
    url3 := "https://www.google.com/"

    resp, _ := Get(url1, cl, header)
    resp, _ = Get(url2, cl, header)
    resp, _ = Get(url3, cl, header)
    fmt.Println(resp)
}

The time of resp, _ := Get(url1, cl, header) is always slow Regardless of url1 change to https://example2.com or https://www.google.com/

like this

1 254.156959ms
2 34.183151ms
2 87.880252ms

Upvotes: 2

Views: 1154

Answers (1)

Oleg Butuzov
Oleg Butuzov

Reputation: 5395

There is a beautiful article on medium on resolving go's DNS issues. Shortly it refers to the Name_Resolution of the net package documentation.

More info can be found in src/net/lookup.go, if you like to read code (and comments).

TL/DR: go can use different dns resolvers, wich you can enable/or test with

GODEBUG=netdns=1 go run main.go
> go package net: hostLookupOrder(redis) = cgo
// osx/macosx case
GODEBUG=netdns=go+2 go run main.go
> go package net: GODEBUG setting forcing use of Go’s resolver go 
> package net: hostLookupOrder(redis) = files,dns

Upvotes: 2

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