Post Context deadline exceeded (Client.Timeout exceeded while awaiting headers)

Question

I am running a simple query using Clickhouse HTTP Interface

package main

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

func main() {

    url := "http://localhost:8123" + "?query=select%201"
    req, _ := http.NewRequest("Post", url, nil)

    // set headers
    req.Header.Set("X-ClickHouse-User", "user")      //user
    req.Header.Set("X-ClickHouse-Key", "password") //password

    client := &http.Client{
        Timeout: 5 * time.Second,
    }
    resp, err := client.Do(req)
    if err != nil {
        fmt.Println(err.Error())
    } else {
        fmt.Println("Success")
    }
}

It is giving me this error Post "http://localhost:8123?query=select%201": context deadline exceeded (Client.Timeout exceeded while awaiting headers)

Note: If I use insert query instead of this select query it will give me the same error but also will insert the data correctly.

Any help would be appreciated.

Thanks

Answer 1

I did a quick sample here using your code, and as I suspected, locally this error only happens when the server times out. Maybe postman is doing something that hides this behavior.

Also, don't forget that the http.Client timeout is for the entire request-response cycle that is constituted up of Dialer, TLS Handshake, Request Header, Request Body, Response Header and Response Body timeouts.

Please take a look in the POC below and change the timeout() for different values to see the success (4- sec) or fail (5+ sec).

package main

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


func timeout(w http.ResponseWriter, req *http.Request) {
    time.Sleep(5 * time.Second)
}

func server() {
    go func() {
        http.HandleFunc("/", timeout)
        log.Fatal(http.ListenAndServe(":8123", nil))
    }()
}

func main() {
    server()

        url := "http://localhost:8123" + "?query=select%201"
    req, _ := http.NewRequest("Post", url, nil)

    // set headers
    req.Header.Set("X-ClickHouse-User", "user")      //user
    req.Header.Set("X-ClickHouse-Key", "password") //password

    client := &http.Client{
        Timeout: 5 * time.Second,
    }
    resp, err := client.Do(req)
    if err != nil {
        fmt.Println(err.Error())
    } else {
        fmt.Println("Success", resp)
    }
}

you can also try to make use of specific http.Client timeouts as for example:

c := &http.Client{
    Transport: &http.Transport{
        Dial: (&net.Dialer{
                Timeout:   30 * time.Second,
                KeepAlive: 30 * time.Second,
        }).Dial,
        TLSHandshakeTimeout:   10 * time.Second,
        ResponseHeaderTimeout: 10 * time.Second,
        ExpectContinueTimeout: 1 * time.Second,
    }
}

Some references that may help you: https://blog.cloudflare.com/the-complete-guide-to-golang-net-http-timeouts/ https://itnext.io/http-request-timeouts-in-go-for-beginners-fe6445137c90 https://gosamples.dev/http-client-timeout/