HTTP DB Context

context.go

package main

import (
	"context"
	"database/sql"
	"log"
	"net/http"

	_ "github.com/lib/pq"
)

var db *sql.DB

func usersNoCtx() {
	txn, err := db.Begin()
	if err != nil {
		log.Fatal(err)
	}
	log.Println("In txn")
	if _, err := txn.Exec("SELECT pg_sleep(5)"); err != nil {
		log.Println("SELECT error:", err)
	}
	if err := txn.Commit(); err != nil {
		log.Fatal(err)
	}
	log.Println("Committed")
}

func users(ctx context.Context) {
	txn, err := db.BeginTx(ctx, &sql.TxOptions{ReadOnly: true})
	if err != nil {
		log.Fatal(err)
	}
	log.Println("In txn")
	if _, err := txn.ExecContext(ctx, "SELECT pg_sleep(5)"); err != nil {
		log.Println("SELECT error:", err)
	}
	if ctx.Err() != nil {
		log.Println("Context cancelled:", ctx.Err())
		return
	}
	if err := txn.Commit(); err != nil {
		log.Fatal(err)
	}
	log.Println("Committed")
}

func handler(w http.ResponseWriter, r *http.Request) {
	ctx := r.Context()
	users(ctx)
	w.Write([]byte("OK\n"))
}

func main() {
	var err error
	db, err = sql.Open("postgres", "dbname=webthing sslmode=disable")
	if err != nil {
		panic(err)
	}
	if err := db.Ping(); err != nil {
		log.Fatal(err)
	}

	http.HandleFunc("/", handler)

	log.Fatal(http.ListenAndServe("localhost:8088", nil))
}

postgresql.conf

log_min_messages = info
log_connections = on
log_disconnections = on
log_duration = on
log_line_prefix = '[%m] %u@%d '
log_statement = 'all'

$ gtimeout 0.2 curl localhost:8088
2019/01/01 16:09:20 In txn
2019/01/01 16:09:21 SELECT error: pq: canceling statement due to user request
2019/01/01 16:09:21 Context cancelled: context canceled
$ curl localhost:8088
2019/01/01 16:09:32 In txn
2019/01/01 16:09:37 Committed
OK