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@divan
Created March 21, 2017 15:01
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Golang database/sql+http example (postgres)
// Run PostgreSQL server:
// docker run -e POSTGRES_PASSWORD="" -p 5432:5432 postgres
// Monitor running processes:
// watch -n 1 'echo "select pid,query_start,state,query from pg_stat_activity;" | psql -h localhost -U postgres
//
// For all handlers, call to db takes 5 seconds,
//
// Three endpoints:
// - "/" - take 5 seconds
// - "/ctx" - take 1 seconds, due to 1 second cancellation policy
// - "/disconnect" - aborts as soon as client disconnected
//
// To test, run:
// curl http://localhost:3000/
// curl http://localhost:3000/ctx
// curl http://localhost:3000/disconnect
package main
import (
"context"
"database/sql"
"log"
"net/http"
"time"
_ "github.com/lib/pq"
)
type server struct {
db *sql.DB
}
func (s *server) handler(w http.ResponseWriter, r *http.Request) {
// slow 5 seconds query
_, err := s.db.Exec("SELECT pg_sleep(5)")
if err != nil {
log.Println("[ERROR]", err)
w.WriteHeader(http.StatusBadRequest)
}
w.Write([]byte("ok"))
}
func (s *server) handlerCtx(w http.ResponseWriter, r *http.Request) {
ctx := context.Background()
ctx, _ = context.WithTimeout(ctx, 1*time.Second)
// slow 5 seconds query
_, err := s.db.ExecContext(ctx, "SELECT pg_sleep(5)")
if err != nil {
log.Println("[ERROR]", err)
w.WriteHeader(http.StatusBadRequest)
}
w.Write([]byte("ok"))
}
func (s *server) handlerDisconnect(w http.ResponseWriter, r *http.Request) {
ctx := context.Background()
ctx, cancelFunc := context.WithCancel(ctx)
// in case of client disconnect, cancel context
if cn, ok := w.(http.CloseNotifier); ok {
go func() {
<-cn.CloseNotify()
cancelFunc()
}()
}
// slow 5 seconds query
_, err := s.db.ExecContext(ctx, "SELECT pg_sleep(5)")
if err != nil {
log.Println("[ERROR]", err)
w.WriteHeader(http.StatusBadRequest)
}
w.Write([]byte("ok"))
}
func main() {
db, err := sql.Open("postgres", "user=postgres sslmode=disable")
if err != nil {
log.Fatal(err)
}
defer db.Close()
s := server{db: db}
http.HandleFunc("/", s.handler)
http.HandleFunc("/ctx", s.handlerCtx)
http.HandleFunc("/disconnect", s.handlerDisconnect)
log.Println("Starting server on :3000...")
log.Fatal(http.ListenAndServe(":3000", nil))
if err != nil && err != http.ErrServerClosed {
log.Fatal(err)
}
}
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