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responder.go
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/
responder.go
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package greenlight
import (
"context"
"fmt"
"log/slog"
"net/http"
"sync"
)
type Responder struct {
addr string
current Signal
mu *sync.Mutex
ch chan Signal
logger *slog.Logger
}
func NewResponder(cfg *ResponderConfig) (*Responder, chan Signal) {
ch := make(chan Signal, 1)
return &Responder{
addr: cfg.Addr,
mu: &sync.Mutex{},
ch: ch,
logger: slog.With("module", "responder"),
}, ch
}
func (r *Responder) Run(ctx context.Context) error {
r.logger.Info("starting responder")
defer r.logger.Info("responder exited")
srv := http.Server{
Addr: r.addr,
Handler: r.handler(),
}
go func() {
<-ctx.Done()
srv.Shutdown(ctx)
}()
go r.signalLisetener(ctx)
r.logger.Info(fmt.Sprintf("listening on %s", r.addr))
if err := srv.ListenAndServe(); err != nil {
r.logger.Error("failed to listen and serve", slog.String("error", err.Error()))
return err
}
return nil
}
func (r *Responder) setCurrentSignal(s Signal) {
r.mu.Lock()
defer r.mu.Unlock()
if r.current == s {
return
} else {
r.logger.Info(fmt.Sprintf("signal changed %s -> %s", r.current, s))
}
r.current = s
}
func (r *Responder) getCurrentSignal() Signal {
r.mu.Lock()
defer r.mu.Unlock()
return r.current
}
func (r *Responder) signalLisetener(ctx context.Context) {
for {
select {
case <-ctx.Done():
return
case s := <-r.ch:
r.logger.Debug("received", slog.String("signal", string(s)))
r.setCurrentSignal(s)
}
}
}
func (r *Responder) handler() http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
code := http.StatusOK
msg := "OK"
defer func() {
req.Body.Close()
r.logger.Info(
msg,
slog.String("method", req.Method),
slog.String("path", req.URL.Path),
slog.String("proto", req.Proto),
slog.Int("status", code),
slog.String("remote_addr", req.RemoteAddr),
slog.String("host", req.Host),
slog.String("user_agent", req.UserAgent()),
)
}()
w.Header().Set("Content-Type", "text/plain")
w.Header().Set("Server", "greenlight/"+Version)
s := r.getCurrentSignal()
switch s {
case SignalGreen:
case SignalYellow, SignalRed:
code = http.StatusServiceUnavailable
msg = "Service Unavailable"
default:
r.logger.Warn(fmt.Sprintf("unknown signal: %s", s))
code = http.StatusInternalServerError
msg = "Internal Server Error"
}
w.WriteHeader(code)
fmt.Fprintln(w, msg)
})
}