go-app/pkg/srv/http.go

package srv

import (
	"context"
	"net"
	"net/http"
	"time"

	"github.com/prometheus/client_golang/prometheus/promhttp"
	"github.com/rs/zerolog"
	"go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
	"go.opentelemetry.io/otel/metric"
	"go.opentelemetry.io/otel/trace"

	"gitea.libretechconsulting.com/rmcguire/go-app/pkg/config"
	"gitea.libretechconsulting.com/rmcguire/go-app/pkg/otel"
)

var (
	httpMeter       metric.Meter
	httpTracer      trace.Tracer
	defReadTimeout  = 10 * time.Second
	defWriteTimeout = 10 * time.Second
	defIdleTimeout  = 15 * time.Second
)

type HTTPFunc struct {
	Path        string
	HandlerFunc http.HandlerFunc
}

type HTTPServerOpts struct {
	Ctx              context.Context
	HandleFuncs      []HTTPFunc
	Middleware       []http.Handler
	HealthCheckFuncs []HealthCheckFunc
}

func prepHTTPServer(opts *HTTPServerOpts) *http.Server {
	var (
		cfg = config.MustFromCtx(opts.Ctx)
		l   = zerolog.Ctx(opts.Ctx)
		mux = &http.ServeMux{}
	)

	// NOTE: Wraps handle func with otelhttp handler and
	// inserts route tag
	otelHandleFunc := func(pattern string, handlerFunc func(http.ResponseWriter, *http.Request)) {
		handler := otelhttp.WithRouteTag(pattern, http.HandlerFunc(handlerFunc))
		mux.Handle(pattern, handler) // Associate pattern with handler
	}

	healthChecks := handleHealthCheckFunc(opts.Ctx, opts.HealthCheckFuncs...)
	otelHandleFunc("/health", healthChecks)
	otelHandleFunc("/", healthChecks)

	for _, f := range opts.HandleFuncs {
		otelHandleFunc(f.Path, f.HandlerFunc)
	}

	// Prometheus metrics endpoint
	if cfg.OTEL.PrometheusEnabled {
		mux.Handle(cfg.OTEL.PrometheusPath, promhttp.Handler())
		l.Info().Str("prometheusPath", cfg.OTEL.PrometheusPath).
			Msg("mounted prometheus metrics endpoint")
	}

	// Add OTEL, skip health-check spans
	// NOTE: Add any other span exclusions here
	handler := otelhttp.NewHandler(mux, "/",
		otelhttp.WithFilter(func(r *http.Request) bool {
			switch r.URL.Path {
			case "/health":
				return false
			case cfg.OTEL.PrometheusPath:
				return false
			default:
				return true
			}
		}))

	// Set timeouts from defaults, override
	// with config timeouts if set
	readTimeout := defReadTimeout
	writeTimeout := defWriteTimeout
	idleTimeout := defIdleTimeout

	rT, wT, iT := cfg.HTTP.Timeouts()
	if rT != nil {
		readTimeout = *rT
	}
	if wT != nil {
		writeTimeout = *wT
	}
	if iT != nil {
		idleTimeout = *iT
	}

	// Inject any supplied middleware
	for i := len(opts.Middleware) - 1; i >= 0; i-- {
		mw := opts.Middleware[i]
		next := handler
		handler = http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			mw.ServeHTTP(w, r)
			next.ServeHTTP(w, r)
		})
	}

	// Inject logging middleware
	if cfg.HTTP.LogRequests {
		handler = loggingMiddleware(opts.Ctx, handler)
	}

	return &http.Server{
		Addr:         cfg.HTTP.Listen,
		ReadTimeout:  readTimeout,
		WriteTimeout: writeTimeout,
		IdleTimeout:  idleTimeout,
		Handler:      handler,
		BaseContext: func(_ net.Listener) context.Context {
			return opts.Ctx
		},
	}
}

// Returns a shutdown func and a done channel if the
// server aborts abnormally. Panics on error.
func MustInitHTTPServer(opts *HTTPServerOpts) (
	func(context.Context) error, <-chan interface{},
) {
	shutdownFunc, doneChan, err := InitHTTPServer(opts)
	if err != nil {
		panic(err)
	}
	return shutdownFunc, doneChan
}

// Returns a shutdown func and a done channel if the
// server aborts abnormally. Returns error on failure to start
func InitHTTPServer(opts *HTTPServerOpts) (
	func(context.Context) error, <-chan interface{}, error,
) {
	l := zerolog.Ctx(opts.Ctx)
	doneChan := make(chan interface{})

	var server *http.Server

	httpMeter = otel.GetMeter(opts.Ctx, "http")
	httpTracer = otel.GetTracer(opts.Ctx, "http")

	server = prepHTTPServer(opts)

	go func() {
		l.Debug().Msg("HTTP Server Started")
		err := server.ListenAndServe()
		if err != nil && err != http.ErrServerClosed {
			l.Err(err).Msg("HTTP server error")
		} else {
			l.Info().Msg("HTTP server shut down")
		}
		doneChan <- nil
	}()

	// Shut down http server with a deadline
	return func(shutdownCtx context.Context) error {
		l.Debug().Msg("stopping http server")
		server.Shutdown(shutdownCtx)
		return nil
	}, doneChan, nil
}