golang-saas-starter-kit/example-project/internal/mid/errors.go

package mid

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

	"geeks-accelerator/oss/saas-starter-kit/example-project/internal/platform/web"
	"go.opencensus.io/trace"
)

// Errors handles errors coming out of the call chain. It detects normal
// application errors which are used to respond to the client in a uniform way.
// Unexpected errors (status >= 500) are logged.
func Errors(log *log.Logger) web.Middleware {

	// This is the actual middleware function to be executed.
	f := func(before web.Handler) web.Handler {

		// Create the handler that will be attached in the middleware chain.
		h := func(ctx context.Context, w http.ResponseWriter, r *http.Request, params map[string]string) error {
			ctx, span := trace.StartSpan(ctx, "internal.mid.Errors")
			defer span.End()

			// If the context is missing this value, request the service
			// to be shutdown gracefully.
			v, ok := ctx.Value(web.KeyValues).(*web.Values)
			if !ok {
				return web.NewShutdownError("web value missing from context")
			}

			if err := before(ctx, w, r, params); err != nil {

				// Log the error.
				log.Printf("%s : ERROR : %+v", v.TraceID, err)

				// Respond to the error.
				if err := web.RespondError(ctx, w, err); err != nil {
					return err
				}

				// If we receive the shutdown err we need to return it
				// back to the base handler to shutdown the service.
				if ok := web.IsShutdown(err); ok {
					return err
				}
			}

			// The error has been handled so we can stop propagating it.
			return nil
		}

		return h
	}

	return f
}