feat: middleware, expvar

projects/greenlight/cmd/api/main.go

@@ -3,8 +3,10 @@ package main
 import (
 	"context"
 	"database/sql"
+	"expvar"
 	"flag"
 	"os"
+	"runtime"
 	"strings"
 	"sync"
 	"time"
@@ -34,7 +36,8 @@ type config struct {
 		maxOpenConns int
 		maxIdleConns int
 		maxIdleTime  string
-	} // Add a new limiter struct containing fields for the requests-per-second and burst
+	}
+	// Add a new limiter struct containing fields for the requests-per-second and burst
 	// values, and a boolean field which we can use to enable/disable rate limiting
 	// altogether.
 	limiter struct {
@@ -138,6 +141,23 @@ func main() {
 	// established.
 	logger.PrintInfo("database connection pool established", nil)
 
+	// Publish a new "version" variable in the expvar handler containing our application
+	// version number (currently the constant "1.0.0").
+	expvar.NewString("version").Set(version)
+	expvar.Publish("goroutines", expvar.Func(func() any {
+		return runtime.NumGoroutine()
+	}))
+
+	// Publish the database connection pool statistics.
+	expvar.Publish("database", expvar.Func(func() any {
+		return db.Stats()
+	}))
+
+	// Publish the current Unix timestamp.
+	expvar.Publish("timestamp", expvar.Func(func() any {
+		return time.Now().Unix()
+	}))
+
 	app := &application{
 		config: cfg,
 		logger: logger,