Added metrics server support

Author: mxmauro

METRICS.md

@@ -0,0 +1,63 @@
+# Health and Metrics controller
+
+## Usage with example
+
+```golang
+package example
+
+import (
+	"encoding/json"
+	"math/rand"
+
+	"github.com/randlabs/go-webserver/v2/metrics"
+)
+
+func main() {
+	// Create a new health & metrics controller with a web server
+	srvOpts := metrics.Options{
+		Address:             "127.0.0.1",
+		Port:                3000,
+		HealthCallback:      healthCallback, // Setup our health check callback
+		EnableDebugProfiles: true,
+	}
+	mc, err := metrics.CreateController(srvOpts)
+	if err != nil {
+		// handle error
+	}
+	defer mc.Stop()
+
+	// Create a custom prometheus counter
+	err = mc.NewCounterWithCallback(
+		"random_counter", "A random counter",
+		func() float64 {
+			// Return the counter value.
+			// The common scenario is to have a shared set of variables you regularly update with the current
+			// state of your application.
+			return rand.Float64()
+		},
+	)
+
+	// Start health & metrics web server
+	err = mc.Start()
+	if err != nil {
+		// handle error
+	}
+
+	// your app code may go here
+}
+
+// Health output will be in JSON format.
+type exampleHealthOutput struct {
+	Status string `json:"status"`
+}
+
+// Our health callback routine.
+func healthCallback() string {
+	state := exampleHealthOutput{
+		Status: "ok",
+	}
+
+	j, _ := json.Marshal(state)
+	return string(j)
+}
+```

go.mod

@@ -1,6 +1,8 @@
 module github.com/randlabs/go-webserver/v2
 
-go 1.20
+go 1.21
+
+toolchain go1.22.2
 
 require (
 	github.com/VictoriaMetrics/fastcache v1.12.2
@@ -10,11 +12,18 @@ require (
 
 require (
 	github.com/andybalholm/brotli v1.1.0 // indirect
+	github.com/beorn7/perks v1.0.1 // indirect
 	github.com/cespare/xxhash/v2 v2.3.0 // indirect
 	github.com/golang/snappy v0.0.4 // indirect
 	github.com/klauspost/compress v1.17.8 // indirect
+	github.com/prometheus/client_golang v1.19.0 // indirect
+	github.com/prometheus/client_model v0.6.1 // indirect
+	github.com/prometheus/common v0.53.0 // indirect
+	github.com/prometheus/procfs v0.14.0 // indirect
+	github.com/randlabs/rundown-protection v1.1.1 // indirect
 	github.com/savsgio/gotils v0.0.0-20240303185622-093b76447511 // indirect
 	github.com/valyala/bytebufferpool v1.0.0 // indirect
 	github.com/valyala/tcplisten v1.0.0 // indirect
-	golang.org/x/sys v0.19.0 // indirect
+	golang.org/x/sys v0.20.0 // indirect
+	google.golang.org/protobuf v1.34.0 // indirect
 )

go.sum

@@ -4,6 +4,8 @@ github.com/allegro/bigcache v1.2.1-0.20190218064605-e24eb225f156 h1:eMwmnE/GDgah
 github.com/allegro/bigcache v1.2.1-0.20190218064605-e24eb225f156/go.mod h1:Cb/ax3seSYIx7SuZdm2G2xzfwmv3TPSk2ucNfQESPXM=
 github.com/andybalholm/brotli v1.1.0 h1:eLKJA0d02Lf0mVpIDgYnqXcUn0GqVmEFny3VuID1U3M=
 github.com/andybalholm/brotli v1.1.0/go.mod h1:sms7XGricyQI9K10gOSf56VKKWS4oLer58Q+mhRPtnY=
+github.com/beorn7/perks v1.0.1 h1:VlbKKnNfV8bJzeqoa4cOKqO6bYr3WgKZxO8Z16+hsOM=
+github.com/beorn7/perks v1.0.1/go.mod h1:G2ZrVWU2WbWT9wwq4/hrbKbnv/1ERSJQ0ibhJ6rlkpw=
 github.com/cespare/xxhash/v2 v2.2.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
 github.com/cespare/xxhash/v2 v2.3.0 h1:UL815xU9SqsFlibzuggzjXhog7bL6oX9BbNZnL2UFvs=
 github.com/cespare/xxhash/v2 v2.3.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
@@ -16,6 +18,16 @@ github.com/golang/snappy v0.0.4/go.mod h1:/XxbfmMg8lxefKM7IXC3fBNl/7bRcc72aCRzEW
 github.com/klauspost/compress v1.17.8 h1:YcnTYrq7MikUT7k0Yb5eceMmALQPYBW/Xltxn0NAMnU=
 github.com/klauspost/compress v1.17.8/go.mod h1:Di0epgTjJY877eYKx5yC51cX2A2Vl2ibi7bDH9ttBbw=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/prometheus/client_golang v1.19.0 h1:ygXvpU1AoN1MhdzckN+PyD9QJOSD4x7kmXYlnfbA6JU=
+github.com/prometheus/client_golang v1.19.0/go.mod h1:ZRM9uEAypZakd+q/x7+gmsvXdURP+DABIEIjnmDdp+k=
+github.com/prometheus/client_model v0.6.1 h1:ZKSh/rekM+n3CeS952MLRAdFwIKqeY8b62p8ais2e9E=
+github.com/prometheus/client_model v0.6.1/go.mod h1:OrxVMOVHjw3lKMa8+x6HeMGkHMQyHDk9E3jmP2AmGiY=
+github.com/prometheus/common v0.53.0 h1:U2pL9w9nmJwJDa4qqLQ3ZaePJ6ZTwt7cMD3AG3+aLCE=
+github.com/prometheus/common v0.53.0/go.mod h1:BrxBKv3FWBIGXw89Mg1AeBq7FSyRzXWI3l3e7W3RN5U=
+github.com/prometheus/procfs v0.14.0 h1:Lw4VdGGoKEZilJsayHf0B+9YgLGREba2C6xr+Fdfq6s=
+github.com/prometheus/procfs v0.14.0/go.mod h1:XL+Iwz8k8ZabyZfMFHPiilCniixqQarAy5Mu67pHlNQ=
+github.com/randlabs/rundown-protection v1.1.1 h1:M0ltneeZ0efBPERxWOLC5JbCP0I3TZce41IUQoQNNJA=
+github.com/randlabs/rundown-protection v1.1.1/go.mod h1:rCfZhLfCKhedcQ0uQvpZbvyaCsPTsreynI2FqwuesGA=
 github.com/savsgio/gotils v0.0.0-20240303185622-093b76447511 h1:KanIMPX0QdEdB4R3CiimCAbxFrhB3j7h0/OvpYGVQa8=
 github.com/savsgio/gotils v0.0.0-20240303185622-093b76447511/go.mod h1:sM7Mt7uEoCeFSCBM+qBrqvEo+/9vdmj19wzp3yzUhmg=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
@@ -29,3 +41,7 @@ github.com/valyala/tcplisten v1.0.0/go.mod h1:T0xQ8SeCZGxckz9qRXTfG43PvQ/mcWh7Fw
 golang.org/x/sys v0.14.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
 golang.org/x/sys v0.19.0 h1:q5f1RH2jigJ1MoAWp2KTp3gm5zAGFUTarQZ5U386+4o=
 golang.org/x/sys v0.19.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
+golang.org/x/sys v0.20.0 h1:Od9JTbYCk261bKm4M/mw7AklTlFYIa0bIp9BgSm1S8Y=
+golang.org/x/sys v0.20.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
+google.golang.org/protobuf v1.34.0 h1:Qo/qEd2RZPCf2nKuorzksSknv0d3ERwp1vFG38gSmH4=
+google.golang.org/protobuf v1.34.0/go.mod h1:c6P6GXX6sHbq/GpV6MGZEdwhWPcYBgnhAHhKbcUYpos=

helpers_test/helpers.go

@@ -49,7 +49,6 @@ func RunWebServer(t *testing.T, initCB func(srv *webserver.Server) error) *TestW
 	}
 
 	// Add some dummy endpoints
-	tws.Server.OPTIONS("/api/version", renderApiVersion)
 	tws.Server.GET("/api/version", renderApiVersion)
 	tws.Server.POST("/api/version", renderApiVersion)
 
@@ -139,8 +138,8 @@ func QueryApiVersion(doPost bool, queryParams map[string]string, headers http.He
 	return resp.StatusCode, resp.Header, nil
 }
 
-func OpenBrowser() {
-	rawUrl := "http://127.0.0.1:3000/"
+func OpenBrowser(path string) {
+	rawUrl := "http://127.0.0.1:3000" + path
 	switch runtime.GOOS {
 	case "linux":
 		_ = exec.Command("xdg-open", rawUrl).Start()

metrics/helpers.go

@@ -0,0 +1,29 @@
+package metrics
+
+// -----------------------------------------------------------------------------
+
+func isJSON(s string) bool {
+	// An official (?) method but a plain text is also considered a valid JSON
+	// var js interface{}
+	// return json.Unmarshal([]byte(s), &js) == nil
+
+	// Our quick approach
+	startIdx := 0
+	endIdx := len(s)
+
+	// Skip blanks at the beginning and the end
+	for startIdx < endIdx && isBlank(s[startIdx]) {
+		startIdx += 1
+	}
+	for endIdx > startIdx && isBlank(s[endIdx-1]) {
+		endIdx -= 1
+	}
+
+	return startIdx < endIdx &&
+		((s[startIdx] == '{' && s[endIdx-1] == '}') ||
+			(s[startIdx] == '[' && s[endIdx-1] == ']'))
+}
+
+func isBlank(ch byte) bool {
+	return ch == ' ' || ch == '\t' || ch == '\r' || ch == '\n'
+}

metrics/metric_handlers.go

@@ -0,0 +1,46 @@
+package metrics
+
+import (
+	"strconv"
+
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+	webserver "github.com/randlabs/go-webserver/v2"
+	"github.com/randlabs/go-webserver/v2/util"
+)
+
+// -----------------------------------------------------------------------------
+
+func (mws *Controller) getHealthHandler() webserver.HandlerFunc {
+	return func(req *webserver.RequestContext) error {
+		// Get current health status from callback
+		status := mws.healthCallback()
+
+		// Send output
+		respHdrs := req.ResponseHeaders()
+		if isJSON(status) {
+			respHdrs.SetBytesKV(util.HeaderContentType, util.ContentTypeApplicationJSON)
+		} else {
+			respHdrs.SetBytesKV(util.HeaderContentType, util.ContentTypeTextPlain)
+		}
+
+		if !req.IsHead() {
+			_, _ = req.WriteString(status)
+		} else {
+			respHdrs.SetBytesK(util.HeaderContentLength, strconv.FormatUint(uint64(int64(len(status))), 10))
+		}
+
+		// Done
+		req.Success()
+		return nil
+	}
+}
+
+func (mws *Controller) getMetricsHandler() webserver.HandlerFunc {
+	return webserver.NewHandlerFromHttpHandler(promhttp.HandlerFor(
+		mws.registry,
+		promhttp.HandlerOpts{
+			EnableOpenMetrics:   true,
+			MaxRequestsInFlight: 5,
+		},
+	))
+}