feat: add transport-neutral request metrics

metrics/metrics.go

@@ -0,0 +1,106 @@
+// Package metrics provides a small transport-neutral request metrics collector.
+// It is intentionally in-memory and dependency-free; applications can expose
+// Snapshot through any route or export it to their monitoring system.
+package metrics
+
+import (
+	"sync/atomic"
+	"time"
+
+	apierrors "git.yuntuo.hk/k2safe/go-omni/errors"
+	"git.yuntuo.hk/k2safe/go-omni/httpx"
+)
+
+// Snapshot is a point-in-time view of request metrics collected by Metrics.
+type Snapshot struct {
+	Requests        uint64            `json:"requests"`
+	Errors          uint64            `json:"errors"`
+	InFlight        int64             `json:"inFlight"`
+	TotalDurationMs float64           `json:"totalDurationMs"`
+	StatusCounts    map[string]uint64 `json:"statusCounts"`
+}
+
+// Metrics collects request counts, status counts, in-flight requests and
+// cumulative handler time. A zero Metrics value is ready for use.
+type Metrics struct {
+	requests   atomic.Uint64
+	errors     atomic.Uint64
+	inFlight   atomic.Int64
+	durationNs atomic.Int64
+	statuses   [600]atomic.Uint64
+}
+
+// New creates an empty metrics collector.
+func New() *Metrics { return &Metrics{} }
+
+// Middleware records every request that reaches the middleware chain. Errors
+// include returned handler errors and responses with a status of 400 or greater.
+func (m *Metrics) Middleware() httpx.Middleware {
+	return func(next httpx.Handler) httpx.Handler {
+		return func(ctx *httpx.Context) error {
+			if m == nil {
+				return next(ctx)
+			}
+			m.inFlight.Add(1)
+			started := time.Now()
+			err := next(ctx)
+			status := ctx.Status()
+			if err != nil && !ctx.Responded() {
+				status = apierrors.From(err).Status
+			}
+			m.requests.Add(1)
+			if err != nil || status >= 400 {
+				m.errors.Add(1)
+			}
+			if status >= 0 && status < len(m.statuses) {
+				m.statuses[status].Add(1)
+			}
+			m.durationNs.Add(time.Since(started).Nanoseconds())
+			m.inFlight.Add(-1)
+			return err
+		}
+	}
+}
+
+// Handler exposes the current snapshot through the standard GoOmni response
+// envelope. Register it explicitly, for example app.GET("/metrics", m.Handler()).
+func (m *Metrics) Handler() httpx.Handler {
+	return func(ctx *httpx.Context) error {
+		return ctx.OK(m.Snapshot())
+	}
+}
+
+// Snapshot returns a consistent-enough point-in-time view for operational
+// reporting. Counters may advance while the snapshot is being assembled.
+func (m *Metrics) Snapshot() Snapshot {
+	if m == nil {
+		return Snapshot{StatusCounts: map[string]uint64{}}
+	}
+	statuses := make(map[string]uint64)
+	for status := 100; status < len(m.statuses); status++ {
+		if count := m.statuses[status].Load(); count > 0 {
+			statuses[itoa(status)] = count
+		}
+	}
+	return Snapshot{
+		Requests:        m.requests.Load(),
+		Errors:          m.errors.Load(),
+		InFlight:        m.inFlight.Load(),
+		TotalDurationMs: float64(m.durationNs.Load()) / float64(time.Millisecond),
+		StatusCounts:    statuses,
+	}
+}
+
+func itoa(value int) string {
+	if value == 0 {
+		return "0"
+	}
+	var digits [3]byte
+	index := len(digits)
+	for value > 0 {
+		index--
+		digits[index] = byte('0' + value%10)
+		value /= 10
+	}
+	return string(digits[index:])
+}