From f1c107c43d25e841fa0a3a0807448d2a473e4724 Mon Sep 17 00:00:00 2001
From: bryan newbold <bnewbold@robocracy.org>
Date: Fri, 28 Mar 2025 16:10:10 -0700
Subject: [PATCH] new svcutil package, with MetricsMiddleware

---
 util/svcutil/metrics_middleware.go | 99 ++++++++++++++++++++++++++++++
 1 file changed, 99 insertions(+)
 create mode 100644 util/svcutil/metrics_middleware.go

diff --git a/util/svcutil/metrics_middleware.go b/util/svcutil/metrics_middleware.go
new file mode 100644
index 00000000..10c5e08d
--- /dev/null
+++ b/util/svcutil/metrics_middleware.go
@@ -0,0 +1,99 @@
+package svcutil
+
+import (
+	"errors"
+	"net/http"
+	"strconv"
+	"time"
+
+	"github.com/labstack/echo/v4"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+)
+
+var reqSz = promauto.NewHistogramVec(prometheus.HistogramOpts{
+	Name:    "http_request_size_bytes",
+	Help:    "A histogram of request sizes for requests.",
+	Buckets: prometheus.ExponentialBuckets(100, 10, 8),
+}, []string{"code", "method", "path"})
+
+var reqDur = promauto.NewHistogramVec(prometheus.HistogramOpts{
+	Name:    "http_request_duration_seconds",
+	Help:    "A histogram of latencies for requests.",
+	Buckets: prometheus.ExponentialBuckets(0.001, 2, 15),
+}, []string{"code", "method", "path"})
+
+var reqCnt = promauto.NewCounterVec(prometheus.CounterOpts{
+	Name: "http_requests_total",
+	Help: "A counter for requests to the wrapped handler.",
+}, []string{"code", "method", "path"})
+
+var resSz = promauto.NewHistogramVec(prometheus.HistogramOpts{
+	Name:    "http_response_size_bytes",
+	Help:    "A histogram of response sizes for requests.",
+	Buckets: prometheus.ExponentialBuckets(100, 10, 8),
+}, []string{"code", "method", "path"})
+
+// MetricsMiddleware defines handler function for metrics middleware
+func MetricsMiddleware(next echo.HandlerFunc) echo.HandlerFunc {
+	return func(c echo.Context) error {
+		path := c.Path()
+		if path == "/metrics" || path == "/_health" {
+			return next(c)
+		}
+
+		start := time.Now()
+		requestSize := computeApproximateRequestSize(c.Request())
+
+		err := next(c)
+
+		status := c.Response().Status
+		if err != nil {
+			var httpError *echo.HTTPError
+			if errors.As(err, &httpError) {
+				status = httpError.Code
+			}
+			if status == 0 || status == http.StatusOK {
+				status = http.StatusInternalServerError
+			}
+		}
+
+		elapsed := float64(time.Since(start)) / float64(time.Second)
+
+		statusStr := strconv.Itoa(status)
+		method := c.Request().Method
+
+		responseSize := float64(c.Response().Size)
+
+		reqDur.WithLabelValues(statusStr, method, path).Observe(elapsed)
+		reqCnt.WithLabelValues(statusStr, method, path).Inc()
+		reqSz.WithLabelValues(statusStr, method, path).Observe(float64(requestSize))
+		resSz.WithLabelValues(statusStr, method, path).Observe(responseSize)
+
+		return err
+	}
+}
+
+func computeApproximateRequestSize(r *http.Request) int {
+	s := 0
+	if r.URL != nil {
+		s = len(r.URL.Path)
+	}
+
+	s += len(r.Method)
+	s += len(r.Proto)
+	for name, values := range r.Header {
+		s += len(name)
+		for _, value := range values {
+			s += len(value)
+		}
+	}
+	s += len(r.Host)
+
+	// N.B. r.Form and r.MultipartForm are assumed to be included in r.URL.
+
+	if r.ContentLength != -1 {
+		s += int(r.ContentLength)
+	}
+	return s
+}
-- 
2.51.2