[feature] Initial Prometheus metrics implementation (#2334)

* feat: Initial OTEL metrics

* docs: add metrics documentation

* fix: metrics endpoint conditional check

* feat: metrics endpoint basic auth

* fix: make metrics-auth-enabled default false

* fix: go fmt helpers.gen.go

* fix: add metric-related env vars to envparsing.sh

* fix: metrics docs

* fix: metrics related stuff in envparsing.sh

* fix: metrics docs

* chore: metrics docs wording

* fix: metrics stuff in envparsing?

* bump otel versions

---------

Co-authored-by: Tsuribori <user@acertaindebian>
Co-authored-by: Tsuribori <none@example.org>
Co-authored-by: tsmethurst <tobi.smethurst@protonmail.com>

vendor/github.com/technologize/otel-go-contrib/otelginmetrics/middleware.go

@@ -0,0 +1,94 @@
+package otelginmetrics
+
+import (
+	"net/http"
+	"time"
+
+	"github.com/gin-gonic/gin"
+	semconv "go.opentelemetry.io/otel/semconv/v1.7.0"
+)
+
+// Middleware returns middleware that will trace incoming requests.
+// The service parameter should describe the name of the (virtual)
+// server handling the request.
+func Middleware(service string, options ...Option) gin.HandlerFunc {
+	cfg := defaultConfig()
+	for _, option := range options {
+		option.apply(cfg)
+	}
+	recorder := cfg.recorder
+	if recorder == nil {
+		recorder = GetRecorder("")
+	}
+	return func(ginCtx *gin.Context) {
+
+		ctx := ginCtx.Request.Context()
+
+		route := ginCtx.FullPath()
+		if len(route) <= 0 {
+			route = "nonconfigured"
+		}
+		if !cfg.shouldRecord(service, route, ginCtx.Request) {
+			ginCtx.Next()
+			return
+		}
+
+		start := time.Now()
+		reqAttributes := cfg.attributes(service, route, ginCtx.Request)
+
+		if cfg.recordInFlight {
+			recorder.AddInflightRequests(ctx, 1, reqAttributes)
+			defer recorder.AddInflightRequests(ctx, -1, reqAttributes)
+		}
+
+		defer func() {
+
+			resAttributes := append(reqAttributes[0:0], reqAttributes...)
+
+			if cfg.groupedStatus {
+				code := int(ginCtx.Writer.Status()/100) * 100
+				resAttributes = append(resAttributes, semconv.HTTPStatusCodeKey.Int(code))
+			} else {
+				resAttributes = append(resAttributes, semconv.HTTPAttributesFromHTTPStatusCode(ginCtx.Writer.Status())...)
+			}
+
+			recorder.AddRequests(ctx, 1, resAttributes)
+
+			if cfg.recordSize {
+				requestSize := computeApproximateRequestSize(ginCtx.Request)
+				recorder.ObserveHTTPRequestSize(ctx, requestSize, resAttributes)
+				recorder.ObserveHTTPResponseSize(ctx, int64(ginCtx.Writer.Size()), resAttributes)
+			}
+
+			if cfg.recordDuration {
+				recorder.ObserveHTTPRequestDuration(ctx, time.Since(start), resAttributes)
+			}
+		}()
+
+		ginCtx.Next()
+	}
+}
+
+func computeApproximateRequestSize(r *http.Request) int64 {
+	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 int64(s)
+}