Open telemetry integration (#3972)

This PR adds opentelemetry and chi wrapper to have basic instrumentation

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## Draft release notes
<!--URL:https://codeberg.org/forgejo/forgejo-->
- Features
  - [PR](https://codeberg.org/forgejo/forgejo/pulls/3972): <!--number 3972 --><!--line 0 --><!--description YWRkIHN1cHBvcnQgZm9yIGJhc2ljIHJlcXVlc3QgdHJhY2luZyB3aXRoIG9wZW50ZWxlbWV0cnk=-->add support for basic request tracing with opentelemetry<!--description-->
<!--end release-notes-assistant-->

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/3972
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Co-authored-by: TheFox0x7 <thefox0x7@gmail.com>
Co-committed-by: TheFox0x7 <thefox0x7@gmail.com>

modules/opentelemetry/resource.go

@@ -0,0 +1,90 @@
+// Copyright 2024 TheFox0x7. All rights reserved.
+// SPDX-License-Identifier: EUPL-1.2
+
+package opentelemetry
+
+import (
+	"context"
+	"net/url"
+	"strings"
+
+	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/setting"
+
+	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/sdk/resource"
+	semconv "go.opentelemetry.io/otel/semconv/v1.25.0"
+)
+
+const (
+	decoderTelemetrySdk = "sdk"
+	decoderProcess      = "process"
+	decoderOS           = "os"
+	decoderHost         = "host"
+)
+
+func newResource(ctx context.Context) (*resource.Resource, error) {
+	opts := []resource.Option{
+		resource.WithAttributes(parseSettingAttributes(setting.OpenTelemetry.ResourceAttributes)...),
+	}
+	opts = append(opts, parseDecoderOpts()...)
+	opts = append(opts, resource.WithAttributes(
+		semconv.ServiceName(setting.OpenTelemetry.ServiceName),
+		semconv.ServiceVersion(setting.ForgejoVersion),
+	))
+	return resource.New(ctx, opts...)
+}
+
+func parseDecoderOpts() []resource.Option {
+	var opts []resource.Option
+	for _, v := range strings.Split(setting.OpenTelemetry.ResourceDetectors, ",") {
+		switch v {
+		case decoderTelemetrySdk:
+			opts = append(opts, resource.WithTelemetrySDK())
+		case decoderProcess:
+			opts = append(opts, resource.WithProcess())
+		case decoderOS:
+			opts = append(opts, resource.WithOS())
+		case decoderHost:
+			opts = append(opts, resource.WithHost())
+		case "": // Don't warn on empty string
+		default:
+			log.Warn("Ignoring unknown resource decoder option: %s", v)
+		}
+	}
+	return opts
+}
+
+func parseSettingAttributes(s string) []attribute.KeyValue {
+	var attrs []attribute.KeyValue
+	rawAttrs := strings.TrimSpace(s)
+
+	if rawAttrs == "" {
+		return attrs
+	}
+
+	pairs := strings.Split(rawAttrs, ",")
+
+	var invalid []string
+	for _, p := range pairs {
+		k, v, found := strings.Cut(p, "=")
+		if !found {
+			invalid = append(invalid, p)
+			continue
+		}
+		key := strings.TrimSpace(k)
+		val, err := url.PathUnescape(strings.TrimSpace(v))
+		if err != nil {
+			// Retain original value if decoding fails, otherwise it will be
+			// an empty string.
+			val = v
+			log.Warn("Otel resource attribute decoding error, retaining unescaped value. key=%s, val=%s", key, val)
+		}
+		attrs = append(attrs, attribute.String(key, val))
+	}
+	if len(invalid) > 0 {
+		log.Warn("Partial resource, missing values: %v", invalid)
+	}
+
+	return attrs
+}