feat(prometheus): add metrics to Subsonic API and Plugins (#4266)

* Add prometheus metrics to subsonic and plugins

* address feedback, do not log error if operation is not supported

* add missing timestamp and client to stats

* remove .view from subsonic route

* directly inject DataStore in Prometheus, to avoid having to pass it in every call

Signed-off-by: Deluan <deluan@navidrome.org>

---------

Signed-off-by: Deluan <deluan@navidrome.org>
Co-authored-by: Deluan <deluan@navidrome.org>

plugins/wasm_base_plugin.go

@@ -2,13 +2,28 @@ package plugins
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"time"
 
+	"github.com/navidrome/navidrome/core/agents"
+	"github.com/navidrome/navidrome/core/metrics"
 	"github.com/navidrome/navidrome/log"
 	"github.com/navidrome/navidrome/model/id"
 )
 
+// newWasmBasePlugin creates a new instance of wasmBasePlugin with the required parameters.
+func newWasmBasePlugin[S any, P any](wasmPath, id, capability string, m metrics.Metrics, loader P, loadFunc loaderFunc[S, P]) *wasmBasePlugin[S, P] {
+	return &wasmBasePlugin[S, P]{
+		wasmPath:   wasmPath,
+		id:         id,
+		capability: capability,
+		loader:     loader,
+		loadFunc:   loadFunc,
+		metrics:    m,
+	}
+}
+
 // LoaderFunc is a generic function type that loads a plugin instance.
 type loaderFunc[S any, P any] func(ctx context.Context, loader P, path string) (S, error)
 
@@ -20,6 +35,7 @@ type wasmBasePlugin[S any, P any] struct {
 	capability string
 	loader     P
 	loadFunc   loaderFunc[S, P]
+	metrics    metrics.Metrics
 }
 
 func (w *wasmBasePlugin[S, P]) PluginID() string {
@@ -34,6 +50,10 @@ func (w *wasmBasePlugin[S, P]) serviceName() string {
 	return w.id + "_" + w.capability
 }
 
+func (w *wasmBasePlugin[S, P]) getMetrics() metrics.Metrics {
+	return w.metrics
+}
+
 // getInstance loads a new plugin instance and returns a cleanup function.
 func (w *wasmBasePlugin[S, P]) getInstance(ctx context.Context, methodName string) (S, func(), error) {
 	start := time.Now()
@@ -57,7 +77,9 @@ func (w *wasmBasePlugin[S, P]) getInstance(ctx context.Context, methodName strin
 }
 
 type wasmPlugin[S any] interface {
+	PluginID() string
 	getInstance(ctx context.Context, methodName string) (S, func(), error)
+	getMetrics() metrics.Metrics
 }
 
 type errorMapper interface {
@@ -73,10 +95,25 @@ func callMethod[S any, R any](ctx context.Context, w wasmPlugin[S], methodName s
 	if err != nil {
 		return r, err
 	}
+	start := time.Now()
 	defer done()
 	r, err = fn(inst)
+	elapsed := time.Since(start)
+
 	if em, ok := any(w).(errorMapper); ok {
-		return r, em.mapError(err)
+		mappedErr := em.mapError(err)
+
+		if !errors.Is(mappedErr, agents.ErrNotFound) {
+			id := w.PluginID()
+			isOk := mappedErr == nil
+			metrics := w.getMetrics()
+			if metrics != nil {
+				metrics.RecordPluginRequest(ctx, id, methodName, isOk, elapsed.Milliseconds())
+			}
+			log.Trace(ctx, "callMethod", "plugin", id, "method", methodName, "ok", isOk, elapsed)
+		}
+
+		return r, mappedErr
 	}
 	return r, err
 }