feat(metrics): bound HTTP path labels, add reset, custom push endpoint and JSON pull

- normalize the HTTP path label (ServeMux pattern, custom normalizer, ID
  collapsing) and cap distinct values via HTTPMaxPaths (default 1024)
- add Reset, PushAndReset, ResetHandler and reset-on-push options
- add POST push to a custom endpoint (text or json) with optional reset
- add JSONHandler for JSON pull
- honour Config.Enabled; log Pushgateway push failures

pkg/metrics/config.go

@@ -1,5 +1,7 @@
 package metrics
 
+import "net/http"
+
 // Config holds configuration for the metrics provider
 type Config struct {
 	// Enabled determines whether metrics collection is enabled
@@ -19,6 +21,17 @@ type Config struct {
 	// Default: [0.001, 0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5]
 	DBQueryBuckets []float64 `mapstructure:"db_query_buckets"`
 
+	// HTTPMaxPaths caps the number of distinct values of the "path" label on HTTP
+	// metrics. Paths beyond the cap are reported as "other". Paths are already
+	// normalized (route pattern, or dynamic segments replaced with ":id").
+	// Default: 1024. Set to a negative value to disable the cap.
+	HTTPMaxPaths int `mapstructure:"http_max_paths"`
+
+	// HTTPPathNormalizer optionally maps a request to its "path" label (e.g. the
+	// matched route template of your router). Return "" to fall back to the
+	// default behaviour (ServeMux pattern, then generic ID normalization).
+	HTTPPathNormalizer func(*http.Request) string `mapstructure:"-"`
+
 	// PushgatewayURL is the URL of the Prometheus Pushgateway (optional)
 	// If set, metrics will be pushed to this gateway instead of only being scraped
 	// Example: "http://pushgateway:9091"
@@ -32,6 +45,34 @@ type Config struct {
 	// Only used if PushgatewayURL is set. If 0, automatic pushing is disabled.
 	// Default: 0 (no automatic pushing)
 	PushgatewayInterval int `mapstructure:"pushgateway_interval"`
+
+	// PushEndpointURL is a custom HTTP endpoint that metrics are POSTed to
+	// (independent of Pushgateway). Example: "https://collector.example.com/metrics"
+	PushEndpointURL string `mapstructure:"push_endpoint_url"`
+
+	// PushEndpointFormat is the request body format: "text" (Prometheus text
+	// exposition, Content-Type text/plain; version=0.0.4) or "json".
+	// Default: "text"
+	PushEndpointFormat string `mapstructure:"push_endpoint_format"`
+
+	// PushEndpointHeaders are extra headers sent with each POST (e.g. Authorization).
+	PushEndpointHeaders map[string]string `mapstructure:"push_endpoint_headers"`
+
+	// PushEndpointInterval is the interval in seconds for automatic POSTs.
+	// If 0, automatic posting is disabled (PushToEndpoint can still be called manually).
+	PushEndpointInterval int `mapstructure:"push_endpoint_interval"`
+
+	// PushEndpointTimeout is the per-request timeout in seconds. Default: 10
+	PushEndpointTimeout int `mapstructure:"push_endpoint_timeout"`
+
+	// PushEndpointResetOnSuccess clears local counters and histograms after the
+	// endpoint answers with a 2xx status. Default: false.
+	PushEndpointResetOnSuccess bool `mapstructure:"push_endpoint_reset_on_success"`
+
+	// PushgatewayResetOnPush clears the local counters and histograms after each
+	// successful push (automatic or via PushAndReset), so each push carries only
+	// the activity since the previous one. Default: false.
+	PushgatewayResetOnPush bool `mapstructure:"pushgateway_reset_on_push"`
 }
 
 // DefaultConfig returns a Config with sensible defaults
@@ -43,6 +84,7 @@ func DefaultConfig() *Config {
 		HTTPRequestBuckets: []float64{0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5, 10},
 		// DB queries are usually faster
 		DBQueryBuckets: []float64{0.001, 0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5},
+		HTTPMaxPaths:   defaultHTTPMaxPaths,
 	}
 }
 
@@ -57,6 +99,17 @@ func (c *Config) ApplyDefaults() {
 	if len(c.DBQueryBuckets) == 0 {
 		c.DBQueryBuckets = []float64{0.001, 0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5}
 	}
+	if c.PushEndpointURL != "" {
+		if c.PushEndpointFormat == "" {
+			c.PushEndpointFormat = "text"
+		}
+		if c.PushEndpointTimeout <= 0 {
+			c.PushEndpointTimeout = 10
+		}
+	}
+	if c.HTTPMaxPaths == 0 {
+		c.HTTPMaxPaths = defaultHTTPMaxPaths
+	}
 	// Set default job name if pushgateway is configured but job name is empty
 	if c.PushgatewayURL != "" && c.PushgatewayJobName == "" {
 		c.PushgatewayJobName = "resolvespec"