feat: Add webhook notification and conflict retry for Reloader v2

internal/pkg/webhook/webhook.go

@@ -0,0 +1,95 @@
+// Package webhook handles sending reload notifications to external endpoints.
+// When --webhook-url is set, Reloader sends HTTP POST requests instead of modifying workloads.
+package webhook
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"time"
+
+	"github.com/go-logr/logr"
+)
+
+// Payload represents the data sent to the webhook endpoint.
+type Payload struct {
+	Kind         string    `json:"kind"`
+	Namespace    string    `json:"namespace"`
+	ResourceName string    `json:"resourceName"`
+	ResourceType string    `json:"resourceType"`
+	Hash         string    `json:"hash"`
+	Timestamp    time.Time `json:"timestamp"`
+
+	// Workloads contains the list of workloads that would be reloaded.
+	Workloads []WorkloadInfo `json:"workloads"`
+}
+
+// WorkloadInfo describes a workload that would be reloaded.
+type WorkloadInfo struct {
+	Kind      string `json:"kind"`
+	Name      string `json:"name"`
+	Namespace string `json:"namespace"`
+}
+
+// Client sends reload notifications to webhook endpoints.
+type Client struct {
+	httpClient *http.Client
+	url        string
+	log        logr.Logger
+}
+
+// NewClient creates a new webhook client.
+func NewClient(url string, log logr.Logger) *Client {
+	return &Client{
+		httpClient: &http.Client{
+			Timeout: 30 * time.Second,
+		},
+		url: url,
+		log: log,
+	}
+}
+
+// Send posts the payload to the configured webhook URL.
+func (c *Client) Send(ctx context.Context, payload Payload) error {
+	if c.url == "" {
+		return nil
+	}
+
+	data, err := json.Marshal(payload)
+	if err != nil {
+		return fmt.Errorf("marshaling payload: %w", err)
+	}
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, c.url, bytes.NewReader(data))
+	if err != nil {
+		return fmt.Errorf("creating request: %w", err)
+	}
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("User-Agent", "Reloader/2.0")
+
+	resp, err := c.httpClient.Do(req)
+	if err != nil {
+		return fmt.Errorf("sending request: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		return fmt.Errorf("webhook returned status %d", resp.StatusCode)
+	}
+
+	c.log.V(1).Info("webhook notification sent",
+		"url", c.url,
+		"resourceType", payload.ResourceType,
+		"resourceName", payload.ResourceName,
+		"workloadCount", len(payload.Workloads),
+	)
+
+	return nil
+}
+
+// IsConfigured returns true if the webhook URL is set.
+func (c *Client) IsConfigured() bool {
+	return c != nil && c.url != ""
+}