feat: concatenate custom Caddy configs for services into final Caddyfile (no upstream interpolation)

internal/machine/caddyconfig/validator.go

@@ -0,0 +1,71 @@
+package caddyconfig
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net"
+	"net/http"
+	"strings"
+	"time"
+
+	"github.com/caddyserver/caddy/v2"
+)
+
+// CaddyAdminValidator validates Caddyfile via the Caddy admin API.
+type CaddyAdminValidator struct {
+	socketPath string
+	client     *http.Client
+}
+
+func NewCaddyAdminValidator(socketPath string) *CaddyAdminValidator {
+	return &CaddyAdminValidator{
+		socketPath: socketPath,
+		client: &http.Client{
+			Timeout: 5 * time.Second,
+			Transport: &http.Transport{
+				DialContext: func(_ context.Context, _, _ string) (net.Conn, error) {
+					return net.Dial("unix", socketPath)
+				},
+			},
+		},
+	}
+}
+
+// Validate checks if the provided Caddyfile can be adapted to Caddy JSON config using the running Caddy instance via
+// its admin API. It doesn't guarantee that the Caddyfile is actually valid and can be loaded. For example, a tls
+// directive with a missing certificate will pass the adaptation but will fail when Caddy tries to load it.
+// But this is the best we can do over the admin API.
+// TODO: run 'docker exec caddy-container caddy validate' to do proper validation or implement a Caddy module that
+// exposes a validation endpoint.
+func (c *CaddyAdminValidator) Validate(ctx context.Context, caddyfile string) error {
+	// Bogus host is used so that http.NewRequest is happy but it doesn't matter since we're using a Unix socket.
+	req, err := http.NewRequestWithContext(ctx, "POST", "http://localhost/adapt", strings.NewReader(caddyfile))
+	if err != nil {
+		return fmt.Errorf("create adapt request: %w", err)
+	}
+	req.Header.Set("Content-Type", "text/caddyfile")
+
+	resp, err := c.client.Do(req)
+	if err != nil {
+		return fmt.Errorf("send adapt request: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode == http.StatusOK {
+		return nil
+	}
+
+	body, _ := io.ReadAll(resp.Body)
+	// If the response is a 400 Bad Request, try to parse the error message from it.
+	if resp.StatusCode == http.StatusBadRequest {
+		var apiError caddy.APIError
+		if err = json.Unmarshal(body, &apiError); err == nil {
+			return errors.New(apiError.Message)
+		}
+	}
+
+	return errors.New(string(body))
+}