feat(19.3-03): storage.uploads.public_url for direct bucket or CDN file URLs

- OpenBucket validates public_url (absolute http/https, host, no user info, query
  or fragment; the error names the key) and records it next to public_path_prefix
- a set public_url logs one start-up line: the bucket behind it must hold only
  public files, since it bypasses the is_public check
- attach.PublicURLBase; PublicURL, File.URL and thumbnail URLs use the base when
  set and keep the public_path_prefix proxy URLs otherwise
- TestPublicURLSmoke; storage Public URL base section, attachments, configuration
  and lagoon README

modules/lagoon/attach/bucket.go

@@ -3,6 +3,7 @@ package attach
 import (
 	"context"
 	"fmt"
+	"log/slog"
 	"net/url"
 	"strings"
 	"sync"
@@ -24,6 +25,7 @@ const S3BuildTag = "summercms_s3"
 var (
 	prefixMu         sync.RWMutex
 	publicPathPrefix = defaultPublicPathPrefix
+	publicURLBase    string
 )
 
 func setPublicPathPrefix(prefix string) {
@@ -32,6 +34,38 @@ func setPublicPathPrefix(prefix string) {
 	prefixMu.Unlock()
 }
 
+func setPublicURLBase(base string) {
+	prefixMu.Lock()
+	publicURLBase = base
+	prefixMu.Unlock()
+}
+
+// PublicURLBase is storage.uploads.public_url as recorded by OpenBucket: an
+// absolute http or https base (a public bucket or a CDN) that file and
+// thumbnail URLs start with instead of PublicPathPrefix. Empty when unset.
+func PublicURLBase() string {
+	prefixMu.RLock()
+	defer prefixMu.RUnlock()
+	return publicURLBase
+}
+
+// parsePublicURL validates storage.uploads.public_url: empty means unset,
+// anything else must be an absolute http or https URL with a host and
+// without user info, query or fragment.
+func parsePublicURL(raw string) (*url.URL, error) {
+	value := strings.TrimSpace(raw)
+	if value == "" {
+		return nil, nil
+	}
+	u, err := url.Parse(value)
+	bad := err != nil || u.Host == "" || u.User != nil || u.RawQuery != "" || u.ForceQuery || u.Fragment != "" ||
+		(!strings.EqualFold(u.Scheme, "http") && !strings.EqualFold(u.Scheme, "https"))
+	if bad {
+		return nil, fmt.Errorf("attach: storage.uploads.public_url must be an absolute http or https URL such as https://cdn.example.com/uploads, without user info, query or fragment (set SUMMER_STORAGE__UPLOADS__PUBLIC_URL)")
+	}
+	return u, nil
+}
+
 // PublicPathPrefix is the URL prefix prepended to partition+filename.
 func PublicPathPrefix() string {
 	prefixMu.RLock()
@@ -79,7 +113,9 @@ func checkS3Driver(bucketURL string) error {
 
 // OpenBucket opens storage.uploads.bucket_url (file://, mem://, or s3:// in a
 // binary built with S3BuildTag) and records
-// storage.uploads.public_path_prefix. An empty bucket_url fails boot.
+// storage.uploads.public_path_prefix and storage.uploads.public_url. An
+// empty bucket_url or a malformed public_url fails boot; a set public_url
+// logs one info line saying the bucket behind it must hold only public files.
 func OpenBucket(ctx context.Context, cfg *compass.Config) (*blob.Bucket, error) {
 	if cfg == nil {
 		return nil, fmt.Errorf("attach: config is nil")
@@ -95,6 +131,10 @@ func OpenBucket(ctx context.Context, cfg *compass.Config) (*blob.Bucket, error)
 	if err := checkS3Driver(bucketURL); err != nil {
 		return nil, err
 	}
+	publicURL, err := parsePublicURL(cfg.String("storage.uploads.public_url"))
+	if err != nil {
+		return nil, err
+	}
 	bucket, err := blob.OpenBucket(ctx, bucketURL)
 	if err != nil {
 		return nil, fmt.Errorf("attach: open bucket %q: %w", raw, err)
@@ -104,6 +144,14 @@ func OpenBucket(ctx context.Context, cfg *compass.Config) (*blob.Bucket, error)
 		prefix = defaultPublicPathPrefix
 	}
 	setPublicPathPrefix(prefix)
+	if publicURL == nil {
+		setPublicURLBase("")
+		return bucket, nil
+	}
+	setPublicURLBase(publicURL.String())
+	slog.Default().InfoContext(ctx, "attach: storage.uploads.public_url is set; every file and thumbnail URL points at this host, "+
+		"which serves any key without the is_public check, so the bucket behind it must hold only public files",
+		slog.String("host", publicURL.Host))
 	return bucket, nil
 }
 

modules/lagoon/attach/infra_smoke_test.go

@@ -58,3 +58,49 @@ func TestOpenBucketS3Smoke(t *testing.T) {
 		t.Fatalf("close: %v", err)
 	}
 }
+
+// TestPublicURLSmoke checks storage.uploads.public_url (D-12): set, URLs
+// are the base plus the partition path; unset, they keep the proxy prefix;
+// malformed, OpenBucket fails naming the key.
+func TestPublicURLSmoke(t *testing.T) {
+	t.Cleanup(func() {
+		setPublicPathPrefix(defaultPublicPathPrefix)
+		setPublicURLBase("")
+	})
+	key := BlobKey("651a2b3c4d5e61234567.png")
+
+	cfg := openTestConfig(t, "uploads:\n  bucket_url: \"mem://\"\n  public_url: \"https://cdn.example.com/uploads/\"\n")
+	bucket, err := OpenBucket(t.Context(), cfg)
+	if err != nil {
+		t.Fatal(err)
+	}
+	_ = bucket.Close()
+	if got, want := PublicURL(key), "https://cdn.example.com/uploads/"+key; got != want {
+		t.Fatalf("PublicURL with public_url = %q, want %q", got, want)
+	}
+	if got, want := (&File{DiskName: "651a2b3c4d5e61234567.png"}).URL(), "https://cdn.example.com/uploads/651/a2b/3c4/651a2b3c4d5e61234567.png"; got != want {
+		t.Fatalf("File.URL with public_url = %q, want %q", got, want)
+	}
+
+	cfg = openTestConfig(t, "uploads:\n  bucket_url: \"mem://\"\n")
+	bucket, err = OpenBucket(t.Context(), cfg)
+	if err != nil {
+		t.Fatal(err)
+	}
+	_ = bucket.Close()
+	if PublicURLBase() != "" || !strings.HasPrefix(PublicURL(key), "/storage/uploads/") {
+		t.Fatalf("without public_url: base %q, URL %q", PublicURLBase(), PublicURL(key))
+	}
+
+	for _, bad := range []string{"ftp://x", "https://u:p@cdn.example.com", "/storage/uploads", "https://cdn.example.com/?v=1"} {
+		cfg = openTestConfig(t, "uploads:\n  bucket_url: \"mem://\"\n  public_url: \""+bad+"\"\n")
+		bucket, err = OpenBucket(t.Context(), cfg)
+		if err == nil {
+			_ = bucket.Close()
+			t.Fatalf("public_url %q accepted", bad)
+		}
+		if !strings.Contains(err.Error(), "storage.uploads.public_url") || strings.Contains(err.Error(), "u:p") {
+			t.Fatalf("public_url %q: error %q", bad, err)
+		}
+	}
+}

modules/lagoon/attach/thumb.go

@@ -76,13 +76,18 @@ func fileExt(diskName string) string {
 	return strings.ToLower(ext)
 }
 
-// PublicURL returns the public URL of a blob key: storage.uploads.
-// public_path_prefix and the key joined by exactly one slash. With the
-// WinterCMS layout (bucket rooted at storage/app/uploads/public, prefix
-// /storage/app/uploads/public) it is Winter's File::getPath() path.
+// PublicURL returns the public URL of a blob key. With
+// storage.uploads.public_url set (PublicURLBase) it is that base and the key
+// joined by exactly one slash. Otherwise it is
+// storage.uploads.public_path_prefix and the key joined the same way; with
+// the WinterCMS layout (bucket rooted at storage/app/uploads/public, prefix
+// /storage/app/uploads/public) that is Winter's File::getPath() path.
 func PublicURL(key string) string {
-	prefix := strings.TrimRight(PublicPathPrefix(), "/")
 	key = strings.TrimLeft(key, "/")
+	if base := PublicURLBase(); base != "" {
+		return strings.TrimRight(base, "/") + "/" + key
+	}
+	prefix := strings.TrimRight(PublicPathPrefix(), "/")
 	if prefix == "" {
 		return "/" + key
 	}