fix(05): CR-01 serve thumb URLs from the validated path key

lagoon/attach/static.go

@@ -10,9 +10,10 @@ import (
 
 const defaultStaticContentType = "application/octet-stream"
 
-// StaticHandler serves GET prefix/<partition>/<disk_name> from bucket.
-// The blob key is rebuilt from disk_name via PartitionDirectory; request
-// path segments never reach NewReader unvalidated (T-05-13).
+// StaticHandler serves GET prefix/<partition>/<filename> from bucket.
+// filename is the original disk_name or a thumb_* sibling stored in the
+// original's partition. The blob key is the validated 4-segment path;
+// unvalidated request segments never reach NewReader (T-05-13).
 func StaticHandler(bucket *blob.Bucket, prefix string) http.Handler {
 	prefix = strings.TrimSuffix(prefix, "/")
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
@@ -29,12 +30,11 @@ func StaticHandler(bucket *blob.Bucket, prefix string) http.Handler {
 			http.NotFound(w, r)
 			return
 		}
-		diskName, ok := parsePublicBlobPath(rel)
+		key, ok := parsePublicBlobPath(rel)
 		if !ok {
 			http.NotFound(w, r)
 			return
 		}
-		key := BlobKey(diskName)
 		reader, err := bucket.NewReader(r.Context(), key, nil)
 		if err != nil {
 			http.NotFound(w, r)
@@ -66,10 +66,13 @@ func stripStaticPrefix(path, prefix string) (string, bool) {
 	return "", false
 }
 
-// parsePublicBlobPath accepts exactly 3 partition groups plus disk_name
-// whose PartitionDirectory matches those groups. Rejects "..", empty
-// segments, extra slashes, and mismatched partitions.
-func parsePublicBlobPath(p string) (string, bool) {
+// parsePublicBlobPath accepts exactly 3 partition groups plus a filename
+// and returns that path as the blob key. Originals must live in
+// PartitionDirectory(filename); thumb_* names are stored beside the
+// original, so their partition is not derived from the thumb filename.
+// Rejects "..", empty segments, extra slashes, and mismatched original
+// partitions.
+func parsePublicBlobPath(p string) (key string, ok bool) {
 	if p == "" || strings.Contains(p, "\\") || strings.Contains(p, "..") || strings.Contains(p, "//") {
 		return "", false
 	}
@@ -82,11 +85,13 @@ func parsePublicBlobPath(p string) (string, bool) {
 			return "", false
 		}
 	}
-	diskName := parts[3]
+	filename := parts[3]
 	got := strings.Join(parts[:3], "/")
-	want := strings.TrimSuffix(PartitionDirectory(diskName), "/")
-	if got != want {
-		return "", false
+	if !strings.HasPrefix(filename, "thumb_") {
+		want := strings.TrimSuffix(PartitionDirectory(filename), "/")
+		if got != want {
+			return "", false
+		}
 	}
-	return diskName, true
+	return got + "/" + filename, true
 }

lagoon/attach/static_test.go

@@ -69,3 +69,48 @@ func TestStaticHandler(t *testing.T) {
 		}
 	}
 }
+
+func TestStaticHandlerServesThumbURL(t *testing.T) {
+	ctx := t.Context()
+	bucket := memblob.OpenBucket(nil)
+	t.Cleanup(func() { _ = bucket.Close() })
+
+	f := &File{ID: 42, DiskName: "abc123xyz.jpg"}
+	if err := bucket.WriteAll(ctx, BlobKey(f.DiskName), testJPEG(t), &blob.WriterOptions{ContentType: "image/jpeg"}); err != nil {
+		t.Fatal(err)
+	}
+	thumbURL, err := f.Thumb(ctx, bucket, 200, 200, "crop")
+	if err != nil {
+		t.Fatal(err)
+	}
+	const wantURL = "/storage/uploads/abc/123/xyz/thumb_42_200_200_0_0_crop.jpg"
+	if thumbURL != wantURL {
+		t.Fatalf("Thumb URL = %q, want %q", thumbURL, wantURL)
+	}
+
+	h := StaticHandler(bucket, "/storage/uploads")
+	srv := httptest.NewServer(h)
+	t.Cleanup(srv.Close)
+
+	res, err := http.Get(srv.URL + thumbURL)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer res.Body.Close()
+	if res.StatusCode != http.StatusOK {
+		t.Fatalf("thumb GET status = %d, want 200", res.StatusCode)
+	}
+	body, err := io.ReadAll(res.Body)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(body) == 0 {
+		t.Fatal("thumb body is empty")
+	}
+
+	mismatch := httptest.NewRecorder()
+	h.ServeHTTP(mismatch, httptest.NewRequest(http.MethodGet, "/storage/uploads/foo/bar/baz/abc123xyz.jpg", nil))
+	if mismatch.Code != http.StatusNotFound {
+		t.Fatalf("mismatched original partition status = %d, want 404", mismatch.Code)
+	}
+}