fix(partykit): preserve delete tombstones

Encode PartyKit messages with undefined-aware JSON and decode them without using a reviver so tombstone keys are preserved. This keeps delete changes intact across transport instead of dropping row and cell deletions during parse.

Fixes: #281

Author: clentfort

src/common/json.ts

@@ -1,5 +1,5 @@
 import {object} from './obj.ts';
-import {isInstanceOf, isUndefined} from './other.ts';
+import {isArray, isInstanceOf, isUndefined} from './other.ts';
 import {UNDEFINED} from './strings.ts';
 
 export const jsonString = JSON.stringify;
@@ -13,5 +13,36 @@ export const jsonStringWithMap = (obj: unknown): string =>
 export const jsonStringWithUndefined = (obj: unknown): string =>
   jsonString(obj, (_key, value) => (isUndefined(value) ? UNDEFINED : value));
 
-export const jsonParseWithUndefined = (str: string): any =>
-  jsonParse(str, (_key, value) => (value === UNDEFINED ? undefined : value));
+const replaceUndefinedString = (obj: any): any => {
+  if (obj === UNDEFINED) {
+    return undefined;
+  }
+  if (isArray(obj)) {
+    return obj.map(replaceUndefinedString);
+  }
+  if (isInstanceOf(obj, Object)) {
+    object
+      .entries(obj)
+      .forEach(
+        ([key, value]) => ((obj as any)[key] = replaceUndefinedString(value)),
+      );
+  }
+  return obj;
+};
+
+export const jsonParseWithUndefined = (str: string): any => {
+  // Do not use a JSON.parse reviver for this mapping. It removes properties
+  // with undefined values, which is not what we want.
+  //
+  // That would remove tombstone keys such as {rowId: undefined} and break
+  // delete propagation.
+  //
+  // > If the reviver function returns undefined (or returns no value - for
+  // > example, if execution falls off the end of the function), the property is
+  // > deleted from the object."
+  // See
+  // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/parse#the_reviver_parameter
+  // Related bug report:
+  // https://github.com/tinyplex/tinybase/issues/281
+  return replaceUndefinedString(jsonParse(str));
+};

src/persisters/common/partykit.ts

@@ -1,4 +1,7 @@
-import {jsonParse, jsonStringWithMap} from '../../common/json.ts';
+import {
+  jsonParseWithUndefined,
+  jsonStringWithUndefined,
+} from '../../common/json.ts';
 import {isString, size, slice} from '../../common/other.ts';
 import {T, V, strStartsWith} from '../../common/strings.ts';
 
@@ -15,7 +18,9 @@ export const construct = (
   type: MessageType | StorageKeyType,
   payload: any,
 ): string =>
-  prefix + type + (isString(payload) ? payload : jsonStringWithMap(payload));
+  prefix +
+  type +
+  (isString(payload) ? payload : jsonStringWithUndefined(payload));
 
 export const deconstruct = (
   prefix: string,
@@ -26,7 +31,9 @@ export const deconstruct = (
   return strStartsWith(message, prefix)
     ? [
         message[prefixSize] as MessageType | StorageKeyType,
-        (stringified ? jsonParse : String)(slice(message, prefixSize + 1)),
+        (stringified ? jsonParseWithUndefined : String)(
+          slice(message, prefixSize + 1),
+        ),
       ]
     : undefined;
 };