fix: Correctly handle empty/undefined fallbacks

Swift/Kotlin protos always set a default value for optional fields
this results in differences between sdks and no real way for an undefined value to be returned even if it is expected and typed

Updated to check if there is a fallback, if there is use it, if not set back to undefined

android/src/main/java/expo/modules/xmtpreactnativesdk/wrappers/DecodedMessageWrapper.kt

@@ -13,14 +13,19 @@ class DecodedMessageWrapper {
             return gson.toJson(message)
         }
 
-        fun encodeMap(model: DecryptedMessage): Map<String, Any> = mapOf(
-            "id" to model.id,
-            "topic" to model.topic,
-            "contentTypeId" to model.encodedContent.type.description,
-            "content" to ContentJson(model.encodedContent).toJsonMap(),
-            "senderAddress" to model.senderAddress,
-            "sent" to model.sentAt.time,
-            "fallback" to model.encodedContent.fallback
-        )
+        fun encodeMap(model: DecryptedMessage): Map<String, Any?> {
+            // Kotlin/Java Protos don't support null values and will always put the default ""
+            // Check if there is a fallback, if there is then make it the set fallback, if not null
+            val fallback = if (model.encodedContent.hasFallback()) model.encodedContent.fallback else null
+            return mapOf(
+                "id" to model.id,
+                "topic" to model.topic,
+                "contentTypeId" to model.encodedContent.type.description,
+                "content" to ContentJson(model.encodedContent).toJsonMap(),
+                "senderAddress" to model.senderAddress,
+                "sent" to model.sentAt.time,
+                "fallback" to fallback
+            )
+        }
     }
 }

example/src/tests.ts

@@ -31,6 +31,20 @@ const ContentTypeNumber: ContentTypeId = {
   versionMinor: 0,
 }
 
+const ContentTypeNumberWithUndefinedFallback: ContentTypeId = {
+  authorityId: 'org',
+  typeId: 'number_undefined_fallback',
+  versionMajor: 1,
+  versionMinor: 0,
+}
+
+const ContentTypeNumberWithEmptyFallback: ContentTypeId = {
+  authorityId: 'org',
+  typeId: 'number_empty_fallback',
+  versionMajor: 1,
+  versionMinor: 0,
+}
+
 export type NumberRef = {
   topNumber: {
     bottomNumber: number
@@ -66,6 +80,20 @@ class NumberCodec implements JSContentCodec<NumberRef> {
   }
 }
 
+class NumberCodecUndefinedFallback extends NumberCodec {
+  contentType = ContentTypeNumberWithUndefinedFallback
+  fallback(content: NumberRef): string | undefined {
+    return undefined
+  }
+}
+
+class NumberCodecEmptyFallback extends NumberCodec {
+  contentType = ContentTypeNumberWithEmptyFallback
+  fallback(content: NumberRef): string | undefined {
+    return ''
+  }
+}
+
 const LONG_STREAM_DELAY = 20000
 
 export type Test = {
@@ -1184,6 +1212,62 @@ test('correctly handles lowercase addresses', async () => {
   return true
 })
 
+test('handle fallback types appropriately', async () => {
+  const bob = await Client.createRandom({
+    env: 'local',
+    codecs: [
+      new NumberCodecEmptyFallback(),
+      new NumberCodecUndefinedFallback(),
+    ],
+  })
+  const alice = await Client.createRandom({
+    env: 'local',
+  })
+  bob.register(new NumberCodecEmptyFallback())
+  bob.register(new NumberCodecUndefinedFallback())
+  const bobConvo = await bob.conversations.newConversation(alice.address)
+  const aliceConvo = await alice.conversations.newConversation(bob.address)
+
+  await bobConvo.send(12, { contentType: ContentTypeNumberWithEmptyFallback })
+
+  await bobConvo.send(12, {
+    contentType: ContentTypeNumberWithUndefinedFallback,
+  })
+
+  const messages = await aliceConvo.messages()
+  assert(messages.length === 2, 'did not get messages')
+
+  const messageUndefinedFallback = messages[0]
+  const messageWithDefinedFallback = messages[1]
+
+  let message1Content = undefined
+  try {
+    message1Content = messageUndefinedFallback.content()
+  } catch {
+    message1Content = messageUndefinedFallback.fallback
+  }
+
+  assert(
+    message1Content === undefined,
+    'did not get content properly when empty fallback: ' +
+      JSON.stringify(message1Content)
+  )
+
+  let message2Content = undefined
+  try {
+    message2Content = messageWithDefinedFallback.content()
+  } catch {
+    message2Content = messageWithDefinedFallback.fallback
+  }
+
+  assert(
+    message2Content === '',
+    'did not get content properly: ' + JSON.stringify(message2Content)
+  )
+
+  return true
+})
+
 test('instantiate frames client correctly', async () => {
   const frameUrl =
     'https://fc-polls-five.vercel.app/polls/01032f47-e976-42ee-9e3d-3aac1324f4b8'

ios/Wrappers/DecodedMessageWrapper.swift

@@ -5,14 +5,17 @@ import XMTP
 // into react native.
 struct DecodedMessageWrapper {
 	static func encodeToObj(_ model: XMTP.DecryptedMessage, client: Client) throws -> [String: Any] {
+    // Swift Protos don't support null values and will always put the default ""
+    // Check if there is a fallback, if there is then make it the set fallback, if not null
+		let fallback = model.encodedContent.hasFallback ? model.encodedContent.fallback : nil
 		return [
 			"id": model.id,
 			"topic": model.topic,
 			"contentTypeId": model.encodedContent.type.description,
 			"content": try ContentJson.fromEncoded(model.encodedContent, client: client).toJsonMap() as Any,
 			"senderAddress": model.senderAddress,
 			"sent": UInt64(model.sentAt.timeIntervalSince1970 * 1000),
-			"fallback": model.encodedContent.fallback,
+			"fallback": fallback,
 		]
 	}
 

src/lib/DecodedMessage.ts

@@ -1,13 +1,11 @@
+import { Buffer } from 'buffer'
+
 import { Client } from './Client'
 import {
-  ContentCodec,
   JSContentCodec,
   NativeContentCodec,
   NativeMessageContent,
 } from './ContentCodec'
-import { ReplyCodec } from './NativeCodecs/ReplyCodec'
-import { TextCodec } from './NativeCodecs/TextCodec'
-import { Buffer } from 'buffer'
 
 const allowEmptyProperties: (keyof NativeMessageContent)[] = [
   'text',
@@ -81,7 +79,8 @@ export class DecodedMessage<ContentTypes = any> {
     this.senderAddress = senderAddress
     this.sent = sent
     this.nativeContent = content
-    this.fallback = fallback
+    // undefined comes back as null when bridged, ensure undefined so integrators don't have to add a new check for null as well
+    this.fallback = fallback ?? undefined
   }
 
   content(): ContentTypes {