Add Peer.maxMessageSize()

docs/api-reference.md

@@ -96,6 +96,7 @@ Subscribe to events using `network.on(eventName, callback)`:
 ```typescript
 interface Peer {
   id: string;          // Unique peer identifier
+  maxMessageSize: number | null; // Max bytes per data channel message for this peer
   latency?: {
     last: number;      // Most recent latency measurement (in ms)
     average: number;   // Average latency over time
@@ -105,3 +106,15 @@ interface Peer {
   };
 }
 ```
+
+##### `peer.maxMessageSize: number | null` (read-only)
+Maximum message size, in bytes, that can be sent in a single WebRTC data channel message to this peer.
+
+- `null`: the SCTP transport is not available yet or unsupported in the current environment.
+- `0`: no practical message size limit is reported by the transport.
+- `> 0`: maximum safe payload size in bytes.
+
+Notes:
+- This value is negotiated per peer and can differ across connections.
+- Use this to decide when to chunk large payloads.
+- If this is `null` or `0` you should use a conservative message size such as `16 * 1024` bytes for large payloads.

docs/basic-usage.md

@@ -100,6 +100,20 @@ network.on('disconnected', peer => {
 })
 ```
 
+##### Inspecting Message Size Limits
+```js
+network.on('connected', peer => {
+  const limit = peer.maxMessageSize
+
+  if (limit === null) {
+    limit = 16 * 1024
+    console.log(`No SCTP max message size available for ${peer.id} yet, using conservative limit of ${limit} bytes`)
+  }
+
+  console.log(`Max payload for ${peer.id}: ${limit} bytes`)
+})
+```
+
 #### 6. Listing Lobbies
 You can list available lobbies using the `list` function. This function supports filtering using MongoDB-style filters:
 

lib/peer.ts

@@ -289,6 +289,10 @@ export default class Peer {
     }
   }
 
+  get maxMessageSize (): number | null {
+    return this.conn.sctp?.maxMessageSize ?? null
+  }
+
   toString (): string {
     return `[Peer: ${this.id}]`
   }