1 files changed, 95 insertions, 0 deletions
diff --git a/src/main/overleafProtocol.ts b/src/main/overleafProtocol.ts
new file mode 100644
index 0000000..49b06d7
--- /dev/null
+++ b/src/main/overleafProtocol.ts
@@ -0,0 +1,95 @@
+// Socket.IO v0.9 protocol encoding/decoding
+
+export interface ParsedMessage {
+  type: 'disconnect' | 'connect' | 'heartbeat' | 'event' | 'ack' | 'error' | 'noop'
+  id?: number
+  data?: unknown
+  name?: string
+  args?: unknown[]
+}
+
+/**
+ * Parse a Socket.IO v0.9 message frame.
+ *
+ * Frame format:
+ *   0::              disconnect
+ *   1::              connect
+ *   2::              heartbeat
+ *   5:::{"name":"x","args":[...]}         event
+ *   5:N+::{"name":"x","args":[...]}       event with ack request
+ *   6:::N+[jsonData]                       ack response
+ *   8::              noop
+ */
+export function parseSocketMessage(raw: string): ParsedMessage | null {
+  if (!raw || raw.length === 0) return null
+
+  const type = raw[0]
+
+  switch (type) {
+    case '0':
+      return { type: 'disconnect' }
+    case '1':
+      return { type: 'connect' }
+    case '2':
+      return { type: 'heartbeat' }
+    case '8':
+      return { type: 'noop' }
+    case '5': {
+      // Event: 5:::{"name":"x","args":[...]} or 5:N+::{"name":"x","args":[...]}
+      const ackMatch = raw.match(/^5:(\d+)\+::(.*)$/s)
+      if (ackMatch) {
+        try {
+          const payload = JSON.parse(ackMatch[2])
+          return {
+            type: 'event',
+            id: parseInt(ackMatch[1]),
+            name: payload.name,
+            args: payload.args || []
+          }
+        } catch {
+          return null
+        }
+      }
+      const evtMatch = raw.match(/^5:::(.*)$/s)
+      if (evtMatch) {
+        try {
+          const payload = JSON.parse(evtMatch[1])
+          return { type: 'event', name: payload.name, args: payload.args || [] }
+        } catch {
+          return null
+        }
+      }
+      return null
+    }
+    case '6': {
+      // Ack: 6:::N+[jsonData]
+      const ackMatch = raw.match(/^6:::(\d+)\+([\s\S]*)/)
+      if (ackMatch) {
+        try {
+          const data = JSON.parse(ackMatch[2])
+          return { type: 'ack', id: parseInt(ackMatch[1]), data }
+        } catch {
+          return { type: 'ack', id: parseInt(ackMatch[1]), data: null }
+        }
+      }
+      return null
+    }
+    default:
+      return null
+  }
+}
+
+/** Encode a Socket.IO v0.9 event (no ack) */
+export function encodeEvent(name: string, args: unknown[]): string {
+  return '5:::' + JSON.stringify({ name, args })
+}
+
+/** Encode a Socket.IO v0.9 event that expects an ack response */
+export function encodeEventWithAck(ackId: number, name: string, args: unknown[]): string {
+  return `5:${ackId}+::` + JSON.stringify({ name, args })
+}
+
+/** Encode a heartbeat response */
+export function encodeHeartbeat(): string {
+  return '2::'
+}