0.10.6

Sources/Shared/Models/ArchiveSyncPagination.swift

@@ -0,0 +1,33 @@
+import Foundation
+
+enum ArchiveSyncPageDecision: Equatable, Sendable {
+    case finished
+    case next(String)
+    case invalidCursor
+}
+
+/// Validates XEP-0313/RSM cursors so a misbehaving server cannot leave
+/// history synchronization spinning forever on the same page.
+struct ArchiveSyncPagination: Sendable {
+    private(set) var seenCursors: Set<String> = []
+
+    mutating func decision(
+        complete: Bool,
+        lastCursor: String?,
+        requestedAfter: String?
+    ) -> ArchiveSyncPageDecision {
+        if complete { return .finished }
+        guard let cursor = lastCursor?.trimmingCharacters(in: .whitespacesAndNewlines),
+              !cursor.isEmpty else {
+            // An incomplete response without an RSM cursor cannot prove that
+            // the archive is exhausted. Advancing the checkpoint here would
+            // silently skip the remaining history.
+            return .invalidCursor
+        }
+        guard cursor != requestedAfter,
+              seenCursors.insert(cursor).inserted else {
+            return .invalidCursor
+        }
+        return .next(cursor)
+    }
+}