1 files changed, 16 insertions, 0 deletions
diff --git a/src/lib/nip40.ts b/src/lib/nip40.ts
new file mode 100644
index 00000000..030fe0df
--- /dev/null
+++ b/src/lib/nip40.ts
@@ -0,0 +1,16 @@
+// Returns true if the message has an expiration in the past, false otherwise.
+export const expired = (event: object): boolean => {
+    const expiryTime = expiration(event);
+    return expiryTime !== null && Date.now() / 1000 >= expiryTime;
+}
+
+// Returns the provided event's expiration time, as a Unix ms integer.
+// If it has none, returns null.
+export const expiration = (event: object): number | null => {
+    for (const tag of event.tags) {
+        if (tag[0] == "expiration") {
+            return parseInt(tag[1]);
+        }
+    }
+    return null;
+}