test: add deterministic browse cursor helpers

server/utils/queries/libraryBrowseCursor.js

@@ -0,0 +1,22 @@
+function encodeBrowseCursor(payload) {
+  return Buffer.from(JSON.stringify(payload)).toString('base64url')
+}
+
+function decodeBrowseCursor(cursor) {
+  const decoded = JSON.parse(Buffer.from(cursor, 'base64url').toString('utf8'))
+
+  if (!Array.isArray(decoded.keys) || !Array.isArray(decoded.values) || decoded.keys.length !== decoded.values.length) {
+    throw new Error('Cursor is missing the full ordered key set')
+  }
+
+  if (!decoded.keys.length || decoded.keys[decoded.keys.length - 1] !== 'id') {
+    throw new Error('Cursor is missing the tie-breaker value')
+  }
+
+  return decoded
+}
+
+module.exports = {
+  encodeBrowseCursor,
+  decodeBrowseCursor
+}