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
+}

test/server/utils/libraryBrowseCursor.test.js

@@ -0,0 +1,43 @@
+const chai = require('chai')
+const expect = chai.expect
+
+const {
+  encodeBrowseCursor,
+  decodeBrowseCursor
+} = require('../../../server/utils/queries/libraryBrowseCursor')
+
+describe('libraryBrowseCursor', () => {
+  it('round-trips a deterministic title cursor with id tie-breaker', () => {
+    const encoded = encodeBrowseCursor({
+      sortBy: 'media.metadata.title',
+      desc: false,
+      keys: ['titleIgnorePrefix', 'id'],
+      values: ['Dune', 'item_42']
+    })
+
+    expect(decodeBrowseCursor(encoded)).to.deep.equal({
+      sortBy: 'media.metadata.title',
+      desc: false,
+      keys: ['titleIgnorePrefix', 'id'],
+      values: ['Dune', 'item_42']
+    })
+  })
+
+  it('rejects a cursor without the full ordered key set', () => {
+    expect(() => decodeBrowseCursor(encodeBrowseCursor({
+      sortBy: 'media.metadata.title',
+      desc: false,
+      keys: ['titleIgnorePrefix', 'id'],
+      values: ['Dune']
+    }))).to.throw('full ordered key set')
+  })
+
+  it('rejects a cursor without the id tie-breaker', () => {
+    expect(() => decodeBrowseCursor(encodeBrowseCursor({
+      sortBy: 'media.metadata.title',
+      desc: false,
+      keys: ['titleIgnorePrefix'],
+      values: ['Dune']
+    }))).to.throw('tie-breaker')
+  })
+})