[object-persistor] import ProjectKey helper from history-v1 (#30600)

GitOrigin-RevId: c72aa4bf91569904a2072c74d6ed2f3c764d97bb

libraries/object-persistor/src/ProjectKey.js

@@ -0,0 +1,22 @@
+const path = require('node:path')
+
+//
+// The advice in http://docs.aws.amazon.com/AmazonS3/latest/dev/
+// request-rate-perf-considerations.html is to avoid sequential key prefixes,
+// so we reverse the project ID part of the key as they suggest.
+//
+function format(projectId) {
+  const prefix = naiveReverse(pad(projectId))
+  return path.join(prefix.slice(0, 3), prefix.slice(3, 6), prefix.slice(6))
+}
+
+function pad(number) {
+  return (number || 0).toString().padStart(9, '0')
+}
+
+function naiveReverse(string) {
+  return string.split('').reverse().join('')
+}
+
+exports.format = format
+exports.pad = pad

libraries/object-persistor/test/unit/ProjectKeyTests.js

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+const { expect } = require('chai')
+
+const { format, pad } = require('../../src/ProjectKey.js')
+
+describe('projectKey', function () {
+  it('reverses padded keys', function () {
+    expect(format(1)).to.equal('100/000/000')
+    expect(format(12)).to.equal('210/000/000')
+    expect(format(123456789)).to.equal('987/654/321')
+    expect(format(9123456789)).to.equal('987/654/3219')
+  })
+
+  it('pads numbers with zeros to length 9', function () {
+    expect(pad(undefined)).to.equal('000000000')
+    expect(pad(null)).to.equal('000000000')
+    expect(pad(1)).to.equal('000000001')
+    expect(pad(10)).to.equal('000000010')
+    expect(pad(100000000)).to.equal('100000000')
+    expect(pad(1000000000)).to.equal('1000000000')
+  })
+})