google.golang.org/api v0.273.1: iterator.NewPager

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify iterator.NewPager in pkg:golang/google.golang.org/api@v0.273.1
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/google.golang.org/api@v0.273.1
Demonstrate these symbols/APIs:
  - iterator.NewPager

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

{"case":{"caseId":"case:sha256:1a9105396c296269bb89c8f4228d59bca88fc8ebd4ebb4ac5a361a889d6f93ee","contract":["iterator.NewPager(iter, pageSize, pageToken) creates a *Pager whose NextPage(\u0026slice) appends exactly pageSize items and returns the nextPageToken","iterator.NewPager(iter, pageSize, nextPageToken) resumes iteration from nextPageToken and returns an empty token on the final partial page","iterator.NewPager(iter, 0, \"\") sets a latched error on the iterator's PageInfo so NextPage returns an error for non-positive pageSize"],"goal":"verify iterator.NewPager in pkg:golang/google.golang.org/api@v0.273.1","kind":"HOW","packages":["pkg:golang/google.golang.org/api@v0.273.1"],"schemaVersion":1,"symbols":["iterator.NewPager"]},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/google.golang.org/api@v0.273.1"],"schemaVersion":1,"subject":"pkg:golang/google.golang.org/api@v0.273.1","symbols":["iterator.NewPager"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

require google.golang.org/api v0.273.1

google.golang.org/api v0.273.1 h1:L7G/TmpAMz0nKx/ciAVssVmWQiOF6+pOuXeKrWVsquY=
google.golang.org/api v0.273.1/go.mod h1:JbAt7mF+XVmWu6xNP8/+CTiGH30ofmCmk9nM8d8fHew=

{
  "schemaVersion": 1,
  "goal": "verify iterator.NewPager in pkg:golang/google.golang.org/api@v0.273.1",
  "kind": "HOW",
  "packages": [
    "pkg:golang/google.golang.org/api@v0.273.1"
  ],
  "symbols": [
    "iterator.NewPager"
  ]
}

package main

import (
	"fmt"
	"os"
	"reflect"

	"google.golang.org/api/iterator"
)

type sliceIterator struct {
	all      []string
	buf      []string
	pageInfo *iterator.PageInfo
}

func newSliceIterator(items []string) *sliceIterator {
	it := &sliceIterator{all: items}
	it.pageInfo, _ = iterator.NewPageInfo(
		it.fetch,
		func() int { return len(it.buf) },
		func() interface{} { b := it.buf; it.buf = nil; return b },
	)
	return it
}

func (it *sliceIterator) PageInfo() *iterator.PageInfo {
	return it.pageInfo
}

func (it *sliceIterator) fetch(pageSize int, pageToken string) (string, error) {
	start := 0
	if pageToken != "" {
		if _, err := fmt.Sscanf(pageToken, "idx-%d", &start); err != nil {
			return "", err
		}
	}
	if start >= len(it.all) {
		return "", nil
	}
	end := start + pageSize
	nextToken := ""
	if end < len(it.all) {
		nextToken = fmt.Sprintf("idx-%d", end)
	} else {
		end = len(it.all)
	}
	it.buf = append(it.buf, it.all[start:end]...)
	return nextToken, nil
}

func main() {
	items := []string{"a", "b", "c", "d", "e"}
	it := newSliceIterator(items)
	pager := iterator.NewPager(it, 2, "")

	var page1 []string
	token1, err := pager.NextPage(&page1)
	if err != nil || token1 != "idx-2" || !reflect.DeepEqual(page1, []string{"a", "b"}) {
		fmt.Fprintf(os.Stderr, "unexpected page1: %v, token: %q, err: %v\n", page1, token1, err)
		os.Exit(1)
	}

	resumedPager := iterator.NewPager(newSliceIterator(items), 2, token1)
	var page2 []string
	token2, err := resumedPager.NextPage(&page2)
	if err != nil || token2 != "idx-4" || !reflect.DeepEqual(page2, []string{"c", "d"}) {
		fmt.Fprintf(os.Stderr, "unexpected page2: %v, token: %q, err: %v\n", page2, token2, err)
		os.Exit(1)
	}

	var page3 []string
	token3, err := resumedPager.NextPage(&page3)
	if err != nil || token3 != "" || !reflect.DeepEqual(page3, []string{"e"}) {
		fmt.Fprintf(os.Stderr, "unexpected page3: %v, token: %q, err: %v\n", page3, token3, err)
		os.Exit(1)
	}

	badPager := iterator.NewPager(newSliceIterator(items), 0, "")
	var badPage []string
	if _, err := badPager.NextPage(&badPage); err == nil {
		fmt.Fprintln(os.Stderr, "expected error for non-positive pageSize")
		os.Exit(1)
	}
}