package main

import (
	"archive/zip"
	"bytes"
	"io"
	"log"
	"os"
	"path/filepath"
	"runtime"
	"runtime/pprof"
)

func main() {
	file := filepath.Join(runtime.GOROOT(), "lib/time/zoneinfo.zip")
	data, err := os.ReadFile(file)
	if err != nil {
		log.Fatal(err)
	}
	zr, err := zip.NewReader(bytes.NewReader(data), int64(len(data)))
	if err != nil {
		log.Fatal(err)
	}
	zw := zip.NewWriter(io.Discard)
	if err := zw.Copy(zr.File[0]); err != nil {
		log.Fatal(err)
	}
	writeHeapProfile()
	if err := zw.Close(); err != nil {
		log.Fatal(err)
	}
}

func writeHeapProfile() {
	const filename = "heap.prof"
	f, err := os.Create(filename)
	if err != nil {
		log.Fatal(err)
	}
	runtime.GC()
	if err := pprof.WriteHeapProfile(f); err != nil {
		log.Fatal(err)
	}
	if err := f.Close(); err != nil {
		log.Fatal(err)
	}
}

> go build zipmem.go && ./zipmem && go tool pprof zipmem heap.prof

(pprof) top

Showing nodes accounting for 1761.95kB, 100% of 1761.95kB total
      flat  flat%   sum%        cum   cum%
 1024.17kB 58.13% 58.13%  1024.17kB 58.13%  archive/zip.(*Reader).init
  737.78kB 41.87%   100%   737.78kB 41.87%  os.ReadFile
         0     0%   100%  1024.17kB 58.13%  archive/zip.NewReader
         0     0%   100%  1761.95kB   100%  main.main
         0     0%   100%  1761.95kB   100%  runtime.main

fw, err := w.CreateRaw(&f.FileHeader)

type File struct {
    FileHeader
    ...
    zipr         io.ReaderAt // the argument to NewReader
    ...
}

func zipWriterCopy(w *zip.Writer, f *zip.File) error {
	r, err := f.OpenRaw()
	if err != nil {
		return err
	}
	fh := f.FileHeader
	fw, err := w.CreateRaw(&fh)
	if err != nil {
		return err
	}
	_, err = io.Copy(fw, r)
	return err
}