const (
	magicGNU, versionGNU     = "ustar ", " \x00"
	magicUSTAR, versionUSTAR = "ustar\x00", "00"
	trailerSTAR              = "tar\x00"
)

// Size constants from various tar specifications.
const (
	blockSize  = 512 // Size of each block in a tar stream
	nameSize   = 100 // Max length of the name field in USTAR format
	prefixSize = 155 // Max length of the prefix field in USTAR format

	if format > formatV7 {
		ustar := tr.blk.toUSTAR()
		hdr.Uname = p.parseString(ustar.userName())
		hdr.Gname = p.parseString(ustar.groupName())
		hdr.Devmajor = p.parseNumeric(ustar.devMajor())
		hdr.Devminor = p.parseNumeric(ustar.devMinor())

		var prefix string
		switch {
		case format.has(FormatUSTAR | FormatPAX):
			hdr.Format = format
			ustar := tr.blk.toUSTAR()

		}
	}

	// Check basic fields.
	var blk block
	v7 := blk.toV7()
	ustar := blk.toUSTAR()
	gnu := blk.toGNU()
	verifyString(h.Name, len(v7.name()), "Name", paxPath)
	verifyString(h.Linkname, len(v7.linkName()), "Linkname", paxLinkpath)
	verifyString(h.Uname, len(ustar.userName()), "Uname", paxUname)
	verifyString(h.Gname, len(ustar.groupName()), "Gname", paxGname)
	verifyNumeric(h.Mode, len(v7.mode()), "Mode", paxNone)

osik?t??iat??raban??o&dat?hik?n&amuk?ihseru?o&du?mok????ust????kilbew,lasrepus,mihe!.&a&m&a&h&ataway?iin??yustam??ij&awu?imak???taki!man???ebot?i&anoh?kasam?rabami??n&ania?egokamuk?oot??o&jias?kihcu?nustam?uhcukokihs?yi!es???u&kohik?zo????n!.&arukas,lapo,n&erukom,riheg,?omomus,stnim,teniesa.resu,xob-liam,yrovi,zapot,?amihs!.&a&d&amah?ho?usam??kustay?m&a?ihsoni&hsin?ko???wakih??e&namihs?ustam??i&g&aka?usay??konikak?mikih??nannu?o&mu&kay?zi!ihsagih?uko???nawust?tasim??u&stog?yamat????nep,?rotsnoih...

				Gname:    "guillaume",
				ModTime:  time.Unix(1399583047, 0),
			}, nil},
		},
	}, {
		// This file was produced using GNU tar v1.17.
		//	gnutar -b 4 --format=ustar (longname/)*15 + file.txt
		file: "testdata/ustar.tar",
		tests: []testFnc{
			testHeader{Header{
				Typeflag: TypeReg,
				Name:     strings.Repeat("longname/", 15) + "file.txt",
				Size:     6,
				Mode:     0644,

Pero los detalles entre *concurrencia* y *paralelismo* son bastante diferentes.

Para entender las diferencias, imagina la siguiente historia sobre hamburguesas:

### Hamburguesas Concurrentes

Vas con la persona que te gusta 😍 a pedir comida rápida 🍔, haces cola mientras el cajero 💁 recoge los pedidos de las personas de delante tuyo.

<img src="https://fastapi.tiangolo.com/img/async/concurrent-burgers/concurrent-burgers-01.png" alt="illustration">

//
// Keys and values should be UTF-8, but the number of bad writers out there
// forces us to be a more liberal.
// Thus, we only reject all keys with NUL, and only reject NULs in values
// for the PAX version of the USTAR string fields.
// The key must not contain an '=' character.
func validPAXRecord(k, v string) bool {
	if k == "" || strings.Contains(k, "=") {
		return false
	}
	switch k {

			Uid:      010000000,
			ModTime:  time.Unix(0, 0),
			Typeflag: '0',
		}},
	}, {
		// USTAR archive with a regular entry with non-zero device numbers.
		file: "testdata/ustar-file-devs.tar",
		headers: []*Header{{
			Name:     "file",
			Mode:     0644,
			Typeflag: '0',
			ModTime:  time.Unix(0, 0),
			Devmajor: 1,
			Devminor: 1,

Waterworth, Danijar Hafner, Darren Garvey, Denis Gorbachev, @DjangoPeng,
Egor-Krivov, Elia Palme, Eric Platon, Fabrizio Milo, Gaetan Semet, Georg
Nebehay, Gu Wang, Gustav Larsson, @haosdent, Harold Cooper, Hw-Zz, @ichuang,
Igor Babuschkin, Igor Macedo Quintanilha, Ilya Edrenkin, @ironhead, Jakub
Kolodziejczyk, Jennifer Guo, Jihun Choi, Jonas Rauber, Josh Bleecher Snyder,

		}
	}
}

func Benchmark(b *testing.B) {
	type file struct {
		hdr  *Header
		body []byte
	}

	vectors := []struct {
		label string
		files []file
	}{{
		"USTAR",
		[]file{{
			&Header{Name: "bar", Mode: 0640, Size: int64(3)},
			[]byte("foo"),
		}, {
			&Header{Name: "world", Mode: 0640, Size: int64(5)},
			[]byte("hello"),
		}},
	}, {
		"GNU",