random_payload_generator.go

package main

import (
	"fmt"
	"math/rand"
)

func main() {
	for i := 0; i < 4; i++ {
		if i > 0 {
			fmt.Println()
		}
		fmt.Println(NewPayload(2 * lineLen * (i + 1)))
	}
}

const lineLen = 64

type Payload []byte

func NewPayload(size int) Payload {
	p := Payload(make([]byte, size))

	alphabet := [...]byte{
		'0', '1', '2', '3',
		'4', '5', '6', '7',
		'8', '9', 'a', 'b',
		'c', 'd', 'e', 'f',
		'g', 'h', 'i', 'j',
		'k', 'l', 'm', 'n',
		'o', 'p', 'q', 'r',
	}

	n := len(alphabet)
	for i := 0; i < size; i++ {
		p[i] = alphabet[rand.Intn(n)]
	}

	return p
}

func (p Payload) String() string {
	n := len(p)
	out := make([]byte, 0, n*(1+1/lineLen)-1)

	for i := 0; i < n; i += lineLen {
		if i > 0 {
			// Add new line
			out = append(out, '\n')
		}
		out = append(out, p[i:i+lineLen]...)
	}

	return string(out)
}

Live code - https://play.golang.org/p/guS2QeQ-uH

Sample output:

dnf7dihc48irih8i7dlq32o6f3fkinlorbhkl75ida67dfm4rpdl578pgajrje1o
q4lmj2f0m23il7kc71lh53prfq6o6jobkrd2d3jhjae1ecilrmc5r97a26prq6di

7pobdqjd8qobo7ok0bgebo4jcc93he2e37memre87omaj0c21ffjqpk74724be12
hggobqkgp0b5egnejcg334icjnlk75ljh5ig64o4ihp8gjak0f59gg39hhc1pnnq
gao08lnnpie5a8aoorilg92goo2j5jhmb81rlr7r1i73404diojeqpqnmaf2nk7l
an7mbg8ap40rpihera503l2apf18ch1gdicf4q5jej5c8jdqg6nmdk1678k132q0

ro92mf6a3agld205ihamfkg4b7ch1an8d6hjlbn5hfrokr9e15jfo5660rqideie
7e3i95d3kam76hb625fpp4k25kh82fqo1i7p2lo7kbc3hqr8iqgkf6fm5l5af2l2
lq5cgc8nq05oeh7hj9mobj5gra48prlo2lo8a9je47qndk29dldkd42f5qjk0inq
1r07oknrhkqa2p2a6m08m8hg6r719pl2lq1i2l56i0rj9k89ejhfhc4kmeb7k2gc
airg22ne1egi1a69pohq9ec7569jkqbqlnce824nif9595nel776njbbg8bhrgad
ef75306p0fcoef8h8j3fr0rrli9lpj8jfag080hc0efdgq8rjigjlic841fdijoe

0opaj2rmjrf8ab4mh813a8kp3c4gnf3p6jh57482ga0ip4dck380c1mbl9c506b3
e3l48a844377nnm8p7k1o01ch25ni98j53nk2iffilg193lido4ib5ld3ljgnrrk
ifinfocibd1g79g6legaq0q1p1hnmkfghgjceipmbi5il9cmkqn07no1n375na6l
56mn4ca9255k9cfb4lm594ie6510rdgjd2mq2ime99n67p8a8qhf5pgd3d40ooim
h9la217enfajcbiqjjnlgpk05210ndqn85qm87op7qkmi7552m0rarjq75j2580r
f00al89e76d1gbrd23n9a7hppld6lgqgj3j8dhncdma4oqrbcrr6ojiram2dder8
ca4f033akd04kq8opgkgr1bih262ifj15lmd25cfmnc45oflb2pq5g7gl2jqgfo6
lm1a5o2r1mnhqfkkc66c8l5h7dpp6p9ae4ao84jkd6n2a56dgf04oepclidf5j82