AWS lambda example in Go

main.go

// Testrun with:
// go build *.go && docker run --rm -v "$PWD":/var/task lambci/lambda:go1.x main '{"prefix":"23727483927892"}'
// Deploy by:
// zip main.zip main
// upload main.zip to https://console.aws.amazon.com/lambda/home

package main

import (
	"context"

	"github.com/aws/aws-lambda-go/lambda"
)

func handleRequest(ctx context.Context, event map[string]string) (string, error) {
	return Prefix(event["prefix"])
}

func main() {
	lambda.Start(handleRequest)
}

prefix.go

package main

import (
	"errors"
	"math/big"
	"strings"

	"github.com/tscholl2/prime/prime"
)

var (
	base = 10
)

// Prefix takes a integer N in base 10 as a string,
// and returns a prime number whose digits start with N.
func Prefix(N string) (string, error) {
	a, ok := new(big.Int).SetString(N, base)
	if !ok {
		return "", errors.New("unable to read prefix integer")
	}
	if a.Sign() <= 0 {
		return "", errors.New("prefix number must be positive")
	}
	return nextPrimeWithPrefix(a).Text(base), nil
}

func nextPrimeWithPrefix(N *big.Int) *big.Int {
	prefix := N.Text(base)
	a := new(big.Int).Set(N)
	b := big.NewInt(int64(base))
	for {
		p := prime.NextPrime(a)
		if strings.HasPrefix(p.Text(base), prefix) {
			return p
		}
		a.Mul(a, b)
	}
}