Creating a large csv file for testing file access

Question

I want to create a 10 GB file that looks like:

prefix:username:timestamp, number

So an example is like:

login:jbill:2013/3/25, 1

I want to create a 10GB file, by creating random rows like the one above.

How could I do this in Go?

I can have an array of prefixes like:

login, logout, register

And also an array of usernames:

jbill, dkennedy

Answer 1

For example,

package main

import (
    "bufio"
    "fmt"
    "math/rand"
    "os"
    "strconv"
    "time"
)

func main() {
    fileSize := int64(10e9) // 10GB
    f, err := os.Create("/tmp/largefile")
    if err != nil {
        fmt.Println(err)
        return
    }
    w := bufio.NewWriter(f)
    prefixes := []string{"login", "logout", "register"}
    names := []string{"jbill", "dkennedy"}
    timeStart := time.Date(2012, 1, 1, 0, 0, 0, 0, time.UTC)
    timeDur := timeStart.AddDate(1, 0, 0).Sub(timeStart)
    rand.Seed(time.Now().UnixNano())
    size := int64(0)
    for size < fileSize {
        // prefix:username:timestamp, number
        // login:jbill:2012/3/25, 1
        prefix := prefixes[int(rand.Int31n(int32(len(prefixes))))]
        name := names[int(rand.Int31n(int32(len(names))))]
        time := timeStart.Add(time.Duration(rand.Int63n(int64(timeDur)))).Format("2006/1/2")
        number := strconv.Itoa(int(rand.Int31n(100) + 1))
        line := prefix + ":" + name + ":" + time + ", " + number + "\n"
        n, err := w.WriteString(line)
        if err != nil {
            fmt.Println(n, err)
            return
        }
        size += int64(len(line))
    }
    err = w.Flush()
    if err != nil {
        fmt.Println(err)
        return
    }
    err = f.Close()
    if err != nil {
        fmt.Println(err)
        return
    }
    fmt.Println("Size:", size)
}

Output:

register:jbill:2012/8/24, 15
login:jbill:2012/10/7, 98
register:dkennedy:2012/8/29, 70
register:jbill:2012/6/1, 89
register:jbill:2012/5/24, 63
login:dkennedy:2012/3/29, 48
logout:jbill:2012/7/8, 93
logout:dkennedy:2012/1/12, 74
login:jbill:2012/4/12, 14
login:jbill:2012/2/5, 83