String Decoding in Golang

Question

In Ruby, I'm using the string.unpack method to decode some data. I'm migrating this code into a Golang app, however I can't find a corresponding method in the standard library?

The ruby code is: str.unpack('>LLLff')

What is the best way to implement this in Go?

Example data:

]\x00\x00@\x00\x8C\xD2\x00\x00\x00\x00\x00\x00\x00\x00h.\x9FAjK\x8FG\xC0T\x87UX\xA1CH\xB7\x80\x82}\xBB\xF9\x8F\xBAcqF{\xE31/Zx\xC0\x04\xFF\b\xA0\xBD\a\x9E\x0F\x14c+\b\xD3\xE8\xE1\xC2\x1C7\xBCmd/j\xC1H\x191~\x91F\b5-\x8A\x9F(\\\xF1\x16/\x0F\xEA\xD9\x94rV\xEC\xBB\xCB\x12qJ\x05\b\x04 {R\xB8\xA4\xA9\xD0)v\x97<\xCA\x92\xB6U\b)\x1D\x1D\xF1\x00\xE4U\x8DB\x16/v\xEC[bLTW\xB2\xFB\x0F\x91\x05\xAA\x9C\xBD\x8E\x1A\xFB\xDFUJ\xB8\xDE\xF5m\xC8Z\xC1\v\\|\r;\xB6\xE6\xA6\x13o\x91\xE1\xBA\x9An\x8B\x01W\xB9\"\x12+\x9B[\xC7\xCD\xC2O+\f^|\xE1G\x86.%m\xB2x\xF1j\e\"\xE41Bu_\x16J\xE4M\x7F\xC5U[\xB9\xD0\xC7\xECu\xE53\xB4)\xD5\x80|\xB7.\xD2\f\xF3\x16\x8B\xE3\x13\x81\x02:5\x88\x0F

Should map to: [1073741917, 13798400, 0, 2.4178516392292583e+24, 5.851859700165677e+25]

Possible duplicate of [How do I unpack various form of integers in a byte buffer in Golang?](https://stackoverflow.com/questions/12357865/how-do-i-unpack-various-form-of-integers-in-a-byte-buffer-in-golang) — Leon, Oct 07 '18 at 21:04
I don't think its quite a duplicate, and it will be useful for those coming from Ruby to see it answered in this context. — Will, Oct 08 '18 at 00:42

score 4 · Accepted Answer · answered Oct 08 '18 at 00:41

Try this:

package main

import (
    "bytes"
    "encoding/binary"
    "log"
)

type UnpackedThing struct {
    First  uint32
    Second uint32
    Third  uint32

    Fourth float32
    Fifth  float32
}

func main() {
    input := bytes.NewBufferString("]\x00\x00@\x00\x8C\xD2\x00\x00\x00\x00\x00\x00\x00\x00h.\x9FAjK\x8FG\xC0T\x87UX\xA1CH\xB7\x80\x82}\xBB\xF9\x8F\xBAcqF{\xE31/Zx\xC0\x04\xFF\b\xA0\xBD\a\x9E\x0F\x14c+\b\xD3\xE8\xE1\xC2\x1C7\xBCmd/j\xC1H\x191~\x91F\b5-\x8A\x9F(\\\xF1\x16/\x0F\xEA\xD9\x94rV\xEC\xBB\xCB\x12qJ\x05\b\x04 {R\xB8\xA4\xA9\xD0)v\x97<\xCA\x92\xB6U\b)\x1D\x1D\xF1\x00\xE4U\x8DB\x16/v\xEC[bLTW\xB2\xFB\x0F\x91\x05\xAA\x9C\xBD\x8E\x1A\xFB\xDFUJ\xB8\xDE\xF5m\xC8Z\xC1\v\\|\r;\xB6\xE6\xA6\x13o\x91\xE1\xBA\x9An\x8B\x01W\xB9\"\x12+\x9B[\xC7\xCD\xC2O+\f^|\xE1G\x86.%m\xB2x\xF1j\x1B\"\xE41Bu_\x16J\xE4M\x7F\xC5U[\xB9\xD0\xC7\xECu\xE53\xB4)\xD5\x80|\xB7.\xD2\f\xF3\x16\x8B\xE3\x13\x81\x02:5\x88\x0F")
    var unpacked UnpackedThing

    err := binary.Read(input, binary.LittleEndian, &unpacked)
    if err != nil {
        log.Fatal(err)
    }

    log.Printf("[%d, %d, %d, %f, %f]\n",
        unpacked.First, unpacked.Second, unpacked.Third, unpacked.Fourth, unpacked.Fifth)
}

We're creating a struct that properly represents the binary format, then using binary.Read() to read our bytes into this struct. One thing to note is that golang's strings don't understand \e, so it must be converted to \x1b.

Output:

*@x~/go/src/stackoverflow.com/binunpack⦕ go run main.go
2018/10/07 17:39:16 [1073741917, 13798400, 0, 2417851639229258349412352.000000, 58518597001656773736660992.000000]
*@x~/go/src/stackoverflow.com/binunpack⦕

Huh, that's cool. I've used encoding/binary before, but somehow up until now I never noticed that it handled structs :) — hobbs, Oct 08 '18 at 01:28

String Decoding in Golang

1 Answers1