If I have a slice of bytes in Go, similar to this:
numBytes := []byte { 0xFF, 0x10 }
How would I convert it to it's uint16 value (0xFF10, 65296)?
you may use binary.BigEndian.Uint16(numBytes)
like this working sample code (with commented output):
package main
import (
"encoding/binary"
"fmt"
)
func main() {
numBytes := []byte{0xFF, 0x10}
u := binary.BigEndian.Uint16(numBytes)
fmt.Printf("%#X %[1]v\n", u) // 0XFF10 65296
}
and see inside binary.BigEndian.Uint16(b []byte):
func (bigEndian) Uint16(b []byte) uint16 {
_ = b[1] // bounds check hint to compiler; see golang.org/issue/14808
return uint16(b[1]) | uint16(b[0])<<8
}
I hope this helps.
To combine two bytes into uint16
x := uint16(numBytes[i])<<8 | uint16(numBytes[i+1])
where i is the starting position of the uint16. So if your array is always only two items it would be x := uint16(numBytes[0])<<8 | uint16(numBytes[1])
Firstly you have a slice not an array - an array has a fixed size and would be declared like this [2]byte.
If you just have a 2 bytes slice, I wouldn't do anything fancy, I'd just do
numBytes := []byte{0xFF, 0x10}
n := int(numBytes[0])<<8 + int(numBytes[1])
fmt.Printf("n =0x%04X = %d\n", n, n)
Playground
EDIT: Just noticed you wanted uint16 - replace int with that in the above!
You can use the following unsafe conversion:
*(*uint16)(unsafe.Pointer(&numBytes[0])
Related
I generated a hash value using sha3 and I need to convert it to a big.Int value. Is it possible ? or is there a method to get the integervalue of the hash ?
the following code throws an error that cannot convert type hash.Hash to type int64 :
package main
import (
"math/big"
"golang.org/x/crypto/sha3"
"fmt"
)
func main(){
chall := "hello word"
b := byte[](chall)
h := sha3.New244()
h.Write(chall)
h.Write(b)
d := make([]byte, 16)
h.Sum(d)
val := big.NewInt(int64(h))
fmt.Println(val)
}
TL;DR;
sha3.New224() cannot be represented in uint64 type.
There are many hash types - and of differing sizes. Go standard library picks a very generic interface to cover all type of hashes: https://golang.org/pkg/hash/#Hash
type Hash interface {
io.Writer
Sum(b []byte) []byte
Reset()
Size() int
BlockSize() int
}
Having said that some Go hash implementations optionally include extra methods like hash.Hash64:
type Hash64 interface {
Hash
Sum64() uint64
}
others may implement encoding.BinaryMarshaler:
type BinaryMarshaler interface {
MarshalBinary() (data []byte, err error)
}
which one can use to preserve a hash state.
sha3.New224() does not implement the above 2 interfaces, but crc64 hash does.
To do a runtime check:
h64, ok := h.(hash.Hash64)
if ok {
fmt.Printf("64-bit: %d\n", h64.Sum64())
}
Working example: https://play.golang.org/p/uLUfw0gMZka
(See Peter's comment for the simpler version of this.)
Interpreting a series of bytes as a big.Int is the same as interpreting a series of decimal digits as an arbitrarily large number. For example, to convert the digits 1234 into a "number", you'd do this:
Start with 0
Multiply by 10 = 0
Add 1 = 1
Multiply by 10 = 10
Add 2 = 12
Multiply by 10 = 120
Add 3 = 123
Multiply by 10 = 1230
Add 4 = 1234
The same applies to bytes. The "digits" are just base-256 rather than base-10:
val := big.NewInt(0)
for i := 0; i < h.Size(); i++ {
val.Lsh(val, 8)
val.Add(val, big.NewInt(int64(d[i])))
}
(Lsh is a left-shift. Left shifting by 8 bits is the same as multiplying by 256.)
Playground
I have a []byte object and I want to get the size of it in bytes. Is there an equivalent to C's sizeof() in golang? If not, Can you suggest other ways to get the same?
To return the number of bytes in a byte slice use the len function:
bs := make([]byte, 1000)
sz := len(bs)
// sz == 1000
If you mean the number of bytes in the underlying array use cap instead:
bs := make([]byte, 1000, 2000)
sz := cap(bs)
// sz == 2000
A byte is guaranteed to be one byte: https://golang.org/ref/spec#Size_and_alignment_guarantees.
I think your best bet would be;
package main
import "fmt"
import "encoding/binary"
func main() {
thousandBytes := make([]byte, 1000)
tenBytes := make([]byte, 10)
fmt.Println(binary.Size(tenBytes))
fmt.Println(binary.Size(thousandBytes))
}
https://play.golang.org/p/HhJif66VwY
Though there are many options, like just importing unsafe and using sizeof;
import unsafe "unsafe"
size := unsafe.Sizeof(bytes)
Note that for some types, like slices, Sizeof is going to give you the size of the slice descriptor which is likely not what you want. Also, bear in mind the length and capacity of the slice are different and the value returned by binary.Size reflects the length.
I have a function which receives a []byte but what I have is an int, what is the best way to go about this conversion ?
err = a.Write([]byte(myInt))
I guess I could go the long way and get it into a string and put that into bytes, but it sounds ugly and I guess there are better ways to do it.
I agree with Brainstorm's approach: assuming that you're passing a machine-friendly binary representation, use the encoding/binary library. The OP suggests that binary.Write() might have some overhead. Looking at the source for the implementation of Write(), I see that it does some runtime decisions for maximum flexibility.
func Write(w io.Writer, order ByteOrder, data interface{}) error {
// Fast path for basic types.
var b [8]byte
var bs []byte
switch v := data.(type) {
case *int8:
bs = b[:1]
b[0] = byte(*v)
case int8:
bs = b[:1]
b[0] = byte(v)
case *uint8:
bs = b[:1]
b[0] = *v
...
Right? Write() takes in a very generic data third argument, and that's imposing some overhead as the Go runtime then is forced into encoding type information. Since Write() is doing some runtime decisions here that you simply don't need in your situation, maybe you can just directly call the encoding functions and see if it performs better.
Something like this:
package main
import (
"encoding/binary"
"fmt"
)
func main() {
bs := make([]byte, 4)
binary.LittleEndian.PutUint32(bs, 31415926)
fmt.Println(bs)
}
Let us know how this performs.
Otherwise, if you're just trying to get an ASCII representation of the integer, you can get the string representation (probably with strconv.Itoa) and cast that string to the []byte type.
package main
import (
"fmt"
"strconv"
)
func main() {
bs := []byte(strconv.Itoa(31415926))
fmt.Println(bs)
}
Check out the "encoding/binary" package. Particularly the Read and Write functions:
binary.Write(a, binary.LittleEndian, myInt)
Sorry, this might be a bit late. But I think I found a better implementation on the go docs.
buf := new(bytes.Buffer)
var num uint16 = 1234
err := binary.Write(buf, binary.LittleEndian, num)
if err != nil {
fmt.Println("binary.Write failed:", err)
}
fmt.Printf("% x", buf.Bytes())
i thought int type has any method for getting int hash to bytes, but first i find math / big method for this
https://golang.org/pkg/math/big/
var f int = 52452356235; // int
var s = big.NewInt(int64(f)) // int to big Int
var b = s.Bytes() // big Int to bytes
// b - byte slise
var r = big.NewInt(0).SetBytes(b) // bytes to big Int
var i int = int(r.Int64()) // big Int to int
https://play.golang.org/p/VAKSGw8XNQq
However, this method uses an absolute value.
If you spend 1 byte more, you can transfer the sign
func IntToBytes(i int) []byte{
if i > 0 {
return append(big.NewInt(int64(i)).Bytes(), byte(1))
}
return append(big.NewInt(int64(i)).Bytes(), byte(0))
}
func BytesToInt(b []byte) int{
if b[len(b)-1]==0 {
return -int(big.NewInt(0).SetBytes(b[:len(b)-1]).Int64())
}
return int(big.NewInt(0).SetBytes(b[:len(b)-1]).Int64())
}
https://play.golang.org/p/mR5Sp5hu4jk
or new(https://play.golang.org/p/7ZAK4QL96FO)
(The package also provides functions for fill into an existing slice)
https://golang.org/pkg/math/big/#Int.FillBytes
Adding this option for dealing with basic uint8 to byte[] conversion
foo := 255 // 1 - 255
ufoo := uint16(foo)
far := []byte{0,0}
binary.LittleEndian.PutUint16(far, ufoo)
bar := int(far[0]) // back to int
fmt.Println("foo, far, bar : ",foo,far,bar)
output :
foo, far, bar : 255 [255 0] 255
Here is another option, based on the Go source code [1]:
package main
import (
"encoding/binary"
"fmt"
"math/bits"
)
func encodeUint(x uint64) []byte {
buf := make([]byte, 8)
binary.BigEndian.PutUint64(buf, x)
return buf[bits.LeadingZeros64(x) >> 3:]
}
func main() {
for x := 0; x <= 64; x += 8 {
buf := encodeUint(1<<x-1)
fmt.Println(buf)
}
}
Result:
[]
[255]
[255 255]
[255 255 255]
[255 255 255 255]
[255 255 255 255 255]
[255 255 255 255 255 255]
[255 255 255 255 255 255 255]
[255 255 255 255 255 255 255 255]
Much faster than math/big:
BenchmarkBig-12 28348621 40.62 ns/op
BenchmarkBit-12 731601145 1.641 ns/op
https://github.com/golang/go/blob/go1.16.5/src/encoding/gob/encode.go#L113-L117
You can try musgo_int. All you need to do is to cast your variable:
package main
import (
"github.com/ymz-ncnk/musgo_int"
)
func main() {
var myInt int = 1234
// from int to []byte
buf := make([]byte, musgo_int.Int(myInt).SizeMUS())
musgo_int.Int(myInt).MarshalMUS(buf)
// from []byte to int
_, err := (*musgo_int.Int)(&myInt).UnmarshalMUS(buf)
if err != nil {
panic(err)
}
}
Convert Integer to byte slice.
import (
"bytes"
"encoding/binary"
"log"
)
func IntToBytes(num int64) []byte {
buff := new(bytes.Buffer)
bigOrLittleEndian := binary.BigEndian
err := binary.Write(buff, bigOrLittleEndian, num)
if err != nil {
log.Panic(err)
}
return buff.Bytes()
}
Maybe the simple way is using protobuf, see the Protocol Buffer Basics: Go
define message like
message MyData {
int32 id = 1;
}
get more in Defining your protocol format
// Write
out, err := proto.Marshal(mydata)
read more in Writing a Message
Try math/big package to convert bytes array to int and to convert int to bytes array.
package main
import (
"fmt"
"math/big"
)
func main() {
// Convert int to []byte
var int_to_encode int64 = 65535
var bytes_array []byte = big.NewInt(int_to_encode).Bytes()
fmt.Println("bytes array", bytes_array)
// Convert []byte to int
var decoded_int int64 = new(big.Int).SetBytes(bytes_array).Int64()
fmt.Println("decoded int", decoded_int)
}
This is the most straight forward (and shortest (and safest) (and maybe most performant)) way:
buf.Bytes() is of type bytes slice.
var val uint32 = 42
buf := new(bytes.Buffer)
err := binary.Write(buf, binary.LittleEndian, val)
if err != nil {
fmt.Println("binary.Write failed:", err)
}
fmt.Printf("% x\n", buf.Bytes())
see also https://stackoverflow.com/a/74819602/589493
What's wrong with converting it to a string?
[]byte(fmt.Sprintf("%d", myint))
package main
import (
"bytes"
"encoding/binary"
"fmt"
)
func main() {
aa := uint(0xFFFFFFFF)
fmt.Println(aa)
byteNewbuf := []byte{0xFF, 0xFF, 0xFF, 0xFF}
buf := bytes.NewBuffer(byteNewbuf)
tt, _ := binary.ReadUvarint(buf)
fmt.Println(tt)
}
Need to convert 4 bytes array to uint32 but why the results are not same ?
go verion : beta 1.1
You can do this with one of the ByteOrder objects from the encoding/binary package. For instance:
package main
import (
"encoding/binary"
"fmt"
)
func main() {
aa := uint(0x7FFFFFFF)
fmt.Println(aa)
slice := []byte{0xFF, 0xFF, 0xFF, 0x7F}
tt := binary.LittleEndian.Uint32(slice)
fmt.Println(tt)
}
If your data is in big endian format, you can instead use the same methods on binary.BigEndian.
tt := uint32(buf[0])<<24 | uint32(buf[1])<<16 | uint32(buf[2]) <<8 |
uint32(buf[3])
for BE or
tt := uint32(buf[0]) | uint32(buf[1])<<8 | uint32(buf[2]) <<16 |
uint32(buf[3]) <<24
for LE.
[u]varint is a different kind of encoding (32 bit numbers can have as much as 5 bytes in the encoded form, 64 bit numbers up to 10).
No need to create a buffer for []byte. Use Varint or Uvarint directly on the byte slice instead.
You're throwing away the error returned by the function. The second result indicates how many bytes were read or if there was a problem. There is a problem while decoding 0xff, 0xff, 0xff, 0xff as an uvarint.
Here is how to use the encoding/binary package to do what you want. Note that you don't want to use any of the var functions as those do variable length encoding.
Playground version
package main
import (
"bytes"
"encoding/binary"
"fmt"
"log"
)
func main() {
aa := uint(0xFFFFFF0F)
fmt.Println(aa)
tt := uint32(0)
byteNewbuf := []byte{0x0F, 0xFF, 0xFF, 0xFF}
buf := bytes.NewBuffer(byteNewbuf)
err := binary.Read(buf, binary.LittleEndian, &tt)
if err != nil {
log.Fatalf("Decode failed: %s", err)
}
fmt.Println(tt)
}
Result is
4294967055
4294967055
Numeric types
byte alias for uint8
Since byte is an alias for uint8, your question, "Need to convert 4 bytes array to uint32", has already been answered:
How to convert [4]uint8 into uint32 in Go?
Package binary
[Uvarints and] Varints are a method of encoding integers using one
or more bytes; numbers with smaller absolute value take a smaller
number of bytes. For a specification, see
http://code.google.com/apis/protocolbuffers/docs/encoding.html.
Since Uvarints are a peculiar form of integer representation and storage, you should only use the ReadUvarint function on values that have been written with the Uvarint function.
For example,
package main
import (
"bytes"
"encoding/binary"
"fmt"
)
func main() {
buf := make([]byte, 10)
x := uint64(0xFFFFFFFF)
fmt.Printf("%2d %2d %v\n", x, len(buf), buf)
n := binary.PutUvarint(buf, x)
buf = buf[:n]
fmt.Printf("%2d %2d %v\n", x, len(buf), buf)
y, err := binary.ReadUvarint(bytes.NewBuffer(buf))
if err != nil {
fmt.Println(err)
return
}
fmt.Printf("%2d %2d %v\n", y, len(buf), buf)
}
Output:
4294967295 10 [0 0 0 0 0 0 0 0 0 0]
4294967295 5 [255 255 255 255 15]
4294967295 5 [255 255 255 255 15]
I want to assign string to bytes array:
var arr [20]byte
str := "abc"
for k, v := range []byte(str) {
arr[k] = byte(v)
}
Have another method?
Safe and simple:
[]byte("Here is a string....")
For converting from a string to a byte slice, string -> []byte:
[]byte(str)
For converting an array to a slice, [20]byte -> []byte:
arr[:]
For copying a string to an array, string -> [20]byte:
copy(arr[:], str)
Same as above, but explicitly converting the string to a slice first:
copy(arr[:], []byte(str))
The built-in copy function only copies to a slice, from a slice.
Arrays are "the underlying data", while slices are "a viewport into underlying data".
Using [:] makes an array qualify as a slice.
A string does not qualify as a slice that can be copied to, but it qualifies as a slice that can be copied from (strings are immutable).
If the string is too long, copy will only copy the part of the string that fits (and multi-byte runes may then be copied only partly, which will corrupt the last rune of the resulting string).
This code:
var arr [20]byte
copy(arr[:], "abc")
fmt.Printf("array: %v (%T)\n", arr, arr)
...gives the following output:
array: [97 98 99 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0] ([20]uint8)
I also made it available at the Go Playground
For example,
package main
import "fmt"
func main() {
s := "abc"
var a [20]byte
copy(a[:], s)
fmt.Println("s:", []byte(s), "a:", a)
}
Output:
s: [97 98 99] a: [97 98 99 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0]
Piece of cake:
arr := []byte("That's all folks!!")
I think it's better..
package main
import "fmt"
func main() {
str := "abc"
mySlice := []byte(str)
fmt.Printf("%v -> '%s'",mySlice,mySlice )
}
Check here: http://play.golang.org/p/vpnAWHZZk7
Go, convert a string to a bytes slice
You need a fast way to convert a []string to []byte type. To use in situations such as storing text data into a random access file or other type of data manipulation that requires the input data to be in []byte type.
package main
func main() {
var s string
//...
b := []byte(s)
//...
}
which is useful when using ioutil.WriteFile, which accepts a bytes slice as its data parameter:
WriteFile func(filename string, data []byte, perm os.FileMode) error
Another example
package main
import (
"fmt"
"strings"
)
func main() {
stringSlice := []string{"hello", "world"}
stringByte := strings.Join(stringSlice, " ")
// Byte array value
fmt.Println([]byte(stringByte))
// Corresponding string value
fmt.Println(string([]byte(stringByte)))
}
Output:
[104 101 108 108 111 32 119 111 114 108 100] hello world
Please check the link playground
Besides the methods mentioned above, you can also do a trick as
s := "hello"
b := *(*[]byte)(unsafe.Pointer((*reflect.SliceHeader)(unsafe.Pointer(&s))))
Go Play: http://play.golang.org/p/xASsiSpQmC
You should never use this :-)
Ended up creating array specific methods to do this. Much like the encoding/binary package with specific methods for each int type. For example binary.BigEndian.PutUint16([]byte, uint16).
func byte16PutString(s string) [16]byte {
var a [16]byte
if len(s) > 16 {
copy(a[:], s)
} else {
copy(a[16-len(s):], s)
}
return a
}
var b [16]byte
b = byte16PutString("abc")
fmt.Printf("%v\n", b)
Output:
[0 0 0 0 0 0 0 0 0 0 0 0 0 97 98 99]
Notice how I wanted padding on the left, not the right.
http://play.golang.org/p/7tNumnJaiN
Arrays are values... slices are more like pointers. That is [n]type is not compatible with []type as they are fundamentally two different things. You can get a slice that points to an array by using arr[:] which returns a slice that has arr as it's backing storage.
One way to convert a slice of for example []byte to [20]byte is to actually allocate a [20]byte which you can do by using var [20]byte (as it's a value... no make needed) and then copy data into it:
buf := make([]byte, 10)
var arr [10]byte
copy(arr[:], buf)
Essentially what a lot of other answers get wrong is that []type is NOT an array.
[n]T and []T are completely different things!
When using reflect []T is not of kind Array but of kind Slice and [n]T is of kind Array.
You also can't use map[[]byte]T but you can use map[[n]byte]T.
This can sometimes be cumbersome because a lot of functions operate for example on []byte whereas some functions return [n]byte (most notably the hash functions in crypto/*).
A sha256 hash for example is [32]byte and not []byte so when beginners try to write it to a file for example:
sum := sha256.Sum256(data)
w.Write(sum)
they will get an error. The correct way of is to use
w.Write(sum[:])
However, what is it that you want? Just accessing the string bytewise? You can easily convert a string to []byte using:
bytes := []byte(str)
but this isn't an array, it's a slice. Also, byte != rune. In case you want to operate on "characters" you need to use rune... not byte.
If someone is looking for a quick consider use unsafe conversion between slices, you can refer to the following comparison.
package demo_test
import (
"testing"
"unsafe"
)
var testStr = "hello world"
var testBytes = []byte("hello world")
// Avoid copying the data.
func UnsafeStrToBytes(s string) []byte {
return *(*[]byte)(unsafe.Pointer(&s))
}
// Avoid copying the data.
func UnsafeBytesToStr(b []byte) string {
return *(*string)(unsafe.Pointer(&b))
}
func Benchmark_UnsafeStrToBytes(b *testing.B) {
for i := 0; i < b.N; i++ {
_ = UnsafeStrToBytes(testStr)
}
}
func Benchmark_SafeStrToBytes(b *testing.B) {
for i := 0; i < b.N; i++ {
_ = []byte(testStr)
}
}
func Benchmark_UnSafeBytesToStr(b *testing.B) {
for i := 0; i < b.N; i++ {
_ = UnsafeBytesToStr(testBytes)
}
}
func Benchmark_SafeBytesToStr(b *testing.B) {
for i := 0; i < b.N; i++ {
_ = string(testBytes)
}
}
go test -v -bench="^Benchmark" -run=none
output
cpu: Intel(R) Core(TM) i7-8565U CPU # 1.80GHz
Benchmark_UnsafeStrToBytes
Benchmark_UnsafeStrToBytes-8 1000000000 0.2465 ns/op
Benchmark_SafeStrToBytes
Benchmark_SafeStrToBytes-8 289119562 4.181 ns/op
Benchmark_UnSafeBytesToStr
Benchmark_UnSafeBytesToStr-8 1000000000 0.2530 ns/op
Benchmark_SafeBytesToStr
Benchmark_SafeBytesToStr-8 342842938 3.623 ns/op
PASS