Add function to convert to byte array

cast.go

@@ -6,7 +6,10 @@
 // Package cast provides easy and safe casting in Go.
 package cast
 
-import "time"
+import (
+	"encoding/binary"
+	"time"
+)
 
 // ToBool casts an interface to a bool type.
 func ToBool(i interface{}) bool {
@@ -169,6 +172,12 @@ func ToIntSlice(i interface{}) []int {
 	return v
 }
 
+// ToBytes casts an interface to a []byte type.
+func ToBytes(i interface{}, b binary.ByteOrder) []byte {
+	v, _ := ToBytesE(i, b)
+	return v
+}
+
 // ToDurationSlice casts an interface to a []time.Duration type.
 func ToDurationSlice(i interface{}) []time.Duration {
 	v, _ := ToDurationSliceE(i)

cast_test.go

@@ -6,10 +6,12 @@
 package cast
 
 import (
+	"encoding/binary"
 	"encoding/json"
 	"errors"
 	"fmt"
 	"html/template"
+	"math"
 	"path"
 	"reflect"
 	"testing"
@@ -289,6 +291,93 @@ func TestToStringE(t *testing.T) {
 	}
 }
 
+func TestToBytesE(t *testing.T) {
+	c := qt.New(t)
+
+	//Overkill?
+	expected8 := []byte{math.MaxInt8}
+	expectedLittle16 := append([]byte{math.MaxUint8}, math.MaxInt8)
+	expectedBig16 := append(expected8, math.MaxUint8)
+	expectedLittle32 := append([]byte{math.MaxUint8, math.MaxUint8}, expectedLittle16...)
+	expectedBig32 := append(expectedBig16, math.MaxUint8, math.MaxUint8)
+	expectedLittle64 := append([]byte{math.MaxUint8, math.MaxUint8, math.MaxUint8, math.MaxUint8}, expectedLittle32...)
+	expectedBig64 := append(expectedBig32, math.MaxUint8, math.MaxUint8, math.MaxUint8, math.MaxUint8)
+
+	expectedU8 := []byte{math.MaxUint8}
+	expectedLittleU16 := append(expectedU8, expectedU8...)
+	expectedLittleU32 := append(expectedLittleU16, expectedLittleU16...)
+	expectedLittleU64 := append(expectedLittleU32, expectedLittleU32...)
+	expectedBigU16 := append(expected8, expectedU8...)
+	expectedBigU32 := append(expectedBigU16, expectedLittleU16...)
+	expectedBigU64 := append(expectedBigU32, expectedLittleU32...)
+
+	tests := []struct {
+		input     interface{}
+		byteOrder binary.ByteOrder
+		expect    []byte
+		iserr     bool
+	}{
+		//LittleEndian
+		{byte(math.MaxUint8), binary.LittleEndian, expectedU8, false},
+		{math.MaxInt32, binary.LittleEndian, expectedLittle32, false},
+		{math.MaxInt64, binary.LittleEndian, expectedLittle64, false},
+		{uint(math.MaxUint32), binary.LittleEndian, expectedLittleU32, false},
+		{uint(math.MaxUint64), binary.LittleEndian, expectedLittleU64, false},
+		{int8(math.MaxInt8), binary.LittleEndian, expected8, false},
+		{int16(math.MaxInt16), binary.LittleEndian, expectedLittle16, false},
+		{int32(math.MaxInt32), binary.LittleEndian, expectedLittle32, false},
+		{int64(math.MaxInt64), binary.LittleEndian, expectedLittle64, false},
+		{uint8(math.MaxUint8), binary.LittleEndian, expectedU8, false},
+		{uint16(math.MaxUint16), binary.LittleEndian, expectedLittleU16, false},
+		{uint32(math.MaxUint32), binary.LittleEndian, expectedLittleU32, false},
+		{uint64(math.MaxUint64), binary.LittleEndian, expectedLittleU64, false},
+		{[]byte("one time"), binary.LittleEndian, []byte("one time"), false},
+		{"one more time", binary.LittleEndian, []byte("one more time"), false},
+		//BigEndian
+		{byte(math.MaxUint8), binary.BigEndian, expectedU8, false},
+		{math.MaxInt32, binary.BigEndian, expectedBig32, false},
+		{math.MaxInt64, binary.BigEndian, expectedBig64, false},
+		{uint(math.MaxInt32), binary.BigEndian, expectedBigU32, false},
+		{uint(math.MaxInt64), binary.BigEndian, expectedBigU64, false},
+		{int8(math.MaxInt8), binary.BigEndian, expected8, false},
+		{int16(math.MaxInt16), binary.BigEndian, expectedBig16, false},
+		{int32(math.MaxInt32), binary.BigEndian, expectedBig32, false},
+		{int64(math.MaxInt64), binary.BigEndian, expectedBig64, false},
+		{uint8(math.MaxUint8), binary.BigEndian, expectedU8, false},
+		{uint16(math.MaxInt16), binary.BigEndian, expectedBigU16, false},
+		{uint32(math.MaxInt32), binary.BigEndian, expectedBigU32, false},
+		{uint64(math.MaxInt64), binary.BigEndian, expectedBigU64, false},
+		{[]byte("one time"), binary.BigEndian, []byte("one time"), false},
+		{"one more time", binary.BigEndian, []byte("one more time"), false},
+		// errors
+		{testing.T{}, binary.LittleEndian, []byte{}, true},
+		{int8(-8), binary.LittleEndian, []byte{}, true},
+		{int16(-136), binary.LittleEndian, []byte{}, true},
+		{int32(-2184), binary.LittleEndian, []byte{}, true},
+		{int64(-34952), binary.LittleEndian, []byte{}, true},
+		{true, binary.LittleEndian, []byte{}, true},
+		{false, binary.LittleEndian, []byte{}, true},
+		{nil, binary.LittleEndian, []byte{}, true},
+	}
+
+	for i, test := range tests {
+		errmsg := qt.Commentf("i = %d", i) // assert helper message
+
+		v, err := ToBytesE(test.input, test.byteOrder)
+		if test.iserr {
+			c.Assert(err, qt.IsNotNil, errmsg)
+			continue
+		}
+
+		c.Assert(err, qt.IsNil, errmsg)
+		c.Assert(v, qt.DeepEquals, test.expect, errmsg)
+
+		// Non-E test
+		v = ToBytes(test.input, test.byteOrder)
+		c.Assert(v, qt.DeepEquals, test.expect, errmsg)
+	}
+}
+
 type foo struct {
 	val string
 }

caste.go

@@ -6,10 +6,12 @@
 package cast
 
 import (
+	"encoding/binary"
 	"encoding/json"
 	"errors"
 	"fmt"
 	"html/template"
+	"math"
 	"reflect"
 	"strconv"
 	"strings"
@@ -1340,6 +1342,92 @@ func ToIntSliceE(i interface{}) ([]int, error) {
 	}
 }
 
+func ToBytesE(i interface{}, b binary.ByteOrder) ([]byte, error) {
+	i = indirect(i)
+
+	if i == nil {
+		return []byte{}, fmt.Errorf("unable to cast %#v of type %T to []byte", i, i)
+	}
+
+	switch v := i.(type) {
+	case []byte:
+		return v, nil
+	case byte:
+		return []byte{v}, nil
+	case int8:
+		if v < 0 {
+			return []byte{}, errNegativeNotAllowed
+		}
+		return []byte{byte(v)}, nil
+	case int16:
+		if v < 0 {
+			return []byte{}, errNegativeNotAllowed
+		}
+		a := make([]byte, 2)
+		b.PutUint16(a, uint16(v))
+		return a, nil
+	case int32:
+		if v < 0 {
+			return []byte{}, errNegativeNotAllowed
+		}
+		a := make([]byte, 4)
+		b.PutUint32(a, uint32(v))
+		return a, nil
+	case int64:
+		if v < 0 {
+			return []byte{}, errNegativeNotAllowed
+		}
+		a := make([]byte, 8)
+		b.PutUint64(a, uint64(v))
+		return a, nil
+	case uint16:
+		a := make([]byte, 2)
+		b.PutUint16(a, v)
+		return a, nil
+	case uint32:
+		a := make([]byte, 4)
+		b.PutUint32(a, v)
+		return a, nil
+	case uint64:
+		a := make([]byte, 8)
+		b.PutUint64(a, v)
+		return a, nil
+	case int:
+		switch true {
+		case v < 0:
+			return []byte{}, errNegativeNotAllowed
+		case v <= math.MaxUint32:
+			a := make([]byte, 4)
+			b.PutUint32(a, uint32(v))
+			return a, nil
+		default:
+			a := make([]byte, 8)
+			b.PutUint64(a, uint64(v))
+			return a, nil
+		}
+	case uint:
+		switch true {
+		case v < 0:
+			return []byte{}, errNegativeNotAllowed
+		case v <= math.MaxUint32:
+			a := make([]byte, 4)
+			b.PutUint32(a, uint32(v))
+			return a, nil
+		case v <= math.MaxUint64:
+			a := make([]byte, 8)
+			b.PutUint64(a, uint64(v))
+			return a, nil
+		default:
+			return []byte{}, fmt.Errorf("unable to cast %#v of type %T to []byte", i, i)
+		}
+	case string:
+		return []byte(v), nil
+	default:
+		return []byte{}, fmt.Errorf("unable to cast %#v of type %T to []byte", i, i)
+	}
+
+}
+
 // ToDurationSliceE casts an interface to a []time.Duration type.
 func ToDurationSliceE(i interface{}) ([]time.Duration, error) {
 	if i == nil {