Adding support for Byte array serialization (#583)

* implement helper for byte-array serialisation

utils/Felt.go

@@ -1,7 +1,11 @@
 package utils
 
 import (
+	"encoding/hex"
+	"fmt"
 	"math/big"
+	"regexp"
+	"strings"
 
 	"github.com/NethermindEth/juno/core/felt"
 )
@@ -41,15 +45,15 @@ func HexToFelt(hex string) (*felt.Felt, error) {
 // - error: an error if any
 func HexArrToFelt(hexArr []string) ([]*felt.Felt, error) {
 
- feltArr := make([]*felt.Felt, len(hexArr))
- for i, e := range hexArr {
-  felt, err := HexToFelt(e)
-  if err != nil {
-   return nil, err
-  }
-  feltArr[i] = felt
- }
- return feltArr, nil
+	feltArr := make([]*felt.Felt, len(hexArr))
+	for i, e := range hexArr {
+		felt, err := HexToFelt(e)
+		if err != nil {
+			return nil, err
+		}
+		feltArr[i] = felt
+	}
+	return feltArr, nil
 
 }
 
@@ -87,3 +91,114 @@ func FeltArrToBigIntArr(f []*felt.Felt) []*big.Int {
 	}
 	return bigArr
 }
+
+// StringToByteArrFelt converts string to array of Felt objects.
+// The returned array of felts will be of the format
+//
+// [number of felts with 31 characters in length, 31 byte felts..., pending word with max size of 30 bytes, pending words bytes size]
+//
+// For further explanation, refer the [article]
+//
+// Parameters:
+//
+// - s: string/bytearray to convert
+//
+// Returns:
+//
+// - []*felt.Felt: the array of felt.Felt objects
+//
+// - error: an error, if any
+//
+// [article]: https://docs.starknet.io/architecture-and-concepts/smart-contracts/serialization-of-cairo-types/#serialization_of_byte_arrays
+func StringToByteArrFelt(s string) ([]*felt.Felt, error) {
+	const SHORT_LENGTH = 31
+	exp := fmt.Sprintf(".{1,%d}", SHORT_LENGTH)
+	r := regexp.MustCompile(exp)
+
+	arr := r.FindAllString(s, -1)
+	if len(arr) == 0 {
+		return []*felt.Felt{}, fmt.Errorf("invalid string no matches found, s: %s", s)
+	}
+
+	hexarr := []string{}
+	var count, size uint64
+
+	for _, val := range arr {
+		if len(val) == SHORT_LENGTH {
+			count += 1
+		} else {
+			size = uint64(len(val))
+		}
+		hexarr = append(hexarr, "0x"+hex.EncodeToString([]byte(val)))
+	}
+
+	harr, err := HexArrToFelt(hexarr)
+	if err != nil {
+		return nil, err
+	}
+
+	if size == 0 {
+		harr = append(harr, new(felt.Felt).SetUint64(0))
+	}
+
+	harr = append(harr, new(felt.Felt).SetUint64(size))
+	return append([]*felt.Felt{new(felt.Felt).SetUint64(count)}, harr...), nil
+}
+
+// ByteArrFeltToString converts array of Felts to string.
+// The input array of felts will be of the format
+//
+// [number of felts with 31 characters in length, 31 byte felts..., pending word with max size of 30 bytes, pending words bytes size]
+//
+// For further explanation, refer the [article]
+//
+// Parameters:
+//
+// - []*felt.Felt: the array of felt.Felt objects
+//
+// Returns:
+//
+// - s: string/bytearray
+//
+// - error: an error, if any
+//
+// [article]: https://docs.starknet.io/architecture-and-concepts/smart-contracts/serialization-of-cairo-types/#serialization_of_byte_arrays
+func ByteArrFeltToString(arr []*felt.Felt) (string, error) {
+	if len(arr) < 3 {
+		return "", fmt.Errorf("invalid felt array, require atleast 3 elements in array")
+	}
+
+	count := FeltToBigInt(arr[0]).Uint64()
+	var index uint64
+	var res []string
+	for index = 0; index < count; index++ {
+		f := arr[1+index]
+		s, err := feltToString(f)
+		if err != nil {
+			return "", err
+		}
+		res = append(res, s)
+	}
+
+	pendingWordLength := arr[len(arr)-1]
+	if pendingWordLength.IsZero() {
+		return strings.Join(res, ""), nil
+	}
+
+	pendingWordFelt := arr[1+index]
+	s, err := feltToString(pendingWordFelt)
+	if err != nil {
+		return "", fmt.Errorf("invalid pending word")
+	}
+
+	res = append(res, s)
+	return strings.Join(res, ""), nil
+}
+
+func feltToString(f *felt.Felt) (string, error) {
+	b, err := hex.DecodeString(f.String()[2:])
+	if err != nil {
+		return "", fmt.Errorf("unable to decode to string")
+	}
+	return string(b), nil
+}

utils/Felt_test.go

@@ -0,0 +1,97 @@
+package utils
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestStringToByteArrFelt(t *testing.T) {
+	var tests = []struct {
+		in  string
+		out []string
+	}{
+		{
+			in:  "hello",
+			out: []string{"0x0", "0x68656c6c6f", "0x5"},
+		},
+		{
+			in:  "Long string, more than 31 characters.",
+			out: []string{"0x1", "0x4c6f6e6720737472696e672c206d6f7265207468616e203331206368617261", "0x63746572732e", "0x6"},
+		},
+		{
+			in:  "Blockchain secure digital asset",
+			out: []string{"0x1", "0x426c6f636b636861696e20736563757265206469676974616c206173736574", "0x0", "0x0"},
+		},
+		{
+			in:  "Decentralized applications offer transparency and user control",
+			out: []string{"0x2", "0x446563656e7472616c697a6564206170706c69636174696f6e73206f666665", "0x72207472616e73706172656e637920616e64207573657220636f6e74726f6c", "0x0", "0x0"},
+		},
+		{
+			in:  "12345",
+			out: []string{"0x0", "0x3132333435", "0x5"},
+		},
+		{
+			in:  "1234567890123456789012345678901",
+			out: []string{"0x1", "0x31323334353637383930313233343536373839303132333435363738393031", "0x0", "0x0"},
+		},
+		{
+			in:  "12345678901234567890123456789012",
+			out: []string{"0x1", "0x31323334353637383930313233343536373839303132333435363738393031", "0x32", "0x1"},
+		},
+	}
+
+	for _, tc := range tests {
+		res, err := StringToByteArrFelt(tc.in)
+		require.NoError(t, err, "error returned from StringToByteArrFelt")
+		require.Len(t, res, len(tc.out), "invalid conversion: array sizes do not match")
+
+		out, err := HexArrToFelt(tc.out)
+		require.NoError(t, err, "error returned from HexArrToFelt")
+		require.Exactly(t, out, res, "invalid conversion: values do not match")
+	}
+}
+
+func TestByteArrFeltToString(t *testing.T) {
+	var tests = []struct {
+		in  []string
+		out string
+	}{
+		{
+			in:  []string{"0x0", "0x68656c6c6f", "0x5"},
+			out: "hello",
+		},
+		{
+			in:  []string{"0x1", "0x4c6f6e6720737472696e672c206d6f7265207468616e203331206368617261", "0x63746572732e", "0x6"},
+			out: "Long string, more than 31 characters.",
+		},
+		{
+			in:  []string{"0x1", "0x426c6f636b636861696e20736563757265206469676974616c206173736574", "0x0", "0x0"},
+			out: "Blockchain secure digital asset",
+		},
+		{
+			in:  []string{"0x2", "0x446563656e7472616c697a6564206170706c69636174696f6e73206f666665", "0x72207472616e73706172656e637920616e64207573657220636f6e74726f6c", "0x0", "0x0"},
+			out: "Decentralized applications offer transparency and user control",
+		},
+		{
+			in:  []string{"0x0", "0x3132333435", "0x5"},
+			out: "12345",
+		},
+		{
+			in:  []string{"0x1", "0x31323334353637383930313233343536373839303132333435363738393031", "0x0", "0x0"},
+			out: "1234567890123456789012345678901",
+		},
+		{
+			in:  []string{"0x1", "0x31323334353637383930313233343536373839303132333435363738393031", "0x32", "0x1"},
+			out: "12345678901234567890123456789012",
+		},
+	}
+
+	for _, tc := range tests {
+		in, err := HexArrToFelt(tc.in)
+		require.NoError(t, err, "error returned from HexArrToFelt")
+		res, err := ByteArrFeltToString(in)
+		require.NoError(t, err, "error returned from ByteArrFeltToString")
+		require.Equal(t, tc.out, res, "invalid conversion: output does not match")
+	}
+}