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Encoding and Decoding

When working with data from an algorand REST server or preparing transactions there is often a need to encode or decode fields.

Encoding Types

JSON

The encoding most often returned when querying the state of the chain is JSON.

It is easy to visually inspect but may be relatively slow to parse.

All byte arrays are base 64 encoded strings

MessagePack

The encoding used when transmitting transactions to a node is MessagePack

To inspect a given msgpack file contents a convenience commandline tool is provided:

    msgpacktool -d < file.msgp

Base64

The encoding for byte arrays is Base64.

This is to make it safe for the byte array to be transmitted as part of a json object.

Base32

The encoding used for Addresses and Transaction Ids is Base32

Individual Field encodings

Address

In Algorand a public key is a 32 byte array.

The Address developers or users are typically shown is a 58 byte string corresponding to a base32 encoding of the byte array of the public key + a checksum.

Given an address 4H5UNRBJ2Q6JENAXQ6HNTGKLKINP4J4VTQBEPK5F3I6RDICMZBPGNH6KD4, encoding to and from the public key format can be done as follows:

const address = '4H5UNRBJ2Q6JENAXQ6HNTGKLKINP4J4VTQBEPK5F3I6RDICMZBPGNH6KD4';
const pk = algosdk.decodeAddress(address);
const addr = algosdk.encodeAddress(pk.publicKey);
console.log(address, addr);
Snippet Source

address = "4H5UNRBJ2Q6JENAXQ6HNTGKLKINP4J4VTQBEPK5F3I6RDICMZBPGNH6KD4"
pk = encoding.decode_address(address)
addr = encoding.encode_address(pk)

assert addr == address
Snippet Source

address := "4H5UNRBJ2Q6JENAXQ6HNTGKLKINP4J4VTQBEPK5F3I6RDICMZBPGNH6KD4"
pk, _ := types.DecodeAddress(address)
addr := pk.String()
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String addrAsStr = "4H5UNRBJ2Q6JENAXQ6HNTGKLKINP4J4VTQBEPK5F3I6RDICMZBPGNH6KD4";
// Instantiate a new Address object with string
Address addr = new Address(addrAsStr);
// Or with the bytes
Address addrAgain = new Address(addr.getBytes());
assert addrAgain.equals(addr);
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Byte Arrays

When transmitting an array of bytes over the network, byte arrays are base64 encoded. The SDK will handle encoding from a byte array to base64 but may not decode some fields and you'll have to handle it yourself. For example compiled program results or the keys and values in a state delta in an application call will be returned as base64 encoded strings.

Example:

Given a base64 encoded byte array SGksIEknbSBkZWNvZGVkIGZyb20gYmFzZTY0 it may be decoded as follows:

const b64Encoded = 'SGksIEknbSBkZWNvZGVkIGZyb20gYmFzZTY0';
const b64Decoded = Buffer.from(b64Encoded, 'base64').toString();
console.log(b64Encoded, b64Decoded);
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encoded_str = "SGksIEknbSBkZWNvZGVkIGZyb20gYmFzZTY0"
decoded_str = base64.b64decode(encoded_str).decode("utf-8")
print(decoded_str)
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encoded := "SGksIEknbSBkZWNvZGVkIGZyb20gYmFzZTY0"
decoded, _ := base64.StdEncoding.DecodeString(encoded)
reencoded := base64.StdEncoding.EncodeToString(decoded)
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String encodedStr = "SGksIEknbSBkZWNvZGVkIGZyb20gYmFzZTY0";
byte[] decodedBytes = Encoder.decodeFromBase64(encodedStr);
String reEncodedStr = Encoder.encodeToBase64(decodedBytes);
assert encodedStr.equals(reEncodedStr);
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Integers

Integers in algorand are almost always uint64, sometimes its required to encode them as bytes. For example when passing them as application arguments in an ApplicationCallTransaction. When encoding an integer to pass as an application argument, the integer should be encoded as the big endian 8 byte representation of the integer value.

Example:

Given an integer 1337, you may encode it as:

const int = 1337;
const encoded = algosdk.encodeUint64(int);
const safeDecoded = algosdk.decodeUint64(encoded, 'safe');
const mixedDecoded = algosdk.decodeUint64(encoded, 'bigint');
console.log(int, encoded, safeDecoded, mixedDecoded);
Snippet Source

val = 1337
encoded_uint = val.to_bytes(8, "big")
decoded_uint = int.from_bytes(encoded_uint, byteorder="big")
assert decoded_uint == val
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val := 1337
encodedInt := make([]byte, 8)
binary.BigEndian.PutUint64(encodedInt, uint64(val))

decodedInt := binary.BigEndian.Uint64(encodedInt)
// decodedInt == val
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BigInteger val = BigInteger.valueOf(1337);
byte[] encodedVal = Encoder.encodeUint64(val);
BigInteger decodedVal = Encoder.decodeUint64(encodedVal);
assert val.equals(decodedVal);
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Working with encoded structures

Transaction

Sometimes an application needs to transmit a transaction or transaction group between the front end and back end. This can be done by msgpack encoding the transaction object on one side and msgpack decoding it on the other side. Often the msgpack'd bytes will be base64 encoded so that they can be safely transmitted in some json payload so we use that encoding here.

Essentially the encoding is:

tx_byte_str = base64encode(msgpack_encode(tx_obj))

and decoding is:

tx_obj = msgpack_decode(base64decode(tx_byte_str))

Example

Create a payment transaction from one account to another using suggested parameters and amount 10000, we write the msgpack encoded bytes

const txn = algosdk.makePaymentTxnWithSuggestedParamsFromObject({
  from: sender.addr,
  to: receiver.addr,
  amount: 1e6,
  suggestedParams,
});

const txnBytes = txn.toByte();
const txnB64 = Buffer.from(txnBytes).toString('base64');
const restoredTxn = algosdk.decodeUnsignedTransaction(
  Buffer.from(txnB64, 'base64')
);
console.log(restoredTxn);
Snippet Source
const signedTxn = txn.signTxn(sender.privateKey);
const signedB64Txn = Buffer.from(signedTxn).toString('base64');
const restoredSignedTxn = algosdk.decodeSignedTransaction(
  Buffer.from(signedB64Txn, 'base64')
);
console.log(restoredSignedTxn);
Snippet Source

sp = algod_client.suggested_params()
pay_txn = transaction.PaymentTxn(acct.address, sp, acct.address, 10000)

# Write message packed transaction to disk
with open("pay.txn", "w") as f:
    f.write(encoding.msgpack_encode(pay_txn))

# Read message packed transaction and decode it to a Transaction object
with open("pay.txn", "r") as f:
    recovered_txn = encoding.msgpack_decode(f.read())

print(recovered_txn.dictify())
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# Sign transaction
spay_txn = pay_txn.sign(acct.private_key)
# write message packed signed transaction to disk
with open("signed_pay.txn", "w") as f:
    f.write(encoding.msgpack_encode(spay_txn))

# read message packed signed transaction into a SignedTransaction object
with open("signed_pay.txn", "r") as f:
    recovered_signed_txn = encoding.msgpack_decode(f.read())

print(recovered_signed_txn.dictify())
Snippet Source

// Error handling omitted for brevity
sp, _ := algodClient.SuggestedParams().Do(context.Background())
ptxn, _ := transaction.MakePaymentTxn(
    acct1.Address.String(), acct1.Address.String(), 10000, nil, "", sp,
)

// Encode the txn as bytes,
// if sending over the wire (like to a frontend) it should also be b64 encoded
encodedTxn := msgpack.Encode(ptxn)
os.WriteFile("pay.txn", encodedTxn, 0655)

var recoveredPayTxn = types.Transaction{}

msgpack.Decode(encodedTxn, &recoveredPayTxn)
log.Printf("%+v", recoveredPayTxn)
Snippet Source
// Assuming we already have a pay transaction `ptxn`

// Sign the transaction
_, signedTxn, err := crypto.SignTransaction(acct1.PrivateKey, ptxn)
if err != nil {
    log.Fatalf("failed to sign transaction: %s", err)
}

// Save the signed transaction to file
os.WriteFile("pay.stxn", signedTxn, 0644)

signedPayTxn := types.SignedTxn{}
err = msgpack.Decode(signedTxn, &signedPayTxn)
if err != nil {
    log.Fatalf("failed to decode signed transaction: %s", err)
}
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Response<TransactionParametersResponse> rsp = algodClient.TransactionParams().execute();
TransactionParametersResponse sp = rsp.body();
// Wipe the `reserve` address through an AssetConfigTransaction
Transaction ptxn = Transaction.PaymentTransactionBuilder().suggestedParams(sp)
        .sender(acct.getAddress()).receiver(acct.getAddress()).amount(100).build();

byte[] encodedTxn = Encoder.encodeToMsgPack(ptxn);

Transaction decodedTxn = Encoder.decodeFromMsgPack(encodedTxn, Transaction.class);
assert decodedTxn.equals(ptxn);
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SignedTransaction signedTxn = acct.signTransaction(ptxn);
byte[] encodedSignedTxn = Encoder.encodeToMsgPack(signedTxn);

SignedTransaction decodedSignedTransaction = Encoder.decodeFromMsgPack(encodedSignedTxn,
        SignedTransaction.class);
assert decodedSignedTransaction.equals(signedTxn);
Snippet Source

ABI Encoding

All the SDKs support encoding and decoding of ABI values. The encoding is done using the Algorand ABI specification.

const stringTupleCodec = algosdk.ABIType.from('(string,string)');

const stringTupleData = ['hello', 'world'];
const encodedTuple = stringTupleCodec.encode(stringTupleData);
console.log(Buffer.from(encodedTuple).toString('hex'));

const decodedTuple = stringTupleCodec.decode(encodedTuple);
console.log(decodedTuple); // ['hello', 'world']

const uintArrayCodec = algosdk.ABIType.from('uint64[]');

const uintArrayData = [1, 2, 3, 4, 5];
const encodedArray = uintArrayCodec.encode(uintArrayData);
console.log(Buffer.from(encodedArray).toString('hex'));

const decodeArray = uintArrayCodec.decode(encodedArray);
console.log(decodeArray); // [1, 2, 3, 4, 5]
Snippet Source

from algosdk import abi

# generate a codec from the string representation of the ABI type
# in this case, a tuple of two strings
codec = abi.ABIType.from_string("(string,string)")

# encode the value to its ABI encoding with the codec
to_encode = ["hello", "world"]
encoded = codec.encode(to_encode)
print(encoded.hex())

# decode the value from its ABI encoding with the codec
decoded = codec.decode(encoded)
print(decoded)  # prints ["hello", "world"]

# generate a codec for a uint64 array
uint_array_codec = abi.ABIType.from_string("uint64[]")
uint_array = [1, 2, 3, 4, 5]
encoded_array = uint_array_codec.encode(uint_array)
print(encoded_array.hex())

decoded_array = uint_array_codec.decode(encoded_array)
print(decoded_array)  # prints [1, 2, 3, 4, 5]
Snippet Source

tupleCodec, _ := abi.TypeOf("(string,string)")

tupleVal := []string{"hello", "world"}
encodedTuple, _ := tupleCodec.Encode(tupleVal)
log.Printf("%x", encodedTuple)

decodedTuple, _ := tupleCodec.Decode(encodedTuple)
log.Printf("%v", decodedTuple) // [hello world]

arrCodec, _ := abi.TypeOf("uint64[]")
arrVal := []uint64{1, 2, 3, 4, 5}
encodedArr, _ := arrCodec.Encode(arrVal)
log.Printf("%x", encodedArr)

decodedArr, _ := arrCodec.Decode(encodedArr)
log.Printf("%v", decodedArr) // [1 2 3 4 5]
Snippet Source

ABIType tupleCodec = ABIType.valueOf("(string,string)");
Object[] tupleData = new Object[] { "hello", "world" };
byte[] tupleEncoded = tupleCodec.encode(tupleData);
System.out.printf("Encoded: '%s'\n", Hex.encodeHexString(tupleEncoded));
Object tupleDecoded = tupleCodec.decode(tupleEncoded);
// prints [hello, world]
System.out.printf("Decoded: %s\n", Arrays.toString((Object[]) tupleDecoded));

ABIType arrCodec = ABIType.valueOf("uint64[]");
Object[] arrData = new Object[] { 1, 2, 3, 4, 5 };
byte[] arrEncoded = arrCodec.encode(arrData);
System.out.printf("Encoded: '%s'\n", Hex.encodeHexString(arrEncoded));

Object arrDecoded = arrCodec.decode(arrEncoded);
// prints [1, 2, 3, 4, 5]
System.out.printf("Decoded: %s\n", Arrays.toString((Object[]) arrDecoded));
Snippet Source