logic

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 Go to latest Published: Nov 24, 2019 License: AGPL-3.0 Imports: 25 Imported by: 0

README

Transaction Execution Approval Language (TEAL)

TEAL is a bytecode based stack language that executes inside Algorand transactions to check the parameters of the transaction and approve the transaction as if by a signature. Programs have read-only access to the transaction they are attached to, transactions in their atomic transaction group, and a few global values. Programs cannot modify or create transactions, only reject or approve them. Approval is signaled by finishing with the stack containing a single non-zero uint64 value.

TEAL programs should be short and run fast as they are run in-line along with signature checking, transaction balance rule checking, and other checks during block assembly and validation. Many useful programs are less than 100 instructions.

The Stack

The stack starts empty and contains values of either uint64 or bytes (bytes are implemented in Go as a []byte slice). Most operations act on the stack, popping arguments from it and pushing results to it.

The maximum stack depth is currently 1000.

Scratch Space

In addition to the stack there are 256 positions of scratch space, also uint64-bytes union values, accessed by the load and store ops moving data from or to scratch space, respectively.

Execution Environment

TEAL runs in Algorand nodes as part of testing a proposed transaction to see if it is valid and authorized to be committed into a block.

If an authorized program executes and finishes with a single non-zero uint64 value on the stack then that program has validated the transaction it is attached to.

The TEAL program has access to data from the transaction it is attached to (txn op), any transactions in a transaction group it is part of (gtxn op), and a few global values like consensus parameters (global op). Some "Args" may be attached to a transaction being validated by a TEAL program. Args are an array of byte strings. A common pattern would be to have the key to unlock some contract as an Arg. Args are recorded on the blockchain and publicly visible when the transaction is submitted to the network.

A program can either authorize some delegated action on a normal private key signed or multisig account or be wholly in charge of a contract account.

  • If the account has signed the program (an ed25519 signature on "Program" concatenated with the program bytes) then if the program returns true the transaction is authorized as if the account had signed it. This allows an account to hand out a signed program so that other users can carry out delegated actions which are approved by the program.
  • If the SHA512_256 hash of the program (prefixed by "Program") is equal to the transaction Sender address then this is a contract account wholly controlled by the program. No other signature is necessary or possible. The only way to execute a transaction against the contract account is for the program to approve it.

The TEAL bytecode plus the length of any Args must add up to less than 1000 bytes (consensus parameter LogicSigMaxSize). Each TEAL op has an associated cost estimate and the program cost estimate must total less than 20000 (consensus parameter LogicSigMaxCost). Most ops have an estimated cost of 1, but a few slow crypto ops are much higher.

Constants

Constants are loaded into the environment into storage separate from the stack. They can then be pushed onto the stack by referring to the type and index. This makes for efficient re-use of byte constants used for account addresses, etc.

The assembler will hide most of this, allowing simple use of int 1234 and byte 0xcafed00d. These constants will automatically get assembled into int and byte pages of constants, de-duplicated, and operations to load them from constant storage space inserted.

Constants are loaded into the environment by two opcodes, intcblock and bytecblock. Both of these use proto-buf style variable length unsigned int, reproduced here. The intcblock opcode is followed by a varuint specifying the length of the array and then that number of varuint. The bytecblock opcode is followed by a varuint array length then that number of pairs of (varuint, bytes) length prefixed byte strings. This should efficiently load 32 and 64 byte constants which will be common as addresses, hashes, and signatures.

Constants are pushed onto the stack by intc, intc_[0123], bytec, and bytec_[0123]. The assembler will handle converting int N or byte N into the appropriate form of the instruction needed.

Operations

Most operations work with only one type of argument, uint64 or bytes, and panic if the wrong type value is on the stack. The instruction set was designed to execute calculator-like expressions. What might be a one line expression with various parenthesized clauses should be efficiently representable in TEAL.

Looping is not possible, by design, to ensure predictably fast execution. There is a branch instruction (bnz, branch if not zero) which allows forward branching only so that some code may be skipped.

Many programs need only a few dozen instructions. The instruction set has some optimization built in. intc, bytec, and arg take an immediate value byte, making a 2-byte op to load a value onto the stack, but they also have single byte versions for loading the most common constant values. Any program will benefit from having a few common values loaded with a smaller one byte opcode. Cryptographic hashes and ed25519verify are single byte opcodes with powerful libraries behind them. These operations still take more time than other ops (and this is reflected in the cost of each op and the cost limit of a program) but are efficient in compiled code space.

This summary is supplemented by more detail in the opcodes document.

Some operations 'panic' and immediately end execution of the program. A transaction checked by a program that panics is not valid. A contract account governed by a buggy program might not have a way to get assets back out of it. Code carefully.

Arithmetic, Logic, and Cryptographic Operations

For one-argument ops, X is the last element on the stack, which is typically replaced by a new value.

For two-argument ops, A is the previous element on the stack and B is the last element on the stack. These typically result in popping A and B from the stack and pushing the result.

ed25519verify is currently the only 3 argument opcode and is described in detail in the opcode refrence.

Op Description
sha256 SHA256 hash of value X, yields [32]byte
keccak256 Keccak256 hash of value X, yields [32]byte
sha512_256 SHA512_256 hash of value X, yields [32]byte
ed25519verify for (data A, signature B, pubkey C) verify the signature of ("ProgData" || program_hash || data) against the pubkey => {0 or 1}
+ A plus B. Panic on overflow.
- A minus B. Panic if B > A.
/ A divided by B. Panic if B == 0.
* A times B. Panic on overflow.
< A less than B => {0 or 1}
> A greater than B => {0 or 1}
<= A less than or equal to B => {0 or 1}
>= A greater than or equal to B => {0 or 1}
&& A is not zero and B is not zero => {0 or 1}
|| A is not zero or B is not zero => {0 or 1}
== A is equal to B => {0 or 1}
!= A is not equal to B => {0 or 1}
! X == 0 yields 1; else 0
len yields length of byte value X
itob converts uint64 X to big endian bytes
btoi converts bytes X as big endian to uint64
% A modulo B. Panic if B == 0.
| A bitwise-or B
& A bitwise-and B
^ A bitwise-xor B
~ bitwise invert value X
mulw A times B out to 128-bit long result as low (top) and high uint64 values on the stack
Loading Values

Opcodes for getting data onto the stack.

Some of these have immediate data in the byte or bytes after the opcode.

Op Description
intcblock load block of uint64 constants
intc push value from uint64 constants to stack by index into constants
intc_0 push constant 0 from intcblock to stack
intc_1 push constant 1 from intcblock to stack
intc_2 push constant 2 from intcblock to stack
intc_3 push constant 3 from intcblock to stack
bytecblock load block of byte-array constants
bytec push bytes constant to stack by index into constants
bytec_0 push constant 0 from bytecblock to stack
bytec_1 push constant 1 from bytecblock to stack
bytec_2 push constant 2 from bytecblock to stack
bytec_3 push constant 3 from bytecblock to stack
arg push Args[N] value to stack by index
arg_0 push Args[0] to stack
arg_1 push Args[1] to stack
arg_2 push Args[2] to stack
arg_3 push Args[3] to stack
txn push field from current transaction to stack
gtxn push field to the stack from a transaction in the current transaction group
global push value from globals to stack
load copy a value from scratch space to the stack
store pop a value from the stack and store to scratch space

Transaction Fields

Index Name Type Notes
0 Sender []byte 32 byte address
1 Fee uint64 micro-Algos
2 FirstValid uint64 round number
3 FirstValidTime uint64 Seconds since 1970-01-01 00:00:00 UTC of block at FirstValid-1
4 LastValid uint64 round number
5 Note []byte
6 Lease []byte
7 Receiver []byte 32 byte address
8 Amount uint64 micro-Algos
9 CloseRemainderTo []byte 32 byte address
10 VotePK []byte 32 byte address
11 SelectionPK []byte 32 byte address
12 VoteFirst uint64
13 VoteLast uint64
14 VoteKeyDilution uint64
15 Type []byte
16 TypeEnum uint64 See table below
17 XferAsset uint64 Asset ID
18 AssetAmount uint64 value in Asset's units
19 AssetSender []byte 32 byte address. Causes clawback of all value of asset from AssetSender if Sender is the Clawback address of the asset.
20 AssetReceiver []byte 32 byte address
21 AssetCloseTo []byte 32 byte address
22 GroupIndex uint64 Position of this transaction within an atomic transaction group. A stand-alone transaction is implicitly element 0 in a group of 1.
23 TxID []byte The computed ID for this transaction. 32 bytes.

Additional details in the opcodes document on the txn op.

Global Fields

Global fields are fields that are common to all the transactions in the group. In particular it includes consensus parameters.

Index Name Type Notes
0 MinTxnFee uint64 micro Algos
1 MinBalance uint64 micro Algos
2 MaxTxnLife uint64 rounds
3 ZeroAddress []byte 32 byte address of all zero bytes
4 GroupSize uint64 Number of transactions in this atomic transaction group. At least 1.
Flow Control
Op Description
err Error. Panic immediately. This is primarily a fencepost against accidental zero bytes getting compiled into programs.
bnz branch if value X is not zero
pop discard value X from stack
dup duplicate last value on stack

Assembler Syntax

The assembler parses line by line. Ops that just use the stack appear on a line by themselves. Ops that take arguments are the op and then whitespace and then any argument or arguments.

"//" prefixes a line comment.

Constants and Pseudo-Ops

A few pseudo-ops simplify writing code. int and byte and addr followed by a constant record the constant to a intcblock or bytecblock at the beginning of code and insert an intc or bytec reference where the instruction appears to load that value. addr parses an Algorand account address base32 and converts it to a regular bytes constant.

byte constants are:

byte base64 AAAA...
byte b64 AAAA...
byte base64(AAAA...)
byte b64(AAAA...)
byte base32 AAAA...
byte b32 AAAA...
byte base32(AAAA...)
byte b32(AAAA...)
byte 0x0123456789abcdef...

int constants may be 0x prefixed for hex, 0 prefixed for octal, or decimal numbers.

intcblock may be explictly assembled. It will conflict with the assembler gathering int pseudo-ops into a intcblock program prefix, but may be used if code only has explicit intc references. intcblock should be followed by space separated int constants all on one line.

bytecblock may be explicitly assembled. It will conflict with the assembler if there are any byte pseudo-ops but may be used if only explicit bytec references are used. bytecblock should be followed with byte constants all on one line, either 'encoding value' pairs (b64 AAA...) or 0x prefix or function-style values (base64(...)).

Labels and Branches

A label is defined by any string not some other op or keyword and ending in ':'. A label can be an argument (without the trailing ':') to a branch instruction.

Example:

int 1
bnz safe
err
safe:
pop

Encoding and Versioning

A program starts with a varuint declaring the version of the compiled code. Any addition, removal, or change of opcode behavior increments the version. For the most part opcode behavior should not change, addition will be infrequent (not likely more often than every three months and less often as the language matures), and removal should be very rare.

For version 1, subsequent bytes after the varuint are program opcode bytes. Future versions could put other metadata following the version identifier.

Varuint

A 'proto-buf style variable length unsigned int' is encoded with 7 data bits per byte and the high bit is 1 if there is a following byte and 0 for the last byte. The lowest order 7 bits are in the first byte, followed by successively higher groups of 7 bits.

What TEAL Cannot Do

Current design and implementation limitations to be aware of.

  • TEAL cannot create or change a transaction, only approve or reject.
  • TEAL cannot lookup balances of Algos or other assets. (Standard transaction accounting will apply after TEAL has run and authorized a transaction. A TEAL-approved transaction could still be invalid by other accounting rules just as a standard signed transaction could be invalid. e.g. I can't give away money I don't have.)
  • TEAL cannot access information in previous blocks. TEAL cannot access most information in other transactions in the current block. (TEAL can access fields of the transaction it is attached to and the transactions in an atomic transaction group.)
  • TEAL cannot know exactly what round the current transaction will commit in (but it is somewhere in FirstValid through LastValid).
  • TEAL cannot know exactly what time its transaction is committed. (txn FirstValidTime should be approximately the 'unix time' seconds since 1970-01-01 00:00:00 UTC of the block before FirstValid, but there are conditions in which this time may drift and slowly re-align to close to accurate time.)
  • TEAL cannot loop. Its branch instruction bnz "branch if not zero" can only branch forward so as to skip some code.
  • TEAL cannot recurse. There is no subroutine jump operation.

Documentation

Index

Constants

View Source 
const AssemblerDefaultVersion = 1

AssemblerDefaultVersion what version of code do we emit by default

View Source 
const EvalMaxArgs = 255

EvalMaxArgs is the maximum number of arguments to an LSig

View Source 
const EvalMaxScratchSize = 255

EvalMaxScratchSize is the maximum number of scratch slots.

View Source 
const EvalMaxVersion = 1

EvalMaxVersion is the max version we can interpret and run

View Source 
const MaxStackDepth = 1000

MaxStackDepth should move to consensus params

Variables

View Source 
var AccountFieldNames = []string{
	"Balance",
}

AccountFieldNames are arguments to the 'account' opcode

View Source 
var GlobalFieldDocs map[string]string

GlobalFieldDocs are notes on fields available in `global`

View Source 
var GlobalFieldNames []string

GlobalFieldNames are arguments to the 'global' opcode

View Source 
var GlobalFieldTypes []StackType

GlobalFieldTypes is StackUint64 StackBytes in parallel with GlobalFieldNames

View Source 
var OpGroupList = []OpGroup{
	{"Arithmetic", []string{"sha256", "keccak256", "sha512_256", "ed25519verify", "+", "-", "/", "*", "<", ">", "<=", ">=", "&&", "||", "==", "!=", "!", "len", "itob", "btoi", "%", "|", "&", "^", "~", "mulw"}},
	{"Loading Values", []string{"intcblock", "intc", "intc_0", "intc_1", "intc_2", "intc_3", "bytecblock", "bytec", "bytec_0", "bytec_1", "bytec_2", "bytec_3", "arg", "arg_0", "arg_1", "arg_2", "arg_3", "txn", "gtxn", "global", "load", "store"}},
	{"Flow Control", []string{"err", "bnz", "pop", "dup"}},
}

OpGroupList is groupings of ops for documentation purposes.

View Source 
var OpSpecs = []OpSpec{
	{0x00, "err", opErr, nil, nil},
	{0x01, "sha256", opSHA256, oneBytes, oneBytes},
	{0x02, "keccak256", opKeccak256, oneBytes, oneBytes},
	{0x03, "sha512_256", opSHA512_256, oneBytes, oneBytes},
	{0x04, "ed25519verify", opEd25519verify, threeBytes, oneInt},
	{0x08, "+", opPlus, twoInts, oneInt},
	{0x09, "-", opMinus, twoInts, oneInt},
	{0x0a, "/", opDiv, twoInts, oneInt},
	{0x0b, "*", opMul, twoInts, oneInt},
	{0x0c, "<", opLt, twoInts, oneInt},
	{0x0d, ">", opGt, twoInts, oneInt},
	{0x0e, "<=", opLe, twoInts, oneInt},
	{0x0f, ">=", opGe, twoInts, oneInt},
	{0x10, "&&", opAnd, twoInts, oneInt},
	{0x11, "||", opOr, twoInts, oneInt},
	{0x12, "==", opEq, twoAny, oneInt},
	{0x13, "!=", opNeq, twoAny, oneInt},
	{0x14, "!", opNot, oneInt, oneInt},
	{0x15, "len", opLen, oneBytes, oneInt},
	{0x16, "itob", opItob, oneInt, oneBytes},
	{0x17, "btoi", opBtoi, oneBytes, oneInt},
	{0x18, "%", opModulo, twoInts, oneInt},
	{0x19, "|", opBitOr, twoInts, oneInt},
	{0x1a, "&", opBitAnd, twoInts, oneInt},
	{0x1b, "^", opBitXor, twoInts, oneInt},
	{0x1c, "~", opBitNot, oneInt, oneInt},
	{0x1d, "mulw", opMulw, twoInts, twoInts},

	{0x20, "intcblock", opIntConstBlock, nil, nil},
	{0x21, "intc", opIntConstLoad, nil, oneInt},
	{0x22, "intc_0", opIntConst0, nil, oneInt},
	{0x23, "intc_1", opIntConst1, nil, oneInt},
	{0x24, "intc_2", opIntConst2, nil, oneInt},
	{0x25, "intc_3", opIntConst3, nil, oneInt},
	{0x26, "bytecblock", opByteConstBlock, nil, nil},
	{0x27, "bytec", opByteConstLoad, nil, oneBytes},
	{0x28, "bytec_0", opByteConst0, nil, oneBytes},
	{0x29, "bytec_1", opByteConst1, nil, oneBytes},
	{0x2a, "bytec_2", opByteConst2, nil, oneBytes},
	{0x2b, "bytec_3", opByteConst3, nil, oneBytes},
	{0x2c, "arg", opArg, nil, oneBytes},
	{0x2d, "arg_0", opArg0, nil, oneBytes},
	{0x2e, "arg_1", opArg1, nil, oneBytes},
	{0x2f, "arg_2", opArg2, nil, oneBytes},
	{0x30, "arg_3", opArg3, nil, oneBytes},
	{0x31, "txn", opTxn, nil, oneAny},
	{0x32, "global", opGlobal, nil, oneAny},
	{0x33, "gtxn", opGtxn, nil, oneAny},
	{0x34, "load", opLoad, nil, oneAny},
	{0x35, "store", opStore, oneAny, nil},

	{0x40, "bnz", opBnz, oneInt, nil},
	{0x48, "pop", opPop, oneAny, nil},
	{0x49, "dup", opDup, oneAny, twoAny},
}

OpSpecs is the table of operations that can be assembled and evaluated.

Any changes should be reflected in README.md which serves as the language spec.

View Source 
var TxnFieldDocs map[string]string

TxnFieldDocs are notes on fields available by `txn` and `gtxn`

View Source 
var TxnFieldNames []string

TxnFieldNames are arguments to the 'txn' and 'txnById' opcodes

View Source 
var TxnFieldTypes []StackType

TxnFieldTypes is StackBytes or StackUint64 parallel to TxnFieldNames

View Source 
var TxnTypeNames = []string{
	string(protocol.UnknownTx),
	string(protocol.PaymentTx),
	string(protocol.KeyRegistrationTx),
	string(protocol.AssetConfigTx),
	string(protocol.AssetTransferTx),
	string(protocol.AssetFreezeTx),
}

TxnTypeNames is the values of Txn.Type in enum order

Functions

func AssembleString 

func AssembleString(text string) ([]byte, error)

AssembleString takes an entire program in a string and assembles it to bytecode

func Check 

func Check(program []byte, params EvalParams) (cost int, err error)

Check should be faster than Eval. Returns 'cost' which is an estimate of relative execution time.

func Disassemble 

func Disassemble(program []byte) (text string, err error)

Disassemble produces a text form of program bytes. AssembleString(Disassemble()) should result in the same program bytes.

func Eval 

func Eval(program []byte, params EvalParams) (pass bool, err error)

Eval checks to see if a transaction passes logic A program passes succesfully if it finishes with one int element on the stack that is non-zero.

func HashProgram 

func HashProgram(program []byte) crypto.Digest

HashProgram takes program bytes and returns the Digest This Digest can be used as an Address for a logic controlled account.

func OpCost 

func OpCost(opName string) int

OpCost returns the relative cost score for an op

func OpDoc 

func OpDoc(opName string) string

OpDoc returns a description of the op

func OpDocExtra 

func OpDocExtra(opName string) string

OpDocExtra returns extra documentation text about an op

func OpImmediateNote 

func OpImmediateNote(opName string) string

OpImmediateNote returns a short string about immediate data which follows the op byte

func OpSize 

func OpSize(opName string) int

OpSize returns the number of bytes for an op. 0 for variable.

func TypeNameDescription 

func TypeNameDescription(typeName string) string

TypeNameDescription returns extra description about a low level protocol transaction Type string

Types

type EvalParams 

type EvalParams struct {
	// the transaction being evaluated
	Txn *transactions.SignedTxn

	Proto *config.ConsensusParams

	Trace io.Writer

	TxnGroup []transactions.SignedTxnWithAD

	// GroupIndex should point to Txn within TxnGroup
	GroupIndex int

	FirstValidTimeStamp uint64

	Logger logging.Logger
}

EvalParams contains data that comes into condition evaluation.

type GlobalField 

type GlobalField int

GlobalField is an enum for `global` opcode 

const (
	// MinTxnFee ConsensusParams.MinTxnFee
	MinTxnFee GlobalField = iota
	// MinBalance ConsensusParams.MinBalance
	MinBalance
	// MaxTxnLife ConsensusParams.MaxTxnLife
	MaxTxnLife
	// ZeroAddress [32]byte{0...}
	ZeroAddress
	// GroupSize len(txn group)
	GroupSize
)

func (GlobalField) String 

func (i GlobalField) String() string

type Msg 

type Msg struct {
	ProgramHash crypto.Digest `codec:"p"`
	Data        []byte        `codec:"d"`
	// contains filtered or unexported fields
}

Msg is data meant to be signed and then verified with the ed25519verify opcode.

func (Msg) ToBeHashed 

func (msg Msg) ToBeHashed() (protocol.HashID, []byte)

ToBeHashed implements crypto.Hashable

type OpGroup 

type OpGroup struct {
	GroupName string
	Ops       []string
}

OpGroup is a grouping of ops for documentation purposes. e.g. "Arithmetic", ["+", "-", ...]

type OpSpec 

type OpSpec struct {
	Opcode byte
	Name   string

	Args    []StackType // what gets popped from the stack
	Returns []StackType // what gets pushed to the stack
	// contains filtered or unexported fields
}

OpSpec defines one byte opcode

type OpStream 

type OpStream struct {
	Out     bytes.Buffer
	Version uint64
	Trace   io.Writer
	// contains filtered or unexported fields
}

OpStream is destination for program and scratch space

func (*OpStream) Arg 

func (ops *OpStream) Arg(val uint64) error

Arg writes opcodes for loading from Lsig.Args

func (*OpStream) Assemble 

func (ops *OpStream) Assemble(fin io.Reader) error

Assemble reads text from an input and accumulates the program

func (*OpStream) ByteLiteral 

func (ops *OpStream) ByteLiteral(val []byte) error

ByteLiteral writes opcodes and data for loading a []byte literal Values are accumulated so that they can be put into a bytecblock

func (*OpStream) Bytec 

func (ops *OpStream) Bytec(constIndex uint) error

Bytec writes opcodes for loading a []byte constant onto the stack.

func (*OpStream) Bytes 

func (ops *OpStream) Bytes() (program []byte, err error)

Bytes returns the finished program bytes

func (*OpStream) Global 

func (ops *OpStream) Global(val uint64) error

Global writes opcodes for loading an evaluator-global field

func (*OpStream) Gtxn 

func (ops *OpStream) Gtxn(gid, val uint64) error

Gtxn writes opcodes for loading a field from the current transaction

func (*OpStream) Intc 

func (ops *OpStream) Intc(constIndex uint) error

Intc writes opcodes for loading a uint64 constant onto the stack.

func (*OpStream) ReferToLabel 

func (ops *OpStream) ReferToLabel(sourceLine, pc int, label string)

ReferToLabel records an opcode label refence to resolve later

func (*OpStream) SetLabelHere 

func (ops *OpStream) SetLabelHere(label string) error

SetLabelHere inserts a label reference to point to the next instruction

func (*OpStream) Txn 

func (ops *OpStream) Txn(val uint64) error

Txn writes opcodes for loading a field from the current transaction

func (*OpStream) Uint 

func (ops *OpStream) Uint(val uint64) error

Uint writes opcodes for loading a uint literal

type PanicError 

type PanicError struct {
	PanicValue interface{}
	StackTrace string
}

PanicError wraps a recover() catching a panic()

func (PanicError) Error 

func (pe PanicError) Error() string

type Program 

type Program []byte

Program is byte code to be interpreted for validating transactions.

func (Program) ToBeHashed 

func (lsl Program) ToBeHashed() (protocol.HashID, []byte)

ToBeHashed implements crypto.Hashable

type StackType 

type StackType byte

StackType describes the type of a value on the operand stack 

const StackAny StackType = 1

StackAny in an OpSpec shows that the op pops or yield any type 

const StackBytes StackType = 3

StackBytes in an OpSpec shows that the op pops or yields a []byte 

const StackNone StackType = 0

StackNone in an OpSpec shows that the op pops or yields nothing 

const StackUint64 StackType = 2

StackUint64 in an OpSpec shows that the op pops or yields a uint64

func (StackType) String 

func (st StackType) String() string

type TxnField 

type TxnField int

TxnField is an enum type for `txn` and `gtxn` 

const (
	// Sender Transaction.Sender
	Sender TxnField = iota
	// Fee Transaction.Fee
	Fee
	// FirstValid Transaction.FirstValid
	FirstValid
	// FirstValidTime Block[Transaction.FirstValid].TimeStamp
	FirstValidTime
	// LastValid Transaction.LastValid
	LastValid
	// Note Transaction.Note
	Note
	// Lease Transaction.Lease
	Lease
	// Receiver Transaction.Receiver
	Receiver
	// Amount Transaction.Amount
	Amount
	// CloseRemainderTo Transaction.CloseRemainderTo
	CloseRemainderTo
	// VotePK Transaction.VotePK
	VotePK
	// SelectionPK Transaction.SelectionPK
	SelectionPK
	// VoteFirst Transaction.VoteFirst
	VoteFirst
	// VoteLast Transaction.VoteLast
	VoteLast
	// VoteKeyDilution Transaction.VoteKeyDilution
	VoteKeyDilution
	// Type Transaction.Type
	Type
	// TypeEnum int(Transaction.Type)
	TypeEnum
	// XferAsset Transaction.XferAsset
	XferAsset
	// AssetAmount Transaction.AssetAmount
	AssetAmount
	// AssetSender Transaction.AssetSender
	AssetSender
	// AssetReceiver Transaction.AssetReceiver
	AssetReceiver
	// AssetCloseTo Transaction.AssetCloseTo
	AssetCloseTo
	// GroupIndex i for txngroup[i] == Txn
	GroupIndex
	// TxID Transaction.ID()
	TxID
)

func (TxnField) String 

func (i TxnField) String() string

type Writer 

type Writer interface {
	Write([]byte) (int, error)
	WriteByte(c byte) error
}

Writer is what we want here. Satisfied by bufio.Buffer

Source Files

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