go-ethereum/common/README.md

# ethutil

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Status](https://travis-ci.org/ethereum/go-ethereum.png?branch=master)](https://travis-ci.org/ethereum/go-ethereum)

The ethutil package contains the ethereum utility library.

# Installation

`go get github.com/ethereum/ethutil-go`

# Usage

## RLP (Recursive Linear Prefix) Encoding

RLP Encoding is an encoding scheme utilized by the Ethereum project. It
encodes any native value or list to string.

More in depth information about the Encoding scheme see the [Wiki](http://wiki.ethereum.org/index.php/RLP)
article.

```go
rlp := ethutil.Encode("doge")
fmt.Printf("%q\n", rlp) // => "\0x83dog"

rlp = ethutil.Encode([]interface{}{"dog", "cat"})
fmt.Printf("%q\n", rlp) // => "\0xc8\0x83dog\0x83cat"
decoded := ethutil.Decode(rlp)
fmt.Println(decoded) // => ["dog" "cat"]
```

## Patricia Trie

Patricie Tree is a merkle trie utilized by the Ethereum project.

More in depth information about the (modified) Patricia Trie can be
found on the [Wiki](http://wiki.ethereum.org/index.php/Patricia_Tree).

The patricia trie uses a db as backend and could be anything as long as
it satisfies the Database interface found in `ethutil/db.go`.

```go
db := NewDatabase()

// db, root
trie := ethutil.NewTrie(db, "")

trie.Put("puppy", "dog")
trie.Put("horse", "stallion")
trie.Put("do", "verb")
trie.Put("doge", "coin")

// Look up the key "do" in the trie
out := trie.Get("do")
fmt.Println(out) // => verb

trie.Delete("puppy")
```

The patricia trie, in combination with RLP, provides a robust,
cryptographically authenticated data structure that can be used to store
all (key, value) bindings.

```go
// ... Create db/trie

// Note that RLP uses interface slices as list
value := ethutil.Encode([]interface{}{"one", 2, "three", []interface{}{42}})
// Store the RLP encoded value of the list
trie.Put("mykey", value)
```

## Value

Value is a Generic Value which is used in combination with RLP data or
`([])interface{}` structures. It may serve as a bridge between RLP data
and actual real values and takes care of all the type checking and
casting. Unlike Go's `reflect.Value` it does not panic if it's unable to
cast to the requested value. It simple returns the base value of that
type (e.g. `Slice()` returns []interface{}, `Uint()` return 0, etc).

### Creating a new Value

`NewEmptyValue()` returns a new \*Value with it's initial value set to a
`[]interface{}`

`AppendList()` appends a list to the current value.

`Append(v)` appends the value (v) to the current value/list.

```go
val := ethutil.NewEmptyValue().Append(1).Append("2")
val.AppendList().Append(3)
```

### Retrieving values

`Get(i)` returns the `i` item in the list.

`Uint()` returns the value as an unsigned int64.

`Slice()` returns the value as a interface slice.

`Str()` returns the value as a string.

`Bytes()` returns the value as a byte slice.

`Len()` assumes current to be a slice and returns its length.

`Byte()` returns the value as a single byte.

```go
val := ethutil.NewValue([]interface{}{1,"2",[]interface{}{3}})
val.Get(0).Uint() // => 1
val.Get(1).Str()  // => "2"
s := val.Get(2)   // => Value([]interface{}{3})
s.Get(0).Uint()   // => 3
```

## Decoding

Decoding streams of RLP data is simplified

```go
val := ethutil.NewValueFromBytes(rlpData)
val.Get(0).Uint()
```

## Encoding

Encoding from Value to RLP is done with the `Encode` method. The
underlying value can be anything RLP can encode (int, str, lists, bytes)

```go
val := ethutil.NewValue([]interface{}{1,"2",[]interface{}{3}})
rlp := val.Encode()
// Store the rlp data
Store(rlp)
```