mirror of https://github.com/ethereum/go-ethereum
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
140 lines
3.5 KiB
140 lines
3.5 KiB
# common
|
|
|
|
[](https://travis-ci.org/ethereum/go-ethereum)
|
|
|
|
The common package contains the ethereum utility library.
|
|
|
|
# Installation
|
|
|
|
As a subdirectory the main go-ethereum repository, you get it with
|
|
`go get github.com/ethereum/go-ethereum`.
|
|
|
|
# Usage
|
|
|
|
## RLP (Recursive Linear Prefix) Encoding
|
|
|
|
RLP Encoding is an encoding scheme used by the Ethereum project. It
|
|
encodes any native value or list to a string.
|
|
|
|
More in depth information about the encoding scheme see the
|
|
[Wiki](http://wiki.ethereum.org/index.php/RLP) article.
|
|
|
|
```go
|
|
rlp := common.Encode("doge")
|
|
fmt.Printf("%q\n", rlp) // => "\0x83dog"
|
|
|
|
rlp = common.Encode([]interface{}{"dog", "cat"})
|
|
fmt.Printf("%q\n", rlp) // => "\0xc8\0x83dog\0x83cat"
|
|
decoded := common.Decode(rlp)
|
|
fmt.Println(decoded) // => ["dog" "cat"]
|
|
```
|
|
|
|
## Patricia Trie
|
|
|
|
Patricie Tree is a merkle trie used 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 `common/db.go`.
|
|
|
|
```go
|
|
db := NewDatabase()
|
|
|
|
// db, root
|
|
trie := common.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 := common.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 := common.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 := common.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 := common.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 := common.NewValue([]interface{}{1,"2",[]interface{}{3}})
|
|
rlp := val.Encode()
|
|
// Store the rlp data
|
|
Store(rlp)
|
|
```
|
|
|