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// Copyright 2015 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
package abi
import (
"bytes"
"encoding/json"
"fmt"
"io"
)
// The ABI holds information about a contract's context and available
// invokable methods. It will allow you to type check function calls and
// packs data accordingly.
type ABI struct {
Constructor Method
Methods map[string]Method
Events map[string]Event
}
// JSON returns a parsed ABI interface and error if it failed.
func JSON(reader io.Reader) (ABI, error) {
dec := json.NewDecoder(reader)
var abi ABI
if err := dec.Decode(&abi); err != nil {
return ABI{}, err
}
return abi, nil
}
// Pack the given method name to conform the ABI. Method call's data
// will consist of method_id, args0, arg1, ... argN. Method id consists
// of 4 bytes and arguments are all 32 bytes.
// Method ids are created from the first 4 bytes of the hash of the
// methods string signature. (signature = baz(uint32,string32))
func (abi ABI) Pack(name string, args ...interface{}) ([]byte, error) {
// Fetch the ABI of the requested method
if name == "" {
// constructor
arguments, err := abi.Constructor.Inputs.Pack(args...)
if err != nil {
return nil, err
}
return arguments, nil
}
method, exist := abi.Methods[name]
if !exist {
return nil, fmt.Errorf("method '%s' not found", name)
}
arguments, err := method.Inputs.Pack(args...)
if err != nil {
return nil, err
}
// Pack up the method ID too if not a constructor and return
return append(method.Id(), arguments...), nil
}
// Unpack output in v according to the abi specification
func (abi ABI) Unpack(v interface{}, name string, output []byte) (err error) {
if len(output) == 0 {
return fmt.Errorf("abi: unmarshalling empty output")
}
// since there can't be naming collisions with contracts and events,
// we need to decide whether we're calling a method or an event
if method, ok := abi.Methods[name]; ok {
if len(output)%32 != 0 {
return fmt.Errorf("abi: improperly formatted output: %s - Bytes: [%+v]", string(output), output)
}
return method.Outputs.Unpack(v, output)
} else if event, ok := abi.Events[name]; ok {
return event.Inputs.Unpack(v, output)
}
return fmt.Errorf("abi: could not locate named method or event")
}
// UnmarshalJSON implements json.Unmarshaler interface
func (abi *ABI) UnmarshalJSON(data []byte) error {
var fields []struct {
Type string
Name string
Constant bool
Anonymous bool
Inputs []Argument
Outputs []Argument
}
if err := json.Unmarshal(data, &fields); err != nil {
return err
}
abi.Methods = make(map[string]Method)
abi.Events = make(map[string]Event)
for _, field := range fields {
switch field.Type {
case "constructor":
abi.Constructor = Method{
Inputs: field.Inputs,
}
// empty defaults to function according to the abi spec
case "function", "":
abi.Methods[field.Name] = Method{
Name: field.Name,
Const: field.Constant,
Inputs: field.Inputs,
Outputs: field.Outputs,
}
case "event":
abi.Events[field.Name] = Event{
Name: field.Name,
Anonymous: field.Anonymous,
Inputs: field.Inputs,
}
}
}
return nil
}
// MethodById looks up a method by the 4-byte id
// returns nil if none found
func (abi *ABI) MethodById(sigdata []byte) (*Method, error) {
if len(sigdata) < 4 {
return nil, fmt.Errorf("data too short (% bytes) for abi method lookup", len(sigdata))
}
for _, method := range abi.Methods {
if bytes.Equal(method.Id(), sigdata[:4]) {
return &method, nil
}
}
return nil, fmt.Errorf("no method with id: %#x", sigdata[:4])
}
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