path: root/accounts/abi/abi.go

// 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])
}