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 (
    "encoding/json"
    "fmt"
    "io"
    "reflect"
    "strings"

    "github.com/ethereum/go-ethereum/common"
)

// Executer is an executer method for performing state executions. It takes one
// argument which is the input data and expects output data to be returned as
// multiple 32 byte word length concatenated slice
type Executer func(datain []byte) []byte

// 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 {
    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
}

// tests, tests whether the given input would result in a successful
// call. Checks argument list count and matches input to `input`.
func (abi ABI) pack(name string, args ...interface{}) ([]byte, error) {
    method := abi.Methods[name]

    // variable input is the output appended at the end of packed
    // output. This is used for strings and bytes types input.
    var variableInput []byte

    var ret []byte
    for i, a := range args {
        input := method.Inputs[i]
        // pack the input
        packed, err := input.Type.pack(a)
        if err != nil {
            return nil, fmt.Errorf("`%s` %v", name, err)
        }

        // check for a string or bytes input type
        switch input.Type.T {
        case StringTy, BytesTy:
            // calculate the offset
            offset := len(method.Inputs)*32 + len(variableInput)
            // set the offset
            ret = append(ret, packNum(reflect.ValueOf(offset), UintTy)...)
            // Append the packed output to the variable input. The variable input
            // will be appended at the end of the input.
            variableInput = append(variableInput, packed...)
        default:
            // append the packed value to the input
            ret = append(ret, packed...)
        }
    }
    // append the variable input at the end of the packed input
    ret = append(ret, variableInput...)

    return ret, 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) {
    method, exist := abi.Methods[name]
    if !exist {
        return nil, fmt.Errorf("method '%s' not found", name)
    }

    // start with argument count match
    if len(args) != len(method.Inputs) {
        return nil, fmt.Errorf("argument count mismatch: %d for %d", len(args), len(method.Inputs))
    }

    arguments, err := abi.pack(name, args...)
    if err != nil {
        return nil, err
    }

    // Set function id
    packed := abi.Methods[name].Id()
    packed = append(packed, arguments...)

    return packed, nil
}

// toGoType parses the input and casts it to the proper type defined by the ABI
// argument in T.
func toGoType(i int, t Argument, output []byte) (interface{}, error) {
    index := i * 32

    if index+32 > len(output) {
        return nil, fmt.Errorf("abi: cannot marshal in to go type: length insufficient %d require %d", len(output), index+32)
    }

    // Parse the given index output and check whether we need to read
    // a different offset and length based on the type (i.e. string, bytes)
    var returnOutput []byte
    switch t.Type.T {
    case StringTy, BytesTy: // variable arrays are written at the end of the return bytes
        // parse offset from which we should start reading
        offset := int(common.BytesToBig(output[index : index+32]).Uint64())
        if offset+32 > len(output) {
            return nil, fmt.Errorf("abi: cannot marshal in to go type: length insufficient %d require %d", len(output), offset+32)
        }
        // parse the size up until we should be reading
        size := int(common.BytesToBig(output[offset : offset+32]).Uint64())
        if offset+32+size > len(output) {
            return nil, fmt.Errorf("abi: cannot marshal in to go type: length insufficient %d require %d", len(output), offset+32+size)
        }

        // get the bytes for this return value
        returnOutput = output[offset+32 : offset+32+size]
    default:
        returnOutput = output[index : index+32]
    }

    // cast bytes to abi return type
    switch t.Type.T {
    case IntTy:
        return common.BytesToBig(returnOutput), nil
    case UintTy:
        return common.BytesToBig(returnOutput), nil
    case BoolTy:
        return common.BytesToBig(returnOutput).Uint64() > 0, nil
    case AddressTy:
        return common.BytesToAddress(returnOutput), nil
    case HashTy:
        return common.BytesToHash(returnOutput), nil
    case BytesTy, FixedBytesTy:
        return returnOutput, nil
    case StringTy:
        return string(returnOutput), nil
    }
    return nil, fmt.Errorf("abi: unknown type %v", t.Type.T)
}

// Call will unmarshal the output of the call in v. It will return an error if
// invalid type is given or if the output is too short to conform to the ABI
// spec.
//
// Call supports all of the available types and accepts a struct or an interface
// slice if the return is a tuple.
func (abi ABI) Call(executer Executer, v interface{}, name string, args ...interface{}) error {
    callData, err := abi.Pack(name, args...)
    if err != nil {
        return err
    }

    return abi.unmarshal(v, name, executer(callData))
}

// these variable are used to determine certain types during type assertion for
// assignment.
var (
    r_interSlice = reflect.TypeOf([]interface{}{})
    r_hash       = reflect.TypeOf(common.Hash{})
    r_bytes      = reflect.TypeOf([]byte{})
    r_byte       = reflect.TypeOf(byte(0))
)

// unmarshal output in v according to the abi specification
func (abi ABI) unmarshal(v interface{}, name string, output []byte) error {
    var method = abi.Methods[name]

    if len(output) == 0 {
        return fmt.Errorf("abi: unmarshalling empty output")
    }

    value := reflect.ValueOf(v).Elem()
    typ := value.Type()

    if len(method.Outputs) > 1 {
        switch value.Kind() {
        // struct will match named return values to the struct's field
        // names
        case reflect.Struct:
            for i := 0; i < len(method.Outputs); i++ {
                marshalledValue, err := toGoType(i, method.Outputs[i], output)
                if err != nil {
                    return err
                }
                reflectValue := reflect.ValueOf(marshalledValue)

                for j := 0; j < typ.NumField(); j++ {
                    field := typ.Field(j)
                    // TODO read tags: `abi:"fieldName"`
                    if field.Name == strings.ToUpper(method.Outputs[i].Name[:1])+method.Outputs[i].Name[1:] {
                        if err := set(value.Field(j), reflectValue, method.Outputs[i]); err != nil {
                            return err
                        }
                    }
                }
            }
        case reflect.Slice:
            if !value.Type().AssignableTo(r_interSlice) {
                return fmt.Errorf("abi: cannot marshal tuple in to slice %T (only []interface{} is supported)", v)
            }

            // create a new slice and start appending the unmarshalled
            // values to the new interface slice.
            z := reflect.MakeSlice(typ, 0, len(method.Outputs))
            for i := 0; i < len(method.Outputs); i++ {
                marshalledValue, err := toGoType(i, method.Outputs[i], output)
                if err != nil {
                    return err
                }
                z = reflect.Append(z, reflect.ValueOf(marshalledValue))
            }
            value.Set(z)
        default:
            return fmt.Errorf("abi: cannot unmarshal tuple in to %v", typ)
        }

    } else {
        marshalledValue, err := toGoType(0, method.Outputs[0], output)
        if err != nil {
            return err
        }
        if err := set(value, reflect.ValueOf(marshalledValue), method.Outputs[0]); err != nil {
            return err
        }
    }

    return nil
}

// set attempts to assign src to dst by either setting, copying or otherwise.
//
// set is a bit more lenient when it comes to assignment and doesn't force an as
// strict ruleset as bare `reflect` does.
func set(dst, src reflect.Value, output Argument) error {
    dstType := dst.Type()
    srcType := src.Type()

    switch {
    case dstType.AssignableTo(src.Type()):
        dst.Set(src)
    case dstType.Kind() == reflect.Array && srcType.Kind() == reflect.Slice:
        if !dstType.Elem().AssignableTo(r_byte) {
            return fmt.Errorf("abi: cannot unmarshal %v in to array of elem %v", src.Type(), dstType.Elem())
        }

        if dst.Len() < output.Type.Size {
            return fmt.Errorf("abi: cannot unmarshal src (len=%d) in to dst (len=%d)", output.Type.Size, dst.Len())
        }
        reflect.Copy(dst, src)
    default:
        return fmt.Errorf("abi: cannot unmarshal %v in to %v", src.Type(), dst.Type())
    }
    return nil
}

func (abi *ABI) UnmarshalJSON(data []byte) error {
    var fields []struct {
        Type     string
        Name     string
        Constant bool
        Indexed  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 {
        // 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,
                Inputs: field.Inputs,
            }
        }
    }

    return nil
}