path: root/rpc/utils.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 rpc

import (
    "crypto/rand"
    "encoding/hex"
    "errors"
    "math/big"
    "reflect"
    "unicode"
    "unicode/utf8"

    "golang.org/x/net/context"
)

// Is this an exported - upper case - name?
func isExported(name string) bool {
    rune, _ := utf8.DecodeRuneInString(name)
    return unicode.IsUpper(rune)
}

// Is this type exported or a builtin?
func isExportedOrBuiltinType(t reflect.Type) bool {
    for t.Kind() == reflect.Ptr {
        t = t.Elem()
    }
    // PkgPath will be non-empty even for an exported type,
    // so we need to check the type name as well.
    return isExported(t.Name()) || t.PkgPath() == ""
}

var contextType = reflect.TypeOf((*context.Context)(nil)).Elem()

// isContextType returns an indication if the given t is of context.Context or *context.Context type
func isContextType(t reflect.Type) bool {
    for t.Kind() == reflect.Ptr {
        t = t.Elem()
    }
    return t == contextType
}

var errorType = reflect.TypeOf((*error)(nil)).Elem()

// Implements this type the error interface
func isErrorType(t reflect.Type) bool {
    for t.Kind() == reflect.Ptr {
        t = t.Elem()
    }
    return t.Implements(errorType)
}

var subscriptionType = reflect.TypeOf((*Subscription)(nil)).Elem()

// isSubscriptionType returns an indication if the given t is of Subscription or *Subscription type
func isSubscriptionType(t reflect.Type) bool {
    for t.Kind() == reflect.Ptr {
        t = t.Elem()
    }
    return t == subscriptionType
}

// isPubSub tests whether the given method has as as first argument a context.Context
// and returns the pair (Subscription, error)
func isPubSub(methodType reflect.Type) bool {
    // numIn(0) is the receiver type
    if methodType.NumIn() < 2 || methodType.NumOut() != 2 {
        return false
    }

    return isContextType(methodType.In(1)) &&
        isSubscriptionType(methodType.Out(0)) &&
        isErrorType(methodType.Out(1))
}

// formatName will convert to first character to lower case
func formatName(name string) string {
    ret := []rune(name)
    if len(ret) > 0 {
        ret[0] = unicode.ToLower(ret[0])
    }
    return string(ret)
}

var bigIntType = reflect.TypeOf((*big.Int)(nil)).Elem()

// Indication if this type should be serialized in hex
func isHexNum(t reflect.Type) bool {
    if t == nil {
        return false
    }
    for t.Kind() == reflect.Ptr {
        t = t.Elem()
    }

    return t == bigIntType
}

var blockNumberType = reflect.TypeOf((*BlockNumber)(nil)).Elem()

// Indication if the given block is a BlockNumber
func isBlockNumber(t reflect.Type) bool {
    if t == nil {
        return false
    }

    for t.Kind() == reflect.Ptr {
        t = t.Elem()
    }

    return t == blockNumberType
}

// suitableCallbacks iterates over the methods of the given type. It will determine if a method satisfies the criteria
// for a RPC callback or a subscription callback and adds it to the collection of callbacks or subscriptions. See server
// documentation for a summary of these criteria.
func suitableCallbacks(rcvr reflect.Value, typ reflect.Type) (callbacks, subscriptions) {
    callbacks := make(callbacks)
    subscriptions := make(subscriptions)

METHODS:
    for m := 0; m < typ.NumMethod(); m++ {
        method := typ.Method(m)
        mtype := method.Type
        mname := formatName(method.Name)
        if method.PkgPath != "" { // method must be exported
            continue
        }

        var h callback
        h.isSubscribe = isPubSub(mtype)
        h.rcvr = rcvr
        h.method = method
        h.errPos = -1

        firstArg := 1
        numIn := mtype.NumIn()
        if numIn >= 2 && mtype.In(1) == contextType {
            h.hasCtx = true
            firstArg = 2
        }

        if h.isSubscribe {
            h.argTypes = make([]reflect.Type, numIn-firstArg) // skip rcvr type
            for i := firstArg; i < numIn; i++ {
                argType := mtype.In(i)
                if isExportedOrBuiltinType(argType) {
                    h.argTypes[i-firstArg] = argType
                } else {
                    continue METHODS
                }
            }

            subscriptions[mname] = &h
            continue METHODS
        }

        // determine method arguments, ignore first arg since it's the receiver type
        // Arguments must be exported or builtin types
        h.argTypes = make([]reflect.Type, numIn-firstArg)
        for i := firstArg; i < numIn; i++ {
            argType := mtype.In(i)
            if !isExportedOrBuiltinType(argType) {
                continue METHODS
            }
            h.argTypes[i-firstArg] = argType
        }

        // check that all returned values are exported or builtin types
        for i := 0; i < mtype.NumOut(); i++ {
            if !isExportedOrBuiltinType(mtype.Out(i)) {
                continue METHODS
            }
        }

        // when a method returns an error it must be the last returned value
        h.errPos = -1
        for i := 0; i < mtype.NumOut(); i++ {
            if isErrorType(mtype.Out(i)) {
                h.errPos = i
                break
            }
        }

        if h.errPos >= 0 && h.errPos != mtype.NumOut()-1 {
            continue METHODS
        }

        switch mtype.NumOut() {
        case 0, 1:
            break
        case 2:
            if h.errPos == -1 { // method must one return value and 1 error
                continue METHODS
            }
            break
        default:
            continue METHODS
        }

        callbacks[mname] = &h
    }

    return callbacks, subscriptions
}

func newSubscriptionID() (string, error) {
    var subid [16]byte
    n, _ := rand.Read(subid[:])
    if n != 16 {
        return "", errors.New("Unable to generate subscription id")
    }
    return "0x" + hex.EncodeToString(subid[:]), nil
}