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 (
    "bufio"
    "context"
    crand "crypto/rand"
    "encoding/binary"
    "encoding/hex"
    "math/rand"
    "reflect"
    "strings"
    "sync"
    "time"
    "unicode"
    "unicode/utf8"
)

var (
    subscriptionIDGenMu sync.Mutex
    subscriptionIDGen   = idGenerator()
)

// 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)
}

// 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, 2:
            if mtype.NumOut() == 2 && h.errPos == -1 { // method must one return value and 1 error
                continue METHODS
            }
            callbacks[mname] = &h
        }
    }

    return callbacks, subscriptions
}

// idGenerator helper utility that generates a (pseudo) random sequence of
// bytes that are used to generate identifiers.
func idGenerator() *rand.Rand {
    if seed, err := binary.ReadVarint(bufio.NewReader(crand.Reader)); err == nil {
        return rand.New(rand.NewSource(seed))
    }
    return rand.New(rand.NewSource(int64(time.Now().Nanosecond())))
}

// NewID generates a identifier that can be used as an identifier in the RPC interface.
// e.g. filter and subscription identifier.
func NewID() ID {
    subscriptionIDGenMu.Lock()
    defer subscriptionIDGenMu.Unlock()

    id := make([]byte, 16)
    for i := 0; i < len(id); i += 7 {
        val := subscriptionIDGen.Int63()
        for j := 0; i+j < len(id) && j < 7; j++ {
            id[i+j] = byte(val)
            val >>= 8
        }
    }

    rpcId := hex.EncodeToString(id)
    // rpc ID's are RPC quantities, no leading zero's and 0 is 0x0
    rpcId = strings.TrimLeft(rpcId, "0")
    if rpcId == "" {
        rpcId = "0"
    }

    return ID("0x" + rpcId)
}