path: root/eth/downloader/api.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 downloader

import (
    "context"
    "sync"

    ethereum "github.com/ethereum/go-ethereum"
    "github.com/ethereum/go-ethereum/event"
    "github.com/ethereum/go-ethereum/rpc"
)

// PublicDownloaderAPI provides an API which gives information about the current synchronisation status.
// It offers only methods that operates on data that can be available to anyone without security risks.
type PublicDownloaderAPI struct {
    d                         *Downloader
    mux                       *event.TypeMux
    installSyncSubscription   chan chan interface{}
    uninstallSyncSubscription chan *uninstallSyncSubscriptionRequest
}

// NewPublicDownloaderAPI create a new PublicDownloaderAPI. The API has an internal event loop that
// listens for events from the downloader through the global event mux. In case it receives one of
// these events it broadcasts it to all syncing subscriptions that are installed through the
// installSyncSubscription channel.
func NewPublicDownloaderAPI(d *Downloader, m *event.TypeMux) *PublicDownloaderAPI {
    api := &PublicDownloaderAPI{
        d:   d,
        mux: m,
        installSyncSubscription:   make(chan chan interface{}),
        uninstallSyncSubscription: make(chan *uninstallSyncSubscriptionRequest),
    }

    go api.eventLoop()

    return api
}

// eventLoop runs a loop until the event mux closes. It will install and uninstall new
// sync subscriptions and broadcasts sync status updates to the installed sync subscriptions.
func (api *PublicDownloaderAPI) eventLoop() {
    var (
        sub               = api.mux.Subscribe(StartEvent{}, DoneEvent{}, FailedEvent{})
        syncSubscriptions = make(map[chan interface{}]struct{})
    )

    for {
        select {
        case i := <-api.installSyncSubscription:
            syncSubscriptions[i] = struct{}{}
        case u := <-api.uninstallSyncSubscription:
            delete(syncSubscriptions, u.c)
            close(u.uninstalled)
        case event := <-sub.Chan():
            if event == nil {
                return
            }

            var notification interface{}
            switch event.Data.(type) {
            case StartEvent:
                notification = &SyncingResult{
                    Syncing: true,
                    Status:  api.d.Progress(),
                }
            case DoneEvent, FailedEvent:
                notification = false
            }
            // broadcast
            for c := range syncSubscriptions {
                c <- notification
            }
        }
    }
}

// Syncing provides information when this nodes starts synchronising with the Ethereum network and when it's finished.
func (api *PublicDownloaderAPI) Syncing(ctx context.Context) (*rpc.Subscription, error) {
    notifier, supported := rpc.NotifierFromContext(ctx)
    if !supported {
        return &rpc.Subscription{}, rpc.ErrNotificationsUnsupported
    }

    rpcSub := notifier.CreateSubscription()

    go func() {
        statuses := make(chan interface{})
        sub := api.SubscribeSyncStatus(statuses)

        for {
            select {
            case status := <-statuses:
                notifier.Notify(rpcSub.ID, status)
            case <-rpcSub.Err():
                sub.Unsubscribe()
                return
            case <-notifier.Closed():
                sub.Unsubscribe()
                return
            }
        }
    }()

    return rpcSub, nil
}

// SyncingResult provides information about the current synchronisation status for this node.
type SyncingResult struct {
    Syncing bool                  `json:"syncing"`
    Status  ethereum.SyncProgress `json:"status"`
}

// uninstallSyncSubscriptionRequest uninstalles a syncing subscription in the API event loop.
type uninstallSyncSubscriptionRequest struct {
    c           chan interface{}
    uninstalled chan interface{}
}

// SyncStatusSubscription represents a syncing subscription.
type SyncStatusSubscription struct {
    api       *PublicDownloaderAPI // register subscription in event loop of this api instance
    c         chan interface{}     // channel where events are broadcasted to
    unsubOnce sync.Once            // make sure unsubscribe logic is executed once
}

// Unsubscribe uninstalls the subscription from the DownloadAPI event loop.
// The status channel that was passed to subscribeSyncStatus isn't used anymore
// after this method returns.
func (s *SyncStatusSubscription) Unsubscribe() {
    s.unsubOnce.Do(func() {
        req := uninstallSyncSubscriptionRequest{s.c, make(chan interface{})}
        s.api.uninstallSyncSubscription <- &req

        for {
            select {
            case <-s.c:
                // drop new status events until uninstall confirmation
                continue
            case <-req.uninstalled:
                return
            }
        }
    })
}

// SubscribeSyncStatus creates a subscription that will broadcast new synchronisation updates.
// The given channel must receive interface values, the result can either
func (api *PublicDownloaderAPI) SubscribeSyncStatus(status chan interface{}) *SyncStatusSubscription {
    api.installSyncSubscription <- status
    return &SyncStatusSubscription{api: api, c: status}
}