path: root/trie/sync.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 trie

import (
    "fmt"

    "github.com/ethereum/go-ethereum/common"
    "gopkg.in/karalabe/cookiejar.v2/collections/prque"
)

// request represents a scheduled or already in-flight state retrieval request.
type request struct {
    hash   common.Hash // Hash of the node data content to retrieve
    data   []byte      // Data content of the node, cached until all subtrees complete
    object *node       // Target node to populate with retrieved data (hashnode originally)

    parents []*request // Parent state nodes referencing this entry (notify all upon completion)
    depth   int        // Depth level within the trie the node is located to prioritize DFS
    deps    int        // Number of dependencies before allowed to commit this node

    callback TrieSyncLeafCallback // Callback to invoke if a leaf node it reached on this branch
}

// SyncResult is a simple list to return missing nodes along with their request
// hashes.
type SyncResult struct {
    Hash common.Hash // Hash of the originally unknown trie node
    Data []byte      // Data content of the retrieved node
}

// TrieSyncLeafCallback is a callback type invoked when a trie sync reaches a
// leaf node. It's used by state syncing to check if the leaf node requires some
// further data syncing.
type TrieSyncLeafCallback func(leaf []byte, parent common.Hash) error

// TrieSync is the main state trie synchronisation scheduler, which provides yet
// unknown trie hashes to retrieve, accepts node data associated with said hashes
// and reconstructs the trie steb by step until all is done.
type TrieSync struct {
    database Database                 // State database for storing all the assembled node data
    requests map[common.Hash]*request // Pending requests pertaining to a key hash
    queue    *prque.Prque             // Priority queue with the pending requests
}

// NewTrieSync creates a new trie data download scheduler.
func NewTrieSync(root common.Hash, database Database, callback TrieSyncLeafCallback) *TrieSync {
    ts := &TrieSync{
        database: database,
        requests: make(map[common.Hash]*request),
        queue:    prque.New(),
    }
    ts.AddSubTrie(root, 0, common.Hash{}, callback)
    return ts
}

// AddSubTrie registers a new trie to the sync code, rooted at the designated parent.
func (s *TrieSync) AddSubTrie(root common.Hash, depth int, parent common.Hash, callback TrieSyncLeafCallback) {
    // Short circuit if the trie is empty
    if root == emptyRoot {
        return
    }
    // Assemble the new sub-trie sync request
    node := node(hashNode(root.Bytes()))
    req := &request{
        object:   &node,
        hash:     root,
        depth:    depth,
        callback: callback,
    }
    // If this sub-trie has a designated parent, link them together
    if parent != (common.Hash{}) {
        ancestor := s.requests[parent]
        if ancestor == nil {
            panic(fmt.Sprintf("sub-trie ancestor not found: %x", parent))
        }
        ancestor.deps++
        req.parents = append(req.parents, ancestor)
    }
    s.schedule(req)
}

// Missing retrieves the known missing nodes from the trie for retrieval.
func (s *TrieSync) Missing(max int) []common.Hash {
    requests := []common.Hash{}
    for !s.queue.Empty() && (max == 0 || len(requests) < max) {
        requests = append(requests, s.queue.PopItem().(common.Hash))
    }
    return requests
}

// Process injects a batch of retrieved trie nodes data.
func (s *TrieSync) Process(results []SyncResult) (int, error) {
    for i, item := range results {
        // If the item was not requested, bail out
        request := s.requests[item.Hash]
        if request == nil {
            return i, fmt.Errorf("not requested: %x", item.Hash)
        }
        // Decode the node data content and update the request
        node, err := decodeNode(item.Data)
        if err != nil {
            return i, err
        }
        *request.object = node
        request.data = item.Data

        // Create and schedule a request for all the children nodes
        requests, err := s.children(request)
        if err != nil {
            return i, err
        }
        if len(requests) == 0 && request.deps == 0 {
            s.commit(request)
            continue
        }
        request.deps += len(requests)
        for _, child := range requests {
            s.schedule(child)
        }
    }
    return 0, nil
}

// schedule inserts a new state retrieval request into the fetch queue. If there
// is already a pending request for this node, the new request will be discarded
// and only a parent reference added to the old one.
func (s *TrieSync) schedule(req *request) {
    // If we're already requesting this node, add a new reference and stop
    if old, ok := s.requests[req.hash]; ok {
        old.parents = append(old.parents, req.parents...)
        return
    }
    // Schedule the request for future retrieval
    s.queue.Push(req.hash, float32(req.depth))
    s.requests[req.hash] = req
}

// children retrieves all the missing children of a state trie entry for future
// retrieval scheduling.
func (s *TrieSync) children(req *request) ([]*request, error) {
    // Gather all the children of the node, irrelevant whether known or not
    type child struct {
        node  *node
        depth int
    }
    children := []child{}

    switch node := (*req.object).(type) {
    case shortNode:
        children = []child{{
            node:  &node.Val,
            depth: req.depth + len(node.Key),
        }}
    case fullNode:
        for i := 0; i < 17; i++ {
            if node[i] != nil {
                children = append(children, child{
                    node:  &node[i],
                    depth: req.depth + 1,
                })
            }
        }
    default:
        panic(fmt.Sprintf("unknown node: %+v", node))
    }
    // Iterate over the children, and request all unknown ones
    requests := make([]*request, 0, len(children))
    for _, child := range children {
        // Notify any external watcher of a new key/value node
        if req.callback != nil {
            if node, ok := (*child.node).(valueNode); ok {
                if err := req.callback(node, req.hash); err != nil {
                    return nil, err
                }
            }
        }
        // If the child references another node, resolve or schedule
        if node, ok := (*child.node).(hashNode); ok {
            // Try to resolve the node from the local database
            blob, _ := s.database.Get(node)
            if local, err := decodeNode(blob); local != nil && err == nil {
                *child.node = local
                continue
            }
            // Locally unknown node, schedule for retrieval
            requests = append(requests, &request{
                object:   child.node,
                hash:     common.BytesToHash(node),
                parents:  []*request{req},
                depth:    child.depth,
                callback: req.callback,
            })
        }
    }
    return requests, nil
}

// commit finalizes a retrieval request and stores it into the database. If any
// of the referencing parent requests complete due to this commit, they are also
// committed themselves.
func (s *TrieSync) commit(req *request) error {
    // Write the node content to disk
    if err := s.database.Put(req.hash[:], req.data); err != nil {
        return err
    }
    delete(s.requests, req.hash)

    // Check all parents for completion
    for _, parent := range req.parents {
        parent.deps--
        if parent.deps == 0 {
            if err := s.commit(parent); err != nil {
                return err
            }
        }
    }
    return nil
}