109 lines
2.1 KiB
Go
109 lines
2.1 KiB
Go
package util
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import (
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"crypto/sha256"
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"encoding/json"
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"fmt"
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"iter"
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"strings"
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"sync"
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"github.com/evcc-io/evcc/api"
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"github.com/fatih/structs"
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)
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// Sharder splits data into chunks, omitting unmodified chunks
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type Sharder interface {
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ModifiedShards() iter.Seq2[string, any]
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AllShards() iter.Seq2[string, any]
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}
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type Shard struct {
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Key string
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Value any
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}
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type sharderImpl struct {
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prefix string
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struc any
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}
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// shared shard cache
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var (
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shardCache = make(map[string][32]byte)
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shardMu sync.Mutex
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)
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func (s *sharderImpl) MarshalJSON() ([]byte, error) {
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return json.Marshal(s.struc)
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}
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func (s *sharderImpl) AllShards() iter.Seq2[string, any] {
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return s.shards(false)
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}
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func (s *sharderImpl) ModifiedShards() iter.Seq2[string, any] {
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return s.shards(true)
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}
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func (s *sharderImpl) shards(useCache bool) iter.Seq2[string, any] {
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if useCache {
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shardMu.Lock()
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defer shardMu.Unlock()
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}
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return func(yield func(string, any) bool) {
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for _, f := range structs.Fields(s.struc) {
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key := jsonKey(f)
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if useCache && s.skipCachedShard(key, f.Value()) {
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continue
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}
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if !yield(key, f.Value()) {
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break
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}
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}
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}
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}
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func jsonKey(f *structs.Field) string {
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key := f.Name()
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if t := f.Tag("json"); t != "" {
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if n := strings.Split(t, ",")[0]; n != "" {
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key = n
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}
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}
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return key
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}
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func (s *sharderImpl) skipCachedShard(key string, value any) bool {
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// Use JSON for stable hashing (fmt.Append includes pointer addresses)
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b, err := json.Marshal(value)
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if err != nil {
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// Fallback to fmt.Append if JSON fails
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b = fmt.Append(nil, value)
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}
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hash := sha256.Sum256(b)
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cacheKey := s.prefix + key
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if cached, ok := shardCache[cacheKey]; ok && hash == cached {
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return true
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}
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shardCache[cacheKey] = hash
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return false
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}
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var _ api.StructMarshaler = (*sharderImpl)(nil)
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func (s *sharderImpl) MarshalStruct() (any, error) {
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return s.struc, nil
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}
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var _ Sharder = (*sharderImpl)(nil)
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// NewSharder creates a Sharder that splits structs into sub-structs for space-efficient socket publishing
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// Passing anything else than a struct will panic
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func NewSharder(prefix string, struc any) Sharder {
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return &sharderImpl{prefix, struc}
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}
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