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registry.go
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registry.go
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// Copyright 2018 GRAIL, Inc. All rights reserved.
// Use of this source code is governed by the Apache-2.0
// license that can be found in the LICENSE file.
package recordio
import (
"fmt"
"strings"
"sync"
"github.com/Schaudge/grailbase/recordio/recordioiov"
"github.com/pkg/errors"
)
// TransformerFactory is a function that creates a new TransformerFunc given an
// optional config string.
type TransformerFactory func(config string) (TransformFunc, error)
type registerer struct {
sync.RWMutex
transformers map[string]TransformerFactory
untransformers map[string]TransformerFactory
}
var registry = ®isterer{
transformers: make(map[string]TransformerFactory),
untransformers: make(map[string]TransformerFactory),
}
func idTransform(scratch []byte, in [][]byte) ([]byte, error) {
out := recordioiov.Slice(scratch, recordioiov.TotalBytes(in))
n := 0
for _, b := range in {
copy(out[n:], b)
n += len(b)
}
return out, nil
}
func (r *registerer) registerTransformer(name string, t TransformerFactory, u TransformerFactory) {
r.Lock()
defer r.Unlock()
if _, ok := r.transformers[name]; ok {
panic(fmt.Sprintf("Transformer %s already registered", name))
}
r.transformers[name] = t
r.untransformers[name] = u
}
func getTransformers(h []string, factory map[string]TransformerFactory) ([]TransformFunc, error) {
var transformers []TransformFunc
for _, str := range h {
toks := strings.SplitN(str, " ", 2)
name := toks[0]
f, ok := factory[name]
if !ok {
return nil, errors.Errorf("Transformer %s not found", str)
}
var config string
if len(toks) > 1 {
config = toks[1]
}
var tr TransformFunc
var err error
if tr, err = f(config); err != nil {
return nil, err
}
transformers = append(transformers, tr)
}
return transformers, nil
}
func (r *registerer) getTransformer(h []string) (TransformFunc, error) {
r.RLock()
transformers, err := getTransformers(h, r.transformers)
r.RUnlock()
if err != nil {
return nil, err
}
switch {
case len(transformers) == 0:
return idTransform, nil
case len(transformers) == 1:
return transformers[0], nil
default:
combined := func(scratch []byte, data [][]byte) ([]byte, error) {
for _, tr := range transformers {
out, err := tr(scratch, data)
if err != nil {
return nil, err
}
if len(data) == 0 {
data = [][]byte{out}
} else {
data = data[:1]
data[0] = out
}
scratch = nil
// TODO(saito) Maybe reuse one of data[] as scratch?
}
if len(data) != 1 { // At least one transformer should have run.
panic(data)
}
return data[0], nil
}
return combined, nil
}
}
func (r *registerer) GetUntransformer(h []string) (TransformFunc, error) {
r.RLock()
transformers, err := getTransformers(h, r.untransformers)
r.RUnlock()
if err != nil {
return nil, err
}
switch {
case len(transformers) == 0:
return idTransform, nil
case len(transformers) == 1:
return transformers[0], nil
default:
combined := func(scratch []byte, data [][]byte) ([]byte, error) {
for i := len(transformers) - 1; i >= 0; i-- {
tr := transformers[i]
out, err := tr(scratch, data)
if err != nil {
return nil, err
}
if len(data) == 0 {
data = [][]byte{out}
} else {
data = data[:1]
data[0] = out
}
}
if len(data) != 1 { // At least one transformer should have run.
panic(data)
}
return data[0], nil
}
return combined, nil
}
}
// RegisterTransformer registers a block transformer. Factory transformer should
// produce a transformer function. The factory is run by NewWriterV2. The
// transformer function is called by the writer to transform a block just before
// storing it in storage.
//
// The untransformer factory is the reverse of the transformer factory. It is
// run by NewScannerV2. The untransformer function is called by the scanner to
// transform data read from storage into a block.
//
// This function is usually called when the process starts.
//
// The transformer and untransformer factories, as well as the functions
// generated by these factories must be all thread safe.
//
// REQUIRES: A (un)transformer with the same "name" has not been registered
// already.
func RegisterTransformer(name string, transformer TransformerFactory, untransformer TransformerFactory) {
registry.registerTransformer(name, transformer, untransformer)
}