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// Copyright 2015 The Vanadium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// This file implements the BlobMetadata table of a blobmap.
package blobmap
import "v.io/v23/context"
import "v.io/v23/services/syncbase/nosql"
import "v.io/v23/vom"
import "v.io/x/ref/services/syncbase/localblobstore"
import "v.io/x/ref/services/syncbase/store"
// metadataKey() returns the key used in the store to reference the metadata
// for blobId.
func metadataKey(blobId nosql.BlobRef) []byte {
return []byte(metadataPrefix + string(blobId))
}
// SetBlobMetadata() sets the BlobMetadata associated with a blob to *bmd.
func (bm *BlobMap) SetBlobMetadata(ctx *context.T, blobId nosql.BlobRef, bmd *localblobstore.BlobMetadata) (err error) {
var val []byte
val, err = vom.Encode(bmd)
if err == nil {
err = bm.st.Put(metadataKey(blobId), val)
}
return err
}
// GetBlobMetadata() yields in *bmd the BlobMetadata associated with a blob.
func (bm *BlobMap) GetBlobMetadata(ctx *context.T, blobId nosql.BlobRef, bmd *localblobstore.BlobMetadata) (err error) {
var valBuf [maxBlobMetadataLen]byte
var val []byte
val, err = bm.st.Get(metadataKey(blobId), valBuf[:])
if err == nil {
err = vom.Decode(val, bmd)
}
return err
}
// DeleteBlobMetadata() deletes the BlobMetadata for the specified blob.
func (bm *BlobMap) DeleteBlobMetadata(ctx *context.T, blobId nosql.BlobRef) error {
return bm.st.Delete(metadataKey(blobId))
}
// A BlobMetadataStream allows the client to iterate over the BlobMetadatas associated with blob IDs.
// bms := bm.NewBlobMetadataStream(ctx, blob)
// for bms.Advance() {
// blob := bms.BlobId()
// metadata := bms.BlobMetadata()
// ...process blob, metadata...
// }
// if bms.Err() != nil {
// ...there was an error...
// }
type BlobMetadataStream struct {
bm *BlobMap
stream store.Stream
keyBuf [maxKeyLen]byte // buffer for keys
valBuf [maxBlobMetadataLen]byte // buffer for values
blobId nosql.BlobRef // blobId key for current element
metadata localblobstore.BlobMetadata // BlobMetadata of current element
err error // error encountered.
more bool // whether stream may be consulted again
}
// NewBlobMetadataStream() returns, as a localblobstore.BlobMetadataStream
// interface, a pointer to a new blobmap.BlobMetadataStream that allows the
// client to enumerate the BlobMetadatas associated with blob IDs, in order.
func (bm *BlobMap) NewBlobMetadataStream(ctx *context.T) localblobstore.BlobMetadataStream {
// ctx is currently unused.
bms := new(BlobMetadataStream)
bms.bm = bm
bms.stream = bm.st.Scan([]byte(metadataPrefix), metadataStreamKeyLimit)
bms.more = true
return bms
}
// Advance() stages an element so the client can retrieve the blob ID hash with
// BlobId(), or its BlobMetadata with BlobMetadata(). Advance() returns true iff there
// is an element to retrieve. The client must call Advance() before calling
// BlobId() or BlobMetadata() The client must call Cancel if it does not iterate
// through all elements (i.e. until Advance() returns false). Advance() may
// block if an element is not immediately available.
func (bms *BlobMetadataStream) Advance() (ok bool) {
if bms.more && bms.err == nil {
if !bms.stream.Advance() {
bms.err = bms.stream.Err()
bms.more = false // no more stream, even if no error
} else {
bms.blobId = nosql.BlobRef(bms.stream.Key(bms.keyBuf[:])[1:])
var value []byte = bms.stream.Value(bms.valBuf[:])
bms.err = vom.Decode(value, &bms.metadata)
ok = (bms.err == nil)
if !ok {
bms.stream.Cancel()
}
}
}
return ok
}
// BlobId() returns the blob ID of the blob Id and BlobMetadata staged by
// Advance(). BlobId() may panic if Advance() returned false or was not called
// at all. BlobId() does not block.
func (bms *BlobMetadataStream) BlobId() (result nosql.BlobRef) {
return bms.blobId
}
// BlobMetadata() returns the BlobMetadata associated with the blob ID staged by
// Advance(). BlobMetadata() may panic if Advance() returned false or was not
// called at all. BlobMetadata() does not block.
func (bms *BlobMetadataStream) BlobMetadata() localblobstore.BlobMetadata {
return bms.metadata
}
// Err() returns a non-nil error iff the stream encountered any errors. Err()
// does not block.
func (bms *BlobMetadataStream) Err() error {
return bms.err
}
// Cancel() notifies the stream provider that it can stop producing elements.
// The client must call Cancel() if it does not iterate through all elements
// (i.e. until Advance() returns false). Cancel() is idempotent and can be
// called concurrently with a goroutine that is iterating via Advance() and
// BlobId(). Cancel() causes Advance() to subsequently return false.
// Cancel() does not block.
func (bms *BlobMetadataStream) Cancel() {
bms.stream.Cancel()
}