mirror of https://github.com/perkeep/perkeep.git
111 lines
2.6 KiB
Go
111 lines
2.6 KiB
Go
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/*
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Copyright 2011 Google Inc.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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package schema
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import (
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"fmt"
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"os"
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"camli/blobref"
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)
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type FileReader struct {
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fetcher blobref.Fetcher
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ss *Superset
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ci int // index into contentparts
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ccon uint64 // bytes into current chunk already consumed
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}
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func (ss *Superset) NewFileReader(fetcher blobref.Fetcher) *FileReader {
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// TODO: return an error if ss isn't a Type "file" ?
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// TODO: return some error if the redundant ss.Size field doesn't match ContentParts?
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return &FileReader{fetcher, ss, 0, 0}
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}
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func (fr *FileReader) Skip(skipBytes uint64) {
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for skipBytes != 0 && fr.ci < len(fr.ss.ContentParts) {
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cp := fr.ss.ContentParts[fr.ci]
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thisChunkSkippable := cp.Size - fr.ccon
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toSkip := minu64(skipBytes, thisChunkSkippable)
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fr.ccon += toSkip
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if fr.ccon == cp.Size {
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fr.ci++
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fr.ccon = 0
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}
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skipBytes -= toSkip
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}
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}
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func (fr *FileReader) Read(p []byte) (n int, err os.Error) {
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var cp *ContentPart
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for {
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if fr.ci >= len(fr.ss.ContentParts) {
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return 0, os.EOF
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}
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cp = fr.ss.ContentParts[fr.ci]
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thisChunkReadable := cp.Size - fr.ccon
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if thisChunkReadable == 0 {
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fr.ci++
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fr.ccon = 0
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continue
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}
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break
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}
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br := cp.blobref()
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if br == nil {
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return 0, fmt.Errorf("no blobref in content part %d", fr.ci)
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}
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// TODO: performance: don't re-fetch this on every
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// Read call. most parts will be large relative to
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// read sizes. we should stuff the rsc away in fr
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// and re-use it just re-seeking if needed, which
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// could also be tracked.
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rsc, _, ferr := fr.fetcher.Fetch(br)
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if ferr != nil {
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return 0, fmt.Errorf("schema: FileReader.Read error fetching blob %s: %v", br, ferr)
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}
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defer rsc.Close()
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seekTo := cp.Offset + fr.ccon
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if seekTo != 0 {
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_, serr := rsc.Seek(int64(seekTo), 0)
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if serr != nil {
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return 0, fmt.Errorf("schema: FileReader.Read seek error on blob %s: %v", br, serr)
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}
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}
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readSize := cp.Size - fr.ccon
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if uint64(len(p)) < readSize {
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readSize = uint64(len(p))
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}
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n, err = rsc.Read(p[:int(readSize)])
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if err == nil || err == os.EOF {
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fr.ccon += uint64(n)
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}
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return
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}
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func minu64(a, b uint64) uint64 {
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if a < b {
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return a
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}
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return b
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}
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