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92 lines
2.0 KiB
Go
92 lines
2.0 KiB
Go
/*
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Copyright 2016 The go4 Authors
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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 readerutil
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import (
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"io"
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"sort"
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)
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// NewMultiReaderAt is like io.MultiReader but produces a ReaderAt
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// (and Size), instead of just a reader.
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func NewMultiReaderAt(parts ...SizeReaderAt) SizeReaderAt {
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m := &multiRA{
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parts: make([]offsetAndSource, 0, len(parts)),
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}
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var off int64
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for _, p := range parts {
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m.parts = append(m.parts, offsetAndSource{off, p})
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off += p.Size()
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}
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m.size = off
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return m
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}
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type offsetAndSource struct {
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off int64
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SizeReaderAt
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}
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type multiRA struct {
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parts []offsetAndSource
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size int64
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}
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func (m *multiRA) Size() int64 { return m.size }
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func (m *multiRA) ReadAt(p []byte, off int64) (n int, err error) {
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wantN := len(p)
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// Skip past the requested offset.
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skipParts := sort.Search(len(m.parts), func(i int) bool {
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// This function returns whether parts[i] will
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// contribute any bytes to our output.
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part := m.parts[i]
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return part.off+part.Size() > off
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})
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parts := m.parts[skipParts:]
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// How far to skip in the first part.
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needSkip := off
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if len(parts) > 0 {
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needSkip -= parts[0].off
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}
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for len(parts) > 0 && len(p) > 0 {
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readP := p
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partSize := parts[0].Size()
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if int64(len(readP)) > partSize-needSkip {
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readP = readP[:partSize-needSkip]
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}
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pn, err0 := parts[0].ReadAt(readP, needSkip)
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if err0 != nil {
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return n, err0
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}
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n += pn
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p = p[pn:]
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if int64(pn)+needSkip == partSize {
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parts = parts[1:]
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}
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needSkip = 0
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}
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if n != wantN {
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err = io.ErrUnexpectedEOF
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}
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return
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}
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