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71 lines
1.7 KiB
Go
71 lines
1.7 KiB
Go
/*
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Copyright 2014 The Perkeep 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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"errors"
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"fmt"
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"io"
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"os"
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)
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// fakeSeeker can seek to the ends but any read not at the current
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// position will fail.
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type fakeSeeker struct {
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r io.Reader
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size int64
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fakePos int64
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realPos int64
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}
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// NewFakeSeeker returns a ReadSeeker that can pretend to Seek (based
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// on the provided total size of the reader's content), but any reads
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// will fail if the fake seek position doesn't match reality.
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func NewFakeSeeker(r io.Reader, size int64) io.ReadSeeker {
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return &fakeSeeker{r: r, size: size}
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}
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func (fs *fakeSeeker) Seek(offset int64, whence int) (int64, error) {
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var newo int64
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switch whence {
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default:
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return 0, errors.New("invalid whence")
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case os.SEEK_SET:
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newo = offset
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case os.SEEK_CUR:
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newo = fs.fakePos + offset
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case os.SEEK_END:
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newo = fs.size + offset
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}
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if newo < 0 {
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return 0, errors.New("negative seek")
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}
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fs.fakePos = newo
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return newo, nil
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}
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func (fs *fakeSeeker) Read(p []byte) (n int, err error) {
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if fs.fakePos != fs.realPos {
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return 0, fmt.Errorf("attempt to read from fake seek offset %d; real offset is %d", fs.fakePos, fs.realPos)
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}
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n, err = fs.r.Read(p)
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fs.fakePos += int64(n)
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fs.realPos += int64(n)
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return
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}
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