73 lines
1.5 KiB
Go
73 lines
1.5 KiB
Go
package readers
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import (
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"errors"
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"fmt"
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"io"
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)
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// FakeSeeker adapts an io.Seeker into an io.ReadSeeker
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type FakeSeeker struct {
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in io.Reader
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readErr error
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length int64
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offset int64
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read bool
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}
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// NewFakeSeeker creates a fake io.ReadSeeker from an io.Reader
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//
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// This can be seeked before reading to discover the length passed in.
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func NewFakeSeeker(in io.Reader, length int64) io.ReadSeeker {
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if rs, ok := in.(io.ReadSeeker); ok {
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return rs
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}
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return &FakeSeeker{
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in: in,
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length: length,
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}
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}
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// Seek the stream - possible only before reading
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func (r *FakeSeeker) Seek(offset int64, whence int) (abs int64, err error) {
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if r.readErr != nil {
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return 0, r.readErr
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}
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if r.read {
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return 0, fmt.Errorf("FakeSeeker: can't Seek(%d, %d) after reading", offset, whence)
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}
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switch whence {
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case io.SeekStart:
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abs = offset
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case io.SeekCurrent:
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abs = r.offset + offset
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case io.SeekEnd:
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abs = r.length + offset
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default:
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return 0, errors.New("FakeSeeker: invalid whence")
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}
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if abs < 0 {
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return 0, errors.New("FakeSeeker: negative position")
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}
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r.offset = abs
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return abs, nil
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}
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// Read data from the stream. Will give an error if seeked.
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func (r *FakeSeeker) Read(p []byte) (n int, err error) {
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if r.readErr != nil {
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return 0, r.readErr
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}
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if !r.read && r.offset != 0 {
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return 0, errors.New("FakeSeeker: not at start: can't read")
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}
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n, err = r.in.Read(p)
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if n != 0 {
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r.read = true
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}
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if err != nil {
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r.readErr = err
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}
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return n, err
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}
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