92 lines
2.1 KiB
Go
92 lines
2.1 KiB
Go
//go:build unix
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package parse
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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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"runtime"
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"syscall"
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)
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type binaryReaderMmap struct {
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data []byte
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}
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func newBinaryReaderMmap(filename string) (*binaryReaderMmap, error) {
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f, err := os.Open(filename)
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if err != nil {
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return nil, err
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}
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defer f.Close()
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fi, err := f.Stat()
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if err != nil {
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return nil, err
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}
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size := fi.Size()
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if size == 0 {
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// Treat (size == 0) as a special case, avoiding the syscall, since
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// "man 2 mmap" says "the length... must be greater than 0".
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//
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// As we do not call syscall.Mmap, there is no need to call
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// runtime.SetFinalizer to enforce a balancing syscall.Munmap.
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return &binaryReaderMmap{
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data: make([]byte, 0),
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}, nil
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} else if size < 0 {
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return nil, fmt.Errorf("mmap: file %q has negative size", filename)
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} else if size != int64(int(size)) {
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return nil, fmt.Errorf("mmap: file %q is too large", filename)
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}
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data, err := syscall.Mmap(int(f.Fd()), 0, int(size), syscall.PROT_READ, syscall.MAP_SHARED)
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if err != nil {
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return nil, err
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}
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r := &binaryReaderMmap{data}
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runtime.SetFinalizer(r, (*binaryReaderMmap).Close)
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return r, nil
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}
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// Close closes the reader.
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func (r *binaryReaderMmap) Close() error {
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if r.data == nil {
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return nil
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} else if len(r.data) == 0 {
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r.data = nil
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return nil
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}
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data := r.data
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r.data = nil
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runtime.SetFinalizer(r, nil)
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return syscall.Munmap(data)
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}
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// Len returns the length of the underlying memory-mapped file.
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func (r *binaryReaderMmap) Len() int {
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return len(r.data)
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}
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func (r *binaryReaderMmap) Bytes(n int, off int64) ([]byte, error) {
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if r.data == nil {
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return nil, errors.New("mmap: closed")
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} else if off < 0 || int64(len(r.data)) < off {
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return nil, fmt.Errorf("mmap: invalid offset %d", off)
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} else if int64(len(r.data)-n) < off {
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return r.data[off:len(r.data):len(r.data)], io.EOF
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}
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return r.data[off : off+int64(n) : off+int64(n)], nil
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}
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func NewBinaryReader2Mmap(filename string) (*BinaryReader2, error) {
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f, err := newBinaryReaderMmap(filename)
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if err != nil {
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return nil, err
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}
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return NewBinaryReader2(f), nil
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}
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