63 lines
1.7 KiB
Go
63 lines
1.7 KiB
Go
package internal
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import (
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"bufio"
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"compress/gzip"
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"errors"
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"io"
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"os"
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)
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// NewBufferedSectionReader wraps an io.ReaderAt in an appropriately-sized
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// buffered reader. It is a convenience function for reading subsections of
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// ELF sections while minimizing the amount of read() syscalls made.
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//
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// Syscall overhead is non-negligible in continuous integration context
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// where ELFs might be accessed over virtual filesystems with poor random
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// access performance. Buffering reads makes sense because (sub)sections
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// end up being read completely anyway.
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//
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// Use instead of the r.Seek() + io.LimitReader() pattern.
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func NewBufferedSectionReader(ra io.ReaderAt, off, n int64) *bufio.Reader {
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// Clamp the size of the buffer to one page to avoid slurping large parts
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// of a file into memory. bufio.NewReader uses a hardcoded default buffer
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// of 4096. Allow arches with larger pages to allocate more, but don't
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// allocate a fixed 4k buffer if we only need to read a small segment.
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buf := n
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if ps := int64(os.Getpagesize()); n > ps {
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buf = ps
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}
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return bufio.NewReaderSize(io.NewSectionReader(ra, off, n), int(buf))
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}
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// DiscardZeroes makes sure that all written bytes are zero
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// before discarding them.
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type DiscardZeroes struct{}
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func (DiscardZeroes) Write(p []byte) (int, error) {
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for _, b := range p {
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if b != 0 {
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return 0, errors.New("encountered non-zero byte")
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}
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}
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return len(p), nil
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}
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// ReadAllCompressed decompresses a gzipped file into memory.
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func ReadAllCompressed(file string) ([]byte, error) {
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fh, err := os.Open(file)
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if err != nil {
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return nil, err
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}
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defer fh.Close()
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gz, err := gzip.NewReader(fh)
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if err != nil {
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return nil, err
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}
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defer gz.Close()
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return io.ReadAll(gz)
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}
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