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