Re: [pbs-devel] [RFC pxar 2/20] fix #3174: decoder: factor out skip_bytes from skip_entry

[Wolfgang Bumiller <w.bumiller@proxmox.com>]

On Fri, Sep 22, 2023 at 09:16:03AM +0200, Christian Ebner wrote:
> Allows to skip bytes independently of the current entries header, as is
> implemented by skip_entry.
> 
> Signed-off-by: Christian Ebner <c.ebner@proxmox.com>
> ---
>  src/decoder/mod.rs | 19 ++++++++++++-------
>  1 file changed, 12 insertions(+), 7 deletions(-)
> 
> diff --git a/src/decoder/mod.rs b/src/decoder/mod.rs
> index d1fb911..2ca263b 100644
> --- a/src/decoder/mod.rs
> +++ b/src/decoder/mod.rs
> @@ -562,20 +562,25 @@ impl<I: SeqRead> DecoderImpl<I> {
>      // These utilize additional information and hence are not part of the `dyn SeqRead` impl.
>      //
>  
> -    async fn skip_entry(&mut self, offset: u64) -> io::Result<()> {
> -        let mut len = self.current_header.content_size() - offset;
> +    async fn skip_bytes(&mut self, len: usize) -> io::Result<()> {

I think `len` here should be an `u64`, `skip_entry` otherwise gets
limited to 32 bits on some systems for no reason :-)

> +        let mut remaining = len;
>          let scratch = scratch_buffer();
> -        while len >= (scratch.len() as u64) {
> +        while remaining >= scratch.len() {
>              seq_read_exact(&mut self.input, scratch).await?;
> -            len -= scratch.len() as u64;
> +            remaining -= scratch.len();
>          }
> -        let len = len as usize;
> -        if len > 0 {
> -            seq_read_exact(&mut self.input, &mut scratch[..len]).await?;
> +        if remaining > 0 {
> +            seq_read_exact(&mut self.input, &mut scratch[..remaining]).await?;
>          }
>          Ok(())
>      }
>  
> +    async fn skip_entry(&mut self, offset: u64) -> io::Result<()> {
> +        let len =
> +            usize::try_from(self.current_header.content_size() - offset).map_err(io_err_other)?;
> +        self.skip_bytes(len).await
> +    }
> +
>      async fn read_entry_as_bytes(&mut self) -> io::Result<Vec<u8>> {
>          let size = usize::try_from(self.current_header.content_size()).map_err(io_err_other)?;
>          let data = seq_read_exact_data(&mut self.input, size).await?;
> -- 
> 2.39.2