Re: [pbs-devel] [PATCH proxmox-backup 3/4] pxar: add UniqueContext helper

[Max Carrara <m.carrara@proxmox.com>]

On 2/16/24 16:33, Gabriel Goller wrote:
> To create a pxar archive, we recursively traverse the target folder.
> If there is an error further down and we add a context using anyhow,
> the context will be duplicated and we get an output like:
> 
>> Error: error at "xattr/xattr.txt": error at "xattr/xattr.txt": E2BIG [skip]
> 
> This is obviously not optimal, so in recursive contexts we can use the
> UniqueContext, which quickly checks the context from the last item in
> the error chain and only adds it if it is unique.
> 
> Signed-off-by: Gabriel Goller <g.goller@proxmox.com>
> ---
>  pbs-client/src/pxar/create.rs | 25 ++++++++++++++++++++++++-
>  1 file changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/pbs-client/src/pxar/create.rs b/pbs-client/src/pxar/create.rs
> index 06f396e0..7bec35c4 100644
> --- a/pbs-client/src/pxar/create.rs
> +++ b/pbs-client/src/pxar/create.rs
> @@ -1,5 +1,6 @@
>  use std::collections::{HashMap, HashSet};
>  use std::ffi::{CStr, CString, OsStr};
> +use std::fmt::Display;
>  use std::io::{self, Read};
>  use std::os::unix::ffi::OsStrExt;
>  use std::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd, OwnedFd, RawFd};
> @@ -88,8 +89,30 @@ pub fn is_virtual_file_system(magic: i64) -> bool {
>          SYSFS_MAGIC)
>  }
>  
> +trait UniqueContext<T> {
> +    fn unique_context<S>(self, context: S) -> Result<T, anyhow::Error>
> +    where
> +        S: Display + Send + Sync + 'static;
>  }
>  
> +impl<T> UniqueContext<T> for Result<T, anyhow::Error>
> +{
> +    fn unique_context<S>(self, context: S) -> Result<T, anyhow::Error>
> +    where
> +        S: Display + Send + Sync + 'static
> +    {
> +        match self {
> +            Ok(ok) => Ok(ok),
> +            Err(err) => {
> +                let last_error = err.chain().next();
> +                if let Some(e) = last_error {
> +                    if e.to_string() == context.to_string() {
> +                        return Err(err);
> +                    }
> +                }
> +                Err(err.context(context))
> +            },
> +        }
>      }
>  }

The trait plus the impl could perhaps be inlined inside the body of
`Archiver::archive_dir_contents`, as `unique_context()` is only used in there,
but I think it's also fine if it says where it is. Looks good otherwise!

>  
> @@ -242,7 +265,7 @@ impl Archiver {
>                  (self.callback)(&file_entry.path)?;
>                  self.path = file_entry.path;
>                  self.add_entry(encoder, dir_fd, &file_entry.name, &file_entry.stat)
> -                    .await.context(format!("error at {:?}", self.path))?;
> +                    .await.unique_context(format!("error at {:?}", self.path))?;
>              }
>              self.path = old_path;
>              self.entry_counter = entry_counter;