[PATCH proxmox-backup v3] fix #7382: correctly anchor nested paths for include/exclude patterns.

[Manuel Federanko <m.federanko@proxmox.com>]

A pattern in a subdirectory would be built by just prepending the parent
directory. This could break anchored patterns, which wouldn't match if
the parent directory didn't start with a slash.
Fixed this by explicitly checking if the base path starts with a slash
and prepending it if it does not exist.

It worked for anchored patterns in the root backup directory because
here the pattern is "" + "/exclude".

old:
match_path = /level0/level1/exclude
pattern = level0/level1/exclude

new:
match_path = /level0/level1/exclude
pattern = /level0/level1/exclude

Tested by creating a directory structure as described in the bug ticket
and verifying the behavior.

Signed-off-by: Manuel Federanko <m.federanko@proxmox.com>
Fixes: https://bugzilla.proxmox.com/show_bug.cgi?id=7382
---
changed since v2:
* fix clippy warnings (sorry for the churn)
changed since v1:
* use path_bytes.starts_with (thanks Maximiliano for feedback off-list)

 pbs-client/src/pxar/create.rs | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/pbs-client/src/pxar/create.rs b/pbs-client/src/pxar/create.rs
index 7f605a61..e42bcc87 100644
--- a/pbs-client/src/pxar/create.rs
+++ b/pbs-client/src/pxar/create.rs
@@ -537,13 +537,20 @@ impl Archiver {

             let mut buf;
             let (line, mode, anchored) = if line[0] == b'/' {
-                buf = Vec::with_capacity(path_bytes.len() + 1 + line.len());
+                buf = Vec::with_capacity(path_bytes.len() + 2 + line.len());
+                // need to anchor the base path if it is not
+                if !path_bytes.is_empty() && !path_bytes.starts_with(b"/") {
+                    buf.push(b'/');
+                }
                 buf.extend(path_bytes);
                 buf.extend(line);
                 (&buf[..], MatchType::Exclude, true)
             } else if line.starts_with(b"!/") {
                 // inverted case with absolute path
-                buf = Vec::with_capacity(path_bytes.len() + line.len());
+                buf = Vec::with_capacity(path_bytes.len() + 1 + line.len());
+                if !path_bytes.is_empty() && !path_bytes.starts_with(b"/") {
+                    buf.push(b'/');
+                }
                 buf.extend(path_bytes);
                 buf.extend(&line[1..]); // without the '!'
                 (&buf[..], MatchType::Include, true)
--
2.47.3