[PATCH proxmox-backup] fix #7303: tape: handle NUL bytes in SCSI strings better

[Dominik Csapak <d.csapak@proxmox.com>]

When dealing with ASCII fields in answers from drives and changers, we
assumed that the data is simply ascii characters padded by spaces, with
potentially a NUL byte at the end. This is indicated for example by the
IBM library documentation about the Primary Volume Tag Information[0]:

```
This is a 36 byte ASCII field that contains the cartridge bar code
label, left-adjusted and padded on the right with blanks.
```

Some changers may reverse that though, and have a NUL terminated string
followed by space padding (e.g. "FOO\0 ").

When looking into the LTO-9 SCSI reference from IBM[1], they describe an
ASCII field as follows:

```
When used to describe a field, indicates that the field contains only
ASCII printable characters (i.e., code values 20h to 7Eh) and may be
terminated with one or more ASCII null (00h) characters.
```

To be on the safe side here, limit the string to before the first NUL
byte, and then trim the result.

Added some tests to verify the desired behavior here.

0: https://www.ibm.com/docs/en/ts4500-tape-library/1.12.1?topic=storage-dvcidb0
1: https://www.ibm.com/support/pages/node/6490249

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
---
 pbs-tape/src/sgutils2.rs | 44 ++++++++++++++++++++++++++++++++++++----
 1 file changed, 40 insertions(+), 4 deletions(-)

diff --git a/pbs-tape/src/sgutils2.rs b/pbs-tape/src/sgutils2.rs
index 6fec6ed5c..270420ce5 100644
--- a/pbs-tape/src/sgutils2.rs
+++ b/pbs-tape/src/sgutils2.rs
@@ -697,10 +697,12 @@ impl<'a, F: AsRawFd> SgRaw<'a, F> {
 
 /// Converts SCSI ASCII text into String, trim zero and spaces
 pub fn scsi_ascii_to_string(data: &[u8]) -> String {
-    String::from_utf8_lossy(data)
-        .trim_matches(char::from(0))
-        .trim()
-        .to_string()
+    let mut view = data;
+
+    if let Some(idx) = data.iter().position(|c| *c == 0u8) {
+        view = &view[..idx];
+    }
+    String::from_utf8_lossy(view).trim().to_string()
 }
 
 /// Read SCSI Inquiry page
@@ -1012,3 +1014,37 @@ pub fn scsi_request_sense<F: AsRawFd>(file: &mut F) -> Result<RequestSenseFixed,
 
     Ok(sense)
 }
+
+#[cfg(test)]
+mod test {
+    use crate::sgutils2::scsi_ascii_to_string;
+
+    #[test]
+    fn test_scsi_ascii_to_string() {
+        fn test(input: &'static str, expected: &'static str) {
+            let output = scsi_ascii_to_string(input.as_bytes());
+            assert_eq!(&output, expected);
+        }
+
+        test("TAPE00L1", "TAPE00L1");
+        test("TAPE00L1  ", "TAPE00L1");
+        test("TAPE00L1               ", "TAPE00L1");
+        test("TAPE00L1 \0", "TAPE00L1");
+        test("TAPE00L1  \0\0", "TAPE00L1");
+        test("TAPE00L1\0", "TAPE00L1");
+        test("TAPE00L1\0 ", "TAPE00L1");
+        test("TAPE00L1\0\0  ", "TAPE00L1");
+        test("TAPE0\0L1\0\0  ", "TAPE0");
+        test("TAPE0 \0L1  ", "TAPE0");
+        test("\0TAPE00L1", "");
+        test(" TAPE00L1", "TAPE00L1");
+        test("", "");
+        test(" ", "");
+        test("  ", "");
+        test("\0", "");
+        test("\0\0", "");
+        test("\0 ", "");
+        test(" \0 ", "");
+        test("  \0\0  ", "");
+    }
+}
-- 
2.47.3