[PATCH 4/5] hwlatdetect: Add bounds checking and improve code readability

[John Kacur <jkacur@redhat.com>]

Add defensive checks to the Sample.__init__ method to prevent
IndexError on malformed trace input:

- Verify fields array has at least 8 elements
- Check cpu_field is non-empty before accessing first character
- Add comments explaining the two different trace formats
- Improve code readability by using a named variable for cpu_field

Assisted-by: Claude Sonnet 4.5 <noreply@anthropic.com>
Signed-off-by: John Kacur <jkacur@redhat.com>
---
 src/hwlatdetect/hwlatdetect.py | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/src/hwlatdetect/hwlatdetect.py b/src/hwlatdetect/hwlatdetect.py
index 865f62196c26..38671724f3e3 100755
--- a/src/hwlatdetect/hwlatdetect.py
+++ b/src/hwlatdetect/hwlatdetect.py
@@ -257,8 +257,22 @@ class Tracer(Detector):
 
         def __init__(self, line):
             fields = line.split()
+            if len(fields) < 8:
+                raise ValueError(f"Unexpected trace format: {line}")
+
             kv = key_values(fields)
-            self.cpu = int(fields[1][1:-1]) if fields[1][0] == '[' else int(fields[1][:-5])
+
+            # Parse CPU number from either [NNN] or NNd.... format
+            cpu_field = fields[1]
+            if not cpu_field:
+                raise ValueError(f"Empty CPU field in: {line}")
+
+            if cpu_field[0] == '[':
+                # nolatency-format: [007]
+                self.cpu = int(cpu_field[1:-1])
+            else:
+                # latency-format: 13d....
+                self.cpu = int(cpu_field[:-5])
             i, o = fields[6].split('/')
             ts = fields[7][3:]
             self.timestamp = str(ts)
-- 
2.53.0