Expand capture-only NetScaler NITRO simulation and crash recovery

evidence.py

@@ -6,6 +6,7 @@ import os
 import pathlib
 import threading
 import time
+import tempfile
 
 
 class EvidenceError(OSError):
@@ -25,6 +26,21 @@ class Evidence:
         self.used = sum(p.stat().st_size for p in self.directory.rglob('*') if p.is_file())
         self.journal = os.open(self.directory / 'events.jsonl', os.O_WRONLY | os.O_APPEND | os.O_CREAT | os.O_NOFOLLOW, 0o600)
         os.fchmod(self.journal, 0o600)
+        # Preserve a crash-interrupted record without merging the next event into it.
+        with (self.directory / 'events.jsonl').open('rb') as previous:
+            previous.seek(0, os.SEEK_END)
+            if previous.tell():
+                previous.seek(-1, os.SEEK_END)
+                if previous.read(1) != b'\n':
+                    self.reserve(1)
+                    os.write(self.journal, b'\n')
+                    os.fsync(self.journal)
+                    self.used += 1
+        directory = os.open(self.directory, os.O_RDONLY)
+        try:
+            os.fsync(directory)
+        finally:
+            os.close(directory)
 
     def reserve(self, size):
         if self.used + size > self.quota:
@@ -50,14 +66,20 @@ class Evidence:
         with self.lock:
             if not path.exists():
                 self.reserve(len(data))
-                fd = os.open(path, os.O_WRONLY | os.O_CREAT | os.O_EXCL | os.O_NOFOLLOW, 0o600)
+                fd, temporary = tempfile.mkstemp(prefix='.capture-', dir=self.artifacts)
                 try:
                     with os.fdopen(fd, 'wb') as output:
                         output.write(data)
                         output.flush()
                         os.fsync(output.fileno())
+                    os.replace(temporary, path)
+                    directory = os.open(self.artifacts, os.O_RDONLY)
+                    try:
+                        os.fsync(directory)
+                    finally:
+                        os.close(directory)
                 except BaseException:
-                    path.unlink(missing_ok=True)  # do not leave a partial blob with a full-content hash
+                    pathlib.Path(temporary).unlink(missing_ok=True)
                     raise
                 self.used += len(data)
         return dict(sha256=digest, bytes=len(data), artifact='artifacts/' + path.name)