From 9ab32e5b6b91c5bddb59c69923edea1438ec60a0 Mon Sep 17 00:00:00 2001
From: "Peter J. Holzer" <hjp@hjp.at>
Date: Fri, 18 Mar 2022 23:52:42 +0100
Subject: [PATCH] Seek to end unless --start given

---
 kitsune | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/kitsune b/kitsune
index 7c04656..e4eacca 100755
--- a/kitsune
+++ b/kitsune
@@ -9,19 +9,24 @@ import stat
 import time
 
 class WatchedFile:
-    def __init__(self, path):
+    def __init__(self, path, seek_to_end):
         self.path = path
+        self.seek_to_end = seek_to_end
         self.reopen()
 
     def reopen(self):
         self.fd = open(self.path, errors='replace')
         self.fileno = self.fd.fileno()
         self.last_ts = 0
+        if self.seek_to_end:
+            self.fd.seek(0, 2)
+            self.seek_to_end = False
 
 def format_ts(ts_ns):
     return datetime.datetime.fromtimestamp(ts_ns / 1E9).strftime("%H:%M:%S.%f")
 
 def watch(args):
+    seek_to_end = not args.start
     watched_dirs = []
     watched_files = {}
     filename_length = 0
@@ -30,7 +35,7 @@ def watch(args):
         if stat.S_ISDIR(st.st_mode):
             watched_dirs.append(a)
         elif stat.S_ISREG(st.st_mode):
-            watched_files[a] = WatchedFile(a)
+            watched_files[a] = WatchedFile(a, seek_to_end)
             if len(a) > filename_length:
                 filename_length = len(a)
         else:
@@ -47,7 +52,7 @@ def watch(args):
                     if de.is_file():
                         if args.match_filename is None or fnmatch.fnmatch(de.name, args.match_filename):
                             if de.path not in watched_files:
-                                watched_files[de.path] = WatchedFile(de.path)
+                                watched_files[de.path] = WatchedFile(de.path, seek_to_end)
                                 if len(de.path) > filename_length:
                                     filename_length = len(de.path)
 
@@ -65,6 +70,10 @@ def watch(args):
                 # or just mark as deleted?
                 pass
             if st.st_mtime_ns > f.last_ts:
+                if st.st_size < f.fd.tell():
+                    # We are beyond the end of the file, so it has probably
+                    # been truncated and rewritten - read from beginning
+                    f.fd.seek(0, 0)
                 f.last_ts = st.st_mtime_ns
                 new_content = f.fd.read()
                 lines = new_content.split("\n")
@@ -73,9 +82,11 @@ def watch(args):
                 for ln in lines:
                     print(f"{f.path:{filename_length}}", format_ts(f.last_ts), ln)
         time.sleep(0.1)
+        seek_to_end = False
 
 if __name__ == "__main__":
     ap = argparse.ArgumentParser()
+    ap.add_argument("--start", action='store_true')
     ap.add_argument("--match-filename")
     ap.add_argument("files", nargs="*", default=["."])
     args = ap.parse_args()