djbdns/io.py: add a comment about an early return.

[djbdns-logparse.git] / djbdns / io.py

diff --git a/djbdns/io.py b/djbdns/io.py
index 7c70bab3debcf2b78ad43e18146488740cdf1c4e..a3e6e430e8a7e7a19890b7d94af36eff3e42b86d 100644 (file)
--- a/djbdns/io.py
+++ b/djbdns/io.py
@@ -1,3 +1,7 @@
+r"""
+Functions that perform input/output. This forms a layer between the
+executable itself and the more libraryish modules.
+"""
 from subprocess import Popen, PIPE
 from typing import TextIO
 from djbdns.dnscache import handle_dnscache_log
@@ -31,19 +35,31 @@ def parse_logfile(file : TextIO):
     # Open a pipe to tai64nlocal. We'll write lines of our input file
     # (the log file) to it, and read back the same lines but with
     # friendly timestamps in them.
-    tai = Popen(["tai64nlocal"], stdin=PIPE, stdout=PIPE, text=True, bufsize=0)
+    with Popen(["tai64nlocal"],
+               stdin=PIPE,
+               stdout=PIPE,
+               text=True,
+               bufsize=0) as tai:
 
-    for line in file:
-        tai.stdin.write(line)
-        line = tai.stdout.readline()
+        if not tai.stdin or not tai.stdout:
+            # Mypy tells me that this can happen, based on the type
+            # annotations in the standard library I guess?
+            return
 
-        friendly_line = handle_tinydns_log(line)
-        if not friendly_line:
-            friendly_line = handle_dnscache_log(line)
-            if not friendly_line:
-                friendly_line = line
+        for line in file:
+            tai.stdin.write(line)
+            line = tai.stdout.readline()
 
-        print(friendly_line)
+            friendly_line = handle_tinydns_log(line)
+            if not friendly_line:
+                friendly_line = handle_dnscache_log(line)
+                if not friendly_line:
+                    friendly_line = line
 
-    # Ensure that the pipe gets closed.
-    tai.communicate()
+            try:
+                print(friendly_line)
+            except BrokenPipeError:
+                # If our stdout is being piped to another process and if
+                # that process closes the pipe, this error will be raised
+                # the next time we try to write to stdout.
+                break