From 28ededdd045549c3168ea4905c08ef7b2293af0a Mon Sep 17 00:00:00 2001
From: Tim Heiko <175552092+timheiko@users.noreply.github.com>
Date: Fri, 8 Aug 2025 17:19:12 +0200
Subject: [PATCH] Chapter 21 - fix tcp_mojifinder.py crashes on empty search
 result
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Fixes #61

Start the TCP server
```shell
% ./tcp_mojifinder.py
Building index.
Serving on ('127.0.0.1', 2323). Hit CTRL-C to stop.
```

Connect to the TCP server and send a search query which return no results and some results, e.g. `missing` and `hat`
```shell
% nc localhost 2323
?> missing
────────────────────────────────────────────────────────────────── 0 found
?> hat
U+2CD4	Ⳕ	COPTIC CAPITAL LETTER OLD COPTIC HAT
U+2CD5	ⳕ	COPTIC SMALL LETTER OLD COPTIC HAT
U+A271	ꉱ	YI SYLLABLE HAT
U+D571	핱	HANGUL SYLLABLE HAT
U+1F3A9	🎩	TOP HAT
U+1F452	👒	WOMANS HAT
U+1F920	🤠	FACE WITH COWBOY HAT
U+1F973	🥳	FACE WITH PARTY HORN AND PARTY HAT
────────────────────────────────────────────────────────────────── 8 found
?>
```

The TCP server log contains no errors and doesn't crash the TCP connection:
```
 % ./tcp_mojifinder.py
Building index.
Serving on ('127.0.0.1', 2323). Hit CTRL-C to stop.
 From ('127.0.0.1', 63756): 'missing'
   To ('127.0.0.1', 63756): 0 results.
 From ('127.0.0.1', 63756): 'hat'
   To ('127.0.0.1', 63756): 8 results.
```
---
 21-async/mojifinder/tcp_mojifinder.py | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/21-async/mojifinder/tcp_mojifinder.py b/21-async/mojifinder/tcp_mojifinder.py
index 4da7188..4bd4fc4 100755
--- a/21-async/mojifinder/tcp_mojifinder.py
+++ b/21-async/mojifinder/tcp_mojifinder.py
@@ -43,10 +43,11 @@ async def search(query: str,  # <1>
                  index: InvertedIndex,
                  writer: asyncio.StreamWriter) -> int:
     chars = index.search(query)  # <2>
-    lines = (line.encode() + CRLF for line  # <3>
-                in format_results(chars))
-    writer.writelines(lines)  # <4>
-    await writer.drain()      # <5>
+    if chars:
+        lines = (line.encode() + CRLF for line  # <3>
+                    in format_results(chars))
+        writer.writelines(lines)  # <4>
+        await writer.drain()      # <5>
     status_line = f'{"─" * 66} {len(chars)} found'  # <6>
     writer.write(status_line.encode() + CRLF)
     await writer.drain()