From 335fc0bfa2af1238cddc116f9eaffb5d9ab9aabe Mon Sep 17 00:00:00 2001
From: Remy Blank <remy@c-space.org>
Date: Thu, 19 Sep 2024 18:07:12 +0200
Subject: [PATCH] Avoid keeping dangling connections when the client closes.

---
 tdoc/common/cli.py                      | 27 ++++++++++++++++---------
 tdoc/common/static/tdoc-reload.js.jinja |  3 ++-
 2 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/tdoc/common/cli.py b/tdoc/common/cli.py
index 4160b7d..64c34e4 100644
--- a/tdoc/common/cli.py
+++ b/tdoc/common/cli.py
@@ -297,28 +297,37 @@ def dispatch_star_handler(self, write_content):
         url = parse.urlparse(self.path)
         if not url.path.startswith('/*'): return
         if handler := getattr(self, f'handle_star_{url.path[2:]}', None):
-            content = handler(url)
+            content = handler(url, write_content)
             if write_content and content: self.wfile.write(content)
         else:
             self.send_error(server.HTTPStatus.NOT_FOUND)
         return True
 
-    def handle_star_build(self, url):
+    def handle_star_build(self, url, write_content):
         t = None
         for k, v in parse.parse_qsl(url.query):
             if k == 't':
                 t = v
                 break
-        with self.server.lock:
-            while ((mtime := self.server.build_mtime) is None
-                   or t == build_tag(mtime)):
-                self.server.lock.wait()
-        tag = build_tag(mtime).encode('utf-8')
+        # We send padding back at regular intervals, which allows detecting when
+        # the client closes the connection (we get a BrokenPipeError). Since the
+        # content length is needed upfront, we return a fixed size, and
+        # terminate the request if the padding exceeds the available space.
+        size = 600
         self.send_response(server.HTTPStatus.OK)
         self.send_header('Content-type', 'text/plain')
-        self.send_header('Content-Length', str(len(tag)))
+        self.send_header('Content-Length', str(size))
         self.end_headers()
-        return tag
+        if not write_content: return
+        with self.server.lock:
+            while ((mtime := self.server.build_mtime) is None
+                   or t == build_tag(mtime)) and size > 0:
+                if self.server.lock.wait(timeout=1): continue
+                self.wfile.write(b' ')
+                size -= 1
+        tag = build_tag(mtime).encode('utf-8')
+        if len(tag) > size: tag = b''  # Not enough remaining capacity
+        return b' ' * (size - len(tag)) + tag
 
 
 def build_tag(mtime):
diff --git a/tdoc/common/static/tdoc-reload.js.jinja b/tdoc/common/static/tdoc-reload.js.jinja
index 82ab899..6caba79 100644
--- a/tdoc/common/static/tdoc-reload.js.jinja
+++ b/tdoc/common/static/tdoc-reload.js.jinja
@@ -18,7 +18,8 @@ async function reloadOnTagChange() {
                               `${resp.statusText}`);
                 continue;
             }
-            const tag = await resp.text();
+            const tag = (await resp.text()).trim();
+            if (tag === '') continue;
             if (tag !== build) location.reload();
         } catch (e) {
             console.error(e);