Fix READSOCK=2048 request cap (oversized requests spin/hang)

src/glob.h: READSOCK 2048 -> 16384 so normal chat requests (incl. reverse
proxy X-Forwarded-* headers + a message body) fit. Previously requests
>2KB couldn't be fully read; for a POST whose Content-Length exceeded the
buffer the completeness check re-armed the read event forever (per-
connection spin/hang, no crash).

src/sock/sock.cpp handle_client_read: guard both the headers-incomplete
and body-incomplete re-arms with (i_buf_len < READSOCK). If the buffer is
already full the request can never complete (oversized): drop it without
re-arming instead of spinning. Deleting the context inside the read
callback corrupts libevent (verified: heap corruption / SIGSEGV, tried
both del_event+delete and event_del+delete and a 413-via-write-event), so
the oversized request's fd/context is intentionally leaked for that one
abusive request rather than crashing the server. The leak is a known
limitation (filed as a follow-up: defer reaping via the timer so the fd
is reclaimed without deleting inside the read callback).

Verified: oversized headers (17KB, no terminator) and oversized POST body
(20KB) no longer crash or spin the server (0 restarts); an 8KB POST login
now returns 200 (didn't fit in the old 2KB buffer); normal login + multi-
user chat still work. Independent review: APPROVE-WITH-NITS; the
headers-incomplete spin guard was added per the review.

2 files changed, 16 insertions, 5 deletions

diff --git a/ychat/src/glob.h b/ychat/src/glob.h
index 9e3d6c7..7309196 100644
--- a/ychat/src/glob.h
+++ b/ychat/src/glob.h
@@ -82,7 +82,7 @@
 
 #define POSTBUF 1024
 #define READBUF 2048
-#define READSOCK 2048
+#define READSOCK 16384
 #define SERVMSG
 //#define CTCSEGV
 #define VERBOSE
diff --git a/ychat/src/sock/sock.cpp b/ychat/src/sock/sock.cpp
index b145f6b..9202902 100644
--- a/ychat/src/sock/sock.cpp
+++ b/ychat/src/sock/sock.cpp
@@ -311,8 +311,13 @@ sock::handle_client_read(int i_fd, short event, void *p_arg)
 
     if (i_hdr_end == string::npos)
     {
-      // Headers not fully received yet; wait for more.
-      event_add(p_context->p_event, NULL);
+      // Headers not fully received yet. Guard against oversized header
+      // floods: if the buffer is already full with no header terminator, the
+      // request can never be completed - drop it (no re-arm) rather than spin.
+      // The fd leaks for that one abusive request (see the body branch below);
+      // preferable to a crash/spin.
+      if ( p_context->i_buf_len < READSOCK )
+        event_add(p_context->p_event, NULL);
       return;
     }
 
@@ -326,8 +331,14 @@ sock::handle_client_read(int i_fd, short event, void *p_arg)
       int i_have = (int)s_buf.size() - (int)i_body_off;
       if (i_have < i_content_len)
       {
-        // Body still incomplete; wait for the rest.
-        event_add(p_context->p_event, NULL);
+        // Body still incomplete. If the buffer is already full the body
+        // can never fit (oversized POST): drop the request without re-arming
+        // (re-arming a full buffer would spin, and deleting the context
+        // inside this read callback corrupts libevent). The fd leaks for
+        // that one abusive request — acceptable for a toy chat and far
+        // better than a crash/spin. Otherwise wait for the rest.
+        if ( p_context->i_buf_len < READSOCK )
+          event_add(p_context->p_event, NULL);
         return;
       }
     }