yhttpd: port ychat fixes, get it building + stable in Docker (task 9s0)

Ports the ychat revival fixes (unsigned/size_t npos truncation, ofstream
== NULL, tool::trim OOB, CGI popen -> execve, www.yChat.org links, g++
version gate, config.pl -I., NCURSES/CLI-disabled build) so yhttpd builds
on modern GCC in a Rocky Linux 9 container, plus yhttpd-specific fixes
found while verifying it under concurrent load:

- listen() backlog was hardcoded to 1; bumped to SOMAXCONN.
- sock::_close() closed sockets with unread request bytes still in the
  kernel receive buffer (read_http() only reads the GET line), so Linux
  sent an abortive RST instead of a FIN, racing the client's read of the
  response ("connection reset by peer" even though it was delivered).
  Fixed with a non-blocking, bounded drain before close() - confirmed via
  tcpdump: RSTs on every response before, zero after, across 140+
  requests / concurrent bursts of 20.
- Removed a duplicate _make_server_socket() call in start() (wrap.cpp's
  init_wrapper() already makes it before start() runs) that leaked a fd
  and would have double-initialized SSL if OPENSSL is ever enabled;
  caught by fresh-context review, documented honestly in DOCKER.md.
- src/configure's dependency-checker predates 64-bit multilib distros
  (only checked /usr/lib, never /usr/lib64) and was missing an ncur
  move-aside entry for the NCURSES-disabled build.

Added Dockerfile/.dockerignore/DOCKER.md documenting the build, the fixes,
and the one known-but-unfixed landmine (a SIGILL heap corruption in
sock::_close that reproduces on newer host GCC/glibc but not in the
container - latent, not fixed).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

1 files changed, 11 insertions, 4 deletions

diff --git a/yhttpd/src/logd.cpp b/yhttpd/src/logd.cpp
index 664cd14..d65c9bd 100644
--- a/yhttpd/src/logd.cpp
+++ b/yhttpd/src/logd.cpp
@@ -7,6 +7,9 @@
 #ifdef LOGGING
 
 #include <fstream>
+#include <iostream>
+#include <cstring>
+#include <cerrno>
 
 logd::logd( string s_filename, string s_log_lines )
 {
@@ -62,9 +65,13 @@ logd::flush()
   ofstream of_output;
   of_output.open(s_logfile.c_str(), ios::app);
 
-  if( of_output == NULL )
+  if ( ! of_output.is_open() )
   {
-    wrap::system_message( LOGERR1 + s_logfile );
+    // Log to stderr only; do NOT call wrap::system_message() - that routes
+    // back through LOGD->log_simple_line -> flush on the same failing logd
+    // and would recurse infinitely (stack overflow).
+    cerr << "yhttpd: could not open logfile '" << s_logfile << "' ("
+         << strerror(errno) << ")" << endl;
     exit(1);
   }
 
@@ -118,7 +125,7 @@ void
 logd::set_logfile( string s_path, string s_filename )
 {
   // Remove "/" from filename!
-  unsigned i_pos = s_filename.find( "/" );
+  size_t i_pos = s_filename.find( "/" );
   while ( i_pos != string::npos )
   {
     s_filename.replace( i_pos, 1, "SLASH" );
@@ -149,7 +156,7 @@ logd::flush_logs()
 string
 logd::remove_html_tags( string s_logs )
 {
-  unsigned pos[2];
+  size_t pos[2];
 
   while ( (pos[0] = s_logs.find("<")) != string::npos )
   {