Fix daemon processes logging to wrong virtual host error log.

In daemon mode, output to wsgi.errors, sys.stdout and sys.stderr could
be written to the main server ErrorLog instead of the ErrorLog of the
VirtualHost handling the request. The daemon maps each proxied request
back to the correct server using listener address details sent by the
Apache child worker, but that code was guarded by MOD_WSGI_WITH_DAEMONS,
which the 6.0.0 code restructuring left undefined in wsgi_environ.c by
moving its definition into the daemon specific wsgi_daemon.h. The guarded
code was silently compiled out and no listener details were sent.

Move the MOD_WSGI_WITH_DAEMONS definition into the common wsgi_apache.h
so it is visible to every translation unit.

Author: GrahamDumpleton

docs/release-notes/version-6.0.1.rst

@@ -35,3 +35,17 @@ Bugs Fixed
   that variable is only declared when daemon mode is available, which is
   never the case on Windows. The reference is now protected by the
   appropriate conditional.
+
+* When using daemon mode, output written to ``wsgi.errors`` (and anything
+  sent to ``sys.stdout`` or ``sys.stderr``) could be written to the main
+  server ``ErrorLog`` instead of the ``ErrorLog`` of the ``VirtualHost``
+  actually handling the request. The daemon process maps each proxied
+  request back to the correct server using listener address details
+  supplied by the Apache child worker, but the code which populated those
+  details was guarded by ``MOD_WSGI_WITH_DAEMONS``, and that symbol was not
+  defined in the relevant source file, so the guarded code was silently
+  compiled out and no listener details were sent. This was introduced by
+  the 6.0.0 code restructuring, which moved the definition of
+  ``MOD_WSGI_WITH_DAEMONS`` into a daemon specific header that the affected
+  source file did not include. The definition has been moved to a common
+  header visible to all source files.

src/server/wsgi_apache.h

@@ -76,6 +76,27 @@ APR_DECLARE_OPTIONAL_FN(char *, ssl_var_lookup, (apr_pool_t *, server_rec *, con
 #include "util_md5.h"
 #include "scoreboard.h"
 
+/* ------------------------------------------------------------------------- */
+
+/*
+ * Whether mod_wsgi is built with support for separate daemon processes
+ * (WSGIDaemonProcess). This requires fork() and APR other-child support
+ * and is never available on Windows.
+ *
+ * Defined here in the common Apache header, rather than in the daemon
+ * specific wsgi_daemon.h, so that every translation unit which
+ * conditionally compiles daemon mode code sees a consistent value
+ * without having to include the daemon API header. When this is not
+ * visible the guarded code is silently compiled out rather than failing
+ * to build.
+ */
+
+#ifndef WIN32
+#if APR_HAS_OTHER_CHILD && APR_HAS_FORK
+#define MOD_WSGI_WITH_DAEMONS 1
+#endif
+#endif
+
 APLOG_USE_MODULE(wsgi);
 
 #if defined(WIN32) && defined(APR_HAS_UNICODE_FS)

src/server/wsgi_daemon.h

@@ -29,12 +29,6 @@
 
 extern char *wsgi_shutdown_reason;
 
-#ifndef WIN32
-#if APR_HAS_OTHER_CHILD && APR_HAS_FORK
-#define MOD_WSGI_WITH_DAEMONS 1
-#endif
-#endif
-
 /*
  * Apache 2.X and UNIX specific definitions related to
  * distinct daemon processes.