W32: add std stream redirection envvar optionslrn/attachconsole

This commit adds two W32-only environmental variable checks:
* G_WIN32_ALLOC_CONSOLE, if set to 1, will force glib to create
  a new console if the process has no console by itself.
  This option is for GUI apps that are launched from GUI
  processes, in which case there's no console anywhere near them.
* G_WIN32_ATTACH_CONSOLE, if set to a comma-separated list of
  standard stream names (stdint, stdout, stderr), will reopen
  a given std stream and tie it to the console (using existing console
  or parent console).
  This works either with the other option (to create a console),
  or if the app is launched from a console process (often the
  case for developers).
  The redirection is done with freopen(), dup() and dup2().
  If everything goes well, C file descriptors 0, 1 or 2 will
  be bound to stdin, stdout and stderr respectively (only for
  streams listed in the envrionmental variable), and so will
  be stdio streams by the same names.

With these it's possible to see the output of g_log*() functions
when running GTK4 applications, which are linked as GUI applications,
and thus do not get a console by default.

https://bugzilla.gnome.org/show_bug.cgi?id=790857

Fixes issue #1304

3 files changed, 184 insertions, 0 deletions

diff --git a/glib/glib-init.c b/glib/glib-init.c
index 2e229667f..6cb4e4a0d 100644
--- a/glib/glib-init.c
+++ b/glib/glib-init.c
@@ -292,6 +292,8 @@ DllMain (HINSTANCE hinstDLL,
       g_thread_win32_init ();
 #endif
       glib_init ();
+      /* must go after glib_init */
+      g_console_win32_init ();
       break;
 
     case DLL_THREAD_DETACH:
diff --git a/glib/glib-init.h b/glib/glib-init.h
index 5da33c052..695dc044b 100644
--- a/glib/glib-init.h
+++ b/glib/glib-init.h
@@ -34,6 +34,7 @@ void g_quark_init (void);
 void g_thread_win32_process_detach (void);
 void g_thread_win32_thread_detach (void);
 void g_thread_win32_init (void);
+void g_console_win32_init (void);
 void g_clock_win32_init (void);
 extern HMODULE glib_dll;
 #endif
diff --git a/glib/gwin32.c b/glib/gwin32.c
index a176514b1..d698a9141 100644
--- a/glib/gwin32.c
+++ b/glib/gwin32.c
@@ -36,6 +36,7 @@
 #include <string.h>
 #include <wchar.h>
 #include <errno.h>
+#include <fcntl.h>
 
 #define STRICT			/* Strict typing, please */
 #include <windows.h>
@@ -68,6 +69,7 @@
 
 #include "glib.h"
 #include "gthreadprivate.h"
+#include "glib-init.h"
 
 #ifdef G_WITH_CYGWIN
 #include <sys/cygwin.h>
@@ -804,3 +806,182 @@ G_GNUC_END_IGNORE_DEPRECATIONS
 }
 
 #endif
+
+#ifdef G_OS_WIN32
+
+void
+g_console_win32_init (void)
+{
+  const gchar *attach_envvar;
+
+  /* Note: it's not a very good practice to use DllMain()
+   * to call any functions not in Kernel32.dll.
+   * The following only works if there are no weird
+   * circular DLL dependencies that could cause glib DllMain()
+   * to be called before CRT DllMain().
+   */
+
+  if (g_strcmp0 (g_getenv ("G_WIN32_ALLOC_CONSOLE"), "1") == 0)
+    AllocConsole (); /* no error handling, fails if console already exists */
+
+  attach_envvar = g_getenv ("G_WIN32_ATTACH_CONSOLE");
+
+  if (attach_envvar)
+    {
+      gint       i;
+#define NUM_STREAMS 3
+      gboolean   streams_todo[NUM_STREAMS] = { FALSE, FALSE, FALSE }; /* IN, OUT, ERR */
+      gchar    **attach_strs = g_strsplit (attach_envvar, ",", -1);
+
+      /* Re-use parent console, if we don't have our own */
+      if (GetConsoleWindow () == NULL)
+         AttachConsole (ATTACH_PARENT_PROCESS);
+
+      for (i = 0; attach_strs[i]; i++)
+        {
+          if (g_strcmp0 (attach_strs[i], "stdout") == 0)
+            streams_todo[1] = TRUE;
+          else if (g_strcmp0 (attach_strs[i], "stderr") == 0)
+            streams_todo[2] = TRUE;
+          else if (g_strcmp0 (attach_strs[i], "stdin") == 0)
+            streams_todo[0] = TRUE;
+          else
+            g_warning ("Unrecognized stream name %s", attach_strs[i]);
+        }
+
+      for (i = 0; i < NUM_STREAMS; i++)
+        {
+          FILE        *stream = NULL;
+          const gchar *stream_name;
+          int          old_fd;
+          int          backup_fd;
+          int          new_fd;
+          int          flags;
+          int          preferred_fd = i;
+          HANDLE       std_handle;
+          errno_t      error = 0;
+          const char  *mode = NULL;
+
+          if (!streams_todo[i])
+            continue;
+
+          switch (i)
+            {
+            case 1:
+              stream = stdout;
+              stream_name = "stdout";
+              std_handle = GetStdHandle (STD_OUTPUT_HANDLE);
+              flags = 0;
+              mode = "wb";
+              break;
+            case 2:
+              stream = stderr;
+              stream_name = "stderr";
+              std_handle = GetStdHandle (STD_ERROR_HANDLE);
+              flags = 0;
+              mode = "wb";
+              break;
+            case 0:
+              stream = stdin;
+              stream_name = "stdin";
+              std_handle = GetStdHandle (STD_INPUT_HANDLE);
+              flags = _O_RDONLY;
+              mode = "rb";
+              break;
+            }
+
+          if (ferror (stream) != 0)
+            {
+              g_warning ("Stream %s is in error state", stream_name);
+              continue;
+            }
+
+          old_fd = fileno (stream);
+
+          if (old_fd < 0)
+            {
+              if (freopen ("NUL", mode, stream) == NULL)
+                {
+                  error = errno;
+                  g_warning ("Failed to redirect %s: %d - %s",
+                             stream_name,
+                             error,
+                             strerror (error));
+                  continue;
+                }
+
+              old_fd = fileno (stream);
+
+              if (old_fd < 0)
+                {
+                  g_warning ("Stream %s does not have a valid fd", stream_name);
+                  continue;
+                }
+            }
+
+          if (std_handle == INVALID_HANDLE_VALUE)
+            {
+              DWORD gle = GetLastError ();
+              g_warning ("Standard handle for %s can't be obtained: %lu",
+                         stream_name, gle);
+              continue;
+            }
+
+          new_fd = _open_osfhandle ((intptr_t) std_handle, flags);
+
+          if (new_fd < 0)
+            {
+              g_warning ("Failed to create new fd for stream %s", stream_name);
+              continue;
+            }
+
+          backup_fd = dup (old_fd);
+
+          if (backup_fd < 0)
+            g_warning ("Failed to backup old fd %d for stream %s", old_fd, stream_name);
+
+          errno = 0;
+
+          if (dup2 (new_fd, old_fd) == 0)
+            {
+              if (backup_fd >= 0)
+                close (backup_fd);
+
+              /* Sadly, there's no way to check that preferred_fd
+               * is currently valid, so we can't back it up.
+               * Doing operations on invalid FDs invokes invalid
+               * parameter handler, which is bad for us.
+               */
+              if (old_fd != preferred_fd)
+                if (dup2 (new_fd, preferred_fd) != 0)
+                  g_warning ("Failed to dup fd %d into fd %d", new_fd, preferred_fd);
+
+              close (new_fd);
+
+              continue;
+            }
+
+          error = errno;
+          g_warning ("Failed to substitute fd %d for stream %s: %d : %s",
+                     old_fd, stream_name, error, strerror (error));
+
+          close (new_fd);
+
+          if (backup_fd < 0)
+            continue;
+
+          errno = 0;
+
+          if (dup2 (backup_fd, old_fd) != 0)
+            {
+              error = errno;
+              g_warning ("Failed to restore fd %d for stream %s: %d : %s",
+                         old_fd, stream_name, error, strerror (error));
+            }
+
+          close (backup_fd);
+        }
+    }
+}
+
+#endif