exchnld: Add ability to specify the location of the crash report file.

Based on Daniel Atallah's patch:

  https://hg.pidgin.im/util/drmingw/rev/088532978452

Fixes #10.

README.md

@@ -101,7 +101,9 @@ You can use ExcHndl by:
 
     * compiling and linking `exchndl2.cpp` source file
 
-    * or by explicitly calling `LoadLibrary("exchndl.dll")`
+    * or by explicitly calling `LoadLibraryA("exchndl.dll")`
+
+  * you can also override the report location by invoking the exported `SetLogFileNameA` entry-point.
 
 Example
 -------

src/exchndl/exchndl.c

@@ -16,6 +16,8 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
  */
 
+#include "exchndl.h"
+
 #include <assert.h>
 #include <windows.h>
 #include <tchar.h>
@@ -26,6 +28,7 @@
 
 #include "symbols.h"
 #include "log.h"
+#include "outdbg.h"
 
 
 #define REPORT_FILE 1
@@ -171,9 +174,25 @@ static void OnExit(void)
     SetUnhandledExceptionFilter(g_prevExceptionFilter);
 }
 
-BOOL APIENTRY DllMain(HINSTANCE hInstance, DWORD dwReason, LPVOID lpReserved);
 
-BOOL APIENTRY DllMain(HINSTANCE hInstance, DWORD dwReason, LPVOID lpReserved)
+BOOL APIENTRY
+SetLogFileNameA(const char *szLogFileName)
+{
+    size_t size = _countof(g_szLogFileName);
+    if (!szLogFileName ||
+        _tcslen(szLogFileName) > size - 1) {
+        OutputDebug("EXCHNDL: specified log name is too long or invalid (%s)\n",
+                    szLogFileName);
+        return FALSE;
+    }
+    _tcsncpy(g_szLogFileName, szLogFileName, size - 1);
+    g_szLogFileName[size - 1] = _T('\0');
+    return TRUE;
+}
+
+
+BOOL APIENTRY
+DllMain(HINSTANCE hInstance, DWORD dwReason, LPVOID lpReserved)
 {
     switch (dwReason)
     {

src/exchndl/exchndl.def

@@ -1 +1,2 @@
 EXPORTS
+    SetLogFileNameA

src/exchndl/exchndl.h

@@ -0,0 +1,25 @@
+/*
+ * Copyright 2002-2015 Jose Fonseca
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+
+
+#include <windows.h>
+
+
+EXTERN_C BOOL APIENTRY SetLogFileNameA(const char *szLogFileName);
+
+EXTERN_C BOOL APIENTRY DllMain(HINSTANCE hInstance, DWORD dwReason, LPVOID lpReserved);

tests/exchndl_test.c

@@ -79,11 +79,24 @@ main(int argc, char **argv)
 
     SetUnhandledExceptionFilter(topLevelExceptionHandler);
 
-    ok = LoadLibraryA("exchndl.dll");
+    HMODULE hModule = LoadLibraryA("exchndl.dll");
+    ok = hModule != NULL;
     test_line(ok, "LoadLibraryA(\"exchndl.dll\")");
+    if (!ok) {
+        test_diagnostic_last_error();
+        test_exit();
+    }
+
+    typedef BOOL (APIENTRY * PFN_SETLOGFILENAMEA)(const char *szLogFileName);
+    PFN_SETLOGFILENAMEA pfnSetLogFileNameA = (PFN_SETLOGFILENAMEA)GetProcAddress(hModule, "SetLogFileNameA");
+    ok = pfnSetLogFileNameA != NULL;
+    test_line(ok, "GetProcAddress(\"SetLogFileNameA\")");
     if (!ok) {
         test_diagnostic_last_error();
     } else {
+        ok = pfnSetLogFileNameA(szReport);
+        test_line(ok, "SetLogFileNameA(\"%s\")", szReport);
+
         if (!setjmp(g_JmpBuf) ) {
             _snprintf(g_szExceptionPattern, sizeof g_szExceptionPattern, "  %s!%s  [%s @ %u]", PROG_NAME ".exe", __FUNCTION__, __FILE__, __LINE__); *((int *)0) = 0; test_line(false, "longjmp"); exit(1);
         } else {
@@ -120,5 +133,11 @@ main(int argc, char **argv)
         }
     }
 
+    ok = FreeLibrary(hModule);
+    test_line(ok, "FreeLibrary()");
+    if (!ok) {
+        test_diagnostic_last_error();
+    }
+
     test_exit();
 }