Resolve comments from pull request

This converts the map validation function into a macro, tweaks
the GITERR_OS system error automatic appending, and adds a
tentative new error access API and some quick unit tests for
both the old and new error APIs.

1 files changed, 26 insertions, 7 deletions

diff --git a/src/errors.c b/src/errors.c
index 19bc7b77b..70aa641c4 100644
--- a/src/errors.c
+++ b/src/errors.c
@@ -123,33 +123,41 @@ void giterr_set(int error_class, const char *string, ...)
 	char error_str[1024];
 	va_list arglist;
 
+	/* Grab errno before calling vsnprintf() so it won't be overwritten */
+	const char *os_error_msg =
+		(error_class == GITERR_OS && errno != 0) ? strerror(errno) : NULL;
+#ifdef GIT_WIN32
+	DWORD dwLastError = GetLastError();
+#endif
+
 	va_start(arglist, string);
 	p_vsnprintf(error_str, sizeof(error_str), string, arglist);
 	va_end(arglist);
 
 	/* automatically suffix strerror(errno) for GITERR_OS errors */
 	if (error_class == GITERR_OS) {
-		if (errno != 0) {
+		if (os_error_msg != NULL) {
 			strncat(error_str, ": ", sizeof(error_str));
-			strncat(error_str, strerror(errno), sizeof(error_str));
-			errno = 0;
+			strncat(error_str, os_error_msg, sizeof(error_str));
+			errno = 0; /* reset so same error won't be reported twice */
 		}
 #ifdef GIT_WIN32
-		else {
-			LPVOID lpMsgBuf;
-			DWORD dw = GetLastError();
+		else if (dwLastError != 0) {
+			LPVOID lpMsgBuf = NULL;
 
 			FormatMessage(
 				FORMAT_MESSAGE_ALLOCATE_BUFFER | 
 				FORMAT_MESSAGE_FROM_SYSTEM |
 				FORMAT_MESSAGE_IGNORE_INSERTS,
-				NULL, dw, 0, (LPTSTR) &lpMsgBuf, 0, NULL);
+				NULL, dwLastError, 0, (LPTSTR) &lpMsgBuf, 0, NULL);
 
 			if (lpMsgBuf) {
 				strncat(error_str, ": ", sizeof(error_str));
 				strncat(error_str, (const char *)lpMsgBuf, sizeof(error_str));
 				LocalFree(lpMsgBuf);
 			}
+
+			SetLastError(0);
 		}
 #endif
 	}
@@ -185,3 +193,14 @@ void giterr_clear(void)
 {
 	GIT_GLOBAL->last_error = NULL;
 }
+
+const git_error *git_error_last(void)
+{
+	return GIT_GLOBAL->last_error;
+}
+
+void git_error_clear(void)
+{
+	giterr_clear();
+}
+