strerror: Preserve Windows error code in some functions

This is a follow-up to af02162 which removed (SET_)ERRNO macros. That
commit was an earlier draft that I committed by mistake, which was then
remedied by a5834e5 and e909de6, and now this commit. With this commit
there is now no difference between the current code and the changes that
were approved in the final draft.

Thanks-to: Max Dymond, Marcel Raad, Daniel Stenberg, Gisle Vanem
Ref: https://github.com/curl/curl/pull/1589

lib/strerror.c

@@ -49,6 +49,10 @@
 #include "curl_memory.h"
 #include "memdebug.h"
 
+#if defined(WIN32) || defined(_WIN32_WCE)
+#define PRESERVE_WINDOWS_ERROR_CODE
+#endif
+
 const char *
 curl_easy_strerror(CURLcode error)
 {
@@ -432,6 +436,10 @@ curl_share_strerror(CURLSHcode error)
 static const char *
 get_winsock_error (int err, char *buf, size_t len)
 {
+#ifdef PRESERVE_WINDOWS_ERROR_CODE
+  DWORD old_win_err = GetLastError();
+#endif
+  int old_errno = errno;
   const char *p;
 
 #ifndef CURL_DISABLE_VERBOSE_STRINGS
@@ -611,6 +619,15 @@ get_winsock_error (int err, char *buf, size_t len)
 #endif
   strncpy(buf, p, len);
   buf [len-1] = '\0';
+
+  if(errno != old_errno)
+    errno = old_errno;
+
+#ifdef PRESERVE_WINDOWS_ERROR_CODE
+  if(old_win_err != GetLastError())
+    SetLastError(old_win_err);
+#endif
+
   return buf;
 }
 #endif   /* USE_WINSOCK */
@@ -628,19 +645,16 @@ get_winsock_error (int err, char *buf, size_t len)
  */
 const char *Curl_strerror(struct connectdata *conn, int err)
 {
+#ifdef PRESERVE_WINDOWS_ERROR_CODE
+  DWORD old_win_err = GetLastError();
+#endif
+  int old_errno = errno;
   char *buf, *p;
   size_t max;
-  int old_errno;
+
-#ifdef WIN32
-  DWORD old_win_err;
-#endif
   DEBUGASSERT(conn);
   DEBUGASSERT(err >= 0);
 
-  old_errno = errno;
-#ifdef WIN32
-  old_win_err = GetLastError();
-#endif
   buf = conn->syserr_buf;
   max = sizeof(conn->syserr_buf)-1;
   *buf = '\0';
@@ -727,12 +741,14 @@ const char *Curl_strerror(struct connectdata *conn, int err)
   p = strrchr(buf, '\r');
   if(p && (p - buf) >= 1)
     *p = '\0';
-#ifdef WIN32
+
+  if(errno != old_errno)
+    errno = old_errno;
+
+#ifdef PRESERVE_WINDOWS_ERROR_CODE
   if(old_win_err != GetLastError())
     SetLastError(old_win_err);
 #endif
-  if(errno != old_errno)
-    errno = old_errno;
 
   return buf;
 }
@@ -740,17 +756,19 @@ const char *Curl_strerror(struct connectdata *conn, int err)
 #ifdef USE_WINDOWS_SSPI
 const char *Curl_sspi_strerror (struct connectdata *conn, int err)
 {
+#ifdef PRESERVE_WINDOWS_ERROR_CODE
+  DWORD old_win_err = GetLastError();
+#endif
+  int old_errno = errno;
+  const char *txt;
+  char *outbuf;
+  size_t outmax;
 #ifndef CURL_DISABLE_VERBOSE_STRINGS
   char txtbuf[80];
   char msgbuf[sizeof(conn->syserr_buf)];
   char *p, *str, *msg = NULL;
   bool msg_formatted = FALSE;
-  int old_errno;
-  DWORD old_win_err;
 #endif
-  const char *txt;
-  char *outbuf;
-  size_t outmax;
 
   DEBUGASSERT(conn);
 
@@ -760,9 +778,6 @@ const char *Curl_sspi_strerror (struct connectdata *conn, int err)
 
 #ifndef CURL_DISABLE_VERBOSE_STRINGS
 
-  old_errno = errno;
-  old_win_err = GetLastError();
-
   switch(err) {
     case SEC_E_OK:
       txt = "No error";
@@ -1062,12 +1077,6 @@ const char *Curl_sspi_strerror (struct connectdata *conn, int err)
       strncpy(outbuf, str, outmax);
   }
 
-  if(old_win_err != GetLastError())
-    SetLastError(old_win_err);
-
-  if(errno != old_errno)
-    errno = old_errno;
-
 #else
 
   if(err == SEC_E_OK)
@@ -1081,6 +1090,14 @@ const char *Curl_sspi_strerror (struct connectdata *conn, int err)
 
   outbuf[outmax] = '\0';
 
+  if(errno != old_errno)
+    errno = old_errno;
+
+#ifdef PRESERVE_WINDOWS_ERROR_CODE
+  if(old_win_err != GetLastError())
+    SetLastError(old_win_err);
+#endif
+
   return outbuf;
 }
 #endif /* USE_WINDOWS_SSPI */

tests/libtest/lib505.c

@@ -42,7 +42,6 @@ int test(char *URL)
   int hd;
   struct_stat file_info;
   struct curl_slist *hl;
-  int error;
 
   struct curl_slist *headerlist=NULL;
   const char *buf_1 = "RNFR 505";
@@ -55,9 +54,8 @@ int test(char *URL)
 
   hd_src = fopen(libtest_arg2, "rb");
   if(NULL == hd_src) {
-    error = errno;
     fprintf(stderr, "fopen failed with error: %d %s\n",
-            error, strerror(error));
+            errno, strerror(errno));
     fprintf(stderr, "Error opening file: %s\n", libtest_arg2);
     return TEST_ERR_MAJOR_BAD; /* if this happens things are major weird */
   }
@@ -66,9 +64,8 @@ int test(char *URL)
   hd = fstat(fileno(hd_src), &file_info);
   if(hd == -1) {
     /* can't open file, bail out */
-    error = errno;
     fprintf(stderr, "fstat() failed with error: %d %s\n",
-            error, strerror(error));
+            errno, strerror(errno));
     fprintf(stderr, "ERROR: cannot open file %s\n", libtest_arg2);
     fclose(hd_src);
     return TEST_ERR_MAJOR_BAD;

tests/libtest/lib525.c

@@ -35,7 +35,6 @@ int test(char *URL)
   CURL *curl = NULL;
   FILE *hd_src = NULL;
   int hd;
-  int error;
   struct_stat file_info;
   CURLM *m = NULL;
   int running;
@@ -55,9 +54,8 @@ int test(char *URL)
 
   hd_src = fopen(libtest_arg2, "rb");
   if(NULL == hd_src) {
-    error = errno;
     fprintf(stderr, "fopen failed with error: %d (%s)\n",
-            error, strerror(error));
+            errno, strerror(errno));
     fprintf(stderr, "Error opening file: (%s)\n", libtest_arg2);
     return TEST_ERR_FOPEN;
   }
@@ -66,9 +64,8 @@ int test(char *URL)
   hd = fstat(fileno(hd_src), &file_info);
   if(hd == -1) {
     /* can't open file, bail out */
-    error = errno;
     fprintf(stderr, "fstat() failed with error: %d (%s)\n",
-            error, strerror(error));
+            errno, strerror(errno));
     fprintf(stderr, "ERROR: cannot open file (%s)\n", libtest_arg2);
     fclose(hd_src);
     return TEST_ERR_FSTAT;

tests/libtest/lib541.c

@@ -38,7 +38,6 @@ int test(char *URL)
   FILE *hd_src;
   int hd;
   struct_stat file_info;
-  int error;
 
   if(!libtest_arg2) {
     fprintf(stderr, "Usage: <url> <file-to-upload>\n");
@@ -47,9 +46,8 @@ int test(char *URL)
 
   hd_src = fopen(libtest_arg2, "rb");
   if(NULL == hd_src) {
-    error = errno;
     fprintf(stderr, "fopen failed with error: %d %s\n",
-            error, strerror(error));
+            errno, strerror(errno));
     fprintf(stderr, "Error opening file: %s\n", libtest_arg2);
     return -2; /* if this happens things are major weird */
   }
@@ -58,9 +56,8 @@ int test(char *URL)
   hd = fstat(fileno(hd_src), &file_info);
   if(hd == -1) {
     /* can't open file, bail out */
-    error = errno;
     fprintf(stderr, "fstat() failed with error: %d %s\n",
-            error, strerror(error));
+            errno, strerror(errno));
     fprintf(stderr, "ERROR: cannot open file %s\n", libtest_arg2);
     fclose(hd_src);
     return TEST_ERR_MAJOR_BAD;

tests/libtest/lib582.c

@@ -228,7 +228,6 @@ int test(char *URL)
   CURL *curl = NULL;
   FILE *hd_src = NULL;
   int hd;
-  int error;
   struct_stat file_info;
   CURLM *m = NULL;
   struct ReadWriteSockets sockets = {{NULL, 0, 0}, {NULL, 0, 0}};
@@ -244,9 +243,8 @@ int test(char *URL)
 
   hd_src = fopen(libtest_arg2, "rb");
   if(NULL == hd_src) {
-    error = errno;
     fprintf(stderr, "fopen() failed with error: %d (%s)\n",
-            error, strerror(error));
+            errno, strerror(errno));
     fprintf(stderr, "Error opening file: (%s)\n", libtest_arg2);
     return TEST_ERR_FOPEN;
   }
@@ -255,9 +253,8 @@ int test(char *URL)
   hd = fstat(fileno(hd_src), &file_info);
   if(hd == -1) {
     /* can't open file, bail out */
-    error = errno;
     fprintf(stderr, "fstat() failed with error: %d (%s)\n",
-            error, strerror(error));
+            errno, strerror(errno));
     fprintf(stderr, "ERROR: cannot open file (%s)\n", libtest_arg2);
     fclose(hd_src);
     return TEST_ERR_FSTAT;

tests/libtest/lib591.c

@@ -44,15 +44,13 @@ int test(char *URL)
   int msgs_left;
   CURLMsg *msg;
   FILE *upload = NULL;
-  int error;
 
   start_test_timing();
 
   upload = fopen(libtest_arg3, "rb");
   if(!upload) {
-    error = errno;
     fprintf(stderr, "fopen() failed with error: %d (%s)\n",
-            error, strerror(error));
+            errno, strerror(errno));
     fprintf(stderr, "Error opening file: (%s)\n", libtest_arg3);
     return TEST_ERR_FOPEN;
   }