I extended a patch from David Shaw to make libcurl _always_ provide an error

string in the given error buffer to address the flaw mention on 21 sep 2005.

CHANGES

@@ -8,6 +8,10 @@
 
 
 
+Daniel (17 November 2005)
+- I extended a patch from David Shaw to make libcurl _always_ provide an error
+  string in the given error buffer to address the flaw mention on 21 sep 2005.
+
 Daniel (16 November 2005)
 - Applied Albert Chin's patch that makes the libcurl.pc pkgconfig file get
   installed on 'make install' time.

RELEASE-NOTES

@@ -19,6 +19,7 @@ This release includes the following changes:
 
 This release includes the following bugfixes:
 
+ o CURLOPT_ERRORBUFFER is now always filled in on errors
  o curl outputs error on bad --limit-rate units
  o fixed libcurl's use of poll() on cygwin
  o the GnuTLS code didn't support client certificates
@@ -51,6 +52,6 @@ advice from friends like these:
  Dave Dribin, Bradford Bruce, Temprimus, Ofer, Dima Barsky, Amol Pattekar, Jaz
  Fresh, tommink[at]post.pl, Gisle Vanem, Nis Jorgensen, Vilmos Nebehaj,
  Dmitry Bartsevich, David Lang, Eugene Kotlyarov, Jan Kunder, Yang Tse,
- Quagmire, Albert Chin
+ Quagmire, Albert Chin, David Shaw
 
         Thanks! (and sorry if I forgot to mention someone)

docs/libcurl/curl_easy_setopt.3

@@ -270,12 +270,6 @@ debug/trace why errors happen.
 If the library does not return an error, the buffer may not have been
 touched. Do not rely on the contents in those cases.
 
-In a few rare cases, there is no text string associated with the error in
-libcurl and then you may not get a string in the buffer even though it returns
-an error. This is considered a bug and we appreciate your reports about these
-cases. Anyway, you can avoid problems with these cases in your program by
-making sure to clear the first byte of the error buffer before you call
-curl_easy_perform().
 .IP CURLOPT_STDERR
 Pass a FILE * as parameter. Tell libcurl to use this stream instead of stderr
 when showing the progress meter and displaying \fICURLOPT_VERBOSE\fP data.

lib/transfer.c

@@ -2217,6 +2217,19 @@ CURLcode Curl_perform(struct SessionHandle *data)
   if(newurl)
     free(newurl);
 
+  if(res && !data->state.errorbuf) {
+    /*
+     * As an extra precaution: if no error string has been set and there was
+     * an error, use the strerror() string or if things are so bad that not
+     * even that is good, set a bad string that mentions the error code.
+     */
+    char *str = curl_easy_strerror(res);
+    if(!str)
+      failf(data, "unspecified error %d", (int)res);
+    else
+      failf(data, "%s", str);
+  }
+
   /* run post-transfer uncondionally, but don't clobber the return code if
      we already have an error code recorder */
   res2 = Curl_posttransfer(data);