url: Improve CURLOPT_PROXY_CAPATH error handling

- Change CURLOPT_PROXY_CAPATH to return CURLE_NOT_BUILT_IN if the option
  is not supported, which is the same as what we already do for
  CURLOPT_CAPATH.

- Change the curl tool to handle CURLOPT_PROXY_CAPATH error
  CURLE_NOT_BUILT_IN as a warning instead of as an error, which is the
  same as what we already do for CURLOPT_CAPATH.

- Fix CAPATH docs to show that CURLE_NOT_BUILT_IN is returned when the
  respective CAPATH option is not supported by the SSL library.

Ref: https://github.com/curl/curl/pull/1257

4 files changed, 38 insertions, 10 deletions

diff --git a/docs/libcurl/opts/CURLOPT_CAPATH.3 b/docs/libcurl/opts/CURLOPT_CAPATH.3
index 85ef06956..b19994b50 100644
--- a/docs/libcurl/opts/CURLOPT_CAPATH.3
+++ b/docs/libcurl/opts/CURLOPT_CAPATH.3
@@ -49,8 +49,13 @@ TODO
 This option is supported by the OpenSSL, GnuTLS and PolarSSL backends. The NSS
 backend provides the option only for backward compatibility.
 .SH RETURN VALUE
-Returns CURLE_OK if TLS enabled, and CURLE_UNKNOWN_OPTION if not, or
-CURLE_OUT_OF_MEMORY if there was insufficient heap space.
+CURLE_OK if supported; or an error such as:
+
+CURLE_NOT_BUILT_IN - Not supported by the SSL backend
+
+CURLE_UNKNOWN_OPTION
+
+CURLE_OUT_OF_MEMORY
 .SH "SEE ALSO"
 .BR CURLOPT_CAINFO "(3), "
 .BR CURLOPT_STDERR "(3), " CURLOPT_DEBUGFUNCTION "(3), "
diff --git a/docs/libcurl/opts/CURLOPT_PROXY_CAPATH.3 b/docs/libcurl/opts/CURLOPT_PROXY_CAPATH.3
index 372cc9503..dc317f03b 100644
--- a/docs/libcurl/opts/CURLOPT_PROXY_CAPATH.3
+++ b/docs/libcurl/opts/CURLOPT_PROXY_CAPATH.3
@@ -48,8 +48,13 @@ Added in 7.52.0
 This option is supported by the OpenSSL, GnuTLS and PolarSSL backends. The NSS
 backend provides the option only for backward compatibility.
 .SH RETURN VALUE
-Returns CURLE_OK if TLS enabled, and CURLE_UNKNOWN_OPTION if not, or
-CURLE_OUT_OF_MEMORY if there was insufficient heap space.
+CURLE_OK if supported; or an error such as:
+
+CURLE_NOT_BUILT_IN - Not supported by the SSL backend
+
+CURLE_UNKNOWN_OPTION
+
+CURLE_OUT_OF_MEMORY
 .SH "SEE ALSO"
 .BR CURLOPT_CAINFO "(3), "
 .BR CURLOPT_STDERR "(3), " CURLOPT_DEBUGFUNCTION "(3), "
diff --git a/lib/url.c b/lib/url.c
index b8f7cfb9b..a78a2412f 100644
--- a/lib/url.c
+++ b/lib/url.c
@@ -583,8 +583,9 @@ CURLcode Curl_init_userdefined(struct UserDefined *set)
   if(result)
     return result;
 
-  result = setstropt(&set->str[STRING_SSL_CAPATH_PROXY],
-                     (char *) CURL_CA_PATH);
+  result = setstropt(&set->str[STRING_SSL_CAPATH_PROXY], CURL_CA_PATH);
+  if(result)
+    return result;
 #endif
 
   set->wildcardmatch  = FALSE;
@@ -2225,8 +2226,12 @@ CURLcode Curl_setopt(struct Curl_easy *data, CURLoption option,
     /* This does not work on windows. */
     result = setstropt(&data->set.str[STRING_SSL_CAPATH_ORIG],
                        va_arg(param, char *));
+#else
+    result = CURLE_NOT_BUILT_IN;
+#endif
     break;
   case CURLOPT_PROXY_CAPATH:
+#ifdef have_curlssl_ca_path /* not supported by all backends */
     /*
      * Set CA path info for SSL connection proxy. Specify directory name of the
      * CA certificates which have been prepared using openssl c_rehash utility.
diff --git a/src/tool_operate.c b/src/tool_operate.c
index bc36520d9..c30b32046 100644
--- a/src/tool_operate.c
+++ b/src/tool_operate.c
@@ -1014,6 +1014,7 @@ static CURLcode operate_do(struct GlobalConfig *global,
           my_setopt_str(curl, CURLOPT_CAINFO, config->cacert);
         if(config->proxy_cacert)
           my_setopt_str(curl, CURLOPT_PROXY_CAINFO, config->proxy_cacert);
+
         if(config->capath) {
           result = res_setopt_str(curl, CURLOPT_CAPATH, config->capath);
           if(result == CURLE_NOT_BUILT_IN) {
@@ -1024,10 +1025,22 @@ static CURLcode operate_do(struct GlobalConfig *global,
           else if(result)
             goto show_error;
         }
-        if(config->proxy_capath)
-          my_setopt_str(curl, CURLOPT_PROXY_CAPATH, config->proxy_capath);
-        else if(config->capath) /* CURLOPT_PROXY_CAPATH default is capath */
-          my_setopt_str(curl, CURLOPT_PROXY_CAPATH, config->capath);
+        /* For the time being if --proxy-capath is not set then we use the
+           --capath value for it, if any. See #1257 */
+        if(config->proxy_capath || config->capath) {
+          result = res_setopt_str(curl, CURLOPT_PROXY_CAPATH,
+                                  (config->proxy_capath ?
+                                   config->proxy_capath :
+                                   config->capath));
+          if(result == CURLE_NOT_BUILT_IN) {
+            if(config->proxy_capath) {
+              warnf(config->global,
+                    "ignoring --proxy-capath, not supported by libcurl\n");
+            }
+          }
+          else if(result)
+            goto show_error;
+        }
 
         if(config->crlfile)
           my_setopt_str(curl, CURLOPT_CRLFILE, config->crlfile);