curl: show better error message when no homedir is found

Reported-by: Vlastimil Ovčáčík
Fixes #4644
Closes #4665

src/tool_msgs.c

@@ -32,6 +32,7 @@
 
 #define WARN_PREFIX "Warning: "
 #define NOTE_PREFIX "Note: "
+#define ERROR_PREFIX "curl: "
 
 static void voutf(struct GlobalConfig *config,
                   const char *prefix,
@@ -122,3 +123,16 @@ void helpf(FILE *errors, const char *fmt, ...)
 #endif
           "for more information\n");
 }
+
+/*
+ * Emit error message on error stream if not muted.
+ */
+void errorf(struct GlobalConfig *config, const char *fmt, ...)
+{
+  if(!config->mute) {
+    va_list ap;
+    va_start(ap, fmt);
+    voutf(config, ERROR_PREFIX, fmt, ap);
+    va_end(ap);
+  }
+}

src/tool_msgs.h

@@ -25,7 +25,7 @@
 
 void warnf(struct GlobalConfig *config, const char *fmt, ...);
 void notef(struct GlobalConfig *config, const char *fmt, ...);
-
 void helpf(FILE *errors, const char *fmt, ...);
+void errorf(struct GlobalConfig *config, const char *fmt, ...);
 
 #endif /* HEADER_CURL_TOOL_MSGS_H */

src/tool_operate.c

@@ -1615,7 +1615,7 @@ static CURLcode single_transfer(struct GlobalConfig *global,
           if(!config->insecure_ok) {
             char *home;
             char *file;
-            result = CURLE_OUT_OF_MEMORY;
+            result = CURLE_FAILED_INIT;
             home = homedir();
             if(home) {
               file = aprintf("%s/.ssh/known_hosts", home);
@@ -1629,6 +1629,9 @@ static CURLcode single_transfer(struct GlobalConfig *global,
               }
               Curl_safefree(home);
             }
+            else {
+              errorf(global, "Failed to figure out user's home dir!");
+            }
             if(result)
               break;
           }