curl: support XDG_CONFIG_HOME to find .curlrc

Added test433 to verify. Updated documentation.

Reviewed-by: Jay Satiro
Suggested-by: Eli Schwartz
Fixes #5829
Closes #5837

src/tool_homedir.c

@@ -25,6 +25,13 @@
 #  include <pwd.h>
 #endif
 
+#ifdef HAVE_SYS_STAT_H
+#include <sys/stat.h>
+#endif
+#ifdef HAVE_FCNTL_H
+#include <fcntl.h>
+#endif
+
 #include <curl/mprintf.h>
 
 #include "tool_homedir.h"
@@ -45,7 +52,27 @@ static char *GetEnv(const char *variable)
 }
 
 /* return the home directory of the current user as an allocated string */
-char *homedir(void)
+
+/*
+ * The original logic found a home dir to use (by checking a range of
+ * environment variables and last using getpwuid) and returned that for the
+ * parent to use.
+ *
+ * With the XDG_CONFIG_HOME support (added much later than the other), this
+ * variable is treated differently in order to not ruin existing installations
+ * even if this environment variable is set. If this variable is set, and a
+ * file name is set to check, then only if that file name exists in that
+ * directory will it be returned as a "home directory".
+ *
+ * 1. use CURL_HOME if set
+ * 2. use XDG_CONFIG_HOME if set and fname is present
+ * 3. use HOME if set
+ * 4. Non-windows: use getpwuid
+ * 5. Windows: use APPDATA if set
+ * 6. Windows: use "USERPROFILE\Application Data" is set
+ */
+
+char *homedir(const char *fname)
 {
   char *home;
 
@@ -53,6 +80,22 @@ char *homedir(void)
   if(home)
     return home;
 
+  if(fname) {
+    home = GetEnv("XDG_CONFIG_HOME");
+    if(home) {
+      char *c = curl_maprintf("%s" DIR_CHAR "%s", home, fname);
+      if(c) {
+        int fd = open(c, O_RDONLY);
+        curl_free(c);
+        if(fd >= 0) {
+          close(fd);
+          return home;
+        }
+      }
+      free(home);
+    }
+  }
+
   home = GetEnv("HOME");
   if(home)
     return home;

src/tool_homedir.h

@@ -7,7 +7,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2019, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2020, Daniel Stenberg, <daniel@haxx.se>, et al.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -23,6 +23,6 @@
  ***************************************************************************/
 #include "tool_setup.h"
 
-char *homedir(void);
+char *homedir(const char *fname);
 
 #endif /* HEADER_CURL_TOOL_HOMEDIR_H */

src/tool_operate.c

@@ -1696,7 +1696,7 @@ static CURLcode single_transfer(struct GlobalConfig *global,
             char *home;
             char *file;
             result = CURLE_FAILED_INIT;
-            home = homedir();
+            home = homedir(NULL);
             if(home) {
               file = aprintf("%s/.ssh/known_hosts", home);
               if(file) {

src/tool_parsecfg.c

@@ -82,7 +82,7 @@ int parseconfig(const char *filename, struct GlobalConfig *global)
   if(!filename || !*filename) {
     /* NULL or no file name attempts to load .curlrc from the homedir! */
 
-    char *home = homedir();    /* portable homedir finder */
+    char *home = homedir(".curlrc");
 #ifndef WIN32
     if(home) {
       pathalloc = curl_maprintf("%s%s.curlrc", home, DIR_CHAR);