Allow some options taking filenames to refer to mpv config dir

Add the mp_get_user_path() function, and make it expand special path
prefixes. Use it for some things in mpv which take filenames
(--input-config, --screenshot-template, opengl icc-profile suboption).

This allows accessing files in the mpv config dir without hardcoding the
config path by prefixing the path with ~~/. Details see manpage
additions.

DOCS/man/en/mpv.rst

@@ -285,6 +285,28 @@ It has the following format::
 
     ``mpv --ao=pcm:file=%`expr length "$NAME"`%"$NAME" test.avi``
 
+Paths
+-----
+
+Some care must be taken when passing arbitrary paths and filenames to mpv. For
+example, paths starting with ``-`` will be interpreted as options. Likewise,
+if a path contains the sequence ``://``, the string before that might be
+interpreted as protocol prefix, even though ``://`` can be part of a legal
+UNIX path. To avoid problems with arbitrary paths, you should be sure that
+absolute paths passed to mpv start with ``/``, and relative paths with ``./``.
+
+The name ``-`` itself is interpreted as stdin, and will cause mpv to disable
+console controls. (Which makes it suitable for playing data piped to stdin.)
+
+For paths passed to suboptions, the situation is further complicated by the
+need to escape special characters. To work this around, the path can be
+additionally wrapped in the ``%n%string_of_length_n`` syntax (see above).
+
+Some mpv options interpret paths starting with ``~``. Currently, the prefix
+``~~/`` expands to the mpv configuration directory (usually ``~/.mpv/``).
+``~/`` expands to the user's home directory. (The trailing ``/`` is always
+required.)
+
 Per-File Options
 ----------------
 

mpvcore/input/input.c

@@ -2156,23 +2156,31 @@ static int parse_config(struct input_ctx *ictx, bool builtin, bstr data,
 
 static int parse_config_file(struct input_ctx *ictx, char *file, bool warn)
 {
+    int r = 0;
+    void *tmp = talloc_new(NULL);
+    stream_t *s = NULL;
+
+    file = mp_get_user_path(tmp, file);
     if (!mp_path_exists(file)) {
         MP_MSG(ictx, warn ? MSGL_ERR : MSGL_V,
                "Input config file %s not found.\n", file);
-        return 0;
+        goto done;
     }
-    stream_t *s = stream_open(file, NULL);
+    s = stream_open(file, NULL);
     if (!s) {
         MP_ERR(ictx, "Can't open input config file %s.\n", file);
-        return 0;
+        goto done;
     }
-    bstr res = stream_read_complete(s, NULL, 1000000);
-    free_stream(s);
+    bstr data = stream_read_complete(s, tmp, 1000000);
     MP_VERBOSE(ictx, "Parsing input config file %s\n", file);
-    int n_binds = parse_config(ictx, false, res, file, NULL);
-    talloc_free(res.start);
+    int n_binds = parse_config(ictx, false, data, file, NULL);
     MP_VERBOSE(ictx, "Input config file %s parsed: %d binds\n", file, n_binds);
-    return 1;
+    r = 1;
+
+done:
+    free_stream(s);
+    talloc_free(tmp);
+    return r;
 }
 
 // If name is NULL, return "default".

mpvcore/path.c

@@ -97,6 +97,28 @@ char *mp_find_global_config_file(const char *filename)
     }
 }
 
+char *mp_get_user_path(void *talloc_ctx, const char *path)
+{
+    if (!path)
+        return NULL;
+    bstr bpath = bstr0(path);
+    if (bstr_eatstart0(&bpath, "~")) {
+        // parse to "~" <prefix> "/" <rest>
+        bstr prefix, rest;
+        if (bstr_split_tok(bpath, "/", &prefix, &rest)) {
+            const char *rest0 = rest.start; // ok in this case
+            char *res = NULL;
+            if (bstr_equals0(prefix, "~"))
+                res = talloc_steal(talloc_ctx, mp_find_user_config_file(rest0));
+            if (bstr_equals0(prefix, ""))
+                res = mp_path_join(talloc_ctx, bstr0(getenv("HOME")), rest);
+            if (res)
+                return res;
+        }
+    }
+    return talloc_strdup(talloc_ctx, path);
+}
+
 char *mp_basename(const char *path)
 {
     char *s;

mpvcore/path.h

@@ -36,6 +36,11 @@ char *mp_find_global_config_file(const char *filename);
 // Search for the input filename in the user configuration location.
 char *mp_find_user_config_file(const char *filename);
 
+// Normally returns a talloc_strdup'ed copy of the path, except for special
+// paths starting with '~'. Used to allow the user explicitly reference a
+// file from the user's home or mpv config directory.
+char *mp_get_user_path(void *talloc_ctx, const char *path);
+
 // Return pointer to filename part of path
 
 char *mp_basename(const char *path);

mpvcore/player/screenshot.c

@@ -233,7 +233,10 @@ static char *create_fname(struct MPContext *mpctx, char *template,
     }
 
     res = talloc_strdup_append(res, template);
-    return talloc_asprintf_append(res, ".%s", file_ext);
+    res = talloc_asprintf_append(res, ".%s", file_ext);
+    char *fname = mp_get_user_path(NULL, res);
+    talloc_free(res);
+    return fname;
 
 error_exit:
     talloc_free(res);

video/out/gl_lcms.c

@@ -31,6 +31,7 @@
 #include "mpvcore/bstr.h"
 #include "mpvcore/mp_msg.h"
 #include "mpvcore/m_option.h"
+#include "mpvcore/path.h"
 
 #include "gl_video.h"
 #include "gl_lcms.h"
@@ -90,11 +91,13 @@ static void lcms2_error_handler(cmsContext ctx, cmsUInt32Number code,
 static struct bstr load_file(void *talloc_ctx, const char *filename)
 {
     struct bstr res = {0};
-    stream_t *s = stream_open(filename, NULL);
+    char *fname = mp_get_user_path(NULL, filename);
+    stream_t *s = stream_open(fname, NULL);
     if (s) {
         res = stream_read_complete(s, talloc_ctx, 1000000000);
         free_stream(s);
     }
+    talloc_free(fname);
     return res;
 }