Split out xdg.{c,h}

1 files changed, 186 insertions, 0 deletions

diff --git a/xdg.c b/xdg.c
new file mode 100644
index 0000000..7ebd5de
--- /dev/null
+++ b/xdg.c
@@ -0,0 +1,186 @@
+//
+// xdg.c: various *nix desktop utilities
+//
+// Copyright (c) 2021, Přemysl Eric Janouch <p@janouch.name>
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+// SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+// OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+//
+
+#include <glib.h>
+
+/// Add `element` to the `output` set. `relation` is a map of sets of strings
+/// defining is-a relations, and is traversed recursively.
+static void
+add_applying_transitive_closure(
+	const gchar *element, GHashTable *relation, GHashTable *output)
+{
+	// Stop condition.
+	if (!g_hash_table_add(output, g_strdup(element)))
+		return;
+
+	// TODO(p): Iterate over all aliases of `element` in addition to
+	// any direct match (and rename this no-longer-generic function).
+	GHashTable *targets = g_hash_table_lookup(relation, element);
+	if (!targets)
+		return;
+
+	GHashTableIter iter;
+	g_hash_table_iter_init(&iter, targets);
+
+	gpointer key = NULL, value = NULL;
+	while (g_hash_table_iter_next(&iter, &key, &value))
+		add_applying_transitive_closure(key, relation, output);
+}
+
+char *
+get_xdg_home_dir(const char *var, const char *default_)
+{
+	const char *env = getenv(var);
+	if (env && *env == '/')
+		return g_strdup(env);
+
+	// The specification doesn't handle a missing HOME variable explicitly.
+	// Implicitly, assuming Bourne shell semantics, it simply resolves empty.
+	const char *home = getenv("HOME");
+	return g_build_filename(home ? home : "", default_, NULL);
+}
+
+static gchar **
+get_xdg_data_dirs(void)
+{
+	// GStrvBuilder is too new, it would help a little bit.
+	GPtrArray *output = g_ptr_array_new_with_free_func(g_free);
+	g_ptr_array_add(output, get_xdg_home_dir("XDG_DATA_HOME", ".local/share"));
+
+	const gchar *xdg_data_dirs;
+	if (!(xdg_data_dirs = getenv("XDG_DATA_DIRS")) || !*xdg_data_dirs)
+		xdg_data_dirs = "/usr/local/share/:/usr/share/";
+
+	gchar **candidates = g_strsplit(xdg_data_dirs, ":", 0);
+	for (gchar **p = candidates; *p; p++) {
+		if (**p == '/')
+			g_ptr_array_add(output, *p);
+		else
+			g_free(*p);
+	}
+	g_free(candidates);
+	g_ptr_array_add(output, NULL);
+	return (gchar **) g_ptr_array_free(output, FALSE);
+}
+
+// --- Filtering ---------------------------------------------------------------
+
+// Derived from shared-mime-info-spec 0.21.
+
+static void
+read_mime_subclasses(const gchar *path, GHashTable *subclass_sets)
+{
+	gchar *data = NULL;
+	if (!g_file_get_contents(path, &data, NULL /* length */, NULL /* error */))
+		return;
+
+	// The format of this file is unspecified,
+	// but in practice it's a list of space-separated media types.
+	gchar *datasave = NULL;
+	for (gchar *line = strtok_r(data, "\r\n", &datasave); line;
+			line = strtok_r(NULL, "\r\n", &datasave)) {
+		gchar *linesave = NULL,
+			*subclass = strtok_r(line, " ", &linesave),
+			*superclass = strtok_r(NULL, " ", &linesave);
+
+		// Nothing about comments is specified, we're being nice.
+		if (!subclass || *subclass == '#' || !superclass)
+			continue;
+
+		GHashTable *set = NULL;
+		if (!(set = g_hash_table_lookup(subclass_sets, superclass))) {
+			set = g_hash_table_new_full(g_str_hash, g_str_equal, g_free, NULL);
+			g_hash_table_insert(subclass_sets, g_strdup(superclass), set);
+		}
+		g_hash_table_add(set, g_strdup(subclass));
+	}
+	g_free(data);
+}
+
+static gboolean
+filter_mime_globs(const gchar *path, guint is_globs2, GHashTable *supported_set,
+	GHashTable *output_set)
+{
+	gchar *data = NULL;
+	if (!g_file_get_contents(path, &data, NULL /* length */, NULL /* error */))
+		return FALSE;
+
+	gchar *datasave = NULL;
+	for (const gchar *line = strtok_r(data, "\r\n", &datasave); line;
+			line = strtok_r(NULL, "\r\n", &datasave)) {
+		if (*line == '#')
+			continue;
+
+		// We do not support __NOGLOBS__, nor even parse out the "cs" flag.
+		// The weight is irrelevant.
+		gchar **f = g_strsplit(line, ":", 0);
+		if (g_strv_length(f) >= is_globs2 + 2) {
+			const gchar *type = f[is_globs2 + 0], *glob = f[is_globs2 + 1];
+			if (g_hash_table_contains(supported_set, type))
+				g_hash_table_add(output_set, g_utf8_strdown(glob, -1));
+		}
+		g_strfreev(f);
+	}
+	g_free(data);
+	return TRUE;
+}
+
+char **
+extract_mime_globs(const char **media_types)
+{
+	gchar **data_dirs = get_xdg_data_dirs();
+
+	// The mime.cache format is inconvenient to parse,
+	// we'll do it from the text files manually, and once only.
+	GHashTable *subclass_sets = g_hash_table_new_full(
+		g_str_hash, g_str_equal, g_free, (GDestroyNotify) g_hash_table_destroy);
+	for (gsize i = 0; data_dirs[i]; i++) {
+		gchar *path =
+			g_build_filename(data_dirs[i], "mime", "subclasses", NULL);
+		read_mime_subclasses(path, subclass_sets);
+		g_free(path);
+	}
+
+	// A hash set of all supported media types, including subclasses,
+	// but not aliases.
+	GHashTable *supported =
+		g_hash_table_new_full(g_str_hash, g_str_equal, g_free, NULL);
+	while (*media_types) {
+		add_applying_transitive_closure(
+			*media_types++, subclass_sets, supported);
+	}
+	g_hash_table_destroy(subclass_sets);
+
+	// We do not support the distinction of case-sensitive globs (:cs).
+	GHashTable *globs =
+		g_hash_table_new_full(g_str_hash, g_str_equal, g_free, NULL);
+	for (gsize i = 0; data_dirs[i]; i++) {
+		gchar *path2 = g_build_filename(data_dirs[i], "mime", "globs2", NULL);
+		gchar *path1 = g_build_filename(data_dirs[i], "mime", "globs", NULL);
+		if (!filter_mime_globs(path2, TRUE, supported, globs))
+			filter_mime_globs(path1, FALSE, supported, globs);
+		g_free(path2);
+		g_free(path1);
+	}
+	g_strfreev(data_dirs);
+	g_hash_table_destroy(supported);
+
+	gchar **result = (gchar **) g_hash_table_get_keys_as_array(globs, NULL);
+	g_hash_table_steal_all(globs);
+	g_hash_table_destroy(globs);
+	return result;
+}