command/{Queue,File}Commands: drop "file:///" prefix for absolute paths

Requiring this prefix makes the client's intention very clear, but it
was too hard to understand why this prefix was needed.  Initially, my
intention was to differentiate from broken clients which prefix relate
URIs with a slash; once MPD allowed that.  In the past few years
however, MPD has disallowed that, and there was no significant
breakage (except for the "add /" special case which some clients
apparently still do).  So I figure it's about time to define that an
URI that begins with a slash points to an arbitrary file on the file
system.

NEWS

@@ -4,6 +4,7 @@ ver 0.20 (not yet released)
   - "search"/"find" have a "window" parameter
   - report song duration with milliseconds precision
   - "sticker find" can match sticker values
+  - drop the "file:///" prefix for absolute file paths
 * tags
   - ape, ogg: drop support for non-standard tag "album artist"
     affected filetypes: vorbis, flac, opus & all files with ape2 tags

doc/protocol.xml

@@ -1772,7 +1772,7 @@ OK
             <para>
               Clients that are connected via UNIX domain socket may
               use this command to read the tags of an arbitrary local
-              file (URI beginning with "file:///").
+              file (URI is an absolute path).
             </para>
           </listitem>
         </varlistentry>
@@ -1787,8 +1787,7 @@ OK
             <para>
               Read "comments" (i.e. key-value pairs) from the file
               specified by "URI".  This "URI" can be a path relative
-              to the music directory or a URL in the form
-              "file:///foo/bar.ogg".
+              to the music directory or an absolute path.
             </para>
             <para>
               This command may be used to list metadata of remote

src/command/FileCommands.cxx

@@ -202,11 +202,22 @@ read_file_comments(Client &client, const Path path_fs)
 
 }
 
+static const char *
+translate_uri(const char *uri)
+{
+	if (memcmp(uri, "file:///", 8) == 0)
+		/* drop the "file://", leave only an absolute path
+		   (starting with a slash) */
+		return uri + 7;
+
+	return uri;
+}
+
 CommandResult
 handle_read_comments(Client &client, ConstBuffer<const char *> args)
 {
 	assert(args.size == 1);
-	const char *const uri = args.front();
+	const char *const uri = translate_uri(args.front());
 
 	if (memcmp(uri, "file:///", 8) == 0) {
 		/* read comments from arbitrary local file */

src/command/QueueCommands.cxx

@@ -43,18 +43,13 @@
 #include <string.h>
 
 static const char *
-translate_uri(Client &client, const char *uri)
+translate_uri(const char *uri)
 {
 	if (memcmp(uri, "file:///", 8) == 0)
 		/* drop the "file://", leave only an absolute path
 		   (starting with a slash) */
 		return uri + 7;
 
-	if (PathTraitsUTF8::IsAbsolute(uri)) {
-		command_error(client, ACK_ERROR_NO_EXIST, "Malformed URI");
-		return nullptr;
-	}
-
 	return uri;
 }
 
@@ -70,9 +65,7 @@ handle_add(Client &client, ConstBuffer<const char *> args)
 		   here */
 		uri = "";
 
-	uri = translate_uri(client, uri);
-	if (uri == nullptr)
-		return CommandResult::ERROR;
+	uri = translate_uri(uri);
 
 	if (uri_has_scheme(uri) || PathTraitsUTF8::IsAbsolute(uri)) {
 		const SongLoader loader(client);
@@ -101,9 +94,7 @@ handle_add(Client &client, ConstBuffer<const char *> args)
 CommandResult
 handle_addid(Client &client, ConstBuffer<const char *> args)
 {
-	const char *const uri = translate_uri(client, args.front());
-	if (uri == nullptr)
-		return CommandResult::ERROR;
+	const char *const uri = translate_uri(args.front());
 
 	const SongLoader loader(client);
 	Error error;