input_stream: add method _cheap_seeking()

Makefile.am

@@ -1063,6 +1063,7 @@ test_run_input_SOURCES = test/run_input.c \
 	src/io_thread.c src/io_thread.h \
 	src/conf.c src/tokenizer.c src/utils.c src/string_util.c\
 	src/Tag.cxx src/TagNames.c src/TagPool.cxx src/TagSave.cxx \
+	src/uri.c \
 	src/fd_util.c
 
 test_dump_text_file_LDADD = \
@@ -1075,6 +1076,7 @@ test_dump_text_file_SOURCES = test/dump_text_file.c \
 	src/conf.c src/tokenizer.c src/utils.c src/string_util.c\
 	src/Tag.cxx src/TagNames.c src/TagPool.cxx \
 	src/text_input_stream.c src/fifo_buffer.c \
+	src/uri.c \
 	src/fd_util.c
 
 test_dump_playlist_LDADD = \

src/decoder/VorbisDecoderPlugin.cxx

@@ -139,9 +139,7 @@ vorbis_is_open(struct vorbis_input_stream *vis, OggVorbis_File *vf,
 {
 	vis->decoder = decoder;
 	vis->input_stream = input_stream;
-	vis->seekable = input_stream->seekable &&
-		(input_stream->uri == NULL ||
-		 !uri_has_scheme(input_stream->uri));
+	vis->seekable = input_stream_cheap_seeking(input_stream);
 
 	int ret = ov_open_callbacks(vis, vf, NULL, 0, vorbis_is_callbacks);
 	if (ret < 0) {

src/input_stream.c

@@ -22,6 +22,7 @@
 #include "input_registry.h"
 #include "input_plugin.h"
 #include "input/rewind_input_plugin.h"
+#include "uri.h"
 
 #include <glib.h>
 #include <assert.h>
@@ -115,6 +116,12 @@ input_stream_lock_wait_ready(struct input_stream *is)
 }
 
 bool
+input_stream_cheap_seeking(const struct input_stream *is)
+{
+	return is->seekable && (is->uri == NULL || !uri_has_scheme(is->uri));
+}
+
+bool
 input_stream_seek(struct input_stream *is, goffset offset, int whence,
 		  GError **error_r)
 {

src/input_stream.h

@@ -168,6 +168,13 @@ void
 input_stream_lock_wait_ready(struct input_stream *is);
 
 /**
+ * Determines whether seeking is cheap.  This is true for local files.
+ */
+gcc_pure gcc_nonnull(1)
+bool
+input_stream_cheap_seeking(const struct input_stream *is);
+
+/**
  * Seeks to the specified position in the stream.  This will most
  * likely fail if the "seekable" flag is false.
  *