core: stream: replaced cached cursor counter with a tell() function callback

core/include/blue/core/stream.h

@@ -45,6 +45,7 @@ typedef struct b_stream {
 
 	b_status (*s_close)(struct b_stream *);
 	b_status (*s_seek)(struct b_stream *, long long, b_stream_seek_origin);
+	b_status (*s_tell)(const struct b_stream *, size_t *);
 	b_status (*s_getc)(struct b_stream *, int *);
 	b_status (*s_read)(struct b_stream *, unsigned char *, size_t, size_t *);
 	b_status (*s_write)(

core/stream.c

@@ -68,23 +68,38 @@ static enum b_status stdio_seek(
 	return B_SUCCESS;
 }
 
+static enum b_status stdio_tell(const struct b_stream *stream, size_t *cursor)
+{
+	FILE *fp = stream->s_ptr;
+	long pos = ftell(fp);
+	if (pos == -1L) {
+		return B_ERR_NOT_SUPPORTED;
+	}
+
+	*cursor = (size_t)pos;
+	return B_SUCCESS;
+}
+
 static struct b_stream stdio[] = {
 	[IDX_STDIN] = {
 		.s_mode = B_STREAM_READ,
 		.s_read = stdio_read,
 		.s_seek = stdio_seek,
+		.s_tell = stdio_tell,
 		.s_ptr = NULL, /* set to stdin (stdio.h) at runtime */
 	},
 	[IDX_STDOUT] = {
 		.s_mode = B_STREAM_WRITE,
 		.s_write = stdio_write,
 		.s_seek = stdio_seek,
+		.s_tell = stdio_tell,
 		.s_ptr = NULL, /* set to stdout (stdio.h) at runtime */
 	},
 	[IDX_STDERR] = {
 		.s_mode = B_STREAM_WRITE,
 		.s_write = stdio_write,
 		.s_seek = stdio_seek,
+		.s_tell = stdio_tell,
 		.s_ptr = NULL, /* set to stderr (stdio.h) at runtime */
 	},
 };
@@ -169,6 +184,7 @@ struct b_stream *b_stream_open_fp(FILE *fp)
 	stream->s_read = stdio_read;
 	stream->s_write = stdio_write;
 	stream->s_seek = stdio_seek;
+	stream->s_tell = stdio_tell;
 
 	return stream;
 }
@@ -211,7 +227,17 @@ enum b_status b_stream_seek(
 
 size_t b_stream_cursor(const b_stream *stream)
 {
-	return stream->s_cursor;
+	if (!stream->s_tell) {
+		return 0;
+	}
+
+	size_t cursor = 0;
+	enum b_status status = stream->s_tell(stream, &cursor);
+	if (!B_OK(status)) {
+		return 0;
+	}
+
+	return cursor;
 }
 
 enum b_status b_stream_push_indent(b_stream *stream, int indent)