Add peek buffer to io, hide file/buffer private functions

Implements peek buffer on top of the raw io read (with small storage
optimization). Hides implementation details of the file/buffer.

include/bh/io.h

@@ -5,6 +5,7 @@
 
 #define BH_IO_ERROR         0x0001
 #define BH_IO_EOF           0x0002
+#define BH_IO_UNIFIED       0x0004
 
 #define BH_IO_NONE          0x0000
 #define BH_IO_READ          0x0001
@@ -63,13 +64,30 @@ typedef struct bh_io_s
 {
     const bh_io_table_t *table;
     int flags;
+    struct
+    {
+        char *data;
+        size_t head;
+        size_t tail;
+        size_t size;
+        size_t capacity;
+    } buffer;
 } bh_io_t;
 
-bh_io_t *bh_io_new(bh_io_table_t *table,
-                   size_t size);
+void bh_io_destroy_base(bh_io_t *io);
+
+bh_io_t *bh_io_new(const bh_io_table_t *table,
+                   size_t size,
+                   int unified);
 
 void bh_io_free(bh_io_t *io);
 
+void bh_io_init(bh_io_t *io,
+                const bh_io_table_t *table,
+                int unified);
+
+void bh_io_destroy(bh_io_t *io);
+
 int bh_io_open(bh_io_t *io,
                int mode);
 
@@ -81,6 +99,9 @@ size_t bh_io_read(bh_io_t *io,
                   char *data,
                   size_t size);
 
+size_t bh_io_peek(bh_io_t *io,
+                  char *data,
+                  size_t size);
 
 size_t bh_io_write(bh_io_t *io,
                    const char* data,
@@ -97,7 +118,6 @@ bh_off_t bh_io_size(bh_io_t *io);
 
 bh_off_t bh_io_tell(bh_io_t *io);
 
-
 bh_off_t bh_io_available(bh_io_t *io);
 
 int bh_io_error(bh_io_t *io);