feat: multiple audio fetchers support

res/modules/internal/bytearray.lua

@@ -14,6 +14,8 @@ FFI.cdef[[
 
 local malloc = FFI.C.malloc
 local free = FFI.C.free
+local FFIBytearray
+local bytearray_type
 
 local function grow_buffer(self, elems)
     local new_capacity = math.ceil(self.capacity / 0.75 + elems)
@@ -119,6 +121,20 @@ local function get_capacity(self)
     return self.capacity
 end
 
+local function sub(self, offset, length)
+    offset = offset or 1
+    length = length or (self.size - offset + 1)
+    if offset < 1 or offset > self.size then
+        return FFIBytearray(0)
+    end
+    if offset + length - 1 > self.size then
+        length = self.size - offset + 1
+    end
+    local buffer = malloc(length)
+    FFI.copy(buffer, self.bytes + (offset - 1), length)
+    return bytearray_type(buffer, length, length)
+end
+
 local bytearray_methods = {
     append=append,
     insert=insert,
@@ -127,6 +143,7 @@ local bytearray_methods = {
     clear=clear,
     reserve=reserve,
     get_capacity=get_capacity,
+    sub=sub,
 }
 
 local bytearray_mt = {
@@ -168,9 +185,9 @@ local bytearray_mt = {
 }
 bytearray_mt.__pairs = bytearray_mt.__ipairs
 
-local bytearray_type = FFI.metatype("bytearray_t", bytearray_mt)
+bytearray_type = FFI.metatype("bytearray_t", bytearray_mt)
 
-local FFIBytearray = {
+FFIBytearray = {
     __call = function (self, n)
         local t = type(n)
         if t == "string" then