feat: optimize for reading a{sv} messages and headers (#98)

src/dbus_fast/_private/unmarshaller.pxd

@@ -50,10 +50,18 @@ cdef class Unmarshaller:
 
     cpdef read_uint32_cast(self, object type_)
 
+    cpdef read_string_unpack(self, object type_)
+
+    cdef _read_string_unpack(self)
+
+    cpdef read_string_cast(self, object type_)
+
     @cython.locals(
         buf_bytes=cython.bytearray,
     )
-    cpdef read_string_cast(self, object type_)
+    cdef _read_string_cast(self)
+
+    cdef _read_variant(self)
 
     @cython.locals(
         beginning_pos=cython.ulong,
@@ -61,16 +69,19 @@ cdef class Unmarshaller:
     )
     cpdef read_array(self, object type_)
 
+    cpdef read_signature(self, object type_)
+
     @cython.locals(
         o=cython.ulong,
         signature_len=cython.uint,
     )
-    cpdef read_signature(self, object type_)
+    cdef _read_signature(self)
 
     @cython.locals(
         endian=cython.uint,
         protocol_version=cython.uint,
-        can_cast=cython.bint
+        can_cast=cython.bint,
+        key=cython.str
     )
     cdef _read_header(self)
 

src/dbus_fast/_private/unmarshaller.py

@@ -253,6 +253,9 @@ class Unmarshaller:
 
     def read_string_cast(self, type_: SignatureType) -> str:
         """Read a string using cast."""
+        return self._read_string_cast()
+
+    def _read_string_cast(self) -> str:
         self._pos += UINT32_SIZE + (-self._pos & (UINT32_SIZE - 1))  # align
         str_start = self._pos
         # read terminating '\0' byte as well (str_length + 1)
@@ -261,6 +264,9 @@ class Unmarshaller:
         return self._buf[str_start : self._pos - 1].decode()
 
     def read_string_unpack(self, type_: SignatureType) -> str:
+        return self._read_string_unpack()
+
+    def _read_string_unpack(self) -> str:
         """Read a string using unpack."""
         self._pos += UINT32_SIZE + (-self._pos & (UINT32_SIZE - 1))  # align
         str_start = self._pos
@@ -269,6 +275,9 @@ class Unmarshaller:
         return self._buf[str_start : self._pos - 1].decode()
 
     def read_signature(self, type_: SignatureType) -> str:
+        return self._read_signature()
+
+    def _read_signature(self) -> str:
         signature_len = self._buf[self._pos]  # byte
         o = self._pos + 1
         # read terminating '\0' byte as well (str_length + 1)
@@ -276,7 +285,10 @@ class Unmarshaller:
         return self._buf[o : o + signature_len].decode()
 
     def read_variant(self, type_: SignatureType) -> Variant:
-        tree = get_signature_tree(self.read_signature(type_))
+        return self._read_variant()
+
+    def _read_variant(self) -> Variant:
+        tree = get_signature_tree(self._read_signature())
         signature_type = tree.types[0]
         # verify in Variant is only useful on construction not unmarshalling
         return Variant(
@@ -326,13 +338,28 @@ class Unmarshaller:
             beginning_pos = self._pos
             child_0 = child_type.children[0]
             child_1 = child_type.children[1]
-            reader_1 = self._readers[child_1.token]
-            reader_0 = self._readers[child_0.token]
+            child_0_token = child_0.token
+            child_1_token = child_1.token
+
+            # Strings with variant values are the most common case
+            # so we optimize for that by inlining the string reading
+            # and the variant reading here
+            if child_0_token in "os" and child_1_token == "v":
+                while self._pos - beginning_pos < array_length:
+                    self._pos += -self._pos & 7  # align 8
+                    if self._uint32_unpack:  # cannot cast
+                        key = self._read_string_unpack()
+                    else:
+                        key = self._read_string_cast()
+                    result_dict[key] = self._read_variant()
+            else:
+                reader_1 = self._readers[child_1_token]
+                reader_0 = self._readers[child_0_token]
+                while self._pos - beginning_pos < array_length:
+                    self._pos += -self._pos & 7  # align 8
+                    key = reader_0(self, child_0)
+                    result_dict[key] = reader_1(self, child_1)
 
-            while self._pos - beginning_pos < array_length:
-                self._pos += -self._pos & 7  # align 8
-                key = reader_0(self, child_0)
-                result_dict[key] = reader_1(self, child_1)
             return result_dict
 
         if array_length == 0:
@@ -357,13 +384,27 @@ class Unmarshaller:
             field_0 = buf[self._pos - 1]
 
             # Now read the v (variant) of struct (yv)
+            # first we read the signature
             signature_len = buf[self._pos]  # byte
             o = self._pos + 1
             self._pos += signature_len + 2  # one for the byte, one for the '\0'
             type_ = get_signature_tree(buf[o : o + signature_len].decode()).types[0]
-            headers[HEADER_MESSAGE_ARG_NAME[field_0]] = readers[type_.token](
-                self, type_
-            )
+            token = type_.token
+            # Now that we have the token we can read the variant value
+            key = HEADER_MESSAGE_ARG_NAME[field_0]
+            # Strings and signatures are the most common types
+            # so we inline them for performance
+            if token in "os":
+                if self._uint32_unpack:  # cannot cast
+                    headers[key] = self._read_string_unpack()
+                else:
+                    headers[key] = self._read_string_cast()
+            elif token == "g":
+                headers[key] = self._read_signature()
+            else:
+                # There shouldn't be any other types in the header
+                # but just in case, we'll read it using the slow path
+                headers[key] = readers[type_.token](self, type_)
         return headers
 
     def _read_header(self) -> None: