From 8494ab2f2adfc0d3904f7259641ebc21b1fba218 Mon Sep 17 00:00:00 2001
From: Ihor Dutchak <>
Date: Thu, 21 Nov 2024 13:35:06 +0200
Subject: [PATCH] Optimize get_report_descriptor

- use HID_API_MAX_REPORT_DESCRIPTOR_SIZE from hidapi.h
- avoid dynamic memory allocation (use stack variable)
- replace list.append with direct list creation from memory view
---
 chid.pxd |  2 ++
 hid.pyx  | 28 ++++++++--------------------
 2 files changed, 10 insertions(+), 20 deletions(-)

diff --git a/chid.pxd b/chid.pxd
index 523a462..8d3c3ab 100644
--- a/chid.pxd
+++ b/chid.pxd
@@ -1,6 +1,8 @@
 from libc.stddef cimport wchar_t, size_t
 
 cdef extern from "<hidapi.h>":
+    const int HID_API_MAX_REPORT_DESCRIPTOR_SIZE
+
     ctypedef struct hid_device:
         pass
 
diff --git a/hid.pyx b/hid.pyx
index 38cc040..7c47032 100644
--- a/hid.pyx
+++ b/hid.pyx
@@ -330,12 +330,8 @@ cdef class device:
             result = hid_send_feature_report(c_hid, cbuff, c_buff_len)
         return result
 
-    def get_report_descriptor(self, int max_length=4096):
-        """Return the report descriptor up to max_length bytes.
-        If max_length is bigger than the actual descriptor, the full descriptor will be returned.
-
-        :param max_length: Maximum number of bytes to read, must be positive
-        :type max_length: int
+    def get_report_descriptor(self):
+        """Return the HID Report Descriptor for this device.
 
         :return:
         :rtype: List[int]
@@ -345,22 +341,14 @@ cdef class device:
         if self._c_hid == NULL:
             raise ValueError('not open')
 
-        cdef unsigned char* cbuff
-        cdef size_t c_descriptor_length = max(1, max_length)
+        cdef unsigned char cbuff[HID_API_MAX_REPORT_DESCRIPTOR_SIZE]
         cdef hid_device * c_hid = self._c_hid
         cdef int n
-        result = []
-        try:
-            cbuff = <unsigned char *>malloc(max_length)
-            with nogil:
-                n = hid_get_report_descriptor(c_hid, cbuff, c_descriptor_length)
-            if n < 0:
-                raise IOError('read error')
-            for i in range(n):
-                result.append(cbuff[i])
-        finally:
-            free(cbuff)
-        return result
+        with nogil:
+            n = hid_get_report_descriptor(c_hid, cbuff, sizeof(cbuff))
+        if n < 0:
+            raise IOError('read error')
+        return list(cbuff[:n])
 
     def get_feature_report(self, int report_num, int max_length):
         """Receive feature report.