Do not increase max_report_size by one if not using report numbers

Author: build

libusb/hid.c

@@ -297,6 +297,8 @@ static size_t get_max_report_size(uint8_t * report_descriptor, int desc_size, en
 	size_t cur_size = 0;
 	size_t max_size = 0;
 
+	int report_id_used = 0;
+
 	while (i < desc_size) {
 		int key = report_descriptor[i];
 		int key_cmd = key & 0xfc;
@@ -336,6 +338,7 @@ static size_t get_max_report_size(uint8_t * report_descriptor, int desc_size, en
 			cur_size += (report_count * report_size);
 		}
 		if (key_cmd == 0x84) { /* Report ID */
+			report_id_used = 1;
 			if (cur_size > max_size) {
 				max_size = cur_size;
 			}
@@ -355,8 +358,8 @@ static size_t get_max_report_size(uint8_t * report_descriptor, int desc_size, en
 		return 0;
 	} else {
 		/* report_size is in bits. Determine the total size convert to bytes
-		(rounded up), and add one byte for the report number. */
-		return ((max_size + 7) / 8) + 1;
+		(rounded up), and add one byte for the report number (if used). */
+		return ((max_size + 7) / 8) + report_id_used;
 	}
 }
 

libusb/test/max_input_report_size_test.c

@@ -21,6 +21,8 @@ static int parse_max_input_report_size(const char * filename, struct max_report_
 		return -1;
 	}
 
+	int has_report_id = 0;
+
 	char line[256];
 	{
 		while (fgets(line, sizeof(line), file) != NULL) {
@@ -34,11 +36,31 @@ static int parse_max_input_report_size(const char * filename, struct max_report_
 			if (sscanf(line, "pp_data->caps_info[2]->ReportByteLength   = %hu\n", &temp_ushort) == 1) {
 				sizes->feature = (size_t)temp_ushort;
 			}
+			if (sscanf(line, "pp_data->cap[%*hu]->ReportID                     = 0x%hu\n", &temp_ushort) == 1) {
+				if (temp_ushort) {
+					has_report_id = 1;
+				}
+			}
 		}
 	}
 
 	fclose(file);
 
+        // Windows includes ReportID byte in descriptor size even when it is not
+        // used. Our libusb calculation does not include it, so remove one byte
+        // from the sizes to make it match.
+        if (!has_report_id) {
+		if (sizes->input) {
+			sizes->input--;
+		}
+		if (sizes->output) {
+			sizes->output--;
+		}
+		if (sizes->feature) {
+			sizes->feature--;
+		}
+	}
+
 	return 0;
 }