extract_metadata: parse "gcode_start_byte" and "gcode_end_byte"

Determine the byte location of the first and last gcode command (Either Mxxx or Gxxx commands).  This is useful for determining the portion of the file that consists of actual commands.

Signed-off-by:  Eric Callahan <arksine.code@gmail.com>

scripts/extract_metadata.py

@@ -56,9 +56,10 @@ class BaseSlicer(object):
         self.path = file_path
         self.header_data = self.footer_data = self.log = None
 
-    def set_data(self, header_data, footer_data, log):
+    def set_data(self, header_data, footer_data, fsize, log):
         self.header_data = header_data
         self.footer_data = footer_data
+        self.size = fsize
         self.log = log
 
     def _parse_min_float(self, pattern, data, strict=False):
@@ -78,6 +79,19 @@ class BaseSlicer(object):
     def check_identity(self, data):
         return None
 
+    def parse_gcode_start_byte(self):
+        m = re.search(r"\n[MG]\d+\s.*\n", self.header_data)
+        if m is None:
+            return None
+        return m.start()
+
+    def parse_gcode_end_byte(self):
+        rev_data = self.footer_data[::-1]
+        m = re.search(r"\n.*\s\d+[MG]\n", rev_data)
+        if m is None:
+            return None
+        return self.size - m.start()
+
     def parse_first_layer_height(self):
         return None
 
@@ -518,7 +532,8 @@ SUPPORTED_SLICERS = [
 SUPPORTED_DATA = [
     'first_layer_height', 'layer_height', 'object_height',
     'filament_total', 'estimated_time', 'thumbnails',
-    'first_layer_bed_temp', 'first_layer_extr_temp']
+    'first_layer_bed_temp', 'first_layer_extr_temp',
+    'gcode_start_byte', 'gcode_end_byte']
 
 def extract_metadata(file_path, log):
     metadata = {}
@@ -548,7 +563,7 @@ def extract_metadata(file_path, log):
             footer_data = header_data[remaining - READ_SIZE:] + f.read()
         else:
             footer_data = header_data
-        slicer.set_data(header_data, footer_data, log)
+        slicer.set_data(header_data, footer_data, size, log)
         for key in SUPPORTED_DATA:
             func = getattr(slicer, "parse_" + key)
             result = func()