Merge pull request #56 from moyamo/yowsup-2

Add parser for spectrum configuration file

config.py

@@ -0,0 +1,118 @@
+# I'm guessing this is the format of the spectrum config file in BNF
+# <config_file> ::= <line>*
+# <line> ::= <space>* <expr> <space>* <newline> | <space*>
+# <expr> ::= <section> | <assignment>
+# <section> ::= [<identifier>*]
+# <assignment> ::= <identifier> <space>* = <space>* <value>
+
+
+class SpectrumConfig:
+	"""
+	Represents spectrum2 configuration options.
+	"""
+	def __init__(self, path_to_config_file):
+		"""
+		Initialises configuration file.
+
+		Args:
+			path_to_config_file: The absolute path to the configuration file.
+		"""
+		self.config_path = path_to_config_file
+		self.options = self.loadConfig(self.config_path)
+		# Load backend_logging information
+		self.options.update(self.loadConfig(self['logging.backend_config']))
+
+	def loadConfig(self, file_name):
+		section = {'a': ""} # Current section heading,
+		# It's a dictionary because variables in python closures can't be
+		# assigned to.
+		options = dict()
+		# Recursive descent parser
+		def consume_spaces(line):
+			i = 0
+			for c in line:
+				if c != ' ':
+					break
+				i += 1
+			return line[i:]
+
+		def read_identifier(line):
+			i = 0
+			for c in line:
+				if c == ' ' or c==']' or c=='[' or c=='=':
+					break
+				i += 1
+			# no identifier
+			if i == 0:
+				return (None, 'No identifier')
+			return (line[:i], line[i:])
+
+		def parse_section(line):
+			if len(line) == 0 or line[0] != '[':
+				return (None, 'expected [')
+			line = line[1:]
+			identifier, line = read_identifier(line)
+			if len(line) == 0 or line[0] != ']' or identifier is None:
+				return (None, line)
+			return (identifier, line[1:])
+
+		def parse_assignment(line):
+			key, line = read_identifier(line)
+			if key is None:
+				return (None, None, line)
+			line = consume_spaces(line)
+			if len(line) == 0 or line[0] != '=':
+				return (None, None, 'Expected =')
+			line = consume_spaces(line[1:])
+			value = line[:-1]
+			return (key, value, '\n')
+
+		def expr(line):
+			sec, newline = parse_section(line)
+			if sec is not None:
+				section['a'] = sec
+			else:
+				key, value, newline = parse_assignment(line)
+				if key is not None:
+					if section['a'] != '':
+						options[section['a'] + '.' + key] = value
+					else:
+						options[key] = value
+				else:
+					return (None, newline)
+			return (newline, None)
+
+		def parse_line(line, line_number):
+			line = consume_spaces(line)
+			if line == '\n':
+				return
+			newline, error = expr(line)
+			if newline is None:
+				raise ConfigParseError(str(line_number) + ': ' + error + ': ' + repr(line))
+			newline = consume_spaces(newline)
+			if newline != '\n':
+				raise ConfigParseError(str(line_number) + ': Expected newline got ' + repr(newline))
+
+		def strip_comments(line):
+			i = 0
+			for c in line:
+				if c == '#' or c == '\n':
+					break
+				i += 1
+			return line[:i] + '\n'
+
+		with open(file_name, 'r') as f:
+			i = 1
+			while True:
+				line = f.readline()
+				if line == '':
+					break
+				parse_line(strip_comments(line), i)
+				i += 1
+		return options
+
+	def __getitem__(self, key):
+		return self.options[key]
+
+class ConfigParseError(Exception):
+	pass