def read(self):
"""
Wait for a JSON encoded message from the remote side.
The basic communication protocol is really simple:
1. First an ASCII encoded integer number is received, terminated by a
newline.
2. Second the number of bytes given by step 1 is read and interpreted
as a JSON encoded value. This step is not terminated by a newline.
That's it :-).
:returns: The JSON value decoded to a Python value.
:raises: :py:exc:`ProtocolError` when the remote side violates the
defined protocol.
"""
logger.debug("Waiting for message from other side ..")
# Wait for a line containing an integer byte count.
line = self.raw_readline().strip()
if not line.isdigit():
# Complain loudly about protocol errors :-).
raise ProtocolError(
compact("""
Received invalid input from remote side! I was expecting a
byte count, but what I got instead was the line {input}!
""",
input=repr(line)))
else:
# First we get a line containing a byte count, then we read
# that number of bytes from the remote side and decode it as a
# JSON encoded message.
num_bytes = int(line, 10)
logger.debug("Reading message of %i bytes ..", num_bytes)
encoded_value = self.raw_read(num_bytes)
try:
decoded_value = json.loads(encoded_value)
logger.debug("Parsed message: %s", decoded_value)
return decoded_value
except Exception as e:
logger.exception("Failed to parse JSON formatted message!")
raise ProtocolError(
compact("""
Failed to decode message from remote side as JSON!
Tried to decode message {message}. Original error:
{error}.
""",
message=repr(encoded_value),
error=str(e)))
def find_character_device(port_name):
"""
Find the character device for the given port name.
:param port_name: The name of the virtio port (a string).
:returns: The absolute pathname of a character device (a string).
:raises: :py:exc:`Exception` when the character device cannot be found.
"""
root = '/sys/class/virtio-ports'
logger.debug(
"Automatically selecting appropriate character device based on %s ..",
root)
for entry in os.listdir(root):
name_file = os.path.join(root, entry, 'name')
if os.path.isfile(name_file):
with open(name_file) as handle:
contents = handle.read().strip()
if contents == port_name:
character_device = '/dev/%s' % entry
logger.debug("Selected character device: %s", character_device)
return character_device
raise Exception(
compact("""
Failed to select the appropriate character device for the port name
{name}! This is probably caused by a configuration issue on either the
QEMU host or inside the QEMU guest. Please refer to the following web
page for help: http://negotiator.readthedocs.org/en/latest/#character-device-detection-fails
""",
name=repr(port_name)))
def find_character_device(port_name):
"""
Find the character device for the given port name.
:param port_name: The name of the virtio port (a string).
:returns: The absolute pathname of a character device (a string).
:raises: :py:exc:`Exception` when the character device cannot be found.
"""
root = '/sys/class/virtio-ports'
logger.debug("Automatically selecting appropriate character device based on %s ..", root)
for entry in os.listdir(root):
name_file = os.path.join(root, entry, 'name')
if os.path.isfile(name_file):
with open(name_file) as handle:
contents = handle.read().strip()
if contents == port_name:
character_device = '/dev/%s' % entry
logger.debug("Selected character device: %s", character_device)
return character_device
raise Exception(compact("""
Failed to select the appropriate character device for the port name
{name}! This is probably caused by a configuration issue on either the
QEMU host or inside the QEMU guest. Please refer to the following web
page for help: http://negotiator.readthedocs.org/en/latest/#character-device-detection-fails
""", name=repr(port_name)))
def read(self):
"""
Wait for a JSON encoded message from the remote side.
The basic communication protocol is really simple:
1. First an ASCII encoded integer number is received, terminated by a
newline.
2. Second the number of bytes given by step 1 is read and interpreted
as a JSON encoded value. This step is not terminated by a newline.
That's it :-).
:returns: The JSON value decoded to a Python value.
:raises: :exc:`ProtocolError` when the remote side violates the
defined protocol.
"""
logger.debug("Waiting for message from other side ..")
# Wait for a line containing an integer byte count.
line = self.raw_readline().strip()
if not line.isdigit():
# Complain loudly about protocol errors :-).
raise ProtocolError(compact("""
Received invalid input from remote side! I was expecting a
byte count, but what I got instead was the line {input}!
""", input=repr(line)))
else:
# First we get a line containing a byte count, then we read
# that number of bytes from the remote side and decode it as a
# JSON encoded message.
num_bytes = int(line, 10)
logger.debug("Reading message of %i bytes ..", num_bytes)
encoded_value = self.raw_read(num_bytes)
try:
decoded_value = json.loads(encoded_value)
logger.debug("Parsed message: %s", decoded_value)
return decoded_value
except Exception as e:
logger.exception("Failed to parse JSON formatted message!")
raise ProtocolError(compact("""
Failed to decode message from remote side as JSON!
Tried to decode message {message}. Original error:
{error}.
""", message=repr(encoded_value), error=str(e)))
