On 11 Mar 2022, at 16:21, Adrian Moreno wrote:
> Some openflow or dpif flows encode their arguments in lists, eg:
> "some_action(arg1,arg2,arg3)". In order to decode this in a way that can
> be then stored and queried, add ListParser and ListDecoders classes
> that parse lists into KeyValue instances.
>
> The ListParser / ListDecoders mechanism is quite similar to KVParser and
> KVDecoders. Since the "key" of the different KeyValue objects is now
> ommited, it has to be provided by ListDecoders.
>
> For example, take the openflow action "resubmit" that can be written as:
>
> resubmit([port],[table][,ct])
>
> Can be decoded by creating a ListDecoders instance such as:
>
> ListDecoders([
> ("port", decode_default),
> ("table", decode_int),
> ("ct", decode_flag),
> ])
>
> Naturally, the order of the decoders must be kept.
>
> Acked-by: Eelco Chaudron <[email protected]>
> Signed-off-by: Adrian Moreno <[email protected]>
> ---
> python/automake.mk | 1 +
> python/ovs/flows/list.py | 121 +++++++++++++++++++++++++++++++++++++++
> 2 files changed, 122 insertions(+)
> create mode 100644 python/ovs/flows/list.py
>
> diff --git a/python/automake.mk b/python/automake.mk
> index 7ce842d66..73438d615 100644
> --- a/python/automake.mk
> +++ b/python/automake.mk
> @@ -29,6 +29,7 @@ ovs_pyfiles = \
> python/ovs/flows/__init__.py \
> python/ovs/flows/decoders.py \
> python/ovs/flows/kv.py \
> + python/ovs/flows/list.py \
> python/ovs/json.py \
> python/ovs/jsonrpc.py \
> python/ovs/ovsuuid.py \
> diff --git a/python/ovs/flows/list.py b/python/ovs/flows/list.py
> new file mode 100644
> index 000000000..57e7c5908
> --- /dev/null
> +++ b/python/ovs/flows/list.py
> @@ -0,0 +1,121 @@
> +import re
> +
> +from ovs.flows.kv import KeyValue, KeyMetadata, ParseError
> +from ovs.flows.decoders import decode_default
> +
> +
> +class ListDecoders(object):
> + """ListDecoders is used by ListParser to decode the elements in the list.
> +
> + A decoder is a function that accepts a value and returns its decoded
> + object.
> +
> + ListDecoders is initialized with a list of tuples that contains the
> + keyword and the decoding function associated with each position in the
> + list. The order is, therefore, important.
> +
> + Args:
> + decoders (list of tuples): Optional; a list of tuples.
> + The first element in the tuple is the keyword associated with the
> + value. The second element in the tuple is the decoder function.
> + """
> +
> + def __init__(self, decoders=None):
> + self._decoders = decoders or list()
> +
> + def decode(self, index, value_str):
> + """Decode the index'th element of the list.
> +
> + Args:
> + index (int): The position in the list of the element to decode.
> + value_str (str): The value string to decode.
> + """
> + if index < 0 or index >= len(self._decoders):
> + return self._default_decoder(index, value_str)
> +
> + try:
> + key = self._decoders[index][0]
> + value = self._decoders[index][1](value_str)
> + return key, value
> + except Exception as e:
> + raise ParseError(
> + "Failed to decode value_str {}: {}".format(value_str, str(e))
> + )
> +
> + @staticmethod
> + def _default_decoder(index, value):
> + key = "elem_{}".format(index)
> + return key, decode_default(value)
> +
> +
> +class ListParser(object):
> + """ListParser parses a list of values and stores them as key-value pairs.
> +
> + It uses a ListDecoders instance to decode each element in the list.
> +
> + Args:
> + string (str): The string to parse.
> + decoders (ListDecoders): Optional, the decoders to use.
> + delims (list): Optional, list of delimiters of the list. Defaults to
> + [','].
> + """
> + def __init__(self, string, decoders=None, delims=[","]):
> + self._string = string
> + self._decoders = decoders or ListDecoders()
> + self._keyval = list()
> + self._regexp = r"({})".format("|".join(delims))
> +
> + def kv(self):
> + return self._keyval
> +
> + def __iter__(self):
> + return iter(self._keyval)
> +
> + def parse(self):
> + """Parse the list in string.
> +
> + Raises:
> + ParseError if any parsing error occurs.
> + """
> + kpos = 0
> + index = 0
> + while kpos < len(self._string) and self._string[kpos] != "\n":
> + split_parts = re.split(self._regexp, self._string[kpos:], 1)
Was there a specific reason why the below code was removed? Are we accepting
the exception in this case?
-+ if len(split_parts) == 0:
-+ break
> + value_str = split_parts[0]
> +
> + key, value = self._decoders.decode(index, value_str)
> +
> + meta = KeyMetadata(
> + kpos=kpos,
> + vpos=kpos,
> + kstring=value_str,
> + vstring=value_str,
> + )
> + self._keyval.append(KeyValue(key, value, meta))
> +
> + kpos += len(value_str) + 1
> + index += 1
> +
> +
> +def decode_nested_list(decoders, value, delims=[","]):
> + """Decodes a string value that contains a list of elements and returns
> + them in a dictionary.
> +
> + Args:
> + decoders (ListDecoders): The ListDecoders to use.
> + value (str): The value string to decode.
> + delims (list(str)): Optional, the list of delimiters to use.
> + """
> + parser = ListParser(value, decoders, delims)
> + parser.parse()
> + return {kv.key: kv.value for kv in parser.kv()}
> +
> +
> +def nested_list_decoder(decoders=None, delims=[","]):
> + """Helper function that creates a nested list decoder with given
> + ListDecoders and delimiters.
> + """
> + def decoder(value):
> + return decode_nested_list(decoders, value, delims)
> +
> + return decoder
> --
> 2.34.1
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