[ovs-dev,v3,01/18] python: add generic Key-Value parser

Most of ofproto and dpif flows are based on key-value pairs. These
key-value pairs can be represented in several ways, eg: key:value,
key=value, key(value).

Add the following classes that allow parsing of key-value strings:
* KeyValue: holds a key-value pair
* KeyMetadata: holds some metadata associated with a KeyValue such as
  the original key and value strings and their position in the global
  string
* KVParser: is able to parse a string and extract it's key-value pairs
  as KeyValue instances. Before creating the KeyValue instance it tries
  to decode the value via the KVDecoders
* KVDecoders holds a number of decoders that KVParser can use to decode
  key-value pairs. It accepts a dictionary of keys and callables to
  allow users to specify what decoder (i.e: callable) to use for each
  key

Also, flake8 seems to be incorrectly reporting an error (E203) in:
"slice[index + offset : index + offset]" which is PEP8 compliant. So,
ignore this error.

Signed-off-by: Adrian Moreno <amorenoz@redhat.com>
---
 Makefile.am                  |   3 +-
 python/automake.mk           |   6 +-
 python/ovs/flows/__init__.py |   0
 python/ovs/flows/decoders.py |  18 ++
 python/ovs/flows/kv.py       | 314 +++++++++++++++++++++++++++++++++++
 python/setup.py              |   2 +-
 6 files changed, 340 insertions(+), 3 deletions(-)
 create mode 100644 python/ovs/flows/__init__.py
 create mode 100644 python/ovs/flows/decoders.py
 create mode 100644 python/ovs/flows/kv.py

On 11 Mar 2022, at 16:21, Adrian Moreno wrote:

> Most of ofproto and dpif flows are based on key-value pairs. These
> key-value pairs can be represented in several ways, eg: key:value,
> key=value, key(value).
>
> Add the following classes that allow parsing of key-value strings:
> * KeyValue: holds a key-value pair
> * KeyMetadata: holds some metadata associated with a KeyValue such as
>   the original key and value strings and their position in the global
>   string
> * KVParser: is able to parse a string and extract it's key-value pairs
>   as KeyValue instances. Before creating the KeyValue instance it tries
>   to decode the value via the KVDecoders
> * KVDecoders holds a number of decoders that KVParser can use to decode
>   key-value pairs. It accepts a dictionary of keys and callables to
>   allow users to specify what decoder (i.e: callable) to use for each
>   key
>
> Also, flake8 seems to be incorrectly reporting an error (E203) in:
> "slice[index + offset : index + offset]" which is PEP8 compliant. So,
> ignore this error.
>
> Signed-off-by: Adrian Moreno <amorenoz@redhat.com>

Changes look good to me!

Acked-by: Eelco Chaudron <echaudro@redhat.com>

LGTM

Acked-by: Terry Wilson <twilson@redhat.com>

On Fri, Mar 11, 2022 at 9:22 AM Adrian Moreno <amorenoz@redhat.com> wrote:
>
> Most of ofproto and dpif flows are based on key-value pairs. These
> key-value pairs can be represented in several ways, eg: key:value,
> key=value, key(value).
>
> Add the following classes that allow parsing of key-value strings:
> * KeyValue: holds a key-value pair
> * KeyMetadata: holds some metadata associated with a KeyValue such as
>   the original key and value strings and their position in the global
>   string
> * KVParser: is able to parse a string and extract it's key-value pairs
>   as KeyValue instances. Before creating the KeyValue instance it tries
>   to decode the value via the KVDecoders
> * KVDecoders holds a number of decoders that KVParser can use to decode
>   key-value pairs. It accepts a dictionary of keys and callables to
>   allow users to specify what decoder (i.e: callable) to use for each
>   key
>
> Also, flake8 seems to be incorrectly reporting an error (E203) in:
> "slice[index + offset : index + offset]" which is PEP8 compliant. So,
> ignore this error.
>
> Signed-off-by: Adrian Moreno <amorenoz@redhat.com>
> ---
>  Makefile.am                  |   3 +-
>  python/automake.mk           |   6 +-
>  python/ovs/flows/__init__.py |   0
>  python/ovs/flows/decoders.py |  18 ++
>  python/ovs/flows/kv.py       | 314 +++++++++++++++++++++++++++++++++++
>  python/setup.py              |   2 +-
>  6 files changed, 340 insertions(+), 3 deletions(-)
>  create mode 100644 python/ovs/flows/__init__.py
>  create mode 100644 python/ovs/flows/decoders.py
>  create mode 100644 python/ovs/flows/kv.py
>
> diff --git a/Makefile.am b/Makefile.am
> index cb8076433..4f51d225e 100644
> --- a/Makefile.am
> +++ b/Makefile.am
> @@ -391,6 +391,7 @@ ALL_LOCAL += flake8-check
>  #   E128 continuation line under-indented for visual indent
>  #   E129 visually indented line with same indent as next logical line
>  #   E131 continuation line unaligned for hanging indent
> +#   E203 whitespace before ':'
>  #   E722 do not use bare except, specify exception instead
>  #   W503 line break before binary operator
>  #   W504 line break after binary operator
> @@ -403,7 +404,7 @@ ALL_LOCAL += flake8-check
>  #   H233 Python 3.x incompatible use of print operator
>  #   H238 old style class declaration, use new style (inherit from `object`)
>  FLAKE8_SELECT = H231,H232,H233,H238
> -FLAKE8_IGNORE = E121,E123,E125,E126,E127,E128,E129,E131,E722,W503,W504,F811,D,H,I
> +FLAKE8_IGNORE = E121,E123,E125,E126,E127,E128,E129,E131,E203,E722,W503,W504,F811,D,H,I
>  flake8-check: $(FLAKE8_PYFILES)
>         $(FLAKE8_WERROR)$(AM_V_GEN) \
>           src='$^' && \
> diff --git a/python/automake.mk b/python/automake.mk
> index 767512f17..7ce842d66 100644
> --- a/python/automake.mk
> +++ b/python/automake.mk
> @@ -16,7 +16,6 @@ ovs_pyfiles = \
>         python/ovs/compat/sortedcontainers/sorteddict.py \
>         python/ovs/compat/sortedcontainers/sortedset.py \
>         python/ovs/daemon.py \
> -       python/ovs/fcntl_win.py \
>         python/ovs/db/__init__.py \
>         python/ovs/db/custom_index.py \
>         python/ovs/db/data.py \
> @@ -26,6 +25,10 @@ ovs_pyfiles = \
>         python/ovs/db/schema.py \
>         python/ovs/db/types.py \
>         python/ovs/fatal_signal.py \
> +       python/ovs/fcntl_win.py \
> +       python/ovs/flows/__init__.py \
> +       python/ovs/flows/decoders.py \
> +       python/ovs/flows/kv.py \
>         python/ovs/json.py \
>         python/ovs/jsonrpc.py \
>         python/ovs/ovsuuid.py \
> @@ -42,6 +45,7 @@ ovs_pyfiles = \
>         python/ovs/version.py \
>         python/ovs/vlog.py \
>         python/ovs/winutils.py
> +
>  # These python files are used at build time but not runtime,
>  # so they are not installed.
>  EXTRA_DIST += \
> diff --git a/python/ovs/flows/__init__.py b/python/ovs/flows/__init__.py
> new file mode 100644
> index 000000000..e69de29bb
> diff --git a/python/ovs/flows/decoders.py b/python/ovs/flows/decoders.py
> new file mode 100644
> index 000000000..0c2259c76
> --- /dev/null
> +++ b/python/ovs/flows/decoders.py
> @@ -0,0 +1,18 @@
> +"""Defines helpful decoders that can be used to decode information from the
> +flows.
> +
> +A decoder is generally a callable that accepts a string and returns the value
> +object.
> +"""
> +
> +
> +def decode_default(value):
> +    """Default decoder.
> +
> +    It tries to convert into an integer value and, if it fails, just
> +    returns the string.
> +    """
> +    try:
> +        return int(value, 0)
> +    except ValueError:
> +        return value
> diff --git a/python/ovs/flows/kv.py b/python/ovs/flows/kv.py
> new file mode 100644
> index 000000000..9fd87c3cc
> --- /dev/null
> +++ b/python/ovs/flows/kv.py
> @@ -0,0 +1,314 @@
> +"""Common helper classes for flow Key-Value parsing."""
> +
> +import functools
> +import re
> +
> +from ovs.flows.decoders import decode_default
> +
> +
> +class ParseError(RuntimeError):
> +    """Exception raised when an error occurs during parsing."""
> +
> +    pass
> +
> +
> +class KeyMetadata(object):
> +    """Class for keeping key metadata.
> +
> +    Attributes:
> +        kpos (int): The position of the keyword in the parent string.
> +        vpos (int): The position of the value in the parent string.
> +        kstring (string): The keyword string as found in the flow string.
> +        vstring (string): The value as found in the flow string.
> +        delim (string): Optional, the string used as delimiter between the key
> +            and the value.
> +        end_delim (string): Optional, the string used as end delimiter
> +    """
> +
> +    def __init__(self, kpos, vpos, kstring, vstring, delim="", end_delim=""):
> +        """Constructor."""
> +        self.kpos = kpos
> +        self.vpos = vpos
> +        self.kstring = kstring
> +        self.vstring = vstring
> +        self.delim = delim
> +        self.end_delim = end_delim
> +
> +    def __str__(self):
> +        return "key: [{},{}), val:[{}, {})".format(
> +            self.kpos,
> +            self.kpos + len(self.kstring),
> +            self.vpos,
> +            self.vpos + len(self.vstring),
> +        )
> +
> +    def __repr__(self):
> +        return "{}('{}')".format(self.__class__.__name__, self)
> +
> +
> +class KeyValue(object):
> +    """Class for keeping key-value data.
> +
> +    Attributes:
> +        key (str): The key string.
> +        value (any): The value data.
> +        meta (KeyMetadata): The key metadata.
> +    """
> +
> +    def __init__(self, key, value, meta=None):
> +        """Constructor."""
> +        self.key = key
> +        self.value = value
> +        self.meta = meta
> +
> +    def __str__(self):
> +        return "{}: {} ({})".format(self.key, str(self.value), str(self.meta))
> +
> +    def __repr__(self):
> +        return "{}('{}')".format(self.__class__.__name__, self)
> +
> +
> +class KVDecoders(object):
> +    """KVDecoders class is used by KVParser to select how to decode the value
> +    of a specific keyword.
> +
> +    A decoder is simply a function that accepts a value string and returns
> +    the value objects to be stored.
> +    The returned value may be of any type.
> +
> +    Decoders may return a KeyValue instance to indicate that the keyword should
> +    also be modified to match the one provided in the returned KeyValue.
> +
> +    The decoder to be used will be selected using the key as an index. If not
> +    found, the default decoder will be used. If free keys are found (i.e:
> +    keys without a value), the default_free decoder will be used. For that
> +    reason, the default_free decoder, must return both the key and value to be
> +    stored.
> +
> +    Args:
> +        decoders (dict): Optional; A dictionary of decoders indexed by keyword.
> +        default (callable): Optional; A decoder used if a match is not found in
> +            configured decoders. If not provided, the default behavior is to
> +            try to decode the value into an integer and, if that fails,
> +            just return the string as-is.
> +        default_free (callable): Optional; The decoder used if a match is not
> +            found in configured decoders and it's a free value (e.g:
> +            a value without a key) Defaults to returning the free value as
> +            keyword and "True" as value.
> +            The callable must accept a string and return a key-value pair.
> +    """
> +
> +    def __init__(self, decoders=None, default=None, default_free=None):
> +        self._decoders = decoders or dict()
> +        self._default = default or decode_default
> +        self._default_free = default_free or self._default_free_decoder
> +
> +    def decode(self, keyword, value_str):
> +        """Decode a keyword and value.
> +
> +        Args:
> +            keyword (str): The keyword whose value is to be decoded.
> +            value_str (str): The value string.
> +
> +        Returns:
> +            The key (str) and value(any) to be stored.
> +        """
> +
> +        decoder = self._decoders.get(keyword)
> +        if decoder:
> +            result = decoder(value_str)
> +            if isinstance(result, KeyValue):
> +                keyword = result.key
> +                value = result.value
> +            else:
> +                value = result
> +
> +            return keyword, value
> +        else:
> +            if value_str:
> +                return keyword, self._default(value_str)
> +            else:
> +                return self._default_free(keyword)
> +
> +    @staticmethod
> +    def _default_free_decoder(key):
> +        """Default decoder for free keywords."""
> +        return key, True
> +
> +
> +delim_pattern = re.compile(r"(\(|=|:|,|\n|\r|\t)")
> +parenthesis = re.compile(r"(\(|\))")
> +end_pattern = re.compile(r"( |,|\n|\r|\t)")
> +separators = (" ", ",")
> +end_of_string = (",", "\n", "\t", "\r", "")
> +
> +
> +class KVParser(object):
> +    """KVParser parses a string looking for key-value pairs.
> +
> +    Args:
> +        string (str): The string to parse.
> +        decoders (KVDecoders): Optional; the KVDecoders instance to use.
> +    """
> +
> +    def __init__(self, string, decoders=None):
> +        """Constructor."""
> +        self._decoders = decoders or KVDecoders()
> +        self._keyval = list()
> +        self._string = string
> +
> +    def keys(self):
> +        return list(kv.key for kv in self._keyval)
> +
> +    def kv(self):
> +        return self._keyval
> +
> +    def __iter__(self):
> +        return iter(self._keyval)
> +
> +    def parse(self):
> +        """Parse the key-value pairs in string.
> +
> +        The input string is assumed to contain a list of comma (or space)
> +        separated key-value pairs.
> +
> +        Key-values pairs can have multiple different delimiters, eg:
> +            "key1:value1,key2=value2,key3(value3)".
> +
> +        Also, we can stumble upon a "free" keywords, e.g:
> +            "key1=value1,key2=value2,free_keyword".
> +        We consider this as keys without a value.
> +
> +        So, to parse the string we do the following until the end of the
> +        string is found:
> +
> +            1 - Skip any leading comma's or spaces.
> +            2 - Find the next delimiter (or end_of_string character).
> +            3 - Depending on the delimiter, obtain the key and the value.
> +                For instance, if the delimiter is "(", find the next matching
> +                ")".
> +            4 - Use the KVDecoders to decode the key-value.
> +            5 - Store the KeyValue object with the corresponding metadata.
> +
> +        Raises:
> +            ParseError if any parsing error occurs.
> +        """
> +        kpos = 0
> +        while kpos < len(self._string) and self._string[kpos] != "\n":
> +            keyword = ""
> +            delimiter = ""
> +            rest = ""
> +
> +            # 1. Skip separator characters.
> +            if self._string[kpos] in separators:
> +                kpos += 1
> +                continue
> +
> +            # 2. Find the next delimiter or end of string character.
> +            try:
> +                keyword, delimiter, rest = delim_pattern.split(
> +                    self._string[kpos:], 1
> +                )
> +            except ValueError:
> +                keyword = self._string[kpos:]  # Free keyword
> +
> +            # 3. Extract the value from the rest of the string.
> +            value_str = ""
> +            vpos = kpos + len(keyword) + 1
> +            end_delimiter = ""
> +
> +            if delimiter in ("=", ":"):
> +                # If the delimiter is ':' or '=', the end of the value is the
> +                # end of the string or a ', '.
> +                value_parts = end_pattern.split(rest, 1)
> +                value_str = value_parts[0]
> +                next_kpos = vpos + len(value_str)
> +
> +            elif delimiter == "(":
> +                # Find matching ")".
> +                level = 1
> +                index = 0
> +                value_parts = parenthesis.split(rest)
> +                for val in value_parts:
> +                    if val == "(":
> +                        level += 1
> +                    elif val == ")":
> +                        level -= 1
> +                    index += len(val)
> +                    if level == 0:
> +                        break
> +
> +                if level != 0:
> +                    raise ParseError(
> +                        "Error parsing string {}: "
> +                        "Failed to find matching ')' in {}".format(
> +                            self._string, rest
> +                        )
> +                    )
> +
> +                value_str = rest[: index - 1]
> +                next_kpos = vpos + len(value_str) + 1
> +                end_delimiter = ")"
> +
> +                # Exceptionally, if after the () we find -> {}, do not treat
> +                # the content of the parenthesis as the value, consider
> +                # ({})->{} as the string value.
> +                if index < len(rest) - 2 and rest[index : index + 2] == "->":
> +                    extra_val = rest[index + 2 :].split(",")[0]
> +                    value_str = "({})->{}".format(value_str, extra_val)
> +                    # remove the first "(".
> +                    vpos -= 1
> +                    next_kpos = vpos + len(value_str)
> +                    end_delimiter = ""
> +
> +            elif delimiter in end_of_string:
> +                # Key without a value.
> +                next_kpos = kpos + len(keyword)
> +                vpos = -1
> +
> +            # 4. Use KVDecoders to decode the key-value.
> +            try:
> +                key, val = self._decoders.decode(keyword, value_str)
> +            except Exception as e:
> +                raise ParseError(
> +                    "Error parsing key-value ({}, {})".format(
> +                        keyword, value_str
> +                    )
> +                ) from e
> +
> +            # Store the KeyValue object with the corresponding metadata.
> +            meta = KeyMetadata(
> +                kpos=kpos,
> +                vpos=vpos,
> +                kstring=keyword,
> +                vstring=value_str,
> +                delim=delimiter,
> +                end_delim=end_delimiter,
> +            )
> +
> +            self._keyval.append(KeyValue(key, val, meta))
> +
> +            kpos = next_kpos
> +
> +
> +def decode_nested_kv(decoders, value):
> +    """A key-value decoder that extracts nested key-value pairs and returns
> +    them in a dictionary.
> +
> +    Args:
> +        decoders (KVDecoders): The KVDecoders to use.
> +        value (str): The value string to decode.
> +    """
> +    if not value:
> +        # Mark as flag
> +        return True
> +
> +    parser = KVParser(value, decoders)
> +    parser.parse()
> +    return {kv.key: kv.value for kv in parser.kv()}
> +
> +
> +def nested_kv_decoder(decoders=None):
> +    """Helper function that creates a nested kv decoder with given
> +    KVDecoders."""
> +    return functools.partial(decode_nested_kv, decoders)
> diff --git a/python/setup.py b/python/setup.py
> index cfe01763f..0e6b0ea39 100644
> --- a/python/setup.py
> +++ b/python/setup.py
> @@ -71,7 +71,7 @@ setup_args = dict(
>      author='Open vSwitch',
>      author_email='dev@openvswitch.org',
>      packages=['ovs', 'ovs.compat', 'ovs.compat.sortedcontainers',
> -              'ovs.db', 'ovs.unixctl'],
> +              'ovs.db', 'ovs.unixctl', 'ovs.flows'],
>      keywords=['openvswitch', 'ovs', 'OVSDB'],
>      license='Apache 2.0',
>      classifiers=[
> --
> 2.34.1
>
> _______________________________________________
> dev mailing list
> dev@openvswitch.org
> https://mail.openvswitch.org/mailman/listinfo/ovs-dev
>

On 3/11/22 16:21, Adrian Moreno wrote:
> Most of ofproto and dpif flows are based on key-value pairs. These
> key-value pairs can be represented in several ways, eg: key:value,
> key=value, key(value).
> 
> Add the following classes that allow parsing of key-value strings:
> * KeyValue: holds a key-value pair
> * KeyMetadata: holds some metadata associated with a KeyValue such as
>   the original key and value strings and their position in the global
>   string
> * KVParser: is able to parse a string and extract it's key-value pairs
>   as KeyValue instances. Before creating the KeyValue instance it tries
>   to decode the value via the KVDecoders
> * KVDecoders holds a number of decoders that KVParser can use to decode
>   key-value pairs. It accepts a dictionary of keys and callables to
>   allow users to specify what decoder (i.e: callable) to use for each
>   key
> 
> Also, flake8 seems to be incorrectly reporting an error (E203) in:
> "slice[index + offset : index + offset]" which is PEP8 compliant. So,
> ignore this error.
> 
> Signed-off-by: Adrian Moreno <amorenoz@redhat.com>
> ---
>  Makefile.am                  |   3 +-
>  python/automake.mk           |   6 +-
>  python/ovs/flows/__init__.py |   0
>  python/ovs/flows/decoders.py |  18 ++
>  python/ovs/flows/kv.py       | 314 +++++++++++++++++++++++++++++++++++
>  python/setup.py              |   2 +-
>  6 files changed, 340 insertions(+), 3 deletions(-)
>  create mode 100644 python/ovs/flows/__init__.py
>  create mode 100644 python/ovs/flows/decoders.py
>  create mode 100644 python/ovs/flows/kv.py

Nit: Can we rename the library to just 'flow' instead of 'flows'?
Seems more natural this way.

Otherwise, I posted some comments on patches 11-14.  If you can
address those and post a new version, that would be great.
Thanks!

Best regards, Ilya Maximets.