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Config Tokenizer

Tokenizing is the process of transforming input device configuration to a stream of the tokens. Tokenizer accepts raw config and yields lines of parsed tokens. For example, raw config::

interface Fa0/1 description Some interface ip address 10.0.0.1 255.255.255.0

converted into::

["interface", "Fa0/1"] ["interface", "Fa0/1", "description", "Some", "interface"] ["interface", "Fa0/1", "ip", "address", "10.0.0.1", "255.255.255.0"]

Tokenizer must fulfill following requirements:

  • Knows nothing about the meaning of config
  • Low memory usage. Output tokens must be yield whenever ready
  • Backward references should be avoided. Tokenizer should operate current window like a tape. Forward and backward rewinds must be avoided.
  • Output tokens should be grouped and analyzed easy
  • Original context should be preserved whenever possible. See at expanding interface Fa0/1 in following lines
  • Each line of tokens should be further processed independentently of each other

It may seems that you need separate tokenizer per each platform. Luckily you are not. Though various configuration format have different meaning, almost all them maintains some code style. Like some languages are indent-based (Python) and some are curly-bracket-based (C, PHP), and some even all-parenthesis (LISP), there are well distinguishable groups of syntaxes. So the real device configurations are groupped in large syntax families with very few exceptions. Usually you can choose one of existing tokenizers and apply some configuration rather than create own tokenizer for a new platform from zero ground.

Tokenizers

Builtin tokenizers are collected in the noc.core.confdb.tokenizer package. Tokenizer classes form an hierarchy:

graph TD base --> line line --> context context --> indent line --> curly base --> ini line --> routeros

line

line(eol="\n", tab_width=0, line_comment=None, inline_comment=None, keep_indent=False, string_quote=None, rewrite=None)

Basic tokenizer, converting line of config into line of tokens,
separating by spaces and
grouping strings together into single tokens and removing comments.
Line tokenizer is suitable when each line of configuration is
completely self-sufficient and does not depends on previous or
following lines.
Though usable by itself, usually used as base class for more
advanced tokenizers.

:param eol: End-of-line separator.
:param tab_width: When non-zero replace tabs with `tab_width` spaces
:param line_comment: When non-empty sets the sequence which
    starts whole-line comments. I.e. line containing starting spaces
    followed with `line_comment` are completely removed from output.
    (Like `!` in Cisco IOS comments)
:param inline_comment: When non-empty sets the sequence which
    starts inline comments. Unlike the `line_comments` which cover
    whole line, `inline_comment` yields non-empty parts of
    lines before `inline_comments`
    (Like `#` in Python or `//` in C).
:param keep_indent: When False removes leading spaces. When True retains
    leading spaces as single token containing only spaces.
:param string_quote: When non-empty group tokens together when
    enclosed in `string_quote`. (Like `"` in Python).
:param rewrite: List of tuples of (compiled regular expression, replacement)
    to fix input formatting glitches.

context

context(end_of_context=None, contexts=None, **kwargs)

Descendant of :ref:`line<dev-confdb-tokenizer-line>` tokenizer.
Adds extra ability to determine and stack current
contexts from previous lines and apply current
context to each output line of tokens automatically.

Accepts all parameters of :ref:`line<dev-confdb-tokenizer-line>`
with extra new parameters:

:param end_of_context: When non-empty sets explicit context
    termination sequence (Like `}` or `end`). When explicit context
    termination token found at the start of the line, current context
    closed and removed from stack of context and previous context
    became current
:param contexts: When non-empty sets a list of explicit start
    of context matching strings. When found from the start of the
    line the new context is automatically created and pushed to
    the top of the stack

indent

indent(end_of_context=None, **kwargs)

Descendant of :ref:`context<dev-confdb-tokenizer-context>`. Context
are detected by start of line indents, like the Python programming
language and the :ref:`IOS-like<profile-Cisco.IOS>` configs.

Accepts all parameters of :ref:`line<dev-confdb-tokenizer-context>`
but forcefully sets `keep_indent` parameter.

curly

curly(start_of_context="{", end_of_context="}", explicit_eol=None, **kwargs)

Descendant of :ref:`line<dev-confdb-tokenizer-line>` tokenizer.
Adds extra ability to determine and stack current
contexts from previous lines and apply current
context to each output line of tokens automatically.
Context are starting with `start_of_context` sequence
and closed by `end_of_context` sequence.
Unlike :ref:`context<dev-confdb-tokenizer-indent>` tokenizer
context starts and ends are always explicit. Name `curly`
hints to C-style programming languages with their curly braces `{}`
which is good choice for :ref:`JUNOS-line<profile-Juniper.JUNOS>` configs.

:param start_of_context: Explicit start of context sequence (Like `{`)
:param end_of_context: Explicit end of context sequence (Like `}`)

ini

ini()

Basic tokenizer capable of parsing Microsoft Windows INI files.
See Python's `ConfigParser <https://docs.python.org/2.7/library/configparser.html>`_
module for details

routeros

routeros()

Descendant of :ref:`line<dev-confdb-tokenizer-line>` tokenizer
adapted to handle :ref:`MikroTik RouterOS<profile-MikroTik.RouterOS>`
config

Profile Integration

Todo

Refer to Profile API

Following profile parameters are responsible for tokenizer configuration:

config_tokenizer

String containing name of config tokenizer to use. Refer to
:ref:`Tokenizers<dev-confdb-tokenizers>` section for possible values
and for recommendations.

config_tokenizer_settings

Optional dict, containing config tokenizer settings.
Refer to
:ref:`Tokenizers<dev-confdb-tokenizers>` section for possible
values explanation.

get_config_tokenizer(cls, object):

Classmethod returning actual config tokenizer name and its
settings for selected managed object. Returns
(`config_tokenizer`, `config_tokenizer_settings`) by default.
Should be overriden in profile if tokenizer or settings
depends on platform or software version.

:param object: ManagedObject reference
:returns: tuple of (config tokenizer name, config tokenizer settings).
    Must return (None, None) if platform is not supported.

Custom Tokenizer API

Custom tokenizers must be inherited from noc.core.confdb.tokenizer.base.BaseTokenizer class or any of its descendancies. First you must define tokenizer name

 name
    Unique name of tokenizer.

Example::

class MyTokenizer(BaseTokenizer):
    name = "mytokenizer"

Tokenizer configuration passed as parameters to class constructor.

init(self, data, param1=default1, .., paramN=defaultN)

    :param data: String containing device configuration
    :param param1: Custom configuration parameter #1 with default value
    :param paramN: Custom configuration parameter #N with default value

It is advised to call superclass' constructor::

class MyTokenizer(BaseTokenizer):
    ...
    def __init__(self, data, param1=default1, ...):
        super(MyTokenizer, self).__init__(data)

The actual tokenizer must be implemented in __iter__ method

iter(self):

    Iterator yielding tuples of tokens per each line. Tokenizer
    should analyze `self.data` variable and call `yield` operator
    per each matched line of tokens