OpenAPI 3.x.y - validation of runtime expression

[char0n]

We are currently not able to validate runtime expression. Ideally using already existing tool is ideal, but if we cannot find one we can still write one. I have created the parser and validator library here: https://github.com/char0n/openapi-runtime-expression

Implementation will apply both for OpenAPI 3.0.x and OpenAPI 3.1.x.

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The runtime expression is defined by the following ABNF syntax.

expression = ( "$url" / "$method" / "$statusCode" / "$request." source / "$response." source )
      source = ( header-reference / query-reference / path-reference / body-reference )
      header-reference = "header." token
      query-reference = "query." name  
      path-reference = "path." name
      body-reference = "body" ["#" json-pointer ]
      json-pointer    = *( "/" reference-token )
      reference-token = *( unescaped / escaped )
      unescaped       = %x00-2E / %x30-7D / %x7F-10FFFF
         ; %x2F ('/') and %x7E ('~') are excluded from 'unescaped'
      escaped         = "~" ( "0" / "1" )
        ; representing '~' and '/', respectively
      name = *( CHAR )
      token = 1*tchar
      tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" / "+" / "-" / "." /
        "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA

Here, json-pointer is taken from RFC6901, char from RFC7159 and token from RFC7230.

The name identifier is case-sensitive, whereas token is not.

The table below provides examples of runtime expressions and examples of their use in a value: