The Fraidycat spec as I understand it

Kicks Condor’s Fraidycat is something that I’ve been working on porting to a self-hosted, headless Rust application for a while now. One of the things that makes this interestingRead “difficult." is its very type-fluid and apparently undocumented JSON format in which it stores parsing rules.

In order to determine how best to implement this, I need to write a specification for the format such as I understand it from reading the source. So here that is.

Resolver

A Resolver is a set of rules for parsing a document into an RSS feed. Here is Fraidycat’s Atom Resolver:

  "atom": {
    "namespaces": {
      "atom": "http://www.w3.org/2005/Atom",
      "fc": "http://fraidyc.at/ext/1.0",
      "media": "http://search.yahoo.com/mrss/"
    },
    "rules": {
      "entry": [
        {"var": "out:title", "op": "./atom:title/text()"},
        {"var": "out:html", "op": ["./atom:content[@type='html']", "./atom:content[@type='xhtml']"]},
        {"var": "out:url", "op": ["./atom:link[@type='text/html' and @rel='alternate'][1]/@href",
          "./atom:link[@rel='alternate' or @type='text/html'][1]/@href",
          "./atom:link[not(@rel)][1]/@href", "./atom:id/text()"], "mod": ["url"]},
        {"var": "out:graphic:thumb", "op": "./media:group/media:thumbnail[1]/@url"},
        {"var": "out:publishedAt", "op": ["./atom:published/text()", "./atom:updated/text()"], "mod": ["date"]},
        {"var": "out:updatedAt", "op": "./atom:updated/text()", "mod": ["date"]}
      ]
    },
    "acceptXml": [
      {"op": "//atom:feed", "acceptXml": [
        {"var": "out:title", "op": "./atom:title/text()"},
        {"var": "out:photos:avatar", "op": ["./atom:logo/text()", "./atom:link[@rel='avatar']/@href"], "mod": ["url"]},
        {"var": "out:description", "op": "./atom:subtitle/text()"},
        {"var": "out:url", "op": ["./atom:link[@type='text/html' and @rel='alternate'][1]/@href",
          "./atom:link[@rel='alternate' or @type='text/html'][1]/@href",
          "./atom:link[not(@rel)][1]/@href"],
          "mod": ["url"]},
        {"op": "./fc:status", "var": "out:status", "acceptHtml": [
          {"var": "out:label", "op": "@label"},
          {"var": "out:type", "op": "@type"},
          {"rule": "entry"}
        ]},
        {"op": "./atom:entry", "var": "out:posts", "acceptXml": [
          {"rule": "entry"}
        ]}
      ]}
    ]
  }

Element	Description
`acceptText`, `acceptHtml`, `acceptXml`, `acceptJson`	The script (sequence of Rules) with which to parse the document. A `Resolver` must either implement exactly one of these or implement `accept`; it cannot do both.
`accept`	A list of key names of `Resolver`s to attempt to divert to, in order. `Resolver`s implementing `accept` cannot implement any preprocessing fields (S: describe these.) They may post-process the result via `patch`.
`arguments`	An array of local variables to extract from the user-provided URL. Must be specified with `match`. Correspond, in order, to capturing groups in the `match` regex. “0” is used as the first element of the array to represent the unneeded global match `\0`.
`depends`	A list of key names of `Resolver`s to run before this one. Any local variables specified with `arguments` will be respected in the dependency’s execution environment.
`match`	A regex to match the URL against. Resolution will proceed only on a successful match. Capturing groups may be stored in variables using `arguments`.
`namespaces`	A mapping from XML namespaces to namespace URIs.
`patch`	A script (list of Rules) to run on the result of the `Resolver` diverted to with `accept`. Must be specified with `accept`.
`render`	???????
`request`	A list of headers. (S: What schema does this correspond to?) ???
`rules`	A collection of named scripts (lists of Rules.)
`url`	A URL to fetch the data from instead of the user-provided one, for instance to access an API instead of scraping a page. Respects local variables. Must be specified with `match`.

Rule

A Rule is a mapping from one or more nodes in the input document to a node in the output document.

Element	Description
`op`	A single selector or list of selectors to match against the input document.
`var`	A single path in the output document at which to store the result.
`acceptXml`, `acceptHtml`, `acceptJson`, `acceptText`	A script (sequence of Rules) to run on the result. `accept` is illegal.
`rule`	The name of a script (list of Rules) to divert to. Cannot be specified with any other field.
`mod`	A list of post-processing functions to run, in order. (S: document these.)

Table of Contents

Resolver

Rule