livecheck currently doesn't support `POST` requests but it wasn't
entirely clear how best to handle that. I initially approached it as
a `Post` strategy but unfortunately that would have required us to
handle response body parsing (e.g., JSON, XML, etc.) in some fashion.
We could borrow some of the logic from related strategies but we would
still be stuck having to update `Post` whenever we add a strategy for
a new format.
Instead, this implements `POST` support by borrowing ideas from the
`using: :post` and `data` `url` options found in formulae. This uses
a `post_form` option to handle form data and `post_json` to handle
JSON data, encoding the hash argument for each into the appropriate
format. The presence of either option means that curl will use a
`POST` request.
With this approach, we can make a `POST` request using any strategy
that calls `Strategy::page_headers` or `::page_content` (directly or
indirectly) and everything else works the same as usual. The only
change needed in related strategies was to pass the options through
to the `Strategy` methods.
For example, if we need to parse a JSON response from a `POST`
request, we add a `post_data` or `post_json` hash to the `livecheck`
block `url` and use `strategy :json` with a `strategy` block. This
leans on existing patterns that we're already familiar with and
shouldn't require any notable maintenance burden when adding new
strategies, so it seems like a better approach than a `Post` strategy.
This updates the block-handling logic in `Json::versions_from_content`
to naively pass the regex value when the block has two parameters. Up
to now, we have been ensuring that `regex` is not `nil` and this
makes sense with existing usage (the `Crate` strategy's default
block, formulae/cask `strategy` blocks). However, we need to allow a
`nil` `regex` value to make it possible to add an optional `regex`
parameter in the `Pypi::DEFAULT_BLOCK` Proc. This is necessary to
allow the `Pypi` strategy to work with an optional regex from a
`livecheck` block again [without creating an additional
`DEFAULT_BLOCK` variant with a regex parameter].
This setup mimics the `#parse_xml` method that was implemented in the
`Xml` strategy. Isolating the parsing code means that other strategies
can take only what they need from `Json` (i.e., it's not required for
them to use `Json#find_versions`).
This adds a generic `Json` strategy to livecheck that requires a
`strategy` block to operate. This is primarily intended as a
replacement for existing `strategy` blocks in formulae/casks that
use `JSON#parse`, as it allows us to internalize/standardize that
boilerplate while improving error-handling.
Additionally, future strategies that parse JSON data can use the
`Json#find_versions` method instead of having to reinvent the wheel
(similar to how we currently have a number of strategies that
leverage `PageMatch#find_versions`).
