A JSV.Resolver implementation that will fetch the schemas from the web with the help of the :httpc module.

This resolver requires a list of allowed URL prefixes to download from. It also needs a proper JSON library to decode fetched schemas:

• From Elixir 1.18, the JSON module is automatically available in the standard library.
• JSV can use Jason if listed in your dependencies with the "~> 1.0" requirement.

Schemas known by the JSV.Resolver.Embedded will be fetched from that module instead of being fetched from the web. Allowed prefixes are not needed for those schemas.

HTTPS downloads verify the server certificate and hostname against the operating system CA store, using :public_key.cacerts_get/0. Redirect responses fail the resolution with an error tuple; use the final URL directly in your schema references and allowed prefixes.

Options

This resolver supports the following options:

• :allowed_prefixes - This option is mandatory and contains the allowed prefixes to download from. Each prefix must be a full URL with the scheme, host and at least the root path, like https://example.com/. A URL is allowed when it begins with one of the prefixes. A prefix is validated when it is matched against a URL, and raises an ArgumentError at that point if it is malformed.
• :cache_dir - The path of a directory to cache downloaded resources. The default value can be retrieved with default_cache_dir/0 and is a JSV-specific directory in the user cache, given by :filename.basedir(:user_cache, "jsv"), with a fallback on the system temporary directory when the user cache location is undefined. The option also accepts false to disable that cache. Cache directories are created with 0700 permissions and files are written atomically. Note that there is no cache expiration mechanism.
• :max_body_size - The maximum size in bytes of a response body. Larger responses produce a {:body_too_large, url} error. Defaults to 10485760 (10 MiB).
• :request_timeout - The request timeout in milliseconds. Defaults to 30000.

Example

iex> resolver_opts = [allowed_prefixes: ["https://www.schemastore.org/"], cache_dir: "_build/custom/dir"]
iex> {:ok, _root} = JSV.build(%{"$ref": "https://www.schemastore.org/github-action.json"}, resolver: {JSV.Resolver.Httpc, resolver_opts})