x filter requests by method and endpoint
x parse query parameters (typed)
x re-serialize query parameters into upstream request URL
x method/body for denied requests
- create full request objects in tests
- bad request tests (parse error, disabled query types, etc)
- "completeness" over all the below query types and parameters
- real fatcat+scholar request tests
- minimize tokio feature flags
- see what other requests the default python and javascript client libraries use
- put ProxyConfig in Box? less cloning?
- config: TOML, env, args
    => separate parse schema from options schema
    => example file
- refactor unwrap() into error handling
- package/release
    => generate .deb file
    => Makefile
    => manpage
    => example config?
    => README
    => push git repo
- test in with https://search.qa.fatcat.wiki and observable (javascript)

parse method+path (index) -> which validation method
method+path+params+body -> status, upstream request


## general endpoints

- ping
    (?)
- basic info
    GET /
    (?)
- scroll
    POST /_search/scroll
- clear scroll
    DELETE /_search/scroll

## per-index endpoints

- basic info; mapping
    GET /<index>/_mapping
- count
    GET /<index>/_count
- get document
    GET /<index>/_doc/<_id>
    HEAD /<index>/_doc/<_id>
    GET /<index>/_source/<_id>
    HEAD /<index>/_source/<_id>
- search
    GET /<index>/_search
    POST /<index>/_search
- mapping

later:

- multi-get (`_mget`)
- multi-search (`_msearch`)

## query types

compound:
- bool
- boosting
- constant_score
    filter (query)
    boost (float, optional)

fulltext:
- match
    <field>
        (bare str allowed)
        query (str)
- match_phrase
    <field>
        (bare str allowed)
        value (str)
- multi_match
x query_string
- simple_query_string

term-level:
x exists
    field (str)
x ids
    values (array of str)
x prefix
x range
    <field>
        gt, gte, lt, lte: str or number
- NOT regex (?)
x term
    <field>
        value: str or number
x terms
    does not support "lookup" from other indices
    <field>
        (array of str or number)
x wildcard
    <field>
        value (str)
        boost (float, optional)
        rewrite (str, optional)
x match_all
    boost (float, optional)
x match_none
    boost (float, optional)


TODO:
- terms_set
- span queries
- fuzzy (configurable)

## additional stuff

- headers
    - HTTP content-encoding: gzip
    - content-type header; always JSON?
    - set "Via" header in responses (indicating proxy version/context)
- https://www.elastic.co/guide/en/elasticsearch/reference/current/common-options.html
- logging
- switch from 'url' to 'percent-encoding' (?)