body() :: binary().

event() ::
    event_request_sent() |
    event_download_dismissed() |
    event_download_redirected() |
    event_download_failed_to_start() |
    event_download_started() |
    event_download_finished().

event_download_dismissed() :: {download_dismissed, full_http_response()}.

event_download_failed_to_start() ::
    {download_failed_to_start, reason_for_download_failing_to_start()}.

event_download_finished() ::
    {download_finished, BodySize :: non_neg_integer(), {ok, TrailingHeaders :: headers()}} |
    {download_finished, BodySize :: non_neg_integer(), {error, term()}} |
    {download_finished, BodySize :: non_neg_integer(), {error, timeout}}.

event_download_redirected() :: {download_redirected, redirection()}.

event_download_started() :: {download_started, headers()}.

event_request_sent() :: {request_sent, url(), headers()}.

full_http_response() :: {http, response_status(), headers(), body()}.

headers() :: [{string(), string()}].

msg() ::
    {event, event()} |
    {finished, {success, success()}} |
    {finished, dismissed} |
    {finished, {error, term()}}.

opt() ::
    {connect_timeout, timeout()} |
    {download_start_timeout, timeout()} |
    {idle_download_timeout, timeout()} |
    insecure |
    {insecure, boolean()} |
    {censor_query, CensoredKeys :: [atom()]}.

reason_for_download_failing_to_start() ::
    full_http_response() |
    too_many_redirections |
    {invalid_redirection, term()} |
    {error, term()} |
    timeout.

redirection() :: #{url := url(), permanence := permanent | temporary}.

response_status() :: {100..999, binary()}.

state() :: #state{}.

success() :: #{headers := headers(), body := binary()}.

url() :: string().