$ cargo build

$ cargo build --release

$ cargo build --no-default-features

$ ./doh-client /path/to/the/ca/file.pem

# ./doh-client /etc/ca-certificates/extracted/tls-ca-bundle.pem

$ ./doh-client --help
DNS over HTTPS client 3.1.2
LinkTed <[email protected]>
Open a local UDP (DNS) port and forward DNS queries to a remote HTTP/2.0 server.
By default, the client will connect to the Cloudflare DNS service.
This binary uses the env_logger as logger implementations.
See https://github.com/sebasmagri/env_logger/

USAGE:
    doh-client [OPTIONS] [CAFILE]

ARGS:
    <CAFILE>    The path to the pem file, which contains the trusted CA certificates
                If no path is given then the platform's native certificate store will be used

OPTIONS:
    -c, --cache-size <UNSIGNED LONG>
            The size of the private HTTP cache
            If the size is 0 then the private HTTP cache is not used (ignores cache-control)
            [default: 1024]

        --cache-fallback
            Use expired cache entries if no response is received from the server

        --client-auth-certs <CERTSFILE>
            The path to the pem file, which contains the certificates for the client authentication

        --client-auth-key <KEYFILE>
            The path to the pem file, which contains the key for the client authentication

    -d, --domain <Domain>
            The domain name of the remote server [default: cloudflare-dns.com]

    -g, --get
            Use the GET method for the HTTP/2.0 request

    -h, --help
            Print help information

    -l, --listen-addr <Addr:Port>
            Listen address [default: 127.0.0.1:53]

        --listen-activation
            Use file descriptor 3 under Unix as UDP socket or launch_activate_socket() under Mac OS

    -p, --path <STRING>
            The path of the URI [default: dns-query]

        --proxy-credentials <Username:Password>
            The credentials for the proxy

        --proxy-host <Addr/Domain:Port>
            Socks5 or HTTP CONNECT proxy host (see below)

        --proxy-https-cafile <CAFILE>
            The path to the pem file, which contains the trusted CA certificates for the https proxy
            If no path is given then the platform's native certificate store will be used

        --proxy-https-domain <Domain>
            The domain name of the https proxy

        --proxy-scheme <proxy-scheme>
            The protocol of the proxy [possible values: socks5, socks5h, http, https]

    -r, --remote-host <Addr/Domain:Port>
            Remote address/domain to the DOH server (see below) [default: 1.1.1.1:443]

        --retries <UNSIGNED INT>
            The number of retries to connect to the remote server [default: 3]

    -t, --timeout <UNSIGNED LONG>
            The time in seconds after that the connection would be closed if no response is received
            from the server [default: 2]

    -V, --version
            Print version information

CAUTION: If a domain name is used for a <Addr/Domain:Port> value instead of an IP address the system
resolver will be used to resolve the IP address of the domain name. If the `doh-client` is
configured as system resolver, then it will NOT WORK. It is recommended to always use an IP address
for <Addr/Domain:Port> values.

$ dig github.com +nocookie

; <<>> DiG 9.13.5 <<>> github.com +nocookie
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 19752
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1452
;; QUESTION SECTION:
;github.com.            IN  A

;; ANSWER SECTION:
github.com.     8   IN  A   192.30.253.112
github.com.     8   IN  A   192.30.253.113

;; Query time: 35 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Sa Jan 05 20:00:20 CET 2019
;; MSG SIZE  rcvd: 71

$ dig github.com +nocookie

; <<>> DiG 9.13.5 <<>> github.com +nocookie
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 52653
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1452
;; QUESTION SECTION:
;github.com.            IN  A

;; ANSWER SECTION:
github.com.     8   IN  A   192.30.253.112
github.com.     8   IN  A   192.30.253.113

;; Query time: 0 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Sa Jan 05 20:00:21 CET 2019
;; MSG SIZE  rcvd: 71