api!: remove hostname dependency

This change removes `ClientId::hostname()`.
If someone wants to send the hostname,
they have to configure it manually.

For clients default value "[127.0.0.1]"
is a better default as it does
not leak local hostname
and it works successfully
both in Delta Chat and TorBirdy for years.

Cargo.toml

@@ -22,7 +22,6 @@ anyhow = "1"
 async-std = { version = "1.11", features = ["unstable"], optional = true }
 base64 = "^0.13"
 futures = "0.3.21"
-hostname = "0.3.1"
 log = "^0.4"
 nom = "^7.0"
 thiserror = "1"

src/extension.rs

@@ -4,19 +4,11 @@ use crate::authentication::Mechanism;
 use crate::error::Error;
 use crate::response::Response;
 use crate::util::XText;
-use hostname;
 use std::collections::HashSet;
 use std::fmt::{self, Display, Formatter};
 use std::net::{Ipv4Addr, Ipv6Addr};
 use std::result::Result;
 
-/// Default client id.
-///
-/// It passes
-/// `smtpd_helo_restrictions = reject_non_fqdn_helo_hostname`
-/// Postfix check, but not `reject_unknown_helo_hostname`.
-const DEFAULT_DOMAIN_CLIENT_ID: &str = "localhost.localdomain";
-
 /// Client identifier, the parameter to `EHLO`
 #[derive(PartialEq, Eq, Clone, Debug)]
 pub enum ClientId {
@@ -57,17 +49,6 @@ impl ClientId {
     pub fn new(domain: String) -> ClientId {
         ClientId::Domain(domain)
     }
-
-    /// Defines a `ClientId` with the current hostname, or
-    /// `localhost.localdomain` if hostname could not be found.
-    pub fn hostname() -> ClientId {
-        ClientId::Domain(
-            hostname::get()
-                .ok()
-                .and_then(|s| s.into_string().ok())
-                .unwrap_or_else(|| DEFAULT_DOMAIN_CLIENT_ID.to_string()),
-        )
-    }
 }
 
 /// Supported ESMTP keywords