feat: Initial implementation

Signed-off-by: Jagoda Ślązak <jslazak@jslazak.com>

filtermail/src/config.rs

@@ -0,0 +1,73 @@
+//! Configuration file handling for filtermail.
+
+use serde::{Deserialize, Deserializer};
+use std::path::{Path, PathBuf};
+
+/// Chatmail configuration subset used by filtermail.
+#[derive(Debug, Clone, Deserialize)]
+pub struct Config {
+    pub filtermail_smtp_port: u16,
+    pub filtermail_smtp_port_incoming: u16,
+    pub postfix_reinject_port: u16,
+    pub postfix_reinject_port_incoming: u16,
+    pub max_message_size: usize,
+    pub max_user_send_per_minute: usize,
+    #[serde(default, deserialize_with = "deserialize_sequence")]
+    pub passthrough_senders: Vec<String>,
+    #[serde(default, deserialize_with = "deserialize_sequence")]
+    pub passthrough_recipients: Vec<String>,
+    mail_domain: String,
+    mailboxes_dir: Option<PathBuf>,
+}
+
+#[derive(Debug, Clone, Deserialize)]
+struct ConfigWrapper {
+    // The whole actual config is under `params` section.
+    pub params: Config,
+}
+
+/// Custom deserializer to parse space-separated strings into [`Vec<String>`].
+fn deserialize_sequence<'de, D>(deserializer: D) -> Result<Vec<String>, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    let s: Option<String> = Deserialize::deserialize(deserializer)?;
+    Ok(match s {
+        Some(v) => v
+            .split(' ')
+            .map(|item| item.trim().to_string())
+            .filter(|item| !item.is_empty())
+            .collect(),
+        None => Vec::new(),
+    })
+}
+
+impl Config {
+    /// Load configuration from a file.
+    pub fn from_file(path: impl AsRef<Path>) -> Result<Self, crate::error::Error> {
+        let content = std::fs::read_to_string(path)?;
+        let wrapped_config: ConfigWrapper = serini::from_str(&content)?;
+        Ok(wrapped_config.params)
+    }
+
+    /// Get the mailboxes directory, using defaulting to `/home/vmail/mail/<mail_domain>` if not set.
+    fn mailboxes_dir(&self) -> PathBuf {
+        match &self.mailboxes_dir {
+            Some(dir) => dir.clone(),
+            None => PathBuf::from(format!("/home/vmail/mail/{}", self.mail_domain)),
+        }
+    }
+
+    /// Check if not encrypted mail is allowed for the given address.
+    pub fn is_cleartext_ok(&self, addr: &str) -> bool {
+        if addr.is_empty() || !addr.contains('@') || addr.contains('/') {
+            return false;
+        }
+
+        let mut enforce_e2ee = self.mailboxes_dir();
+        enforce_e2ee.push(addr);
+        enforce_e2ee.push("enforceE2EEincoming");
+
+        !enforce_e2ee.exists()
+    }
+}