Add escape/unescape helpers for regexes

- Add helpers for escape/unescape control characters used in regular
  expressions.

src/common/escape.rs

@@ -0,0 +1,37 @@
+//! Functions to escape/unescape control characters
+
+use aho_corasick::AhoCorasick;
+use anyhow::Result;
+
+const REGEX_CONTROL_CHARS: &[&str]
+    = &[ ".", "|", "(", ")", "*", "+", "?", "^", "$", "[", "]", "\\" ];
+const REGEX_ESCAPED_CHARS: &[&str]
+    = &[ "\\.", "\\|", "\\(", "\\)", "\\*", "\\+", "\\?", "\\^", "\\$", "\\[", "\\]", "\\\\" ];
+
+pub fn regex_ctrl_escape(value: &str) -> Result<String> {
+    let r = AhoCorasick::new(REGEX_CONTROL_CHARS)?;
+    Ok(r.replace_all(value, REGEX_ESCAPED_CHARS))
+}
+
+pub fn regex_ctrl_unescape(value: &str) -> Result<String> {
+    let r = AhoCorasick::new(REGEX_ESCAPED_CHARS)?;
+    Ok(r.replace_all(value, REGEX_CONTROL_CHARS))
+}
+
+#[cfg(test)]
+
+pub mod tests {
+
+    use super::*;
+
+    #[test]
+    fn regex_escape_test() -> Result<()> {
+        let original = "(\\.|[.abc])";
+        let escaped = regex_ctrl_escape(original)?;
+        let unescaped = regex_ctrl_unescape(&escaped)?;
+
+        assert_eq!("\\(\\\\\\.\\|\\[\\.abc\\]\\)", escaped);
+        assert_eq!(original, unescaped);
+        Ok(())
+    }
+}

src/common/mod.rs

@@ -0,0 +1 @@
+pub mod escape;

src/main.rs

@@ -18,6 +18,7 @@ pub mod crypto;
 pub mod mail;
 pub mod daemon;
 use daemon::Daemon;
+pub mod common;
 
 #[tokio::main]
 async fn main() {