Rewrite the project

The previous project architecture was far too complicated and hard to
maintain. The new one is much more simple. Although procedural macros
are cools, they are a no-go on Rust-OpenSMTPD.

Reports and filter are implemented (except data-line) but untested.

src/parsers/mod.rs

@@ -0,0 +1,66 @@
+pub(crate) mod entry;
+pub(crate) mod handshake;
+pub(crate) mod parameters;
+
+use nom::branch::alt;
+use nom::bytes::streaming::{tag, take_while1};
+use nom::combinator::map_res;
+use nom::IResult;
+use std::str::FromStr;
+
+fn is_body_char(c: u8) -> bool {
+    !(c as char).is_control()
+}
+
+fn is_parameter_char(c: u8) -> bool {
+    is_body_char(c) && (c as char) != '|'
+}
+
+fn parse_string_parameter(input: &[u8]) -> IResult<&[u8], String> {
+    let (input, s) = take_while1(is_parameter_char)(input)?;
+    Ok((input, String::from_utf8(s.to_vec()).unwrap()))
+}
+
+fn parse_data_structure<T>(input: &[u8]) -> IResult<&[u8], T>
+where
+    T: FromStr,
+{
+    map_res(take_while1(is_parameter_char), |s: &[u8]| {
+        T::from_str(&String::from_utf8_lossy(s))
+    })(input)
+}
+
+fn parse_delimiter(input: &[u8]) -> IResult<&[u8], &[u8]> {
+    tag("|")(input)
+}
+
+fn parse_eol(input: &[u8]) -> IResult<&[u8], &[u8]> {
+    alt((tag("\r\n"), tag("\n")))(input)
+}
+
+fn parse_usize(input: &[u8]) -> IResult<&[u8], usize> {
+    map_res(take_while1(|c| (c as char).is_ascii_digit()), |s| {
+        usize::from_str_radix(&String::from_utf8_lossy(s), 10)
+    })(input)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::is_parameter_char;
+
+    #[test]
+    fn test_valid_parameter_char() {
+        let char_lst = "a0.:-_/";
+        for c in char_lst.bytes() {
+            assert!(is_parameter_char(c));
+        }
+    }
+
+    #[test]
+    fn test_invalid_parameter_char() {
+        let char_lst = "|\n";
+        for c in char_lst.bytes() {
+            assert!(!is_parameter_char(c));
+        }
+    }
+}