WIP optional field parsing

src/main.rs

@@ -1,24 +1,103 @@
 use nom::{
     IResult, 
+    branch::alt,
+    combinator::opt,
     character::complete::alphanumeric1,
+    character::complete::crlf,
+    character::complete::space0,
     bytes::complete::tag,
-    bytes::complete::take_until1,
+    bytes::complete::take_while1,
+    multi::many0,
+    sequence::terminated,
+    sequence::tuple,
 };
 
+//-------------- ABNF rfc5234
+
+/// Permissive CRLF
+///
+/// Theoretically, all lines must end with \r\n
+/// but mail servers support malformated emails,
+/// for example with only \n eol. It works because
+/// \r\n is allowed nowhere else, so we also add this support.
+fn perm_crlf(input: &str) -> IResult<&str, &str> {
+    alt((crlf, tag("\r"), tag("\n")))(input)
+}
+
+// Note: WSP = SP / HTAB = %x20 / %x09
+// nom::*::space0 = *WSP
+// nom::*::space1 = 1*WSP
+
+/// Parse a folding white space
+///
+/// Folding white space are used for long headers splitted on multiple lines
+///
+/// ```abnf
+/// FWS             =   ([*WSP CRLF] 1*WSP) /  obs-FWS
+/// obs-FWS         =   1*WSP *(CRLF 1*WSP)
+/// ```
+fn fws(input: &str) -> IResult<&str, &str> {
+    let (input, _) = opt(terminated(space0, perm_crlf))(input)?;
+    // @FIXME: not implemented obs-FWS
+    space0(input)
+}
+
+/// Sequence of visible chars with the UTF-8 extension
+///
+/// ```abnf
+/// VCHAR   =  %x21-7E
+///            ; visible (printing) characters
+/// VCHAR   =/  UTF8-non-ascii
+/// SEQ     = 1*VCHAR
+///```
+fn vchar_seq(input: &str) -> IResult<&str, &str> {
+   take_while1(|c: char| (c >= '\x21' && c <= '\x7E') || !c.is_ascii())(input)
+}
+
+//--------------- HEADERS
+/// Optional Fields
+///
+/// Fields may appear in messages that are otherwise unspecified in this
+/// document.  They MUST conform to the syntax of an optional-field.
+/// This is a field name, made up of the printable US-ASCII characters
+/// except SP and colon, followed by a colon, followed by any text that
+/// conforms to the unstructured syntax.
+///
+/// https://www.rfc-editor.org/rfc/rfc5322.html#section-3.6.8
+///
+/// ```abnf
+/// optional-field  =   field-name ":" unstructured CRLF
+/// field-name      =   1*ftext
+/// ftext           =   %d33-57 /          ; Printable US-ASCII
+///                     %d59-126           ;  characters not including
+///                                        ;  ":".
+/// ```
 #[derive(Debug, PartialEq)]
-pub struct HeaderField {
-    pub name: String,
+pub struct OptionalField<'a> {
+    pub name: &'a str,
     pub body: String,
 }
 
-fn parse_header_field(input: &str) -> IResult<&str, HeaderField> {
-    let (input, name) = alphanumeric1(input)?;
-    let (input, _) = tag(": ")(input)?;
-    let (input, body) = take_until1("\r\n")(input)?;
-    Ok((input, HeaderField { name: name.to_string(), body: body.to_string() }))
+fn optional_field(input: &str) -> IResult<&str, OptionalField> {
+    let (input, name) = take_while1(|c| c >= '\x21' && c <= '\x7E' && c != '\x3A')(input)?;
+    let (input, _) = tag(":")(input)?;
+    let (input, body) = unstructured(input)?;
+    
+    Ok((input, OptionalField { name, body }))
+}
+
+/// Unstructured header field body
+///
+/// ```abnf
+/// unstructured    =   (*([FWS] VCHAR_SEQ) *WSP) / obs-unstruct
+/// ```
+fn unstructured(input: &str) -> IResult<&str, String> {
+    let (input, _) = many0(tuple((opt(fws), vchar_seq)))(input)?;
+    let (input, _) = space0(input)?;
+    Ok((input, "FIX ME".to_string()))
 }
 
 fn main() {
-    let header_fields = "Subject: Hello\r\n World";
-    println!("{:?}", parse_header_field(header_fields));
+    let header_fields = "Subject: Hello\r\n World\r\n";
+    println!("{:?}", optional_field(header_fields));
 }