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#[derive(Debug)]
pub struct MailHeader<'a> {
key: &'a str,
value: &'a str,
}
#[derive(Debug)]
pub struct MailParseError {
description: String,
position: usize,
}
enum HeaderParseState {
Initial,
Key,
PreValue,
Value,
ValueNewline,
}
pub fn parse_header(raw_data: &str) -> Result<(MailHeader, usize), MailParseError> {
let mut it = raw_data.chars();
let mut ix = 0;
let mut c = match it.next() {
None => {
return Err(MailParseError {
description: "Empty string provided".to_string(),
position: 0,
})
}
Some(v) => v,
};
let mut ix_key_end = None;
let mut ix_value_start = 0;
let mut ix_value_end = 0;
let mut state = HeaderParseState::Initial;
loop {
match state {
HeaderParseState::Initial => {
if c == ' ' {
return Err(MailParseError {
description: "Header cannot start with a space; it is likely an \
overhanging line from a previous header"
.to_string(),
position: ix,
});
};
state = HeaderParseState::Key;
continue;
}
HeaderParseState::Key => {
if c == ':' {
ix_key_end = Some(ix);
state = HeaderParseState::PreValue;
} else if c == '\n' {
return Err(MailParseError {
description: "Unexpected newline in header key".to_string(),
position: ix,
});
}
}
HeaderParseState::PreValue => {
if c != ' ' {
ix_value_start = ix;
ix_value_end = ix;
state = HeaderParseState::Value;
continue;
}
}
HeaderParseState::Value => {
if c == '\n' {
state = HeaderParseState::ValueNewline;
} else {
ix_value_end = ix + 1;
}
}
HeaderParseState::ValueNewline => {
if c == ' ' {
state = HeaderParseState::Value;
continue;
} else {
break;
}
}
}
ix = ix + 1;
c = match it.next() {
None => break,
Some(v) => v,
};
}
match ix_key_end {
Some(v) => {
Ok((MailHeader {
key: &raw_data[0..v],
value: &raw_data[ix_value_start..ix_value_end],
},
ix))
}
None => {
Err(MailParseError {
description: "Unable to determine end of the header key component".to_string(),
position: ix,
})
}
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn parse_basic_header() {
let (parsed, _) = parse_header("Key: Value").unwrap();
assert_eq!(parsed.key, "Key");
assert_eq!(parsed.value, "Value");
let (parsed, _) = parse_header("Key : Value ").unwrap();
assert_eq!(parsed.key, "Key ");
assert_eq!(parsed.value, "Value ");
let (parsed, _) = parse_header("Key:").unwrap();
assert_eq!(parsed.key, "Key");
assert_eq!(parsed.value, "");
let (parsed, _) = parse_header(":\n").unwrap();
assert_eq!(parsed.key, "");
assert_eq!(parsed.value, "");
let (parsed, _) = parse_header("Key:Multi-line\n value").unwrap();
assert_eq!(parsed.key, "Key");
assert_eq!(parsed.value, "Multi-line\n value");
let (parsed, _) = parse_header("Key: Multi\n line\n value\n").unwrap();
assert_eq!(parsed.key, "Key");
assert_eq!(parsed.value, "Multi\n line\n value");
let (parsed, _) = parse_header("Key: One\nKey2: Two").unwrap();
assert_eq!(parsed.key, "Key");
assert_eq!(parsed.value, "One");
parse_header(" Leading: Space").unwrap_err();
parse_header("Just a string").unwrap_err();
parse_header("Key\nBroken: Value").unwrap_err();
}
}
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