http_parse_fold.rs

use std::convert::TryFrom;

#[derive(Debug, Copy, Clone)]
enum HttpMethod {
    GET,
    POST,
    PUT
}

impl TryFrom<String> for HttpMethod {
    type Error = &'static str;

    fn try_from(value: String) -> Result<Self, Self::Error> {
        use HttpMethod::*;
        match value.as_ref() {
            "GET" => Ok(GET),
            "POST" => Ok(POST),
            "PUT" => Ok(PUT),
            _ => Err("HTTP Method is invalid.")
        }
    }
}

#[derive(Debug, Clone)]
struct HttpHeader {
    method: HttpMethod,
    path: String
}

impl HttpHeader {
    fn new(method: HttpMethod, path: String) -> Self {
        HttpHeader {
            method, path
        }
    }
}

#[derive(Debug, Default, Clone)]
struct HttpHeaderBuilder {
    method: Option<HttpMethod>,
    path: Option<String>,
    state: Machine
}

impl TryFrom<HttpHeaderBuilder> for HttpHeader {
    type Error = &'static str;

    fn try_from(value: HttpHeaderBuilder) -> Result<Self, Self::Error> {
       if let Some(method) = value.method {
           if let Some(path) = value.path {
           Ok(HttpHeader::new(method, path))
       } else {
           Err("No HTTP Method found.")
       }
       } else {
           Err("No HTTP Method found.")
       }
       
       
    }
}

impl HttpHeaderBuilder {
    fn extract_value(&mut self, saved: String) {
        match self.state {
            Machine::METHOD => {
                match HttpMethod::try_from(saved) {
                    Ok(val) => self.method = Some(val),
                    Err(msg) => panic!(msg)
                };
                self.state = Machine::PATH;
            },
            Machine::PATH => {
                self.path = Some(saved);
                self.state = Machine::VERSION;
            }
            _ => {}
        }
    }
}

#[derive(Debug, Copy, Clone)]
enum Machine {
    METHOD,
    PATH,
    VERSION,
    FROM,
    USER_AGENT
}

impl Default for Machine {
    fn default() -> Machine {
        Machine::METHOD
    }
}


fn main() {
    let src = String::from("GET /path/file.html HTTP/1.0
From: someuser@jmarshall.com
User-Agent: HTTPTool/1.0");
    let ret:(HttpHeaderBuilder, String) = src.chars().fold((Default::default(), String::new()), |acc, curr| {
        let (mut header, mut saved) = acc;
        if curr.is_ascii_whitespace() {
            header.extract_value(saved);
            saved = String::new();
        } else {
            saved.push(curr);
        }
        (header, saved)
    });
    let header = HttpHeader::try_from(ret.0);
    dbg!(&header);
}