I finished reading The Rust Programming Languange some time ago and I'm creating a simple http-server for the sake of teaching myself Rust.
In a function meant to parse a &[u8] and create a HttpRequest object, I noticed that a loop that should be parsing the headers is actually not updating some variables used to track the state of parsing:
pub fn parse_request(buffer: &[u8]) -> Result<HttpRequest, &'static str> {
let (mut line, mut curr_req_reader_pos) = next_req_line(buffer, 0);
let (method, path, version) = parse_method_path_and_version(&line)?;
let (line, curr_req_reader_pos) = next_req_line(buffer, curr_req_reader_pos);
//eprintln!("--- got next line: {}, {} ---", curr_req_reader_pos, String::from_utf8_lossy(line));
let mut headers = vec![];
let mut lel = 0;
while line.len() > 0 {
//eprintln!("LOOP");
let header = parse_header(&line);
eprintln!("--- parsed header: {} ---", String::from_utf8_lossy(line));
headers.push(header);
let (line, curr_req_reader_pos) = next_req_line(buffer, curr_req_reader_pos);
//eprintln!("--- got next line: {}, {} ---", curr_req_reader_pos, String::from_utf8_lossy(line));
let (line, curr_req_reader_pos) = next_req_line(buffer, curr_req_reader_pos);
//eprintln!("--- got next line: {}, {} ---", curr_req_reader_pos, String::from_utf8_lossy(line));
//eprintln!("LOOP");
lel += 10;
//break;
}
let (line, curr_req_reader_pos) = next_req_line(buffer, curr_req_reader_pos);
//eprintln!("--- got next line: {}, {} ---", curr_req_reader_pos, String::from_utf8_lossy(line));
//eprintln!("{}", lel);
let has_body;
match method.as_ref() {
"POST" | "PUT" | "PATCH" => has_body = true,
_ => has_body = true
};
let body;
if has_body {
let (line, curr_req_reader_pos) = next_req_line(buffer, curr_req_reader_pos);
body = String::from_utf8_lossy(line).to_string();
} else {
body = String::new();
}
Ok(HttpRequest {
method,
path,
version,
headers,
has_body,
body
})
}
There's also tests for each method:
#[test]
fn test_next_req_line() {
let req = "GET / HTTP/1.1\r\nContent-Length: 3\r\n\r\n\r\n\r\nlel".as_bytes();
let (mut lel, mut pos) = next_req_line(req, 0);
assert_eq!("GET / HTTP/1.1", String::from_utf8_lossy(lel));
assert!(lel.len() > 0);
assert_eq!(16, pos);
let (lel, pos) = next_req_line(req, pos);
assert_eq!("Content-Length: 3", String::from_utf8_lossy(lel));
assert!(lel.len() > 0);
assert_eq!(35, pos);
let (lel, pos) = next_req_line(req, pos);
assert_eq!("", String::from_utf8_lossy(lel));
assert!(lel.len() == 0);
assert_eq!(37, pos);
let (lel, pos) = next_req_line(req, pos);
assert_eq!("", String::from_utf8_lossy(lel));
assert!(lel.len() == 0);
let (lel, pos) = next_req_line(req, pos);
assert_eq!("", String::from_utf8_lossy(lel));
assert!(lel.len() == 0);
let (lel, pos) = next_req_line(req, pos);
assert_eq!("lel", String::from_utf8_lossy(lel));
assert!(lel.len() == 3);
}
#[test]
fn test_parse_request() {
let mut request = String::from("GET / HTTP/1.1\r\n");
request.push_str("Content-Length: 3\r\n");
request.push_str("\r\n");
request.push_str("lel");
let request = request.as_bytes();
match parse_request(&request) {
Ok(http_request) => {
assert_eq!(http_request.method, "GET");
assert_eq!(http_request.path, "/");
assert_eq!(http_request.version, "HTTP/1.1");
},
Err(_) => {
println!("Failed");
}
}
}
The commented lines are just to show what's happening, and that's where I saw this output:
Finished test [unoptimized + debuginfo] target(s) in 0.53s
Running target/debug/deps/rweb-6bbc2a3130f7e3d9
running 4 tests
test http::testing::test_next_req_line ... ok
test http::testing::test_parse_header ... ok
test http::testing::test_parse_method_path_and_version ... ok
--- parsed method path version ---
--- got next line: 35, Content-Length: 3 ---
LOOP
--- parsed header: Content-Length: 3 ---
--- got next line: 37, ---
--- got next line: 39, lel ---
LOOP
--- got next line: 37, ---
10
test http::testing::test_parse_request ... ok
test result: ok. 4 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
It seems that the while loop is not re-assigning the line and curr_req_reader_pos variables, but for me it made perfect sense to expect that the loop would update these variables and parse every header. However, it works perfecly outside a loop, as anyone can see in the tests.
I can't figure out why this happens with my current undertanding of Rust, why does it happen?
