Parsing issues

[t-moe]

I discovered that the parser cannot handle a newline followed by a valid URC, which is needed to be able to recover from garbage data being received.

Here is the failing (new) testcase (digest.rs)

    #[test]
    fn newline_garbage_followed_by_urc() {
        let mut digester = AtDigester::<UrcTestParser>::new();
        let mut buf = heapless::Vec::<u8, TEST_RX_BUF_LEN>::new();

        buf.extend_from_slice(
            b"\r\naa\r\n+UUSORD: 0,5\r\n", // 20 bytes
        )
            .unwrap();
        let (res, bytes) = digester.digest(&buf);
        assert_eq!((res, bytes), (DigestResult::Urc(b"+UUSORD: 0,5"), 20)); // fails with (None, 0)
        buf.rotate_left(bytes);
        buf.truncate(buf.len() - bytes);
        assert!(buf.is_empty());
    }

I'm happy to investigate this a bit further and possibly provide a fix, but one question first:
Shouldn't digest return the number of consumed bytes? Or what is the 2nd part of the return tuple? The trait has no documentation...
Here is a reproducer:

    #[test]
    fn consumed_bytes_are_correct_with_prefixed_garbage() {
        let mut digester = AtDigester::<UrcTestParser>::new();
        let mut buf = heapless::Vec::<u8, TEST_RX_BUF_LEN>::new(
        buf.extend_from_slice(
            b"aaaa\r\n+UUSORD: 0,5\r\n", // 20 bytes
        )
            .unwrap();
        let (res, bytes) = digester.digest(&buf);

        assert_eq!((res, bytes), (DigestResult::Urc(b"+UUSORD: 0,5"), 20)); // fails. only 16 are consumed
        buf.rotate_left(bytes);
        buf.truncate(buf.len() - bytes);
        assert!(buf.is_empty()); // followup error
    }

EDIT: Ok the 2nd issue is probably fixed by:

diff --git a/atat/src/digest.rs b/atat/src/digest.rs
--- a/atat/src/digest.rs	(revision 242628d2ad2add452c909a036af036d83ea2fb5a)
+++ b/atat/src/digest.rs	(date 1727770394036)
@@ -128,7 +128,7 @@
 
         // 2. Match for URC's
         match P::parse(buf) {
-            Ok((urc, len)) => return (DigestResult::Urc(urc), len),
+            Ok((urc, len)) => return (DigestResult::Urc(urc), len + space_and_echo_bytes),
             Err(ParseError::Incomplete) => return incomplete,
             _ => {}
         }

EDIT: the 1st issue seems to be more tricky though

[TomDeRybel]

The #214 PR fixes a similar issue I've encountered with a u-blox NINA-W#214

This module sends the +STARTUP URC when it is done booting. This URC is preceded by a whole lot of start-up diagnostic messages, and the URC is not detected properly without the fix.

For completeness, here are the relevant log messages:
[2024-11-18T12:49:55.788462875Z DEBUG atat::ingress] Received echo or whitespace (24/32): "ets Jul 29 2019 12:21:46\r\n\r\nrst:"
[2024-11-18T12:49:56.735184632Z DEBUG atat::ingress] Received URC/128 (338/338): "+STARTUP"
[2024-11-18T12:49:56.735316114Z DEBUG atat::asynch::client] Sending command: "AT\r\n"
[2024-11-18T12:49:56.752052589Z DEBUG atat::ingress] Received OK (10/10)

Without the fix in the PR, the second line "Received URC/128 ... never occurs, and the URC is lost.