Consider making AtDigester support echo off mode

[tmpfs]

Hi,

Great library! I am new to AT commands and just trying to figure out URC parsing. I thought disabling echo (with ATE0) would be a good idea to use less resources and send slightly less data over the UART however when i did that it seems impossible for me to get URC parsing working as intended.

I think the culprit is that the AtDigester assumes echo is enabled: https://github.com/FactbirdHQ/atat/blob/master/atat/src/digest.rs#L121-L125 which means that when echo is disabled more bytes are consumed and Parser::parse never gets called with the bytes it expects.

For now I have re-enabled echo with ATE1 and i can parse URC's ok but I wonder it there is an easy way to make AtDigester echo-aware so it could be used to parse URC when echo is disabled.

Thanks 🙏

[MathiasKoch]

It absolutely should work without echo.
We use it without echo in our thousands of deployed production devices.

[tmpfs]

Thanks @MathiasKoch, it's probably a problem my end but I can't figure out where the issue is.

I am testing with an ESP32 and sending AT+HTTPCGET, with echo on I can parse the +HTTPCGET: URC but with echo off, it fails. I have checked the logs of the ESP32 and in both cases it is sending exactly the same bytes. Perhaps it's a timing issue when the echo bytes are sent it delays just enough for the parsing to work?

This is what the logs look like when it works (echo on) (the final log of HTTP response is receiving the event on the UrcChannel):

0.000915 [INFO ] softdevice RAM: 29360 bytes (nrf_softdevice nrf-softdevice/src/fmt.rs:138)
3.502929 [INFO ] make GET request (http_test http_test/src/main.rs:161)
3.503784 [DEBUG] Sending command: b"AT+HTTPCGET=\"http://192.168.1.3:8080/get\"\r\n" (atat src/asynch/client.rs:56)
3.505737 [DEBUG] parse (raw): 1 b"\x00" (rac_core at/esp32/mod.rs:86)
3.506195 [DEBUG] parse_http_res: 1 b"\x00" (rac_core at/esp32/mod.rs:148)
3.552673 [DEBUG] parse (raw): 3 b"\x00AT" (rac_core at/esp32/mod.rs:86)
3.553192 [DEBUG] parse_http_res: 3 b"\x00AT" (rac_core at/esp32/mod.rs:148)
3.553833 [DEBUG] parse (raw): 16 b"\x00AT+HTTPCGET=\"ht" (rac_core at/esp32/mod.rs:86)
3.554595 [DEBUG] parse_http_res: 16 b"\x00AT+HTTPCGET=\"ht" (rac_core at/esp32/mod.rs:148)
3.556091 [DEBUG] parse (raw): 42 b"\x00AT+HTTPCGET=\"http://192.168.1.3:8080/get\"" (rac_core at/esp32/mod.rs:86)
3.557312 [DEBUG] parse_http_res: 42 b"\x00AT+HTTPCGET=\"http://192.168.1.3:8080/get\"" (rac_core at/esp32/mod.rs:148)
3.559326 [DEBUG] parse (raw): 2 b"\r\n" (rac_core at/esp32/mod.rs:86)
3.559814 [DEBUG] parse_http_res: 0 b"" (rac_core at/esp32/mod.rs:148)
3.560150 [DEBUG] Received echo or whitespace (42/44): b"\x00AT+HTTPCGET=\"http://192.168.1.3:8080/get\"\r\n" (atat atat/src/ingress.rs:228)
3.561462 [DEBUG] parse (raw): 2 b"\r\n" (rac_core at/esp32/mod.rs:86)
3.561950 [DEBUG] parse_http_res: 0 b"" (rac_core at/esp32/mod.rs:148)
5.154174 [DEBUG] parse (raw): 4 b"\r\n+H" (rac_core at/esp32/mod.rs:86)
5.154693 [DEBUG] parse_http_res: 2 b"+H" (rac_core at/esp32/mod.rs:148)
5.155334 [DEBUG] parse (raw): 17 b"\r\n+HTTPCGET:574,L" (rac_core at/esp32/mod.rs:86)
5.156127 [DEBUG] parse_http_res: 15 b"+HTTPCGET:574,L" (rac_core at/esp32/mod.rs:148)
5.156921 [DEBUG] http response length: 574 (rac_core at/esp32/mod.rs:175)
5.183685 [DEBUG] parse_http_res: 212 b"+HTTPCGET:574,Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type" (rac_core at/esp32/mod.rs:148)
5.187988 [DEBUG] http response length: 574 (rac_core at/esp32/mod.rs:175)
5.222442 [DEBUG] http response length: 574 (rac_core at/esp32/mod.rs:175)
5.245483 [DEBUG] http response length: 574 (rac_core at/esp32/mod.rs:175)
5.245788 [INFO ] parse URC b"+HTTPCGET:574,Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum." (rac_core at/esp32/mod.rs:68)
5.281463 [DEBUG] parse (raw): 8 b"\r\n\r\nOK\r\n" (rac_core at/esp32/mod.rs:86)
5.282196 [DEBUG] Received OK (10/10) (atat atat/src/ingress.rs:268)
5.283142 [INFO ] success (http_test http_test/src/main.rs:168)
5.283721 [INFO ] HTTP response: Get Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum. (http_test http_test/src/main.rs:87)

And then when i run with echo off I get:

0.000915 [INFO ] softdevice RAM: 29360 bytes (nrf_softdevice nrf-softdevice/src/fmt.rs:138)
3.502929 [DEBUG] Sending command: b"ATE0\r\n" (atat src/asynch/client.rs:56)
3.503997 [DEBUG] parse (raw): 1 b"\x00" (rac_core at/esp32/mod.rs:86)
3.504547 [DEBUG] parse_http_res: 1 b"\x00" (rac_core at/esp32/mod.rs:148)
3.512542 [DEBUG] parse (raw): 3 b"\x00AT" (rac_core at/esp32/mod.rs:86)
3.513061 [DEBUG] parse_http_res: 3 b"\x00AT" (rac_core at/esp32/mod.rs:148)
3.513702 [DEBUG] parse (raw): 2 b"\r\n" (rac_core at/esp32/mod.rs:86)
3.514190 [DEBUG] parse_http_res: 0 b"" (rac_core at/esp32/mod.rs:148)
3.514526 [DEBUG] Received echo or whitespace (5/7): b"\x00ATE0\r\n" (atat atat/src/ingress.rs:228)
3.515136 [DEBUG] parse (raw): 2 b"\r\n" (rac_core at/esp32/mod.rs:86)
3.515625 [DEBUG] parse_http_res: 0 b"" (rac_core at/esp32/mod.rs:148)
3.520355 [DEBUG] parse (raw): 4 b"\r\n\r\n" (rac_core at/esp32/mod.rs:86)
3.520904 [DEBUG] parse_http_res: 0 b"" (rac_core at/esp32/mod.rs:148)
3.521453 [DEBUG] parse (raw): 8 b"\r\n\r\nOK\r\n" (rac_core at/esp32/mod.rs:86)
3.522186 [DEBUG] Received OK (8/8) (atat atat/src/ingress.rs:268)
3.523162 [INFO ] ATE0 success (http_test http_test/src/main.rs:152)
3.523406 [INFO ] make GET request (http_test http_test/src/main.rs:159)
3.524230 [DEBUG] Sending command: b"AT+HTTPCGET=\"http://192.168.1.3:8080/get\"\r\n" (atat src/asynch/client.rs:56)
4.116668 [DEBUG] http response length: 574 (rac_core at/esp32/mod.rs:175)
4.117370 [DEBUG] parse (raw): 8 b"\r\n\r\nOK\r\n" (rac_core at/esp32/mod.rs:86)
4.118103 [DEBUG] Received OK (596/596) (atat atat/src/ingress.rs:268)
4.119110 [INFO ] success (http_test http_test/src/main.rs:166)

The interesting thing here is that after "Sending command" I don't see either the "parse (raw)" or "parse_http_res" logs that we see in the initial successful log output. The ingress/digester seems to be consuming all the 596 bytes into OK but the command is configured with NoResponse. If I try with echo off to provide a response like this:

#[derive(Clone, Debug, atat::atat_derive::AtatResp)]
pub struct GetResponse {
    pub content: String<1024>,
}

Then i get an error calling send().

I feel like I am misunderstanding something fundamental that would allow me to grok why there is such a big difference in behavior with parsing URCs when echo is on/off.

This is the output of the ESP32 for the AT command (it's the same in both cases):

D (337737) event: running post ESP_HTTP_CLIENT_EVENT:1 with handler 0x400eb464 and context 0x3ffd6f38 on loop 0x3ffc6768
D (337738) HTTP_CLIENT: Write header[2]: GET /get HTTP/1.1
User-Agent: ESP32 HTTP Client/1.0
Host: 192.168.1.3:8080


D (337754) event: running post ESP_HTTP_CLIENT_EVENT:2 with handler 0x400eb464 and context 0x3ffd6f38 on loop 0x3ffc6768
D (337763) HTTP_CLIENT: on_message_begin
D (337764) HTTP_CLIENT: HEADER=Server:tiny-http (Rust)
D (337767) event: running post ESP_HTTP_CLIENT_EVENT:3 with handler 0x400eb464 and context 0x3ffd6f38 on loop 0x3ffc6768
D (337778) HTTP_CLIENT: HEADER=Date:Mon, 23 Jun 2025 00:24:24 GMT
D (337783) event: running post ESP_HTTP_CLIENT_EVENT:3 with handler 0x400eb464 and context 0x3ffd6f38 on loop 0x3ffc6768
D (337794) HTTP_CLIENT: HEADER=Content-Type:text/plain
D (337799) event: running post ESP_HTTP_CLIENT_EVENT:3 with handler 0x400eb464 and context 0x3ffd6f38 on loop 0x3ffc6768
D (337810) HTTP_CLIENT: HEADER=Content-Length:574
D (337814) event: running post ESP_HTTP_CLIENT_EVENT:3 with handler 0x400eb464 and context 0x3ffd6f38 on loop 0x3ffc6768
D (337825) HTTP_CLIENT: http_on_headers_complete, status=200, offset=129, nread=129
D (337831) HTTP_CLIENT: http_on_body zu
I (337836) intf-tx: 0x3ffbb810   2b 48 54 54 50 43 47 45  54 3a 35 37 34 2c 4c 6f  |+HTTPCGET:574,Lo|
I (337844) intf-tx: 0x3ffbb820   72 65 6d 20 49 70 73 75  6d 20 69 73 20 73 69 6d  |rem Ipsum is sim|
I (337853) intf-tx: 0x3ffbb830   70 6c 79 20 64 75 6d 6d  79 20 74 65 78 74 20 6f  |ply dummy text o|
I (337862) intf-tx: 0x3ffbb840   66 20 74 68 65 20 70 72  69 6e 74 69 6e 67 20 61  |f the printing a|
I (337870) intf-tx: 0x3ffbb850   6e 64 20 74 79 70 65 73  65 74 74 69 6e 67 20 69  |nd typesetting i|
I (337879) intf-tx: 0x3ffbb860   6e 64 75 73 74 72 79 2e  20 4c 6f 72 65 6d 20 49  |ndustry. Lorem I|
I (337891) intf-tx: 0x3ffbb870   70 73 75 6d 20 68 61 73  20 62 65 65 6e 20 74 68  |psum has been th|
I (337897) intf-tx: 0x3ffbb880   65 20 69 6e 64 75 73 74  72 79 27 73 20 73 74 61  |e industry's sta|
I (337906) intf-tx: 0x3ffbb890   6e 64 61 72 64 20 64 75  6d 6d 79 20 74 65 78 74  |ndard dummy text|
I (337915) intf-tx: 0x3ffbb8a0   20 65 76 65 72 20 73 69  6e 63 65 20 74 68 65 20  | ever since the |
I (337924) intf-tx: 0x3ffbb8b0   31 35 30 30 73 2c 20 77  68 65 6e 20 61 6e 20 75  |1500s, when an u|
I (337933) intf-tx: 0x3ffbb8c0   6e 6b 6e 6f 77 6e 20 70  72 69 6e 74 65 72 20 74  |nknown printer t|
I (337942) intf-tx: 0x3ffbb8d0   6f 6f 6b 20 61 20 67 61  6c 6c 65 79 20 6f 66 20  |ook a galley of |
I (337950) intf-tx: 0x3ffbb8e0   74 79 70 65 20 61 6e 64  20 73 63 72 61 6d 62 6c  |type and scrambl|
I (337959) intf-tx: 0x3ffbb8f0   65 64 20 69 74 20 74 6f  20 6d 61 6b 65 20 61 20  |ed it to make a |
I (337968) intf-tx: 0x3ffbb900   74 79 70 65 20 73 70 65  63 69 6d 65 6e 20 62 6f  |type specimen bo|
I (337977) intf-tx: 0x3ffbb910   6f 6b 2e 20 49 74 20 68  61 73 20 73 75 72 76 69  |ok. It has survi|
I (337986) intf-tx: 0x3ffbb920   76 65 64 20 6e 6f 74 20  6f 6e 6c 79 20 66 69 76  |ved not only fiv|
I (337995) intf-tx: 0x3ffbb930   65 20 63 65 6e 74 75 72  69 65 73 2c 20 62 75 74  |e centuries, but|
I (338004) intf-tx: 0x3ffbb940   20 61 6c 73 6f 20 74 68  65 20 6c 65 61 70 20 69  | also the leap i|
I (338013) intf-tx: 0x3ffbb950   6e 74 6f 20 65 6c 65 63  74 72 6f 6e 69 63 20 74  |nto electronic t|
I (338021) intf-tx: 0x3ffbb960   79 70 65 73 65 74 74 69  6e 67 2c 20 72 65 6d 61  |ypesetting, rema|
I (338031) intf-tx: 0x3ffbb970   69 6e 69 6e 67 20 65 73  73 65 6e 74 69 61 6c 6c  |ining essentiall|
I (338039) intf-tx: 0x3ffbb980   79 20 75 6e 63 68 61 6e  67 65 64 2e 20 49 74 20  |y unchanged. It |
I (338048) intf-tx: 0x3ffbb990   77 61 73 20 70 6f 70 75  6c 61 72 69 73 65 64 20  |was popularised |
I (338057) intf-tx: 0x3ffbb9a0   69 6e 20 74 68 65 20 31  39 36 30 73 20 77 69 74  |in the 1960s wit|
I (338066) intf-tx: 0x3ffbb9b0   68 20 74 68 65 20 72 65  6c 65 61 73 65 20 6f 66  |h the release of|
I (338075) intf-tx: 0x3ffbb9c0   20 4c 65 74 72 61 73 65  74 20 73 68 65 65 74 73  | Letraset sheets|
I (338084) intf-tx: 0x3ffbb9d0   20 63 6f 6e 74 61 69 6e  69 6e 67 20 4c 6f 72 65  | containing Lore|
I (338093) intf-tx: 0x3ffbb9e0   6d 20 49 70 73 75 6d 20  70 61 73 73 61 67 65 73  |m Ipsum passages|
I (338101) intf-tx: 0x3ffbb9f0   2c 20 61 6e 64 20 6d 6f  72 65 20 72 65 63 65 6e  |, and more recen|
I (338110) intf-tx: 0x3ffbba00   74 6c 79 20 77 69 74 68  20 64 65 73 6b 74 6f 70  |tly with desktop|
I (338119) intf-tx: 0x3ffbba10   20 70 75 62 6c 69 73 68  69 6e 67 20 73 6f 66 74  | publishing soft|
I (338128) intf-tx: 0x3ffbba20   77 61 72 65 20 6c 69 6b  65 20 41 6c 64 75 73 20  |ware like Aldus |
I (338137) intf-tx: 0x3ffbba30   50 61 67 65 4d 61 6b 65  72 20 69 6e 63 6c 75 64  |PageMaker includ|
I (338146) intf-tx: 0x3ffbba40   69 6e 67 20 76 65 72 73  69 6f 6e 73 20 6f 66 20  |ing versions of |
I (338155) intf-tx: 0x3ffbba50   4c 6f 72 65 6d 20 49 70  73 75 6d 2e 0d 0a        |Lorem Ipsum...|
D (338165) event: running post ESP_HTTP_CLIENT_EVENT:4 with handler 0x400eb464 and context 0x3ffd6f38 on loop 0x3ffc6768
D (338174) HTTP_CLIENT: http_on_message_complete, parser=0x3ffd521c
D (338180) HTTP_CLIENT: content_length = ld
D (338184) event: running post ESP_HTTP_CLIENT_EVENT:5 with handler 0x400eb464 and context 0x3ffd6f38 on loop 0x3ffc6768
D (338195) event: running post ESP_HTTP_CLIENT_EVENT:6 with handler 0x400eb464 and context 0x3ffd6f38 on loop 0x3ffc6768
I (338212) intf-tx: 0x3f406018   0d 0a 4f 4b 0d 0a                                 |..OK..|

This is the function that parses the +HTTPCGET URC:

fn parse_http_response_bytes(buf: &[u8]) -> IResult<&[u8], usize> {
    debug!("parse_http_res: {} {}", buf.len(), LossyStr(buf));

    if buf.len() < 11 {
        return Err(nom::Err::Incomplete(Needed::Unknown));
    }

    let (remaining, _) = alt((
        complete::tag("+HTTPCGET:"),
        complete::tag("+HTTPCPOST:"),
    ))(buf)?;
    let (remaining, length_str) = streaming::take_until(",")(remaining)?;

    let length = core::str::from_utf8(length_str)
        .map_err(|_| {
            nom::Err::Error(nom::error::Error::new(
                buf,
                nom::error::ErrorKind::Verify,
            ))
        })?
        .parse::<usize>()
        .map_err(|_| {
            nom::Err::Error(nom::error::Error::new(
                buf,
                nom::error::ErrorKind::Verify,
            ))
        })?;

    debug!("http response length: {}", length);

    // HTTP response body length exceeds our limit.
    if length > BODY_MAX_LEN {
        return Err(nom::Err::Error(nom::error::Error::new(
            buf,
            nom::error::ErrorKind::TooLarge,
        )));
    }

    let (remaining, _) = streaming::tag(",")(remaining)?;
    let (remaining, _payload) = streaming::take(length)(remaining)?;

    let total_consumed = buf.len() - remaining.len();
    let matched_data = &buf[..total_consumed];

    Ok((matched_data, total_consumed))
}

[MathiasKoch]

I don't know if you are already using it, but you might be interested in https://github.com/FactbirdHQ/atat/blob/master/serde_at/src/de/length_delimited.rs