Confusing serial.readUntil behaviour

[Parakleta]

Describe the bug

When using serial.readUntil to read delimited data, the returned string doesn't line up with the delimiters. I cannot figure out how it chooses what data to return. I have tried several different delimiters and the result is always the same.

To Reproduce
Steps to reproduce the behavior:

Load the following program:

serial.setWriteLinePadding(0)
basic.forever(function () {
    serial.writeLine("||" + serial.readUntil(serial.delimiters(Delimiters.Colon)) + "##")
})

Then using a terminal program, send the following text ab:cd:ef:

Expected behavior

I should get back the following strings ||ab##, ||cd##, and ||ef##.

Screenshots

I get the following output in Termite:

61 62 3a 63 64 3a 65 66 3a                       ab:cd:ef:       
7c 7c 61 62 3a 63 23 23 0d 0a 7c 7c 23 23 0d 0a  ||ab:c##..||##..
7c 7c 65 66 23 23 0d 0a                          ||ef##..        

[abchatra]

@pelikhan can you answer this question?

[pelikhan]

It only works with the first character of the string.

[abchatra]

Questions answered

[Parakleta]

Sorry, but what does that mean?

[pelikhan]

Only the first character of the delimiter string is used, the rest is ignored.

[Parakleta]

How does that apply to the example I’ve given? I’m only using the colon character as a delimiter and it’s clearly not breaking at any consistent point

[pelikhan]

Sorry i read the sample wrong.

[abchatra]

@pelikhan is this is a bug?

[Parakleta]

Also curious to know what your basis for saying only the first delimiter character is used. It's not clear from the documentation about the readUntil method but the onDataReceived method clearly states "delimiters is a string containing any of the character to match" which suggests that it delimits on any matching character, and I would have assumed readUntil would operate the same way. Could you also please clarify this point since we're here?

[Parakleta]

I would assume anything with inconsistent behaviour is a bug, which is why I reported it. :)

[pelikhan]

Looks like a bug

…

________________________________ From: Abhijith Chatra ***@***.***> Sent: Friday, March 26, 2021 12:09:07 AM To: microsoft/pxt-microbit ***@***.***> Cc: Peli de Halleux ***@***.***>; Mention ***@***.***> Subject: Re: [microsoft/pxt-microbit] Confusing `serial.readUntil` behaviour (#3355) @pelikhan<https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fpelikhan&data=04%7C01%7Cjhalleux%40microsoft.com%7C84bb929182c846b10dea08d8efe2fe7f%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637523105502150810%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=IbMGl9qcepad1EfcgB3YLvQe3tknwcL2MUgI3ypeI2E%3D&reserved=0> is this is a bug? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub<https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fmicrosoft%2Fpxt-microbit%2Fissues%2F3355%23issuecomment-807691615&data=04%7C01%7Cjhalleux%40microsoft.com%7C84bb929182c846b10dea08d8efe2fe7f%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637523105502160804%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=YAv7DOPCpihRPfzt6Z5Zgrjj9vbM9Rc5VebvuBFPSV8%3D&reserved=0>, or unsubscribe<https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fnotifications%2Funsubscribe-auth%2FAA73QKMQ3YAZAZWNMSONDZ3TFO7BHANCNFSM4QOU7X4Q&data=04%7C01%7Cjhalleux%40microsoft.com%7C84bb929182c846b10dea08d8efe2fe7f%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637523105502160804%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=fK2wFpKkXC8OR4%2BUHkGPijA2kU2SDjLym0BG8oaKbMw%3D&reserved=0>.

[martinwork]

It's OK with V2 but not V1. I've created lancaster-university/microbit-dal#480

[abchatra]

this is a dal external issue.