[ragel-users] Writing a Telnet parser

[Adrian Thurston]

Have you tried leaving actions? It sounds like that is what you want.

-Adrian

On 10-09-29 10:34 AM, Jonathan Castello wrote:
> Hi Adrian,
>
> Thanks for your help. Actually, I know how I want to buffer them; the
> problem is actually extracting them when I want to. I need some way to
> extract the characters only when the next character isn't plain_text
> or there is no next character. I've tried adding an entry action to
> cr_sequence and iac_sequence, but that doesn't work when you reach the
> end of the subject data without seeing a CR or IAC. What I was hoping
> to do is maintain a 'left' pointer to the first plain_text character,
> and use fpc as the 'right' pointer when I reach the last contiguous
> plain_text character. Then I would pass the left pointer and the
> length of that contiguous stretch (fpc-left) to the user-provided
> callback.
>
> I could copy each character to a temporary buffer, but I was hoping to
> avoid extra allocations. I want to just pass pointers into the
> original block of text being parsed, so the calling code can do any
> copying and allocating required. My entry action attempt was the
> closest I could get: it would properly fire before a non plain_text
> sequence, but the major issue is that it wouldn't fire at all when it
> reached the end of the subject line.
>
> Thanks again,
> ~Jonathan
>
> On Wed, Sep 29, 2010 at 10:07 AM, Adrian Thurston
> <adrian.thurston at esentire.com>  wrote:
>> Hi Jonathan,
>>
>> Ragel does not do any buffering of text for you. It's up to you to decide
>> how you want to do that, then implement it yourself. There are a couple
>> options. You can copy text to a buffer as you move over characters, or you
>> can extract them from the input buffer when you need them. The first
>> approach is simpler and guaranteed to work without hitches. The second
>> technique is faster, but you have to consider buffer block boundaries.
>>
>> -Adrian
>>
>> On 10-09-28 08:30 PM, Jonathan Castello wrote:
>>>
>>> Hello,
>>>
>>> I'm building a Telnet parser using Ragel, and I'm having an issue
>>> making the actions do what I want. I've pasted the machine definition
>>> to a gist: http://gist.github.com/602242
>>>
>>> The issue is a little hard for me to describe, so I'll try to
>>> illustrate it as best as I can. If I have a stream of input, and some
>>> part of it is "abcdef<IAC><GA>ghi" (where<x>    is a mnemonic for a
>>> single byte), I want to emit events as such: text("abcdef"),
>>> command("<GA>"), text("ghi"). The caller provides callbacks, and I
>>> would pass the data to them as I interpret it.
>>>
>>> The problem is that I can't figure out how to define actions that
>>> would only trigger when the next character doesn't match plain_text
>>> (or there's no more data left to parse in that particular packet), so
>>> I can get that full stretch of characters. At the moment, I can only
>>> get text("a"), text("b"), text("c") etc. to work, i.e. one plain_text
>>> match at a time.
>>>
>>> I suspect the problem is that cr_sequence and iac_sequence are
>>> supposed to behave this way - they, too, match singular "terms" each
>>> time before returning to the start - but here I am, wanting to give
>>> plain_text special treatment. Am I even coming at this from the right
>>> angle?
>>>
>>> Thanks in advance for any advice!
>>> ~Jonathan Castello
>>>
>>> _______________________________________________
>>> ragel-users mailing list
>>> ragel-users at complang.org
>>> http://www.complang.org/mailman/listinfo/ragel-users
>>>
>>
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