[ragel-users] Writing a Telnet parser

[Jonathan Castello]

I have, actually. If I have "plain_text %leaving", the leaving action
is still executed after every plain_text character, as the generated
graph seems to indicate. If I put %leaving after the telnet_stream
itself, the graph suggests that it's only executed on EOF, which will
never occur as I am processing a potentially infinite network stream.
(Because of this, I explicitly set eof = NULL in the code before "%%
write init", as the documentation suggests.)

~Jonathan

On Wed, Sep 29, 2010 at 10:43 AM, Adrian Thurston
<adrian.thurston at esentire.com> wrote:
> 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
>>>>
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>>>>
>>>
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>>
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