2014-04-10 22:08 GMT+02:00 I?aki Baz Castillo <i...@aliax.net>: > Hi, > > I'm building a parser for a protocol message similar to HTTP (let's > say: a main header and N key: value separated by CRLF until a final > double CRLF). My concern is: > > - I parse the messages in a "Dispatcher" module that just needs to > parse a few fields in each message. > - Then the Dispatcher passes the message to a Worker thread via UNIX > Socket. - And the Worker must parse it again, but in this case I need all > the fields parsed. > > Note that during the Worker's parsing, a C++ complex object is build > with all the parsed fields mapped into member variables, so I don't > want to play with those complex objects in the Dispatcher module. > > How could I reuse the same Ragel machine for both cases? <snip>
Here's an example from my own code. For various reasons (expediency, simplicity) I used different machines to parse individual headers. But they all use the same library of tokenization sub-machines. The first machine is the basic library. You could put this in a separate file, but mine is in the same file as everything else HTTP/RTSP-related. The second and third machines are parser examples. Note that most of the context is missing, so you won't be able to copy+paste this. For example, I have a basic tokenizer written in pure C (which follows DJB's algorithm for structured MIME header parsing) which emits tagged characters as short integers (e.g. an escaped or quoted character will have a high bit set). This made it easier for me to handle things like quoted strings and parenthetical comments. Although, I wrote this years ago and today I might find it easier to handle those problems with Ragel's fcall and fgoto statments. But the truly beautiful thing about Ragel is how it allows you to mix-and-match approaches. So there's really no wrong way. And I would counsel a novice to avoid attempts at Ragel-purity--i.e. trying to do everything in Ragel, such as handle recursive structures directly in Ragel. You can do it (and I do it in some other stuff, like my Flash FLV, Microsoft ASF, and SMTP parsers), but it's not something worth struggling over. %%{ machine tokenizer; crlf = [\r\n]; lwsp = [ \t]; qdigit = (0x0130 - 0x0139); qxdigit = (0x0141 - 0x0146) | (0x0161 - 0x0166) | qdigit; digits = digit | qdigit; xdigits = xdigit | qxdigit; qalpha = (0x0141 - 0x015a) | (0x0161 | 0x017a); action num_begin { num = 0; } action num_write { num *= 10; num += (0xff & fc) - '0'; } action hex_begin { num = 0; } action hex_write { num <<= 4; num += ((0xff & fc) > '9')? (10 + (tolower((0xff & fc)) - 'a')) : (0xff & fc) - '0'; } action str_begin { str = 0; if ((error = obs_new(obs, 0))) goto error; } action str_write { if ((error = obs_putc(obs, 0xff & fc))) goto error; } action str_end { str = obs_top(obs); } }%% %%{ machine x_sessioncookie_parser; alphtype short; include tokenizer; action oops { rtsp_badparse("x-sessioncookie", src, len, p); error = EINVAL; goto error; } token = (alnum | "+" | "/")+ >str_begin $str_write %str_end %{ hdr->token = str; }; main := (token lwsp*) $!oops; write data; }%% %%{ machine content_type_parser; alphtype short; getkey (0xff & (*fpc)); # Mask high-order bits. include tokenizer; action oops { rtsp_badparse("Content-Type", src, len, p); error = EINVAL; goto error; } equal = lwsp** "=" lwsp**; reg_name = (alnum | [!#$&.+\-\^_]){1,127}; # RFC 4288 4.2 charset = "charset" equal reg_name >str_begin $str_write %str_end %{ hdr->charset = str; }; boundary = "boundary" equal reg_name >str_begin $str_write %str_end %{ hdr->boundary = str; }; attrib = (charset | boundary)? <: ^";"**; type = reg_name >str_begin $str_write %str_end %{ hdr->type = str; }; subtype = reg_name >str_begin $str_write %str_end %{ hdr->subtype = str; }; main := (type "/" subtype lwsp** (";" lwsp** attrib)*) $!oops; write data; }%% _______________________________________________ ragel-users mailing list ragel-users@complang.org http://www.complang.org/mailman/listinfo/ragel-users