Question

I have an embedded application which communicates with a RESTful server over HTTP. Some services involve sending some data to the client which is interpreted using a very simple lexer I wrote using flex.

Now I’m in the process of adding a gzip compression layer to reduce bandwidth consumption but I’m not satisfied with the current architecture because of the memory requirements: first I receive the whole data in a buffer, then I decompress the whole buffer into a new buffer and then I feed the whole data to flex.

I can save some memory between the first and second steps by feeding chunked data from the HTTP client to the zlib routines. But I’m wondering whether it’s possible to do the same between the zlib chunked output and the flex input.

Currently I use only yy_scan_bytes and yylex to analyze the input. Does flex have any feature to feed multiple chunks of data to yylex? I’ve read the documentation about multiple input buffers but to no avail.

Answer 1

YY_INPUT seems to be the correct answer:

The nature of how [the scanner] gets its input can be controlled by defining the
YY_INPUT macro. The calling sequence for YY_INPUT() is
YY_INPUT(buf,result,max_size). Its action is to place up to max_size
characters in the character array buf and return in the integer
variable result either the number of characters read or the constant
YY_NULL (0 on Unix systems) to indicate `EOF’.