File extension lookup table - advice needed

Mike G · 2011-02-16 12:03

This is for a Spinneret web server project. The client requests a file resource via HTTP. It could be .htm, gif, whatever. In the response, I send back the proper content-type header. Currently, the logic is wrapped in a bunch of SPIN < if string1 == string2 …elseif…> logic blocks. I want to replace the IF blocks.

I started looking at a hash table but I would need 26^3 rows for 3 lowercase alpha characters. I only need around 30ish rows. I would like to do the same kind of look-up table method for HTTP response codes like “200 OK”.

If someone can point me in the right direction, that would be much appreciated.

MagIO2 · 2011-02-16 12:40

Are all extensions 3 letters? Then simply treat em like longs (4 bytes). Have a look at the SPIN instructions lookup/lookdown. You can use one of them (don't remember which one) to give a list of longs and it gives back the index of your current value inside of the list.

Phil Pilgrim (PhiPi) · 2011-02-16 12:45

If the requested filenames all derive from links in your webpages, you do not have to use standard file extensions. You could simply use .A, .B, .C, etc., if you like. That way the extension itself (after subtracting an offset) can index into a list of string addresses, each pointing to a different content-type.

-Phil

MagIO2 · 2011-02-16 13:01

Here is what I mean:

con
  HTML = "H"<<16+"T"<<8+"M"
  GIF  = "G"<<16+"I"<<8+"F"
  
pub testit | ext,idx

  ' this should copy the extension from wherever you have it in your code into a known long
  byte[@ext+3]:=0
  byte[@ext+2]:="H"
  byte[@ext+1]:="T"
  byte[@ext+0]:="M"

  ' here you will then find either an index of 1 to 2 in this case
  ' or a 0 if the extension is not found in the list
  idx:=lookdown( ext: HTML, GIF )

MagIO2 · 2011-02-16 13:38

After the lookdown you can do a lookup to get the right content-string:

  tmp:=lookup( idx: string("text/html"), string("media/gif",13) )

Mike G · 2011-02-17 19:11

After some thinking, I came up with the attached hashing scheme. A little re-factoring is in order but it works.

Thanks for your input!

File extension lookup table - advice needed

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