Has this been covered elsewhere? Filters are interesting.
|Replies are listed 'Best First'.|
Re^3: Production obfuscation
by eyepopslikeamosquito (Chancellor) on Apr 22, 2012 at 11:59 UTC
I've wondered what's the difference (functionality-wise) between Acme::EyeDrops and Acme::Bleach?I'm not aware of a detailed comparison between them. So I might write one as a top level node in the next week or so, if I can find the time (update: new top level node is The History of Acme::Bleach and Acme::EyeDrops).
Both EyeDrops and Bleach encode the source code. Bleach does so by converting the stream of bits in each source code character to spaces (0) and tabs (1) as indicated by this snippet from its source code:
In contrast, EyeDrops encodes each "unsightly" (i.e. alphanumeric) character by using a bitwise operator on two or more "sightly" (i.e. non-alphanumeric) ones. This is done via a lookup table as indicated by this snippet from its source code:
(See also the "Sightly Encoding" section in the Acme::EyeDrops documentation).
The big difference between the two approaches lies in the decoding. Because EyeDrops encodes into a form that perl can execute unaided, it simply lets perl decode it via eval and so does not require Acme::EyeDrops to be installed on the target system.
In contrast, perl by itself cannot make sense of a raw stream of spaces and tabs and so requires Acme::Bleach to be installed on the target system to decode and eval the "bitstream" of spaces and tabs.
As a consequence, Bleach has to be involved at compile time (which is why it overwrites the file and fiddles with $0). EyeDrops, on the other hand, does not mangle the original file, simply reads it and writes a new (encoded and shaped) one.
Put another way, Bleach is a Perl "source filter" (e.g. see Filter::Simple), while EyeDrops is not. EyeDrops is simply an encoder and shaper of the bytes in a source code file. The hardest part of writing EyeDrops was not the (sightly) encoding, but the heuristics required to pour the encoded bytes into a wide variety of shapes.
Thank you, sir, for your detailed explanation. The differences between the two are now perfectly clear.