Hello list,
I have almost completed a predicate called ‘jread’ which parses a Java .class
file into a term that will allow me to create a database of all of the methods,
fields, superclass and interfaces for that class and ultimately create a
database for a complete “android.jar” file of any required API level.
I am, for educational purposes and my own learning, trying to build a system
like Hoogle/Hayoo for Android. I do a lot of Android and I wanted to create a
sytem I can wire into Emacs/IntelliJ or anything for that matter, a simple HTTP
server that can supply a list of methods that have a certain type signature
using a si mple query language. Searching by types it very very useful when
using Haskell and I wanted to improve my Prolog so I figured why not do
something like that in GNU Prolog? I have already started a simple HTTP library
in pure GNU Prolog as well but this comes first now.
Progress so far is good…if I run it like this from a folder containing the
unpacked android.jar file...
| ?- jread('javax/net/SocketFactory.class',X).
X =
javaclass(super('java/lang/Object'),class('javax/net/SocketFactory'),implements([]),
methods([method(access_flags(4),name('<init>'),returns('()V'),[attr(9,
[0,3,0,1,0,0,0,14,42,183,0,1,187,0,2,89,18,3,183,0,4,191,0,0,0,2,0,10,0,0,0,6,0,1,0,0,0
,4,0,11,0,0,0,12,0,1,0,0,0,14,0,12,0,13,0,0])]),method(access_flags(41),name(getDefault)
,returns('()Ljavax/net/SocketFactory;'),attr(9,0,3,0,0,0,0,0,10,187,0,2,89,18,3,183,0,4,
191,0,0,0,1,0,10,0,0,0,6,0,1,0,0,0,5])]),method(access_flags(1),name(createSocket),
returns('()Ljava/net/Socket;'),[attr(9,0,3,0,1,0,0,0,10,187,0,2,89,18,3,183,0,4,191,
0,0,0,2,0,10,0,0,0,6,0,1,0,0,0,6,0,11,0,0,0,12,0,1,0,0,0,10,0,12,0,13,0,0]),
attr(18,0,1,0,19])]),method(access_flags(1025),name(createSocket),
returns('(Ljava/lang/String;I)Ljava/net/Socket;'),[attr(18,[0,2,0,19,0,21])]),
method(access_flags(1025),name(createSocket),
returns('(Ljava/lang/String;ILjava/net/InetAddress;I)Ljava/net/Socket;’),
[attr(18,[0,2,0,19,0,21])]),method(access_flags(1025),name(createSocket),
returns('(Ljava/net/InetAddress;I)Ljava/net/Socket;’),[attr(18[0,1,0,19])]),method(access_flags(1025),name(createSocket),
returns('(Ljava/net/InetAddress;ILjava/net/InetAddress;I)Ljava/net/Socket;'),[attr(18,[0,1,0,19])])]))
?
The place I am at now is decoding the bit flags for the class (and eventually
the methods etc) into a term.
A typical value would be “1057” decimal, 0x421, this contains the flags:
ACC_PUBLIC 0x0001 Declared public; may be accessed from outside its
package.
ACC_FINAL 0x0010 Declared final; no subclasses allowed.
ACC_SUPER 0x0020 Treat superclass methods specially when invoked by the
invokespecial instruction.
ACC_INTERFACE 0x0200 Is an interface, not a class.
ACC_ABSTRACT 0x0400 Declared abstract; must not be instantiated.
ACC_SYNTHETIC 0x1000 Declared synthetic; not present in the source code.
ACC_ANNOTATION 0x2000 Declared as an annotation type.
ACC_ENUM 0x4000 Declared as an enum type.
So you can see that 0x421 means “ACC_PUBLIC, ACC_SUPER and ACC_ABSTRACT”. I
would like to produce a term something like this:
access_flags(public,super,abstract)
It’s not that I don’t know how to do it or that I can’t do it but I am not sure
what is the *most elegant* way to do it in Prolog! Heaven knows I have written
bit shifting loops to test for flags in a dozen languages but not in Prolog.
So, there’s the challenge, what is the most elegant way to turn a list of bits
into a list of atom terms. Ideally I would make the list of atoms a parameter
so that I can reuse it for the other flag based values.
Consider the gauntlet thrown! In the meantime I am continuing to research the
possibilities for myself. I will of course put it all on GitHub along with my
Redis client. I may even create a Redis database with the information!
:)
Sean.
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