JARs and JAR entries in ABCL
============================

Mark Evenson
Created: 09 JAN 2010
Modified: 24 JAN 2010

Notes towards sketching an implementation of "jar:" references to be
contained in PATHNAMEs within ABCL


Goals
-----

1.  Use Common Lisp pathnames to refer to entries in a JAR file.

    
2.  Use 'jar:' schema as documented in java.net.JarURLConnection for
    namestring representation.

An entry in a JAR file:
    #p"jar:file:baz.jar!/foo"
    
A JAR file:
    #p"jar:file:baz.jar!/"

A JAR file accessible via URL
    #p"jar:http://example.org/abcl.jar!/"

An entry in a ABCL FASL in a URL accessible JAR file
    #p"jar:jar:http://example.org/abcl.jar!/foo.abcl!/foo-1.cls"

3.  MERGE-PATHNAMES working for JAR entries

    (merge-pathnames "foo-1.cls" "jar:jar:file:baz.jar!/foo.abcl!/foo._")
    "jar:jar:file:baz.jar!/foo.abcl!/foo-1.cls"

    (merge-pathnames "foo-1.cls" "jar:file:foo.abcl!/")
    "jar:file:foo.abcl!/foo-1.cls"

4.  TRUENAME and PROBE-FILE working with "jar:" 

4.1  TRUENAME cannonicalizing the JAR reference.

5.  DIRECTORY working within JAR files (and within JAR in JAR).

6.  References "jar:<URL>" for all strings <URL> that java.net.URL can
    resolve works.


Implementation
--------------

Using PATHNAMES

*   A PATHNAME refering to a file within a JAR is known as a JAR
    PATHNAME.  It can either refer to the entire JAR file or an entry
    within the JAR file.

*   A JAR PATHNAME always has a DEVICE which is a proper list.  This
    distinguishes it from other uses of Pathname.  

*   The DEVICE of a JAR PATHNAME will be a list with either one or two
    elements.  The first element of the JAR PATHNAME can be either a
    PATHNAME representing a JAR on the filesystem, or a SimpleString
    representing a URL.

*   a PATHNAME occuring in the list in the DEVICE of a JAR PATHNAME is
    known as a DEVICE PATHNAME.

*   If the DEVICE is a String it must be a String that successfully
    constructs a URL via the java.net.URL(String) constructor

*   Only the first entry in the the DEVICE list may be a String.

*   Otherwise the the DEVICE PATHAME denotes the PATHNAME of the JAR file

*   The DEVICE PATHNAME list of enclosing JARs runs from outermost to
    innermost.
    


Use Cases
---------

// UC1 -- JAR
pathname: {
  namestring: "jar:file:foo/baz.jar!/"
  device: ( 
    pathname: {  
      device: "jar:file:"
      directory: (:RELATIVE "foo")
      name: "baz"
      type: "jar"
    }
  )
}


// UC1 -- JAR entry 
pathname: {
  namestring: "jar:file:baz.jar!/foo.abcl"
  device: ( pathname: {
    device: "jar:file:"
    name: "baz"
    type: "jar"
  }) 
  name: "foo"
  type: "abcl"
}


// UC3 -- JAR file in a JAR entry
pathname: {
  namestring: "jar:jar:file:baz.jar!/foo.abcl!/"
  device: ( 
    pathname: {
      name: "baz"
      type: "jar"
    }
    pathname: {
      name: "foo"
      type: "abcl"
    } 
  )
}

// UC4 -- JAR entry in a JAR entry with directories
pathname: {
  namestring: "jar:jar:file:a/baz.jar!/b/c/foo.abcl!/this/that/foo-20.cls"
  device: ( 
    pathname {
      directory: (:RELATIVE "a")      
      name: "bar"
      type: "jar"
    }
    pathname {
      directory: (:RELATIVE "b")
      name: "foo"
      type: "abcl"
    }
  )
  directory: (:RELATIVE "this" "that")
  name: "foo-20"
  type: "cls" 
}

// UC5 -- JAR Entry in a JAR Entry
pathname: {
  namestring: "jar:jar:file:a/foo/baz.jar!/foo.abcl!/a/b/bar-1.cls"
  device: (
    pathname: {
      device: "jar:file:"
      name: "baz"
      type: "jar"
    }
    pathname: {
      name: "foo"
      type: "abcl"
    }
  )
  name: "bar-1"
  type: "cls"
}

// UC6 -- JAR entry in a http: accessible JAR file
pathname: {
  namestring: "jar:http://example.org/abcl.jar!/org/armedbear/lisp/Version.class",
  device: ( 
    "http://example.org/abcl.jar"
    pathname: {
      directory: (:relative "org" "armedbear" "lisp")
      name: "Version"
      type: "class"
   }
}

// UC7 -- JAR Entry in a JAR Entry in a URL accessible JAR FILE
pathname: {
   namestring  "jar:jar:http://example.org/abcl.jar!/foo.abcl!/foo-1.cls"
   device: (
     "http://example.org/abcl.jar"
     pathname: { 
       name: "foo"
       type: "abcl"
     }
  )
  name: "foo-1"
  type: "cls"
}

// UC8 -- JAR in an absolute directory

pathame: {
   namestring: "jar:file:/a/b/foo.jar!/"
   device: (
     pathname: {
       directory: (:ABSOLUTE "a" "b")
       name: "foo"
       type: "jar"
     }
   )
}

// UC9 -- JAR in an relative directory with entry
pathname: {
   namestring: "jar:file:a/b/foo.jar!/c/d/foo.lisp"
   device: (
     directory: (:RELATIVE "a" "b")
     name: "foo"
     type: "jar"
   )
   directory: (:RELATIVE "c" "d")
   name: "foo"
   type: "lisp
}


  
Problems
--------

1.  DEVICE PATHNAMES require the context within the nested PATHNAME
    structure to be interpreted correctly.

Result:    Be careful when manipulating PATHNAMEs that refer to JARs


History
-------

In the use of PATHNAMEs linked by the DEVICE field, we found the problem
that UNC path support uses the DEVICE field

Result:    JARs located on UNC mounts can't be referenced. via '\\'.

           i.e.  jar:jar:file:\\server\share\a\b\foo.jar!/this\that!/foo.java

would not have 

Solution:  Instead of having DEVICE point to a PATHNAME, have DEVICE
be a list of PATHNAMES

pathname: {
  namestring: "jar:jar:file:\\server\share\foo.jar!/foo.abcl!/"
  device: ( pathname: {
              name: "foo"
              type: "abcl"
            }
            pathname: {
              host: "server"
              device: "share"
              name: "foo"
              type: "jar"
            }
}

Which order for the list? Outermost first or last?  Outermost first.