| 1 | URL Pathnames ABCL |
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| 2 | ================== |
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| 3 | |
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| 4 | Mark Evenson |
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| 5 | Created: 25 MAR 2010 |
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| 6 | Modified: 26 MAR 2010 |
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| 7 | |
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| 8 | Notes towards an implementation of URL references to be contained in |
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| 9 | Common Lisp `PATHNAME` objects within ABCL. |
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| 10 | |
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| 11 | |
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| 12 | References |
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| 13 | ---------- |
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| 14 | |
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| 15 | RFC3986 Uniform Resource Identifier (URI): Generic Syntax |
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| 16 | |
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| 17 | |
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| 18 | URL vs URI |
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| 19 | ---------- |
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| 20 | |
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| 21 | We use the term URL to describe the URL Pathnames, even though RFC3986 |
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| 22 | notes that its use should be obsolete because in the context of Common |
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| 23 | Lisp Pathnames all need a lookup mechanism to be resolved or they |
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| 24 | wouldn't be of much use. |
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| 25 | |
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| 26 | Goals |
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| 27 | ----- |
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| 28 | |
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| 29 | 1. Use Common Lisp pathnames to refer to representations referenced |
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| 30 | by a URL. |
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| 31 | |
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| 32 | 2. The URL schemes supported shall include at least "http", and those |
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| 33 | enabled by the URLStreamHandler extension mechanism. |
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| 34 | |
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| 35 | 3. Use URL schemes that are understood by the java.net.URL object. |
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| 36 | |
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| 37 | A file specified by URL |
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| 38 | |
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| 39 | #p"http://example.org/org/armedbear/systems/pgp.asd" |
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| 40 | |
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| 41 | 4. MERGE-PATHNAMES |
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| 42 | |
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| 43 | (merge-pathnames "url.asd" |
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| 44 | "http://example/org/armedbear/systems/pgp.asd") |
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| 45 | ==> "http://example/org/armedbear/systems/url.asd" |
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| 46 | |
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| 47 | 5. PROBE-FILE returning the state of URL accesibility. |
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| 48 | |
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| 49 | 6. TRUENAME "aliased" to PROBE-FILE signalling an error if the URL is |
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| 50 | not accessible (see "Non-goal 1"). |
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| 51 | |
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| 52 | 7. DIRECTORY for non-wildcards |
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| 53 | |
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| 54 | 8. URL pathname work as a valid argument for OPEN with :DIRECTION :INPUT. |
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| 55 | |
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| 56 | 9. Enable the loading of ASDF2 systems referenced by a URL pathname. |
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| 57 | |
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| 58 | 10. The reserved URL characters (`~`, `/`, `?`, etc.) shall be |
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| 59 | encoded in the proper manner on construction of the Pathname. |
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| 60 | |
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| 61 | 11. The "file" scheme will continue to be represented by an |
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| 62 | "ordinary" Pathname. |
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| 63 | |
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| 64 | 12. The "jar" scheme will continue to be represented by a jar |
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| 65 | Pathname. |
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| 66 | |
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| 67 | |
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| 68 | Non-goals |
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| 69 | --------- |
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| 70 | |
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| 71 | 1. We will not implement canonicalization of URL schemas (such as following |
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| 72 | "http" redirects). |
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| 73 | |
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| 74 | 2. DIRECTORY working for URL pathnames containing wildcards. |
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| 75 | |
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| 76 | |
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| 77 | Implementation |
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| 78 | -------------- |
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| 79 | |
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| 80 | A PATHNAME refering to a resource referenced by a URL is known as a |
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| 81 | URL PATHNAME. |
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| 82 | |
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| 83 | A URL PATHNAME always has a HOST component which is a proper list. |
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| 84 | This list will be an association list (alist). The association list |
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| 85 | values must be a string. |
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| 86 | |
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| 87 | :SCHEME |
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| 88 | Scheme of URI ("http", "ftp", "bundle", etc.) |
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| 89 | :AUTHORITY |
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| 90 | Valid authority according to the URI scheme. For "http" this |
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| 91 | could be "example.org:8080". |
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| 92 | |
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| 93 | The DIRECTORY, NAME and TYPE fields of the PATHNAME are used to form |
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| 94 | the URI `path` according to the conventions of the UNIX filesystem |
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| 95 | (i.e. '/' is the directory separator). If needed, `query` and `fragment` |
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| 96 | portions of a URL are to be included in the URL pathname NAME |
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| 97 | component. In a sense the HOST contains the base URL, to which the |
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| 98 | `path` is a relative URL. |
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| 99 | |
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| 100 | For the purposes of PATHNAME-MATCH-P, two URL pathnames may be said to |
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| 101 | match if their HOST compoments are EQUAL, and all other components are |
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| 102 | considered to match according to the existing rules for Pathnames. |
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| 103 | |
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| 104 | A URL pathname must have a DEVICE whose value is NIL. |
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| 105 | |
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| 106 | Upon creation, the presence of ".." and "." components in the |
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| 107 | DIRECTORY are removed. The DIRECTORY component, if present, is always |
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| 108 | absolute. |
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| 109 | |
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| 110 | The namestring of a URL pathname shall be formed by the usual |
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| 111 | conventions of a URL. |
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| 112 | |
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| 113 | |
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| 114 | Status |
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| 115 | ------ |
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| 116 | |
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| 117 | This design is a proposal. |
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