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README.md
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README.md
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# xattr
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## Interface for extended filesystem attributes
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[Extended attributes](https://en.wikipedia.org/wiki/Extended_attributes) are a special type of file attribute that lets you associate key-value pairs with a file without actually modifying the file's contents. Commonly used for program settings, tagging, and file metadata (i.e., storing a file's author with a key like “author.name”) xattrs can be used for used for pretty much anything you can dream up. They're mega-cool and useful.
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This is a simple interface for accessing them within [Chicken Scheme](https://call-cc.org/), a friendly Scheme.
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## API
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### get-xattr
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`get-xattr path attr`
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Returns the string-value of a file's extended attribute.
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If the file has no such attribute, #f is returned. In other cases (e.g., the file doesn't exist, permission not available, no filesystem support), exceptions are raised.
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### set-xattr
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`set-xattr path attr value`
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Sets the string-value of a file's extended attribute.
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The set value is returned, if successful.
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### remove-xattr
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`remove-xattr path attr`
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Removes an extended attribute from a file.
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The value of the removed attribute is returned, if successful.
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### list-xattrs
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`list-xattrs path`
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Returns a list of the file's extended attribute names.
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## Examples
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```
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(import xattr (chicken io) (chicken file))
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;; Create the test file
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(call-with-output-file "testing.txt"
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(lambda (out-port) (write-line "Just a test!" out-port)))
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(set-xattr "testing.txt" "user.dublincore.author" "Migdal E. F. Lemmings")
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(set-xattr "testing.txt" "user.dublincore.title" "A Treatise on Almonds")
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(get-xattr "testing.txt" "user.dublincore.author")
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;; Returns "Migdal E. F. Lemmings"
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(list-xattrs "testing.txt")
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;; Returns '("user.dublincore.author" "user.dublincore.title")
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(remove-xattr "testing.txt" "user.dublincore.title")
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;; Returns "A Treatise on Almonds"
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(list-xattrs "testing.txt")
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;; Now returns '("user.dublincore.author")
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```
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## On GNU/Linux
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Currently, this egg only supports LiGNUx, a platform that has a particularity: The name of each attribute must contain a “namespace,” separated from the actual name by a period. For example, with the attribute named `user.xdg.origin.url`, the namespace is `user` and the name is `xdg.origin.url`. In most cases, you won't stray from the `user` namespace.
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Don't forget to prepend “user.” to your attribute names!
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A handy list of somewhat-standard extended attributes is hosted on FreeDesktop's website, [here](https://www.freedesktop.org/wiki/CommonExtendedAttributes/).
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## Requirements
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This egg requires `srfi-1` and `srfi-12`.
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## Meta
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**Author:** Jaidyn Ann <jadedctrl@posteo.at>
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**License:** GPLv3
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**Source:** https://github.com/jadedctrl/xattr, https://notabug.org/jadedctrl/xattr
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@ -1,7 +1,9 @@
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;; -*- Scheme -*-
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((synopsis "Access to extended attributes")
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(author "Jaidyn Ann")
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(category io)
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(category net)
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(license "GPLv3")
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(dependencies srfi-1)
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(components (extension xattr)))
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;; (csc-options "-O3" "-d1" "-X" "bind" "-s" "-k" "-emit-link-file" "xattr.link" "-o" "xattr_ext.o"))
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;; (c-object xattr_ext)))
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103
xattr.scm
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xattr.scm
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@ -1,5 +1,5 @@
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;;
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;; Copyright 2024, Jaidyn Levesque <jadedctrl@posteo.at>
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;; Copyright 2022, Jaidyn Levesque <jadedctrl@posteo.at>
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;;
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;; This program is free software: you can redistribute it and/or
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;; modify it under the terms of the GNU General Public License as
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@ -16,23 +16,20 @@
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;;
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(module xattr
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(get-xattr set-xattr remove-xattr list-xattrs)
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(get-xattr set-xattr remove-xattr list-xattr)
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(import scheme
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(chicken base) (chicken condition) (chicken foreign) (chicken memory)
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srfi-1)
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(import (chicken base) (chicken memory) srfi-1 scheme (chicken foreign) srfi-12)
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(foreign-declare "#include \"xattr_ext.c\"")
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(foreign-declare "#include \"xattr_ext.c\"")
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;; The direct foreign binding for `get_xattr`
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(define get-xattr-foreign
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;; The direct foreign binding for `get_xattr`
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(define get-xattr-foreign
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(foreign-lambda c-string* "get_xattr" c-string c-string (c-pointer int)))
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;; Wrapper around get-xattr-foreign, which throws exceptions and such.
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(define (get-xattr path attr)
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;; Wrapper around get-xattr-foreign, which throws exceptions and such.
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(define (get-xattr path attr)
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(let-location ([error-code int])
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(let ([attr-value (get-xattr-foreign path attr (location error-code))]
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[exception (or (getxattr-exception error-code)
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@ -42,16 +39,16 @@
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attr-value))))
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;; The direct foreign binding for `list_xattr`
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(define list-xattrs-foreign
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;; The direct foreign binding for `list_xattr`
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(define list-xattr-foreign
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(foreign-lambda (c-pointer char) "list_xattr" c-string (c-pointer ssize_t) (c-pointer int)))
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;; Wrapper around list-xattrs-foreign, which throws exceptions and such.
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(define (list-xattrs path)
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;; Wrapper around list-xattr-foreign, which throws exceptions and such.
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(define (list-xattr path)
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(let-location ([error-code int]
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[length ssize_t])
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(let ([list-pointer (list-xattrs-foreign path (location length) (location error-code))]
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(let ([list-pointer (list-xattr-foreign path (location length) (location error-code))]
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[exception (or (getxattr-exception error-code)
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(stat-exception error-code))])
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(if exception
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@ -60,13 +57,13 @@
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(pointer->delimited-string-list list-pointer length 0)))))
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;; The direct foreign binding for `set_xattr`
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(define set-xattr-foreign
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;; The direct foreign binding for `set_xattr`
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(define set-xattr-foreign
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(foreign-lambda int "set_xattr" c-string c-string c-string (c-pointer int)))
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;; Wrapper around set-xattr-foreign, throwing exceptions and all that jazz
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(define (set-xattr path attr value)
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;; Wrapper around set-xattr-foreign, throwing exceptions and all that jazz
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(define (set-xattr path attr value)
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(let-location ([error-code int])
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(let ([return-code (set-xattr-foreign path attr value (location error-code))]
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[exception (or (setxattr-exception error-code)
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@ -77,28 +74,29 @@
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value))))
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;; The direct foreign binding for `remove_xattr`
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(define remove-xattr-foreign
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;; The direct foreign binding for `remove_xattr`
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(define remove-xattr-foreign
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(foreign-lambda int "remove_xattr" c-string c-string))
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;; Wrapper around remove-xattr-foreign, blah blah
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(define (remove-xattr path attr)
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(let* ([value (get-xattr path attr)]
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[error-code (remove-xattr-foreign path attr)]
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;; Wrapper around remove-xattr-foreign, blah blah
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(define (remove-xattr path attr)
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(let* ([error-code (remove-xattr-foreign path attr)]
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[exception (or (getxattr-exception error-code)
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(stat-exception error-code))])
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(if exception
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(signal exception)
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value)))
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attr)))
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;; TODO: These exception functions should be constructed with a macro and a simple
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;; list, like `((c-constant symbol error-message) ("E2BIG" 'e2big "The attribute value was too big."))
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;; TODO: These exception functions should be constructed with a macro and a simple
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;; list, like `((c-constant symbol error-message) ("E2BIG" 'e2big "The attribute value was too big."))
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;; Unfortunately, it looks like chicken's macros work a good bit differently from CLs?
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;; orr I'm losing my mind
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;; Return the exception associated with an error-code as per getxattr(2), if it exists
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(define (getxattr-exception error-code)
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;; Return the exception associated with an error-code as per getxattr(2), if it exists
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(define (getxattr-exception error-code)
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(cond
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[(eq? error-code (foreign-value "E2BIG" int))
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(build-exception 'e2big "The attribute value was too big.")]
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#f]))
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;; Return the exception associated with a setxattr(2) error-code, if it exists.
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(define (setxattr-exception error-code)
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;; Return the exception associated with a setxattr(2) error-code, if it exists.
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(define (setxattr-exception error-code)
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(cond
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[(eq? error-code (foreign-value "EDQUOT" int))
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(build-exception 'edquot "Setting this attribute would violate disk quota.")]
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#f]))
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;; Return the exception associated with an error-code as per stat(2), if applicable
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(define (stat-exception error-code)
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;; Return the exception associated with an error-code as per stat(2), if applicable
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(define (stat-exception error-code)
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(cond
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[(eq? error-code (foreign-value "EACCES" int))
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(build-exception 'file "Search permission denied for a parent directory.")]
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#f]))
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;; Creates a generic exception with given symbol and message
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(define (build-exception symbol message)
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;; Creates a generic exception with given symbol and message
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(define (build-exception symbol message)
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(signal (make-property-condition 'exn 'location symbol 'message message)))
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;; Some C functions offer up a string-list that isn't a two-dimensional array, but a
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;; one-dimensional array with given length and strings separated by a given delimeter.
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;; This takes that sort of pointer and gives you a nice list of strings.
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(define (pointer->delimited-string-list pointer length delimiter)
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;; Some C functions offer up a string-list that isn't a two-dimensional array, but a
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;; one-dimensional array with given length and strings separated by a given delimeter.
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;; This takes that sort of pointer and gives you a nice list of strings.
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(define (pointer->delimited-string-list pointer length delimiter)
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(let* ([is-zero (lambda (num) (eq? num 0))]
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[map-to-char (lambda (a) (map integer->char a))]
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[pointer-ints (pointer->integers pointer length)]
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[byte-list (when (list? pointer-ints)
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(drop-right pointer-ints 1))])
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(if (and (list? byte-list)
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(not (null-list? byte-list)))
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[byte-list (drop-right (pointer->integers pointer length) 1)])
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(map list->string
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(map map-to-char
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(split-list is-zero byte-list)))
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'())))
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(split-list is-zero byte-list)))))
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;; Takes a pointer and returns a list of bytes of a given length
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(define (pointer->integers pointer length)
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;; Takes a pointer and returns a list of bytes of a given length
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(define (pointer->integers pointer length)
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(let ([byte (pointer-s8-ref pointer)])
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(if (eq? length 0)
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byte
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(pointer->integers (pointer+ pointer 1) (- length 1))))))
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;; Split a list into sublists, with items passing `test` being the delimiters
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(define (split-list test list)
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;; Split a list into sublists, with items passing `test` being the delimiters
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(define (split-list test list)
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(let ([before (take-while (compose not test) list)]
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[after (drop-while (compose not test) list)])
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(cond
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@ -193,4 +186,6 @@
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[(null-list? before)
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(split-list test (cdr after))]
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[#t
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(append `(,before) (split-list test (cdr after)))]))))
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(append `(,before) (split-list test (cdr after)))])))
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)
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