syscalls: Add 'scandir*'.

* guix/build/syscalls.scm (%struct-dirent-header): New C struct.
(string->pointer/utf-8, pointer->string/utf-8): New procedures.
(opendir*, closedir*, readdir*, scandir*): New procedures.
* tests/syscalls.scm ("scandir*, ENOENT")
("scandir*, ASCII file names", "scandir*, UTF-8 file names")
("scandir*, properties): New tests.

guix/build/syscalls.scm

@@ -28,6 +28,7 @@
   #:use-module (srfi srfi-9 gnu)
   #:use-module (srfi srfi-11)
   #:use-module (srfi srfi-19)
+  #:use-module (srfi srfi-26)
   #:use-module (ice-9 rdelim)
   #:use-module (ice-9 regex)
   #:use-module (ice-9 match)
@@ -68,6 +69,7 @@
             mkdtemp!
             fdatasync
             pivot-root
+            scandir*
             fcntl-flock
 
             set-thread-name
@@ -817,6 +819,128 @@ system to PUT-OLD."
                  (list new-root put-old (strerror err))
                  (list err)))))))
 
+
+;;;
+;;; Opendir & co.
+;;;
+
+(define-c-struct %struct-dirent-header
+  sizeof-dirent-header
+  (lambda (inode offset length type name)
+    ;; Convert TYPE to symbols like 'stat:type' does.
+    (let ((type (cond ((= type DT_REG)  'regular)
+                      ((= type DT_LNK)  'symlink)
+                      ((= type DT_DIR)  'directory)
+                      ((= type DT_FIFO) 'fifo)
+                      ((= type DT_CHR)  'char-special)
+                      ((= type DT_BLK)  'block-special)
+                      ((= type DT_SOCK) 'socket)
+                      (else             'unknown))))
+      `((type . ,type)
+        (inode . ,inode))))
+  read-dirent-header
+  write-dirent-header!
+  (inode  int64)
+  (offset int64)
+  (length unsigned-short)
+  (type   uint8)
+  (name   uint8))                                 ;first byte of 'd_name'
+
+;; Constants for the 'type' field, from <dirent.h>.
+(define DT_UNKNOWN 0)
+(define DT_FIFO 1)
+(define DT_CHR 2)
+(define DT_DIR 4)
+(define DT_BLK 6)
+(define DT_REG 8)
+(define DT_LNK 10)
+(define DT_SOCK 12)
+(define DT_WHT 14)
+
+(define string->pointer/utf-8
+  (cut string->pointer <> "UTF-8"))
+
+(define pointer->string/utf-8
+  (cut pointer->string <> <> "UTF-8"))
+
+(define opendir*
+  (let ((proc (syscall->procedure '* "opendir" '(*))))
+    (lambda* (name #:optional (string->pointer string->pointer/utf-8))
+      (let-values (((ptr err)
+                    (proc (string->pointer name))))
+        (if (null-pointer? ptr)
+            (throw 'system-error "opendir*"
+                   "opendir*: ~A"
+                   (list (strerror err))
+                   (list err))
+            ptr)))))
+
+(define closedir*
+  (let ((proc (syscall->procedure int "closedir" '(*))))
+    (lambda (directory)
+      (let-values (((ret err)
+                    (proc directory)))
+        (unless (zero? ret)
+          (throw 'system-error "closedir"
+                 "closedir: ~A" (list (strerror err))
+                 (list err)))))))
+
+(define readdir*
+  (let ((proc (syscall->procedure '* "readdir64" '(*))))
+    (lambda* (directory #:optional (pointer->string pointer->string/utf-8))
+      (let ((ptr (proc directory)))
+        (and (not (null-pointer? ptr))
+             (cons (pointer->string
+                    (make-pointer (+ (pointer-address ptr)
+                                     (c-struct-field-offset
+                                      %struct-dirent-header name)))
+                    -1)
+                   (read-dirent-header
+                    (pointer->bytevector ptr sizeof-dirent-header))))))))
+
+(define* (scandir* name #:optional
+                   (select? (const #t))
+                   (entry<? (lambda (entry1 entry2)
+                              (match entry1
+                                ((name1 . _)
+                                 (match entry2
+                                   ((name2 . _)
+                                    (string<? name1 name2)))))))
+                   #:key
+                   (string->pointer string->pointer/utf-8)
+                   (pointer->string pointer->string/utf-8))
+  "This procedure improves on Guile's 'scandir' procedure in several ways:
+
+   1. Systematically encode decode file names using STRING->POINTER and
+      POINTER->STRING (UTF-8 by default; this works around a defect in Guile 2.0/2.2
+      where 'scandir' decodes file names according to the current locale, which is
+      not always desirable.
+
+   2. Each entry that is returned has the form (NAME . PROPERTIES).
+      PROPERTIES is an alist showing additional properties about the entry, as
+      found in 'struct dirent'.  An entry may look like this:
+
+        (\"foo.scm\" (type . regular) (inode . 123456))
+
+      Callers must be prepared to deal with the case where 'type' is 'unknown'
+      since some file systems do not provide that information.
+
+   3. Raise to 'system-error' when NAME cannot be opened."
+  (let ((directory (opendir* name string->pointer)))
+    (dynamic-wind
+      (const #t)
+      (lambda ()
+        (let loop ((result '()))
+          (match (readdir* directory pointer->string)
+            (#f
+             (sort result entry<?))
+            (entry
+             (loop (if (select? entry)
+                       (cons entry result)
+                       result))))))
+      (lambda ()
+        (closedir* directory)))))
+
 
 ;;;
 ;;; Advisory file locking.

tests/syscalls.scm

@@ -24,6 +24,8 @@
   #:use-module (srfi srfi-1)
   #:use-module (srfi srfi-26)
   #:use-module (srfi srfi-64)
+  #:use-module (system foreign)
+  #:use-module ((ice-9 ftw) #:select (scandir))
   #:use-module (ice-9 match))
 
 ;; Test the (guix build syscalls) module, although there's not much that can
@@ -184,6 +186,64 @@
                          (status:exit-val status))))
                (eq? #t result))))))))
 
+(test-equal "scandir*, ENOENT"
+  ENOENT
+  (catch 'system-error
+    (lambda ()
+      (scandir* "/does/not/exist"))
+    (lambda args
+      (system-error-errno args))))
+
+(test-equal "scandir*, ASCII file names"
+  (scandir (dirname (search-path %load-path "guix/base32.scm"))
+           (const #t) string<?)
+  (match (scandir* (dirname (search-path %load-path "guix/base32.scm")))
+    (((names . properties) ...)
+     names)))
+
+(test-equal "scandir*, UTF-8 file names"
+  '("." ".." "α" "λ")
+  (call-with-temporary-directory
+   (lambda (directory)
+     ;; Wrap 'creat' to make sure that we really pass a UTF-8-encoded file
+     ;; name to the system call.
+     (let ((creat (pointer->procedure int
+                                      (dynamic-func "creat" (dynamic-link))
+                                      (list '* int))))
+       (creat (string->pointer (string-append directory "/α")
+                               "UTF-8")
+              #o644)
+       (creat (string->pointer (string-append directory "/λ")
+                               "UTF-8")
+              #o644)
+       (let ((locale (setlocale LC_ALL)))
+         (dynamic-wind
+           (lambda ()
+             ;; Make sure that even in a C locale we get the right result.
+             (setlocale LC_ALL "C"))
+           (lambda ()
+             (match (scandir* directory)
+               (((names . properties) ...)
+                names)))
+           (lambda ()
+             (setlocale LC_ALL locale))))))))
+
+(test-assert "scandir*, properties"
+  (let ((directory (dirname (search-path %load-path "guix/base32.scm"))))
+    (every (lambda (entry name)
+             (match entry
+               ((name2 . properties)
+                (and (string=? name2 name)
+                     (let* ((full  (string-append directory "/" name))
+                            (stat  (lstat full))
+                            (inode (assoc-ref properties 'inode))
+                            (type  (assoc-ref properties 'type)))
+                       (and (= inode (stat:ino stat))
+                            (or (eq? type 'unknown)
+                                (eq? type (stat:type stat)))))))))
+           (scandir* directory)
+           (scandir directory (const #t) string<?))))
+
 (false-if-exception (delete-file temp-file))
 (test-equal "fcntl-flock wait"
   42                                              ; the child's exit status