1 files changed, 59 insertions, 0 deletions
diff --git a/module/calp/util/io.scm b/module/calp/util/io.scm
new file mode 100644
index 00000000..7db1eee2
--- /dev/null
+++ b/module/calp/util/io.scm
@@ -0,0 +1,59 @@
+(define-module (calp util io)
+  :use-module ((ice-9 rdelim) :select (read-line)))
+
+(define-public (open-input-port str)
+  (if (string=? "-" str)
+      (current-input-port)
+      (open-input-file str)))
+
+(define-public (open-output-port str)
+  (if (string=? "-" str)
+      (current-output-port)
+      (open-output-file str)))
+
+
+
+(define-public (read-lines port)
+  (with-input-from-port port
+    (lambda ()
+      (let loop ((line (read-line)))
+        (if (eof-object? line)
+            '() (cons line (loop (read-line))))))))
+
+;; Same functionality as the regular @var{with-output-to-file}, but
+;; with the difference that either everything is written, or nothing
+;; is written, and if anything is written it's all written atomicaly at
+;; once (the original file will never contain an intermidiate state).
+;; Does NOT handle race conditions between threads.
+;; Return #f on failure, something truthy otherwise
+(define-public (with-atomic-output-to-file filename thunk)
+  ;; copy to enusre writable string
+  (define tmpfile (string-copy (string-append
+                                (dirname filename)
+                                file-name-separator-string
+                                "." (basename filename)
+                                "XXXXXX")))
+  (define port #f)
+  (dynamic-wind
+    (lambda () (set! port (mkstemp! tmpfile)))
+    (lambda ()
+      (with-output-to-port port thunk)
+      ;; Closing a port forces a write, due to buffering
+      ;; some of the errors that logically would come
+      ;; from write calls are first raised here. But since
+      ;; crashing is acceptable here, that's fine.
+      (close-port port)
+      (rename-file tmpfile filename))
+    (lambda ()
+      (when (access? tmpfile F_OK)
+        ;; I'm a bit unclear on how to trash our write buffer.
+        ;; hopefully first removing the file, followed by closing
+        ;; the port is enough for the kernel to do the sensible
+        ;; thing.
+        (delete-file tmpfile)
+        (close-port port)
+        ;; `when' defaults to the truthy `()', see (calp util)
+        ;; (note that #<unspecified> is thruthy, but shouldn't be
+        ;; counted on, since anything with an unspecified return
+        ;; value might as well return #f)
+        #f))))