janet: add writer helper module

1 files changed, 39 insertions, 0 deletions

diff --git a/jurl/writer.janet b/jurl/writer.janet
new file mode 100644
index 0000000..589271e
--- /dev/null
+++ b/jurl/writer.janet
@@ -0,0 +1,39 @@
+# writer.janet: utility for consistent :readfunction and mime :data-cb use
+(defn- read-cb 
+  [self bytes]
+  (def start (self :pos))
+  (def end (min (length (self :buf)) (+ (self :pos) bytes)))
+  (put self :pos end)
+  (string/slice (self :buf) start end))
+
+# no safety checks, just for fun
+(defn- seek-cb
+  [self offset &opt pos]
+  (default pos :set)
+  (put self :pos (case pos
+                   :set offset
+                   :cur (+ (self :pos) offset)
+                   :end (- (length (self :buf)) offset))))
+
+(defn- make-buf
+  [b]
+  (assert (bytes? b))
+  (def buf (freeze b))
+  @{:pos 0
+    :buf buf
+    :read read-cb
+    :seek seek-cb})
+
+# returns a function you can put into :readfunction
+(defn make-writer
+  [b]
+  (def buf (make-buf b))
+  |(:read buf $))
+
+# returns a function you can put into mime_data_cb
+(defn make-mime-writer
+  [b]
+  (def buf (make-buf b))
+  (fn [mode & args] 
+    (assert (keyword? mode))
+    (mode buf ;args)))