payload: add buffered-payload

http-easy-lib/http-easy/private/payload.rkt

@@ -15,11 +15,28 @@
 
 (provide
  (contract-out
+  [buffered-payload (-> payload-procedure/c payload-procedure/c)]
   [form-payload (-> form-data/c payload-procedure/c)]
   [gzip-payload (-> payload-procedure/c payload-procedure/c)]
   [json-payload (-> jsexpr? payload-procedure/c)]
   [pure-payload (-> (or/c bytes? string? input-port?) payload-procedure/c)]))
 
+(define ((buffered-payload p) hs)
+  (let*-values ([(hs data) (p hs)]
+                [(bs)
+                 (cond
+                   [(input-port? data)
+                    (call-with-output-bytes
+                     (lambda (out)
+                       (copy-port data out)))]
+                   [(string? data)
+                    (string->bytes/utf-8 data)]
+                   [else
+                    data])])
+    (define content-length
+      (number->string (bytes-length bs)))
+    (values (hash-set hs 'content-length content-length) bs)))
+
 (define (form-payload v)
   (define data (alist->form-urlencoded v))
   (lambda (hs)

http-easy-lib/info.rkt

@@ -1,7 +1,7 @@
 #lang info
 
 (define license 'BSD-3-Clause)
-(define version "0.7")
+(define version "0.8")
 (define collection "net")
 (define deps
   '(["base" #:version "8.1.0.4"]

http-easy/http-easy.scrbl

@@ -675,6 +675,14 @@ sent to a remote server.
   value to be used as the request body.
 }
 
+@defproc[(buffered-payload [p payload-procedure/c]) payload-procedure/c]{
+  Produces a payload procedure that buffers the output of @racket[p]
+  in memory in order to determine its length before sending it to the
+  server.
+
+  @history[#:added "0.8"]
+}
+
 @defproc[(form-payload [v form-data/c]) payload-procedure/c]{
   Produces a payload procedure that encodes @racket[v] as form data
   using the @tt{application/x-www-form-urlencoded} content type.