diff --git a/pkgs/net-pkgs/net-doc/net/scribblings/http-client.scrbl b/pkgs/net-pkgs/net-doc/net/scribblings/http-client.scrbl
index 5030fffd9f..8eae5868d8 100644
--- a/pkgs/net-pkgs/net-doc/net/scribblings/http-client.scrbl
+++ b/pkgs/net-pkgs/net-doc/net/scribblings/http-client.scrbl
@@ -74,7 +74,7 @@ Closes the output side of @racket[hc], if it is live.
                           [#:close? close? boolean? #f]
                           [#:headers headers (listof (or/c bytes? string?)) empty]
                           [#:content-decode decodes (listof symbol?) '(gzip)]
-                          [#:data data (or/c false/c bytes? string?) #f])
+                          [#:data data (or/c false/c bytes? string? data-procedure/c) #f])
          void?]{
 
 Sends an HTTP request to @racket[hc] to the URI @racket[uri] using
@@ -82,6 +82,11 @@ HTTP version @racket[version] the method @racket[method] and the
 additional headers given in @racket[headers] and the additional data
 @racket[data].
 
+If @racket[data] is a procedure, it will be called once with a
+procedure of one argument, which is a @racket[string] or
+@racket[byte-string] to be written to the request body using
+chunked transfer encoding.
+
 If @racket[headers] does not contain an @litchar{Accept-Encoding}
 header, then a header indicating that encodings from @racket[decodes]
 are accepted is automatically added.
@@ -117,7 +122,7 @@ to do so.
                               [#:version version (or/c bytes? string?) #"1.1"]
                               [#:method method (or/c bytes? string? symbol?) #"GET"]
                               [#:headers headers (listof (or/c bytes? string?)) empty]
-                              [#:data data (or/c false/c bytes? string?) #f]
+                              [#:data data (or/c false/c bytes? string? data-procedure/c) #f]
                               [#:content-decode decodes (listof symbol?) '(gzip)]
                               [#:close? close? boolean? #f])
          (values bytes? (listof bytes?) input-port?)]{
@@ -132,7 +137,7 @@ Calls @racket[http-conn-send!] and @racket[http-conn-recv!] in sequence.
                         [#:version version (or/c bytes? string?) #"1.1"]                          
                         [#:method method (or/c bytes? string? symbol?) #"GET"]
                         [#:headers headers (listof (or/c bytes? string?)) empty]
-                        [#:data data (or/c false/c bytes? string?) #f]
+                        [#:data data (or/c false/c bytes? string? data-procedure/c) #f]
                         [#:content-decode decodes (listof symbol?) '(gzip)])
          (values bytes? (listof bytes?) input-port?)]{
 
diff --git a/pkgs/net-pkgs/net-doc/net/scribblings/url.scrbl b/pkgs/net-pkgs/net-doc/net/scribblings/url.scrbl
index 3435274752..fbeb0740ca 100644
--- a/pkgs/net-pkgs/net-doc/net/scribblings/url.scrbl
+++ b/pkgs/net-pkgs/net-doc/net/scribblings/url.scrbl
@@ -444,7 +444,7 @@ mapping is the empty list (i.e., no proxies).}
 @defproc[(http-sendrecv/url [u url?]
                             [#:method method (or/c bytes? string? symbol?) #"GET"]
                             [#:headers headers (listof (or/c bytes? string?)) empty]
-                            [#:data data (or/c false/c bytes? string?) #f]
+                            [#:data data (or/c false/c bytes? string? data-procedure/c) #f]
                             [#:content-decode decodes (listof symbol?) '(gzip)])
          (values bytes? (listof bytes?) input-port?)]{
 
diff --git a/pkgs/net-pkgs/net-test/tests/net/http-client.rkt b/pkgs/net-pkgs/net-test/tests/net/http-client.rkt
index 6e9980220a..e9c51d6a7c 100644
--- a/pkgs/net-pkgs/net-test/tests/net/http-client.rkt
+++ b/pkgs/net-pkgs/net-test/tests/net/http-client.rkt
@@ -240,4 +240,12 @@
     #"PUT / HTTP/1.1\r\nHost: localhost:REDACTED\r\nUser-Agent: Racket/REDACTED (net/http-client)\r\nAccept-Encoding: gzip\r\nContent-Length: 4\r\nConnection: close\r\n\r\nfrob"
     #"HTTP/1.1 200 OK"
     '()
+    #""]
+
+   ["PUT"
+    (λ (w) (w "fr") (w "ob"))
+    "HTTP/1.1 200 OK\r\n\r\n"
+    #"PUT / HTTP/1.1\r\nHost: localhost:REDACTED\r\nUser-Agent: Racket/REDACTED (net/http-client)\r\nAccept-Encoding: gzip\r\nTransfer-Encoding: chunked\r\nConnection: close\r\n\r\n2\r\nfr\r\n2\r\nob\r\n\r\n"
+    #"HTTP/1.1 200 OK"
+    '()
     #""]))
diff --git a/racket/collects/net/http-client.rkt b/racket/collects/net/http-client.rkt
index 54d7b628a1..eabb98a91b 100644
--- a/racket/collects/net/http-client.rkt
+++ b/racket/collects/net/http-client.rkt
@@ -24,6 +24,11 @@
     (bytes->string/utf-8 bs)
     bs))
 
+(define (->bytes str)
+  (if (string? str)
+      (string->bytes/utf-8 str)
+      str))
+
 (define (read-bytes-line/not-eof ip kind)
   (define bs (read-bytes-line ip kind))
   (when (eof-object? bs)
@@ -93,14 +98,17 @@
     (abandon to)
     (set-http-conn-to! hc #f)))
 
+(define (write-chunk out data)
+  (let ([bytes (->bytes data)])
+    (fprintf out "~x\r\n~a\r\n" (bytes-length bytes) bytes)))
+
 (define (http-conn-send! hc url-bs
                          #:version [version-bs #"1.1"]
                          #:method [method-bss #"GET"]
                          #:close? [close? #f]
                          #:headers [headers-bs empty]
                          #:content-decode [decodes '(gzip)]
-                         ;; xxx maybe support other kinds of data (ports and writing functions)
-                         #:data [data-bsf #f])
+                         #:data [data #f])
   (match-define (http-conn host port port-usual? to from _) hc)
   (fprintf to "~a ~a HTTP/~a\r\n" method-bss url-bs version-bs)
   (unless (regexp-member #rx"^(?i:Host:) +.+$" headers-bs)
@@ -114,21 +122,22 @@
   (unless (or (not (memq 'gzip decodes))
               (regexp-member #rx"^(?i:Accept-Encoding:) +.+$" headers-bs))
     (fprintf to "Accept-Encoding: gzip\r\n"))
-  (define data
-    (if (string? data-bsf)
-      (string->bytes/utf-8 data-bsf)
-      data-bsf))
-  (when data
-    (unless (regexp-member #rx"^(?i:Content-Length:) +.+$" headers-bs)
-      (fprintf to "Content-Length: ~a\r\n" (bytes-length data))))
+  (define body (->bytes data))
+  (cond [(procedure? body)
+         (fprintf to "Transfer-Encoding: chunked\r\n")]
+        [(and body
+              (not (regexp-member #rx"^(?i:Content-Length:) +.+$" headers-bs)))
+         (fprintf to "Content-Length: ~a\r\n" (bytes-length body))])
   (when close?
     (unless (regexp-member #rx"^(?i:Connection:) +.+$" headers-bs)
       (fprintf to "Connection: close\r\n")))
   (for ([h (in-list headers-bs)])
     (fprintf to "~a\r\n" h))
   (fprintf to "\r\n")
-  (when data
-    (display data to))
+  (cond [(procedure? body)
+         (body (λ (data) (write-chunk to data)))
+         (fprintf to "\r\n")]
+        [body (display body to)])
   (flush-output to))
 
 (define (http-conn-status! hc)
@@ -258,7 +267,7 @@
                              #:version [version-bs #"1.1"]
                              #:method [method-bss #"GET"]
                              #:headers [headers-bs empty]
-                             #:data [data-bsf #f]
+                             #:data [data #f]
                              #:content-decode [decodes '(gzip)]
                              #:close? [close? #f])
   (http-conn-send! hc url-bs
@@ -267,7 +276,7 @@
                    #:close? close?
                    #:headers headers-bs
                    #:content-decode decodes
-                   #:data data-bsf)
+                   #:data data)
   (http-conn-recv! hc 
                    #:content-decode decodes
                    #:close? close?))
@@ -278,18 +287,22 @@
                        #:version [version-bs #"1.1"]
                        #:method [method-bss #"GET"]
                        #:headers [headers-bs empty]
-                       #:data [data-bsf #f]
+                       #:data [data #f]
                        #:content-decode [decodes '(gzip)])
   (define hc (http-conn-open host-bs #:ssl? ssl? #:port port))
   (http-conn-sendrecv! hc url-bs
                        #:version version-bs
                        #:method method-bss
                        #:headers headers-bs
-                       #:data data-bsf
+                       #:data data
                        #:content-decode decodes
                        #:close? #t))
 
+(define data-procedure/c
+  (-> (-> (or/c bytes? string?) any/c) any/c))
+
 (provide
+ data-procedure/c
  (contract-out
   [http-conn?
    (-> any/c
@@ -317,7 +330,7 @@
                #:close? boolean?
                #:headers (listof (or/c bytes? string?))
                #:content-decode (listof symbol?)                           
-               #:data (or/c false/c bytes? string?))
+               #:data (or/c false/c bytes? string? data-procedure/c))
     void)]
   ;; Derived
   [http-conn-open
@@ -335,7 +348,7 @@
         (#:version (or/c bytes? string?)
                    #:method (or/c bytes? string? symbol?)
                    #:headers (listof (or/c bytes? string?))
-                   #:data (or/c false/c bytes? string?)
+                   #:data (or/c false/c bytes? string? data-procedure/c)
                    #:content-decode (listof symbol?) 
                    #:close? boolean?)
         (values bytes? (listof bytes?) input-port?))]
@@ -346,6 +359,6 @@
                 #:version (or/c bytes? string?)
                 #:method (or/c bytes? string? symbol?)
                 #:headers (listof (or/c bytes? string?))
-                #:data (or/c false/c bytes? string?)
+                #:data (or/c false/c bytes? string? data-procedure/c)
                 #:content-decode (listof symbol?))
         (values bytes? (listof bytes?) input-port?))]))
diff --git a/racket/collects/net/url.rkt b/racket/collects/net/url.rkt
index add6bb46ee..5650022916 100644
--- a/racket/collects/net/url.rkt
+++ b/racket/collects/net/url.rkt
@@ -749,7 +749,7 @@
 (define (http-sendrecv/url u
                            #:method [method-bss #"GET"]
                            #:headers [headers-bs empty]
-                           #:data [data-bsf #f]
+                           #:data [data #f]
                            #:content-decode [decodes '(gzip)])
   (unless (member (url-scheme u) '(#f "http" "https"))
     (error 'http-sendrecv/url "URL scheme ~e not supported" (url-scheme u)))
@@ -777,7 +777,7 @@
    #:port port
    #:method method-bss
    #:headers headers-bs
-   #:data data-bsf
+   #:data data
    #:content-decode decodes))
 
 (provide
@@ -786,6 +786,6 @@
    (->* (url?)
         (#:method (or/c bytes? string? symbol?)
                   #:headers (listof (or/c bytes? string?))
-                  #:data (or/c false/c bytes? string?)
+                  #:data (or/c false/c bytes? string? hc:data-procedure/c)
                   #:content-decode (listof symbol?))
         (values bytes? (listof bytes?) input-port?))]))