diff --git a/include/chibi/features.h b/include/chibi/features.h
index 35730dca..ff9567d8 100644
--- a/include/chibi/features.h
+++ b/include/chibi/features.h
@@ -641,6 +641,10 @@
 #define SEXP_USE_MAIN_HELP ! SEXP_USE_NO_FEATURES
 #endif
 
+#ifndef SEXP_USE_SEND_FILE
+#define SEXP_USE_SEND_FILE (!defined(_WIN32) && !defined(PLAN9))
+#endif
+
 #if SEXP_USE_NATIVE_X86
 #undef SEXP_USE_BOEHM
 #define SEXP_USE_BOEHM 1
diff --git a/lib/chibi/io.sld b/lib/chibi/io.sld
index ba6e5a9a..feae0e1d 100644
--- a/lib/chibi/io.sld
+++ b/lib/chibi/io.sld
@@ -11,7 +11,8 @@
           make-filtered-input-port string-count
           open-input-bytevector open-output-bytevector get-output-bytevector
           string->utf8 utf8->string
-          write-string write-u8 read-u8 peek-u8)
+          write-string write-u8 read-u8 peek-u8 send-file
+          is-a-socket?)
   (import (chibi) (chibi ast))
   (include-shared "io/io")
   (include "io/io.scm"))
diff --git a/lib/chibi/io/io.scm b/lib/chibi/io/io.scm
index bc6cd6c6..a1bdfbd1 100644
--- a/lib/chibi/io/io.scm
+++ b/lib/chibi/io/io.scm
@@ -164,6 +164,27 @@
     (port-line-set! in (+ (string-count #\newline str 0 n) (port-line in)))
     res))
 
+;;> Sends the entire contents of a file or input port to an output port.
+
+(define (send-file fd-port-or-filename . o)
+  (let* ((in (if (string? fd-port-or-filename)
+                 (open-input-file fd-port-or-filename)
+                 fd-port-or-filename))
+         (out (if (pair? o) (car o) (current-output-port)))
+         (fd (if (port? in) (port-fileno in) in))
+         (sock (if (port? out) (port-fileno out) out)))
+    (if (and fd sock (is-a-socket? sock))
+        (let lp ((start 0))
+          (let ((res (%send-file fd sock start)))
+            (cond
+             ((not res) (lp start))
+             ((not (zero? res)) (lp (+ start res))))))
+        (let lp ()
+          (let ((str (read-string 8192 in)))
+            (cond ((not (eof-object? str))
+                   (display str out)
+                   (lp))))))))
+
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; higher order port operations
 
diff --git a/lib/chibi/io/io.stub b/lib/chibi/io/io.stub
index e5ed4f0e..04b239a1 100644
--- a/lib/chibi/io/io.stub
+++ b/lib/chibi/io/io.stub
@@ -20,6 +20,11 @@
 
 (c-include "port.c")
 
+(define-c boolean (is-a-socket? "sexp_is_a_socket_p") (fileno))
+
+(define-c errno (%send-file "sexp_send_file")
+  (fileno fileno off_t (default 0 off_t) (result off_t)))
+
 (define-c sexp (%make-custom-input-port "sexp_make_custom_input_port")
   ((value ctx sexp) (value self sexp) sexp sexp sexp))
 
diff --git a/lib/chibi/io/port.c b/lib/chibi/io/port.c
index a1b5483b..7116588c 100644
--- a/lib/chibi/io/port.c
+++ b/lib/chibi/io/port.c
@@ -375,3 +375,23 @@ sexp sexp_peek_u8 (sexp ctx, sexp self, sexp in) {
     sexp_push_char(ctx, sexp_unbox_fixnum(res), in);
   return res;
 }
+
+int sexp_is_a_socket_p (int fd) {
+#if defined(PLAN9) || defined(_WIN32)
+  return 0;
+#else
+  struct stat statbuf;
+  fstat(fd, &statbuf);
+  return S_ISSOCK(statbuf.st_mode);
+#endif
+}
+
+int sexp_send_file (int fd, int s, off_t offset, off_t len, off_t* res) {
+#if SEXP_USE_SEND_FILE
+  *res = len;
+  return sendfile(fd, s, offset, res, NULL, 0);
+#else
+  *res = 0;
+  return 22; /* EINVAL */
+#endif
+}