From 24aeea28c141f3f8af1c8953de55bb48a4272398 Mon Sep 17 00:00:00 2001
From: Matthew Flatt <mflatt@racket-lang.org>
Date: Sun, 9 Dec 2018 12:16:10 -0700
Subject: [PATCH] file-position: repair for OS pipe after peek

Closes #2419
---
 pkgs/racket-test-core/tests/racket/port.rktl | 14 ++++++++++++++
 racket/src/racket/src/port.c                 |  4 +++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/pkgs/racket-test-core/tests/racket/port.rktl b/pkgs/racket-test-core/tests/racket/port.rktl
index fe92fec24f..d2f23f52ae 100644
--- a/pkgs/racket-test-core/tests/racket/port.rktl
+++ b/pkgs/racket-test-core/tests/racket/port.rktl
@@ -921,6 +921,20 @@
 
   (delete-file path))
 
+;; Check `file-position`, OS-level pipes, and peek
+(when (and (memq (system-type) '(unix macosx))
+           (file-exists? "/bin/cat"))
+  (define-values (sp stdout-in stdin-out no-stderr) (subprocess #f #f (current-error-port) "/bin/cat"))
+  (write-bytes #"abcd\n" stdin-out)
+  (close-output-port stdin-out)
+  (test 0 file-position stdout-in)
+  (test #"abc" peek-bytes 3 0 stdout-in)
+  (test 0 file-position stdout-in)
+  (test #\a read-char stdout-in)
+  (test 1 file-position stdout-in)
+  (close-input-port stdout-in)
+  (subprocess-wait sp))
+
 ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; Check reader error-message formatting for a struct port
 
diff --git a/racket/src/racket/src/port.c b/racket/src/racket/src/port.c
index 9c0b688728..89dc3ff298 100644
--- a/racket/src/racket/src/port.c
+++ b/racket/src/racket/src/port.c
@@ -4202,6 +4202,7 @@ do_file_position(const char *who, int argc, Scheme_Object *argv[], int can_false
     return scheme_void;
   } else {
     mzlonglong pll;
+    int already_ungot = 0;
     if (f) {
       pll = BIG_OFF_T_IZE(ftello)(f);
     } else if (fd) {
@@ -4210,6 +4211,7 @@ do_file_position(const char *who, int argc, Scheme_Object *argv[], int can_false
       sz = rktio_get_file_position(scheme_rktio, fd);
       if (!sz) {
         pll = do_tell(argv[0], 0);
+        already_ungot = 1;
       } else {
         pll = *sz;
         free(sz);
@@ -4247,7 +4249,7 @@ do_file_position(const char *who, int argc, Scheme_Object *argv[], int can_false
     }
 
     /* Back up for un-gotten & peeked chars: */
-    if (SCHEME_INPUT_PORTP(argv[0])) {
+    if (!already_ungot && SCHEME_INPUT_PORTP(argv[0])) {
       Scheme_Input_Port *ip;
       ip = scheme_input_port_record(argv[0]);
       pll -= ip->ungotten_count;