From f1da0fefc6ab7f421a081f26b052cd5116c819e6 Mon Sep 17 00:00:00 2001
From: dgp <dgp@users.sourceforge.net>
Date: Thu, 18 Dec 2014 18:06:51 +0000
Subject: [7c187a3773] Fix error in managing inStatePtr->inQueueTail value in
 the byte-moving optimized path of [chan copy].  Thanks to Benno.

---
 generic/tclIO.c |  3 +++
 tests/io.test   | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+)

diff --git a/generic/tclIO.c b/generic/tclIO.c
index 2025742..8a35aee 100644
--- a/generic/tclIO.c
+++ b/generic/tclIO.c
@@ -9215,6 +9215,9 @@ MBWrite(
     }
     outStatePtr->outQueueTail = tail;
     inStatePtr->inQueueHead = bufPtr;
+    if (inStatePtr->inQueueTail == tail) {
+	inStatePtr->inQueueTail = bufPtr;
+    }
     if (bufPtr == NULL) {
 	inStatePtr->inQueueTail = NULL;
     }
diff --git a/tests/io.test b/tests/io.test
index b09d55a..cd8b014 100644
--- a/tests/io.test
+++ b/tests/io.test
@@ -7900,6 +7900,44 @@ test io-53.16 {[ed29c4da21] MBRead: fblocked seen as error} -setup {
     close $c
     removeFile out
 } -result 100
+test io-53.17 {[7c187a3773] MBWrite: proper inQueueTail handling} -setup {
+    proc driver {cmd args} {
+        variable buffer
+        variable index
+        set chan [lindex $args 0]
+        switch -- $cmd {
+            initialize {
+                set index($chan) 0
+                set buffer($chan) [encoding convertto utf-8 \
+                        line\n[string repeat a 100]line\n]
+                return {initialize finalize watch read}
+            }
+            finalize {
+                unset index($chan) buffer($chan)
+                return
+            }
+            watch {}
+            read {
+                set n [lindex $args 1]
+                set new [expr {$index($chan) + $n}]
+                set result [string range $buffer($chan) $index($chan) $new-1]
+                set index($chan) $new
+                return $result
+            }
+        }
+    }
+    set c [chan create read [namespace which driver]]
+    chan configure $c -encoding utf-8 -translation lf -buffersize 107
+    set out [makeFile {} out]
+    set outChan [open $out w]
+    chan configure $outChan -encoding utf-8 -translation lf
+} -body {
+    list [gets $c] [chan copy $c $outChan -size 100] [gets $c]
+} -cleanup {
+    close $outChan
+    close $c
+    removeFile out
+} -result {line 100 line}
 
 test io-54.1 {Recursive channel events} {socket fileevent} {
     # This test checks to see if file events are delivered during recursive
-- 
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