* generic/tclIORChan.c (ReflectOutput): Allow zero return from

	  write when input was zero-length anyway. Otherwise keept it an
	  error, and separate the message from 'written too much'.

	* tests/ioCmd.test (iocmd-24.6): Testcase updated for changed
	  message.

3 files changed, 22 insertions, 4 deletions

diff --git a/ChangeLog b/ChangeLog
index 6031f9e..8cb6958 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,12 @@
 2008-04-04  Andreas Kupries  <andreask@activestate.com>
 
+	* generic/tclIORChan.c (ReflectOutput): Allow zero return from
+	  write when input was zero-length anyway. Otherwise keept it an
+	  error, and separate the message from 'written too much'.
+
+	* tests/ioCmd.test (iocmd-24.6): Testcase updated for changed
+	  message.
+
 	* generic/tclIORChan.c (ReflectClose): Added missing removal of
 	  the now closed channel from the reflection map. Before we could
 	  crash the system by invoking 'chan postevent' on a closed
diff --git a/generic/tclIORChan.c b/generic/tclIORChan.c
index 10d0b2e..b57d157 100644
--- a/generic/tclIORChan.c
+++ b/generic/tclIORChan.c
@@ -15,7 +15,7 @@
  * See the file "license.terms" for information on usage and redistribution of
  * this file, and for a DISCLAIMER OF ALL WARRANTIES.
  *
- * RCS: @(#) $Id: tclIORChan.c,v 1.29 2008/04/04 16:46:57 andreas_kupries Exp $
+ * RCS: @(#) $Id: tclIORChan.c,v 1.30 2008/04/04 17:18:31 andreas_kupries Exp $
  */
 
 #include <tclInt.h>
@@ -434,6 +434,7 @@ static const char *msg_read_unsup = "{read not supported by Tcl driver}";
 static const char *msg_read_toomuch = "{read delivered more than requested}";
 static const char *msg_write_unsup = "{write not supported by Tcl driver}";
 static const char *msg_write_toomuch = "{write wrote more than requested}";
+static const char *msg_write_nothing = "{write wrote nothing}";
 static const char *msg_seek_beforestart = "{Tried to seek before origin}";
 #ifdef TCL_THREADS
 static const char *msg_send_originlost = "{Origin thread lost}";
@@ -1290,7 +1291,17 @@ ReflectOutput(
 
     Tcl_DecrRefCount(resObj);		/* Remove reference held from invoke */
 
-    if ((written == 0) || (toWrite < written)) {
+    if ((written == 0) && (toWrite > 0)) {
+	/*
+	 * The handler claims to have written nothing of what it was
+	 * given. That is bad.
+	 */
+
+	SetChannelErrorStr(rcPtr->chan, msg_write_nothing);
+	*errorCodePtr = EINVAL;
+	return -1;
+    }
+    if (toWrite < written) {
 	/*
 	 * The handler claims to have written more than it was given. That is
 	 * bad. Note that the I/O core would crash if we were to return this
diff --git a/tests/ioCmd.test b/tests/ioCmd.test
index fcb0b74..e246d2a 100644
--- a/tests/ioCmd.test
+++ b/tests/ioCmd.test
@@ -13,7 +13,7 @@
 # See the file "license.terms" for information on usage and redistribution
 # of this file, and for a DISCLAIMER OF ALL WARRANTIES.
 #
-# RCS: @(#) $Id: ioCmd.test,v 1.37 2008/04/04 16:46:57 andreas_kupries Exp $
+# RCS: @(#) $Id: ioCmd.test,v 1.38 2008/04/04 17:18:32 andreas_kupries Exp $
 
 if {[lsearch [namespace children] ::tcltest] == -1} {
     package require tcltest 2
@@ -1039,7 +1039,7 @@ test iocmd-24.6 {chan write, bad result, zero-length write} -match glob -body {
     close $c
     rename foo {}
     set res
-} -result {{write rc* snarf} 1 {write wrote more than requested}}
+} -result {{write rc* snarf} 1 {write wrote nothing}}
 test iocmd-24.7 {chan write, failed write, error return} -match glob -body {
     set res {}
     proc foo {args} {oninit; onfinal; track; return -code error BOOM!}