Subj : Nulls in strings passed back from xpconnect
To   : mozilla-jseng@mozilla.org
From : thomas@thurman.org.uk (Thomas Thurman)
Date : Mon Jan 20 2003 03:48 pm

This is rather a general question, but after quite a bit of searching I
haven't found an answer to it:

I'm using xpconnect to read in a file which will probably contain
nulls. The read() method of nsIScriptableInputStream seems to be what I
want (or am I wrong?), but when the string gets returned it's cut off at
the first null.

Here's an example session from xpcshell to show what I mean. "troll.z5" is
a 64000-byte file; character 1 is a null, but characters 0 and 5 are not.

js> a=new Components.Constructor(
	"@mozilla.org/network/local-file-channel;1",
	"nsIFileChannel")()
[xpconnect wrapped nsIFileChannel]
js> z=new Components.Constructor(
	"@mozilla.org/file/local;1",
	"nsILocalFile",
	"initWithPath")(
	"troll.z5")
[xpconnect wrapped nsILocalFile]
js> b=new Components.Constructor(
	"@mozilla.org/scriptableinputstream;1",
	"nsIScriptableInputStream")()
[xpconnect wrapped nsIScriptableInputStream]
js> a.init(z, 1, 0)
js> b.init(a.open())
js> r=b.read(64000)

js> r.length
1
js> r.charCodeAt(5)
NaN

It's possible to work around the problem by reading the file in a byte at
a time, but that's enormously slow. Is there any way of:

  * allowing the null to be passed back in the string? (Spidermonkey
doesn't seem to have a problem with nulls in strings in general)

  * using something not a string to receive the data (say, an array?)

  * using an XPCOM component to represent the string so that the
conversion never happens?

T

.