-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 All,
On 2/8/16 3:43 PM, Mark Thomas wrote: > On 08/02/2016 18:41, Jason Ricles wrote: >> I have an application that sends binary websocket messages >> between a class and the web application using a websocket server >> written in java. >> >> The data being sent from the java class is encoded in a binary >> buffer with the bytes in ISO8859_1. However, when I receive the >> bytes on the websocket server and the web application end they >> are junk (such as -121, -116, etc.) and not encoded the correct >> way that they need to be. > > The bytes are transmitted as unsigned on the wire (as required by > the WebSocket spec). Java handles them as signed. You need to > convert them. Something like (untested): > > char c = b & 0xFF; I had to read this something like 10 times before I convinced myself that this was correct. For those who want to know what this makes any kind of sense (because, at first glance, it does not make any sense), I'll explain it. For starters, Java uses signed byte primitives but /unsigned/ char primitives. For those coming from the C world, that may be confusing. bytes are 8 (signed) bits and chars are 16 (unsigned) bits. But Java doesn't have any defined arithmetic operations (including bitwise) for anything smaller than an int (32 signed bytes), so the above assignment is actually more like this: byte b = 0xab; // e.g. char c = (char) ( ((int)b) & 0xff ) So, first b is widened from 8 bits to 32 bits -- with a sign-extension. That means that -1 is still -1, it's just represented by a different bit pattern: 1111 1111 1111 1111 1111 1111 1111 1111 instead of 1111 1111. Next, the bitwise && is performed, which zeros-out everything but the bottom 8-bits (now we have .... .... 0000 0000 1111 1111). Then, that value is cast to char which does practically nothing. In the above example (-1), we get a final value of 255 for c, which is exactly what you'd expect for an unsigned char whose signed value is -1. I think the only surprise thing there is that Java widens all types to 32-bit signed int to perform these operations. Without that fact, the above assignment doesn't make much sense. In C, that line of code would do absolutely nothing at all. - -chris -----BEGIN PGP SIGNATURE----- Comment: GPGTools - http://gpgtools.org Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iEYEARECAAYFAla5FywACgkQ9CaO5/Lv0PCvlACfXaUtdj7t6VhKJxTUsurCOeqS 6jgAoJ3Vw1/L2UHatpFN4iDPnLL7JCxH =7P38 -----END PGP SIGNATURE----- --------------------------------------------------------------------- To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
