The data you send is not correct. Here's the command I'm executing:
$ head="POST http://twitter.com/statuses/update.json HTTP/1.1\r\n
Host: twitter.com\r\n
Authorization: Basic myname:passwordinbs64\r\n
Content-type: application/x-www-form-urlencoded\r\n
Content-length: 10\r\n
Connection: Close\r\n\r\n
status=mymessage"; echo $head | nc twitter.com 80
HTTP/1.1 400 Bad Request
Date: Tue, 29 Jun 2010 10:19:38 GMT
Server: Apache
Vary: Accept-Encoding
Content-Length: 226
Connection: close
Content-Type: text/html; charset=iso-8859-1
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<html><head>
<title>400 Bad Request</title>
</head><body>
<h1>Bad Request</h1>
<p>Your browser sent a request that this server could not understand.<br />
</p>
</body></html>
I'm running a tcpdump in parallel and here is what it shows me:
0x0020: 5018 ffff 671f 0000 504f 5354 2068 7474 P...g...POST.htt
0x0030: 703a 2f2f 7477 6974 7465 722e 636f 6d2f p://twitter.com/
0x0040: 7374 6174 7573 6573 2f75 7064 6174 652e statuses/update.
0x0050: 6a73 6f6e 2048 5454 502f 312e 310d 0a20 json.HTTP/1.1...
0x0060: 486f 7374 3a20 7477 6974 7465 722e 636f Host:.twitter.co
0x0070: 6d0d 0a20 4175 7468 6f72 697a 6174 696f m...Authorizatio
0x0080: 6e3a 2042 6173 6963 206d 796e 616d 653a n:.Basic.myname:
0x0090: 7061 7373 776f 7264 696e 6273 3634 0d0a passwordinbs64..
0x00a0: 2043 6f6e 7465 6e74 2d74 7970 653a 2061 .Content-type:.a
0x00b0: 7070 6c69 6361 7469 6f6e 2f78 2d77 7777 pplication/x-www
0x00c0: 2d66 6f72 6d2d 7572 6c65 6e63 6f64 6564 -form-urlencoded
0x00d0: 0d0a 2043 6f6e 7465 6e74 2d6c 656e 6774 ...Content-lengt
0x00e0: 683a 2031 300d 0a20 436f 6e6e 6563 7469 h:.10...Connecti
0x00f0: 6f6e 3a20 436c 6f73 650d 0a0d 0a20 7374 on:.Close.....st
0x0100: 6174 7573 3d6d 796d 6573 7361 6765 0a atus=mymessage.
Do you see the mistake? At each line break are three characters, but there should be only two. This happens because you have a real line break in your variable definition that becomes a space in the shell. E.g.
$ head="line1
line2" ; echo $head
line1 line2
Try writing it all in one line instead.
$ head="POST http://twitter.com/statuses/update.json HTTP/1.1\r\nHost: twitter.com\r\nAuthorization: Basic myname:passwordinbs64\r\nContent-type: application/x-www-form-urlencoded\r\nContent-length: 10\r\nConnection: Close\r\n\r\nstatus=mymessage" ; echo $head | nc twitter.com 80
HTTP/1.1 401 Unauthorized
Date: Tue, 29 Jun 2010 10:25:43 GMT
Server: hi
Status: 401 Unauthorized
X-Runtime: 0.00577
Content-Type: application/json; charset=utf-8
Content-Length: 63
Cache-Control: no-cache, max-age=300
Set-Cookie: k=194.145.236.196.1277807143945525; path=/; expires=Tue, 06-Jul-10 10:25:43 GMT; domain=.twitter.com
Set-Cookie: guest_id=1277807143950191; path=/; expires=Thu, 29 Jul 2010 10:25:43 GMT
Set-Cookie: _twitter_sess=BAh7CDoPY3JlYXRlZF9hdGwrCBOsPYMpAToHaWQiJWQzZDkxNTg2MTY3OTFk%250AMzg5OTUyNWFhZGZlZDY0YjJmIgpmbGFzaElDOidBY3Rpb25Db250cm9sbGVy%250AOjpGbGFzaDo6Rmxhc2hIYXNoewAGOgpAdXNlZHsA--e95d14c755b85ff19606a0bc907c8b7a63d1b508; domain=.twitter.com; path=/
Expires: Tue, 29 Jun 2010 10:30:43 GMT
Vary: Accept-Encoding
Connection: close
{"errors":[{"code":32,"message":"Could not authenticate you"}]}