[ftp] User and password URI support for the FTP protocol

The default user and password are used for anonymous FTP by default.
This patch adds support for an explicit user name and password in an FTP
URI:

    imgfetch ftp://user:password@server.com/path/to/file

Edited-by: Stefan Hajnoczi <stefanha@gmail.com>.  Bugs are my fault.

Signed-off-by: Marty Connor <mdc@etherboot.org>

src/net/tcp/ftp.c

 	return ftp->uri->path;
 }
 
+/**
+ * Retrieve FTP user
+ *
+ * @v ftp		FTP request
+ * @ret user		FTP user
+ */
+static const char * ftp_user ( struct ftp_request *ftp ) {
+	static char *ftp_default_user = "anonymous";
+	return ftp->uri->user ? ftp->uri->user : ftp_default_user;
+}
+
+/**
+ * Retrieve FTP password
+ *
+ * @v ftp		FTP request
+ * @ret password	FTP password
+ */
+static const char * ftp_password ( struct ftp_request *ftp ) {
+	static char *ftp_default_password = "etherboot@etherboot.org";
+	return ftp->uri->password ? ftp->uri->password : ftp_default_password;
+}
+
 /** FTP control channel strings */
 static struct ftp_control_string ftp_strings[] = {
 	[FTP_CONNECT]	= { NULL, NULL },
-	[FTP_USER]	= { "USER anonymous", NULL },
-	[FTP_PASS]	= { "PASS etherboot@etherboot.org", NULL },
+	[FTP_USER]	= { "USER ", ftp_user },
+	[FTP_PASS]	= { "PASS ", ftp_password },
 	[FTP_TYPE]	= { "TYPE I", NULL },
 	[FTP_PASV]	= { "PASV", NULL },
 	[FTP_RETR]	= { "RETR ", ftp_uri_path },