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ControlSocket -- Click element;
opens control sockets for other programs
ControlSocket("TCP", PORTNUMBER [, keywords READONLY, PROXY, VERBOSE, LOCALHOST, RETRIES, RETRY_WARNINGS])
ControlSocket("UNIX", FILENAME [, keywords])
Package: userlevel (core)
Opens a control socket that allows other user-level programs to call read or
write handlers on the router. Depending on its configuration string,
ControlSocket will listen on TCP port PORTNUMBER, or on a UNIX-domain socket
named FILENAME. With the PROXY keyword argument, you can make ControlSocket speak to
a kernel driver; see below.
The "server" (that is, the ControlSocket element) speaks a relatively
simple line-based protocol. Commands sent to the server are single lines of
text; they consist of words separated by spaces. The server responds to
every command with at least one message line followed optionally by some
data. Message lines start with a three-digit response code, as in FTP. When
multiple message lines are sent in response to a single command, all but
the last begin with the response code and a hyphen (as in "200-Hello!");
the last line begins with the response code and a space (as in "200
The server will accept lines terminated by CR, LF, or CRLF. Its response
lines are always terminated by CRLF.
When a connection is opened, the server responds by stating its protocol
version number with a line like "Click::ControlSocket/1.3". The current
version number is 1.3. Changes in minor version number will only add commands
and functionality to this specification, not change existing functionality.
ControlSocket supports hot-swapping, meaning you can change configurations
without interrupting existing clients. The hot-swap will succeed only if the
old ControlSocket and the new ControlSocket have the same element name, and
the same socket type and port/filename parameters. Additionally, the new
ControlSocket must have RETRIES set to 1 or more, since the old ControlSocket
has already bound the relevant socket.
Keyword arguments are:
- Boolean. Disallows write handlers if true (it is false by
- String. Specifies an element proxy. When a user requests the value of handler
E.H, ControlSocket will actually return the value of `PROXY.E.H'. This is
useful with elements like KernelHandlerProxy. Default is empty (no proxy).
- Boolean. When true, ControlSocket will print messages whenever it accepts a
new connection or drops an old one. Default is false.
- Boolean. When true, a TCP ControlSocket will only accept connections from the
local host (127.0.0.1). Default is false.
- Integer. If greater than 0, ControlSocket won't immediately fail when it can't
open its socket. Instead, it will attempt to open the socket once a second
until it succeeds, or until RETRIES unsuccessful attempts (after which it will
stop the router). Default is 0.
- Boolean. If true, ControlSocket will print warning messages every time it
fails to open a socket. If false, it will print messages only on the final
failure. Default is true.
The PORT argument for TCP ControlSockets can also be an integer followed by a
plus sign, as in "ControlSocket(TCP, 41930+)". This means that the
ControlSocket should bind on some port greater than or equal to PORT. If
PORT itself is in use, ControlSocket will try several nearby ports before
giving up. This can be useful in tests.
Many server commands
take a handler argument. These arguments name handlers, and take one of
elementname.handlername names a particular element's
elementnumber.handlername also names an element handler, but
the element is identified by index, starting from 1; and
names a global handler. (There are seven global read handlers, named
requirements. See click.o(8) for more information.)
- READ handler [params...]
- Call a read handler, passing the params, if any,
as arguments, and return the results.
On success, responds with a "success" message (response
code 2xy) followed by a line like "DATA n". Here, n is a
decimal integer indicating the length of the read handler data. The n
bytes immediately following (the CRLF that terminates) the DATA line are
the handler's results.
- READDATA handler n
- Call a read handler, passing the n bytes immediately following (the CRLF
that terminates) the READDATA line as arguments, and return the results with
"DATA n" as in the READ command. Introduced in version 1.2 of the
- READUNTIL handler terminator
- Call a read handler and return the results with "DATA n" as in the READ
command. Parameters for handler are read from the input stream. Parameter
reading stops at the first line that equals terminator. If terminator is
not supplied, parameter reading stops at the first blank line. When searching
for a terminator, ControlSocket removes trailing spaces from both
terminator and the input lines. Introduced in version 1.3 of the
- WRITE handler params...
- Call a write handler, passing the params, if any, as arguments.
- WRITEDATA handler n
- Call a write handler. The arguments to pass are the n bytes immediately
following (the CRLF that terminates) the WRITEDATA line.
- WRITEUNTIL handler terminator
- Call a write handler. The arguments to pass are the read from the input
stream, stopping at the first line that equals terminator.
- CHECKREAD handler
- Checks whether a handler exists and is readable. The return status is 200
for readable handlers, and an appropriate error status for non-readable
handlers or nonexistent handlers.
- CHECKWRITE handler
- Checks whether a handler exists and is writable.
- LLRPC llrpc [n]
- Call an LLRPC llrpc and return the results. Llrpc should have the form
hexnumber is the LLRPC number, from
<click/llrpc.h>, in hexadecimal network format. Translate
constants to network format by calling
CLICK_LLRPC_HTON(CLICK_LLRPC_...). If n is given, then the n bytes
immediately following (the CRLF that terminates) the LLRPC line are passed in
as an argument. The results are returned after a "DATA nn" line, as in
ControlSocket will not call an LLRPC unless it can determine (from the command
number) how much data the LLRPC expects and returns. (Only "flat" LLRPCs may
be called; they are declared using the _CLICK_IOC_[RWS]F macros.)
- Close the connection.
The server's response codes follow this pattern.
- The command succeeded.
- The command failed.
Here are some of the particular error messages:
220 OK, but the handler reported some warnings.
500 Syntax error.
501 Unimplemented command.
510 No such element.
511 No such handler.
520 Handler error.
530 Permission denied.
540 No router installed.
ControlSocket is only available in user-level processes.
- port (read-only)
- Returns the ControlSocket's port number. Only available for TYPE TCP.
- filename (read-only)
- Returns the ControlSocket's UNIX socket filename. Only available for TYPE