Protocol
========
-Empire's client server protocol is plain text. It is simple enough
-that you could play using nothing more than telnet. That's a feature.
+The protocol between Empire client and server is plain text. It is
+simple enough that you could play using nothing more than telnet.
+That's a feature.
A session uses either ASCII or UTF-8, controlled by session option
utf-8. See below for session options. The session always starts in
identification string, followed by a space, then arbitrary text, then
a line feed.
-Identification strings encode small integers called output ids as base
+Identification strings encode small integers called output IDs as base
36 numbers. Characters '0' to '9' represent digits 0 to 9, and 'a' to
-'z' represent 10..35, as do 'A' to 'Z'. Symbolic names for ids are
+'z' represent 10..35, as do 'A' to 'Z'. Symbolic names for IDs are
defined in proto.h.
-emp_client versions before version 4.3.11 parse large output ids
-incorrectly. Such ids do not currently occur.
+empire-client versions before version 4.3.11 parse large output IDs
+incorrectly. Such IDs do not currently occur.
Clients shall be able to safely handle output lines of arbitrary
length. Naturally, a client may not be able to handle a sufficiently
ASCII name decimal meaning
----------------------------------------------------
+ bell 7 ring the bell
horizontal tab 9 move to next tab stop(1)
line feed 10 end of line
shift out 14 begin highlighting(2)
occur and may be ignored.
The server prompts for input. Each prompt `consumes' one line of
-input (except for C_EXECUTE, and when the update aborts a command, as
+input (except for C_EXECUTE, and when a command is aborted, as
described below). Input lines are arbitrary text, terminated by line
feed, which is optionally preceded by carriage return (decimal 13).
Lines should not contain ASCII control characters other than
because the server may well block on output, which then deadlocks the
session.
-An Empire session consists of two phases: login and playing.
-emp_client is synchronous during the former and asynchronous during
-the latter. Versions before 4.3.11 could deadlock as described above.
+An Empire session consists of three phases: login, playing, and
+shutdown. empire-client is synchronous in the login phase, and
+asynchronous afterwards. Versions before 4.3.11 could deadlock as
+described above.
Login phase
-----------
The server starts with a C_INIT prompt. The login phase ends when the
server sends another C_INIT prompt, which starts the playing phase, or
-when it closes the connection.
+when it enters the shutdown phase, as described below
The server replies to a login command with another prompt. Except as
noted below, the server replies C_BADCMD for syntax errors, C_CMDERR
* kill
- If another connection is open for this country, forcibly close it,
- else do nothing. Country must be authenticated.
+ If another connection for this country is in the playing phase,
+ force it into the shutdown phase, else do nothing. Country must be
+ authenticated.
Reply is C_EXIT regardless of success.
* quit
- Terminate the session. The server replies with C_EXIT and closes
- the connection.
+ Terminate the session. The server replies with C_EXIT and enters
+ the shutdown phase.
* sanc
Set the user name. This is optional and defaults to "".
+If the login phase takes more than login_grace_time (default 120s),
+the server enters the shutdown phase.
+
Playing phase
-------------
described below. Anything else is either a command or input for a
command, depending on how the server prompts for the line.
-emp_client signals `EOF' when it encounters an end-of-file condition
-while reading player input. It signals `interrupt' when it catches
-SIGINT, which is normally triggered by Ctrl-C.
+empire-client signals `EOF' when it encounters an end-of-file
+condition while reading player input. It signals `interrupt' when it
+catches SIGINT, which is normally triggered by Ctrl-C.
-The following ids occur:
+The following IDs occur:
* Command prompt C_PROMPT
- The server consumes a line of input. On EOF, the server terminates
- the session. Interrupt is ignored. Anything else is interpreted as
- Empire command.
+ The server consumes a line of input. On EOF, the server enters the
+ shutdown phase. Interrupt is ignored. Anything else is interpreted
+ as Empire command.
Text is minutes used, space, BTUs left. Both numbers are in
decimal. Clients shall ignore additional text separated by another
space.
- emp_client prints this prompt using format "[%d:%d] Command : ".
+ empire-client prints this prompt using format "[%d:%d] Command : ".
Clients with a tty-like user interface are advised to use a similar
format, to minimize differences to the examples in info.
* Argument prompt C_FLUSH
The server consumes a line of input and passes it to the currently
- executing command. Commands usually fail on interrupt. The server
- terminates the session on EOF (but see C_EXECUTE for an exception).
+ executing command.
+
+ The server aborts the command on interrupt and EOF. Any argument
+ prompts it may send before the next command prompt do not consume
+ input. On EOF, the server then enters the shutdown phase (but see
+ C_EXECUTE for an exception).
If an update runs while the server waits for the line of input to
arrive, the current command is aborted. Whether the server consumes
Text is a human-readable prompt supplied by the command.
- emp_client prints the text verbatim.
+ empire-client prints the text verbatim.
* Data C_DATA
Text is human-readable server output.
- emp_client prints the text verbatim.
+ empire-client prints the text verbatim.
* Control C_EXECUTE
line of input after the execute command. Its syntax and semantics
are left to the client.
- emp_client interprets the first word (sequence of non-space
+ empire-client interprets the first word (sequence of non-space
characters) in the text as file name, and sends the contents of that
file.
strips funny characters and interprets and strips '"' characters
when splitting input lines into command and arguments.
- emp_client gets confused when old servers mangle the text that way.
+ empire-client gets confused when old servers mangle the text that
+ way.
The client shall mark the end of the batch file by signalling EOF as
described above. This does not terminate the session. It may
rejects redirections in batch files.
Certain bad failures make the server ignore the rest of the batch
- file file. This feature is too hard to predict to be really useful.
+ file. This feature is too hard to predict to be really useful.
Protocol flaw: strictly asynchronous clients cannot support
C_EXECUTE correctly. By the time C_EXECUTE arrives, the client may
execute comes from a batch file, the server rejects execute commands
there.
- emp_client has this problem.
+ empire-client has this problem.
Clients are not required to support C_EXECUTE. Clients are
encouraged to offer alternative means for scripting.
-* Control C_EXIT
-
- End of session. The server is about to close the connection. Text
- is a human-readable farewell.
-
- emp_client prints this text prepended with "Exit: ".
-
* Control C_FLASH
Asynchronous message. The client should display the text
immediately.
- emp_client prints the text verbatim, prepended by a line feed. This
- is clearly sub-optimal, because it can be inserted in the middle of
- user input. Clients wishing to to display asynchronous messages
- together with normal I/O should insert them before the current
- prompt.
+ empire-client prints the text verbatim, prepended by a line feed.
+ This is clearly sub-optimal, because it can be inserted in the
+ middle of user input. Clients wishing to display asynchronous
+ messages together with normal I/O should insert them before the
+ current prompt.
Although asynchronous messages can be switched off with the toggle
command, client support for C_FLASH is not really optional, because
Notification that the number of unread telegrams changed. The text
is the notification in human-readable form.
- emp_client prints the last received C_INFORM text right before each
- prompt. It also repeats the last prompt when a C_INFORM arrives.
- This is sub-optimal just like its treatment of C_FLASH.
+ empire-client prints the last received C_INFORM text right before
+ each prompt. It also repeats the last prompt when a C_INFORM
+ arrives. This is sub-optimal just like its treatment of C_FLASH.
The user can switch these off with the toggle command. Client
support is not really optional for the same reasons as for C_FLASH.
with '|'. Syntax and semantics of the text after the '|' are left
to the client.
- emp_client executes text after '|' as shell command, with standard
- input connected to the Empire command's output.
+ empire-client executes text after '|' as shell command, with
+ standard input connected to the Empire command's output.
The redirection applies to a single command, i.e. until the next
C_PROMPT.
that the server recognizes redirection only in command lines, not
argument lines. Asynchronous clients cannot distinguish the two.
- emp_client prepares for redirections being recognized in any line,
- and copes with only some of them being actually recognized.
+ empire-client prepares for redirections being recognized in any
+ line, and copes with only some of them being actually recognized.
* Control C_REDIR
'>', optionally followed by '>' or '!'. Syntax and semantics of the
remaining text are left to the client.
- emp_client interprets the first word (sequence of non-space
+ empire-client interprets the first word (sequence of non-space
characters) in the remaining text as file name, and redirects the
command's output to that file. The use of the first word is
unfortunate, as it arbitrarily limits the user's choice of file
The security considerations on C_PIPE apply to C_REDIR as well.
-* Other ids
+* Other IDs
+
+ Other IDs do not occur currently. Clients shall deal gracefully
+ with IDs they don't know.
+
+ empire-client treats unknown IDs like C_DATA. Versions before
+ 4.3.11 prepend "Aborted\n" to C_ABORT lines, and "Error; " to
+ C_CMDERR and C_BADCMD lines for historical reasons.
+
+Shutdown phase
+--------------
+
+In the shutdown phase, the server first sends a C_EXIT message. Its
+text is a human-readable farewell.
+
+empire-client prints this text prepended with "Exit: ".
- Other ids do not occur currently. Clients shall deal gracefully
- with ids they don't know.
+The server then waits for the output queue to drain, then shuts down
+the output direction of the connection. This makes the client detect
+an end-of-file condition after it received all output. The client
+should then close its end of the connection. The server continues to
+read and ignore input until it detects an end-of-file condition. It
+then closes its end of the connection, and the session terminates.
- emp_client treats unknown ids like C_DATA. Versions before 4.3.11
- prepend "Aborted\n" to C_ABORT lines, and "Error; " to C_CMDERR and
- C_BADCMD lines for historical reasons.
+If the server closed its end of the connection without waiting for the
+client to close the other end first, asynchronous clients could lose
+output: an attempt to send input after the server closed its end would
+fail with a connection reset error even when some output is still in
+flight. Versions before 4.3.30 could misbehave like that in certain
+circumstances.
+If the shutdown phase doesn't complete within login_grace_time
+(default 120s), the server closes the connection immediately. Output
+may be lost.
Session Options
===============
projects / empserver / blobdiff