Client-server communication is line-oriented.
-The server sends lines of output. Each output line starts with a
-character identifying the line, followed by a space, then arbitrary
-text, then a line feed.
+The server sends lines of output. Each output line starts with an
+identification string, followed by a space, then arbitrary text, then
+a line feed.
-Identification characters encode small integers called output ids.
-Ids less than 10 are encoded as decimal digits, and larger ids as
-lower case letters, starting with 'a'. Symbolic names for ids are
+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
defined in proto.h.
+emp_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
large line without loss of functionality, but safety must be ensured.
occur and may be ignored.
The server prompts for input. Each prompt `consumes' one line of
-input. 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 horizontal tab.
-Clients should not send overlong or malformed UTF-8 sequences.
+input (except for C_EXECUTE, which see). 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 horizontal tab. Clients should not send
+overlong or malformed UTF-8 sequences.
A client is called synchronous if it waits for a prompt before it
sends another line of input. Else it is called asynchronous.
An Empire session consists of two phases: login and playing.
emp_client is synchronous during the former and asynchronous during
-the latter. It can currently deadlock as described above.
+the latter. Versions before 4.3.11 could deadlock as described above.
Login phase
-----------
may or may not process valid parts of rejected requests.
If there are no arguments, the server lists its options. For each
- option, it sends a C_DATA line with OPTION=VALUE as text.
+ option, it sends a C_DATA line with OPTION=VALUE as text, and
+ finally a C_CMDOK. If it supports no options at all, it may reply
+ with C_BADCMD instead.
See below for supported session options.
Authenticate. Country name must be set already.
-* play [USER [COUNTRY [PASSWORD]]]
+* play [USER COUNTRY PASSWORD]
Start playing.
- Optional argument USER sets the user name.
-
- Optional argument COUNTRY sets the country name.
+ If no arguments are given, the country must be authenticated
+ already.
- Optional argument PASSWORD authenticates. If it isn't present, the
- country must be authenticated already.
+ Else, argument USER sets the user name, COUNTRY sets the country
+ name, and PASSWORD authenticates.
Some error conditions result in a C_EXIT reply. Clients should
treat it just like C_CMDERR.
* Sub-prompt C_FLUSH
The server consumes a line of input and passes it to the currently
- executing command. Commands usually fail on EOF or interrupt.
+ executing command. Commands usually fail on interrupt. The server
+ terminates the session on EOF (but see C_EXECUTE for an exception).
Text is a human-readable prompt supplied by the command.
* Control C_EXECUTE
- Request execution of a script. The text is a copy of the execute
- command's first argument. Its syntax and semantics is left to the
- client.
+ Request execution of a batch file. The text is whatever was on the
+ line of input after the execute command. Its syntax and semantics
+ are left to the client.
- emp_client interprets the text as file name, and sends the contents
- of that file.
+ emp_client interprets the first word (sequence of non-space
+ characters) in the text as file name, and sends the contents of that
+ file.
The security considerations on C_PIPE (below) apply to C_EXECUTE as
well.
- The client shall mark the end of the script by signalling EOF as
- described above. It may signal interrupt if it is unable or
- unwilling to send the complete script.
+ Note that servers before 4.3.11 sent a copy of the execute command's
+ first argument as text. This made it hard for clients to ensure
+ that the text is identical to what was sent, because the server
+ 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.
- While executing the script, the server sends no C_PROMPT command
+ The client shall mark the end of the batch file by signalling EOF as
+ described above. This does not terminate the session. It may
+ signal interrupt if it is unable or unwilling to send the complete
+ batch file.
+
+ While executing the batch file, the server sends no C_PROMPT command
prompts. It still sends C_FLUSH sub-prompts.
- Certain bad failures make the server ignore the rest of the script
- file. This feature is too hard to predict to be really useful.
+ Protocol flaw: not sending C_PROMPT here screws up redirections:
+ they apply until the next C_PROMPT, i.e. from start of redirected
+ command until end of containing batch file.
+
+ 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.
- Strictly asynchronous clients cannot support C_EXECUTE correctly.
- By the time C_EXECUTE arrives, the client may have sent more input
- already. That input `overtakes' the script in the input stream.
+ Protocol flaw: strictly asynchronous clients cannot support
+ C_EXECUTE correctly. By the time C_EXECUTE arrives, the client may
+ have sent more input already. That input `overtakes' the contents
+ of the batch file in the input stream.
emp_client has this problem.
* Control C_EXIT
- End of session. The server will close the connection. Text is a
- human-readable farewell.
+ 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_PIPE
- When a command is redirected to a pipeline, its output is prededed
+ When a command is redirected to a pipeline, its output is preceded
by a C_PIPE line. The text is a copy of the redirection, starting
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.
+ The redirection applies to a single command, i.e. until the next
+ C_PROMPT.
+
For obvious security reasons, clients supporting pipes shall ensure
that the text is identical to whatever was sent to the server. Note
that the server recognizes redirection only in command lines, not
* Control C_REDIR
- When a command is redirected to a file, its output is prededed by a
+ When a command is redirected to a file, its output is preceded by a
C_REDIR line. The text is a copy of the redirection, starting with
'>', optionally followed by '>' or '!'. Syntax and semantics of the
remaining text are left to the client.
existing file, with '>>' it appends to the file, and with just '>'
it refuses to overwrite an existing file.
+ The redirection applies to a single command, i.e. until the next
+ C_PROMPT.
+
The security considerations on C_PIPE apply to C_REDIR as well.
* Other ids
Other ids do not occur currently. Clients shall deal gracefully
with ids they don't know.
- emp_client treats unknown ids like C_DATA. For historical reasons,
- it prepends "Aborted\n" to C_ABORT lines, and "Error; " to C_CMDERR
- and C_BADCMD lines.
+ 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.
Session Options
projects / empserver / commitdiff