Empire is designed as a smart server with dumb clients. An Empire
client need to know nothing about the game. Even telnet would do. In
-fact, emp_client is little more than a slightly specialized telnet.
+fact, empire-client is little more than a slightly specialized telnet.
In such a design, presentation is in the server, and it is designed
for human consumption. Ideally, presentation and logic are cleanly
use '-' in meta-identifiers and omit the concatenation symbol ','.
table = header { record } footer ;
- header = "XDUMP" space [ "meta" space ] name space timestamp newline ;
- name = name-chr { name-chr } ;
- name-chr = ? ASCII characters 33..126 ? ;
+ header = "XDUMP" space [ "meta" space ]
+ identifier space timestamp newline ;
+ identifier = id-char1 { id-char } ;
+ id-char1 = ? ASCII letter ? ;
+ id-char = ? ASCII characters 33..126 except '"#()<>=' ? ;
timestamp = intnum ;
footer = "/" number newline ;
record = [ fields ] newline ;
Semantics:
-* The table name in the header is one of the names in xdump table.
+* The table identifier in the header is one of the names in xdump table.
* The timestamp increases monotonically. It has a noticeable
granularity: game state may change between an xdump and the next
- "d", field uses intnum syntax
- "g", field uses flonum syntax
- "s", field uses string syntax
- - "c", field uses string syntax
+ - "c", field uses string syntax (only until version 4.3.33)
* flags: The field's flags, a symbol set. Flags are:
- "deity", field visible only to deities
- - "extra", field not to be dumped
- - "const", field cannot be changed
- "bits", field is a symbol set, field type must encode symbol "d",
field table must not be -1.
+ - "hidden", field value is masked for contact when option HIDDEN is
+ enabled. Masked values are replaced by -1.
* len: If non-zero, then the record encodes an array with that many
- elements. If field type encodes symbol "c", it is a character
- array, which is dumped as a single string field. Else, the array is
- dumped as len fields.
+ elements. The array is dumped as len fields.
+
+ Only until version 4.3.33: if field type encodes symbol "c", it is a
+ character array, and is dumped as a single string field.
* table: Key for xdump table. Unless -1, it defines the table
referenced by the field value. Field type must encode symbol "d"
for another table (new struct castr member ca_table). The selector
code doesn't use that, yet.
-* Selector flag NSC_EXTRA to flag redundant selectors, so that xdump
- can ignore them.
+* Redundant selectors can be marked so that xdump ignores them (new
+ struct castr member ca_dump).
Meta-data is in empfile[] (table meta-data), src/lib/global/nsc.c
(selector meta-data), src/lib/global/symbol.c (symbol tables). The
its meta-data, and to make sense of that table, we need meta-meta
data. So we start with that:
- [14:640] Command : xdump meta meta
- XDUMP meta meta 1139555204
- "name" 3 4 0 -1
- "type" 5 4 0 32
- "flags" 6 12 0 33
- "len" 8 4 0 -1
- "table" 9 4 0 -1
+ [3:640] Command : xdump meta meta
+ XDUMP meta meta 1466920477
+ "name" 3 0 0 -1
+ "type" 1 0 0 33
+ "flags" 1 8 0 32
+ "len" 1 0 0 -1
+ "table" 1 0 0 26
/5
To interpret this table, we have to know the field names and their
for table IDs and to encode symbols are none of the client's business.
The encoding doesn't normally change within a game. Except when the
-game is migrated to a sufficiently different server. That's a
-difficult and risky thing to do, especially as there are no tools to
-help with migrating (yet). Clients may wish to provide for such
-changes anyway, by decoupling the client's encoding from the server's,
-and dumping fresh meta-data on login. Incremental meta-data dump
-would be nice to have.
+game is migrated to a sufficiently different server. That's a rare
+event. Clients may wish to provide for such changes anyway, by
+decoupling the client's encoding from the server's, and dumping fresh
+meta-data on login. Incremental meta-data dump would be nice to have.
So we don't know how symbol type and symbol set flags are encoded. To
decode them, we need their symbol tables. However, we need flags and
know, namely the table of tables. Let's dump that next, starting with
its meta-data:
- [31:640] Command : xdump meta table
- XDUMP meta table 1139556230
- "uid" 9 0 0 26
- "name" 3 4 0 -1
+ [3:640] Command : xdump meta table
+ XDUMP meta table 1466920477
+ "uid" 1 0 0 26
+ "name" 3 0 0 -1
/2
Because xdump table is referenced from elsewhere (xdump meta meta
field table), the leftmost field must contain the key. Thus, the
leftmost field's meta-data field table must be the table ID of xdump
-table itself. Let's try it:
+table itself. Indeed, its value matches the one we got in xdump meta
+meta. Let's try to dump the table:
- [30:640] Command : xdump 26 *
- XDUMP table 1139556210
+ [5:640] Command : xdump 26 *
+ XDUMP table 1466920477
0 "sect"
1 "ship"
[...]
- 9 "nat"
+ 8 "nat"
[...]
- 16 "sect-chr"
- 17 "ship-chr"
+ 18 "sect-chr"
+ 19 "ship-chr"
[...]
26 "table"
[...]
- /45
+ /48
It worked!
Now dump the two symbol tables we postponed. Because xdump accepts
table IDs as well as names, we don't have to know their names:
- [14:640] Command : xdump meta 32
- XDUMP meta meta-type 1139555298
- "value" 9 4 0 -1
+ [5:640] Command : xdump meta 33
+ XDUMP meta meta-type 1466920477
+ "value" 1 0 0 -1
"name" 3 0 0 -1
/2
- [15:640] Command : xdump 32 *
- XDUMP meta-type 1139555826
+ [6:640] Command : xdump 33 *
+ XDUMP meta-type 1466920477
1 "d"
2 "g"
3 "s"
- 4 "d"
- 5 "d"
- 6 "d"
- 7 "d"
- 8 "d"
- 9 "d"
- 10 "d"
- 11 "d"
- 12 "d"
- 13 "g"
- 14 "c"
- /14
-
- [15:640] Command : xdump meta 33
- XDUMP meta meta-flags 1139555303
- "value" 9 4 0 -1
+ /3
+
+ [7:640] Command : xdump meta 32
+ XDUMP meta meta-flags 1466920477
+ "value" 1 0 0 -1
"name" 3 0 0 -1
/2
- [24:640] Command : xdump 33 *
- XDUMP meta-flags 1139555829
+ [7:640] Command : xdump 32 *
+ XDUMP meta-flags 1466920477
1 "deity"
- 2 "extra"
- 4 "const"
8 "bits"
- /4
+ 16 "hidden"
+ /3
We now have complete meta-meta information:
type d (const) 0 meta-type
flags d (bits const) 0 meta-flags
len d (const) 0
- table d (const) 0
+ table d (const) 0 table
Dumping the remaining tables is easy: just walk the table of tables.
Here's the first one:
- [36:640] Command : xdump meta 0
- XDUMP meta sect 1139556498
- "owner" 6 0 0 9
- "xloc" 10 0 0 -1
- "yloc" 11 0 0 -1
- "des" 4 0 0 16
+ [7:640] Command : xdump meta 0
+ XDUMP meta sect 1466920477
+ "owner" 1 0 0 8
+ "xloc" 1 0 0 -1
+ "yloc" 1 0 0 -1
+ "des" 1 0 0 18
[...]
- /69
+ /78
A whole load of tables referenced! Only one of them (not shown above)
is a symbol table.
expressed in meta-data (yet).
Let's stop here before this gets too long and boring. Experiment
-yourself! Check out example Perl code src/xdump.pl.
+yourself! Check out example Perl code scripts/xdump.pl.
Analysis of xdump as Configuration File Format
- No comment syntax.
* Each table is self-contained. You don't have to look into other
- tables to make sense of it.
+ tables to make sense of it.
This conflicts with xdump's separation of data and meta-data. You
need the table's meta-data to identify fields, and the referenced
Rationale: Follow econfig syntax.
-Tables with a record uid in the leftmost field can be `split
+Tables with a record UID in the leftmost field can be `split
vertically' into multiple parts. Each part must contain the same set
of records. The leftmost field must be repeated in each part. Other
fields may be repeated. Repeated fields must be the same in all
Rationale: This is to let you avoid long lines. Line continuation
syntax would be simpler, but turns out to be illegible. Requiring
-record uid is not technically necessary, as counting records works the
+record UID is not technically necessary, as counting records works the
same whether a table is split or not. Except humans can't count.
Perhaps this should be a recommendation for use rather than part of
the language.
* Header and footer:
- header = "config" name newline colhdr newline ;
+ header = "config" identifier newline colhdr newline ;
colhdr = { identifier [ "(" ( intnum | identifier ) ")" ] } [ "..." ] ;
footer = "/config" newline ;
update.
- The column header is due to the self-containedness requirement.
- It contains just the essential bit of meta-data: the column name.
+ It contains just the essential bit of meta-data: the column names.
* Symbolic fields:
Configuration tables contain values that are not meant to be
customized. For instance, meta-data and symbol tables reflect the
-encoding of C language constructs in the server. Selector flag
-NSC_CONST marks them, so that the code can prohibit changes.
+encoding of C language constructs in the server. Such selectors are
+marked (struct castr member ca_dump), so that the code can prohibit
+changes.
All tables are checked against meta-data on server startup by
ef_verify(). More elaborate checking would be nice, and probably
enemy ships, nations).
(4) Bandwidth will be minimized (i.e. the format will be as
- concise as possible) while remaining human readable (i.e. no
+ concise as possible) while remaining human-readable (i.e. no
binary messages). [Note that data compression may be added at a later
date, but if it is added, it will be added on a separate port to
maintain backwards compatability.]
And here comes the killer:
-f. The data to sync is not readily available the server.
+f. The data to sync is not readily available on the server.
Yup. Think about it. The game state on the server is *not* the
same as on the client. The server grants the client a carefully
limited view on certain parts of server game state on certain
events.
- To be complete, a machine readable protocol must disclose as much
- information as the human readable output. Tracking server game
+ To be complete, a machine-readable protocol must disclose as much
+ information as the human-readable output. Tracking server game
state changes cannot do that alone. For instance, lookout tells
you ship#, owner and location. That event does not trigger any
state change on the server!
- To be correct, a machine readable protocol must disclose no more
- information than the human readable output. When you observe a
+ To be correct, a machine-readable protocol must disclose no more
+ information than the human-readable output. When you observe a
server game state change, you can only guess what event triggered
it, and what it disclosed to which player. You're stuck with
conservative assumptions. That's the death knell for completeness.
all. I believe the only way to get this done right is by tracking
*events*. Whenever something is printed to a player, be it live
connection or telegram, we need to transmit precisely the same
-information in machine readable form. Much more work.
+information in machine-readable form. Much more work.
xdump shares valuable ideas with C_SYNC, e.g. using selector
meta-data. It is, however, much more modest in scope. We're pretty
projects / empserver / blobdiff