-
Welcome to the Citadel system!
Documentation is no longer included with the source code distribution;
--------------------------------------------------
This method is known to work on Linux and FreeBSD systems. It is a way of
-building the Citadel system with its own private copies of Berkeley DB and
-libical. This avoids conflicts with any other version of these libraries
-which may already exist on your host system.
+building the Citadel system with its own private copy of Berkeley DB. This
+avoids conflicts with any other version of these libraries which may already
+exist on your host system.
You can perform your builds in any directory (such as /usr/src or even your
home directory). The target directories will be:
* /usr/local/citadel (Citadel server, text client, utilities)
* /usr/local/webcit (the WebCit front end)
-* /usr/local/ctdlsupport (libical, libdb, and their headers, etc.)
+* /usr/local/ctdlsupport (libdb, libcitadel, and their headers, etc.)
-The behavior of Easy Install is based upon this methodology.
+If you're running the containerized distribution of Citadel, or have done
+the Easy Install script, your installation is based on this methodology.
1. Unpack the Berkeley DB tarball. chdir to the "build_unix" directory
and build the package with these commands:
--- /dev/null
+The totally incomplete guide to Citadel internals
+-----------------------------------------------------
+
+Citadel has evolved quite a bit since its early days, and the data structures
+have evolved with it. This document provides a rough overview of how the
+system works internally. For details you're going to have to dig through the
+code, but this'll get you started.
+
+
+DATABASE TABLES
+---------------
+As you probably already know by now, Citadel uses a group of tables stored
+with a record manager (usually Berkeley DB). Since we're using a record
+manager rather than a relational database, all record structures are managed
+by Citadel. Here are some of the tables we keep on disk:
+
+
+USER RECORDS
+------------
+This table contains all user records. It's indexed by
+user name (translated to lower case for indexing purposes). The records in
+this file look something like this:
+
+ struct ctdluser { // User record
+ int version; // Citadel version. which created this record
+ uid_t uid; // Associate with a unix account?
+ char password[32]; // Account password (unless using external authentication)
+ unsigned flags; // See US_ flags below
+ long timescalled; // Total number of logins
+ long posted; // Number of messages posted (ever)
+ CIT_UBYTE axlevel; // Access level
+ long usernum; // User number (never recycled)
+ time_t lastcall; // Last time the user called
+ int USuserpurge; // Purge time (in days) for user
+ char fullname[64]; // Name for Citadel messages & mail
+ };
+
+ Most fields here should be fairly self-explanatory. The ones that might
+deserve some attention are:
+
+ - `uid` -- if uid is not the same as the *unix uid* Citadel is running as, then the
+ account is assumed to belong to the user on the underlying Unix system with
+ that uid. This allows us to require the user's OS password instead of having
+ a separate Citadel password.
+
+ - `usernum` -- these are assigned sequentially, and **NEVER REUSED**. This is
+ important because it allows us to use this number in other data structures
+ without having to worry about users being added/removed later on, as you'll
+ see later in this document.
+
+
+ROOM RECORDS
+------------
+These are room records. There is a room record for every room on the
+system, public or private or mailbox. It's indexed by room name (also in
+lower case for easy indexing) and it contains records which look like this:
+
+ struct ctdlroom {
+ char QRname[ROOMNAMELEN]; /* Name of room */
+ char QRpasswd[10]; /* Only valid if it's a private rm */
+ long QRroomaide; /* User number of room aide */
+ long QRhighest; /* Highest message NUMBER in room */
+ time_t QRgen; /* Generation number of room */
+ unsigned QRflags; /* See flag values below */
+ char QRdirname[15]; /* Directory name, if applicable */
+ long QRinfo; /* Info file update relative to msgs*/
+ char QRfloor; /* Which floor this room is on */
+ time_t QRmtime; /* Date/time of last post */
+ struct ExpirePolicy QRep; /* Message expiration policy */
+ long QRnumber; /* Globally unique room number */
+ char QRorder; /* Sort key for room listing order */
+ unsigned QRflags2; /* Additional flags */
+ int QRdefaultview; /* How to display the contents */
+ };
+
+Again, mostly self-explanatory. Here are the interesting ones:
+
+`QRnumber` is a globally unique room ID, while `QRgen` is the "generation number"
+of the room (it's actually a timestamp). The two combined produce a unique
+value which identifies the room. The reason for two separate fields will be
+explained below when we discuss the visit table. For now just remember that
+`QRnumber` remains the same for the duration of the room's existence, and `QRgen`
+is timestamped once during room creation but may be restamped later on when
+certain circumstances exist.
+
+FLOORTAB
+--------
+Floors. This is so simplistic it's not worth going into detail about, except
+to note that we keep a reference count of the number of rooms on each floor.
+
+MSGLISTS
+--------
+Each record in this table consists of a bunch of message numbers
+which represent the contents of a room. A message can exist in more than one
+room (for example, a mail message with multiple recipients -- 'single instance
+store'). This table is never, ever traversed in its entirety. When you do
+any type of read operation, it fetches the msglist for the room you're in
+(using the room's ID as the index key) and then you can go ahead and read
+those messages one by one.
+
+Each room is basically just a list of message numbers. Each time
+we enter a new message in a room, its message number is appended to the end
+of the list. If an old message is to be expired, we must delete it from the
+message base. Reading a room is just a matter of looking up the messages
+one by one and sending them to the client for display, printing, or whatever.
+
+
+VISIT
+-----
+This is the tough one. Put on your thinking cap and grab a fresh cup of
+coffee before attempting to grok the visit table.
+
+This table contains records which establish the relationship between users
+and rooms. Its index is a hash of the user and room combination in question.
+When looking for such a relationship, the record in this table can tell the
+server things like "this user has zapped this room," "this user has access to
+this private room," etc. It's also where we keep track of which messages
+the user has marked as "old" and which are "new" (which are not necessarily
+contiguous; contrast with older Citadel implementations which simply kept a
+"last read" pointer).
+
+
+Here's what the records look like:
+
+ struct visit {
+ long v_roomnum;
+ long v_roomgen;
+ long v_usernum;
+ long v_lastseen;
+ unsigned int v_flags;
+ char v_seen[SIZ];
+ int v_view;
+ };
+
+ #define V_FORGET 1 /* User has zapped this room */
+ #define V_LOCKOUT 2 /* User is locked out of this room */
+ #define V_ACCESS 4 /* Access is granted to this room */
+
+This table is indexed by a concatenation of the first three fields. Whenever
+we want to learn the relationship between a user and a room, we feed that
+data to a function which looks up the corresponding record. The record is
+designed in such a way that an "all zeroes" record (which is what you get if
+the record isn't found) represents the default relationship.
+
+With this data, we now know which private rooms we're allowed to visit: if
+the `V_ACCESS` bit is set, the room is one which the user knows, and it may
+appear in his/her known rooms list. Conversely, we also know which rooms the
+user has zapped: if the `V_FORGET` flag is set, we relegate the room to the
+zapped list and don't bring it up during new message searches. It's also
+worth noting that the `V_LOCKOUT` flag works in a similar way to administratively
+lock users out of rooms.
+
+Implementing the "cause all users to forget room" command, then, becomes very
+simple: we simply change the generation number of the room by putting a new
+timestamp in the `QRgen` field. This causes all relevant visit records to
+become irrelevant, because they appear to point to a different room. At the
+same time, we don't lose the messages in the room, because the msglists table
+is indexed by the room number (`QRnumber`), which never changes.
+
+`v_seen` contains a string which represents the set of messages in this room
+which the user has read (marked as 'seen' or 'old'). It follows the same
+syntax used by IMAP and NNTP. When we search for new messages, we simply
+return any messages that are in the room that are **not** represented by this
+set. Naturally, when we do want to mark more messages as seen (or unmark
+them), we change this string. Citadel BBS client implementations are naive
+and think linearly in terms of "everything is old up to this point," but IMAP
+clients want to have more granularity.
+
+
+DIRECTORY
+---------
+This table simply maps Internet e-mail addresses to Citadel network addresses
+for quick lookup. It is generated from data in the Global Address Book room.
+
+USETABLE
+--------
+This table keeps track of message ID's of messages arriving over a network,
+to prevent duplicates from being posted if someone misconfigures the network
+and a loop is created. This table goes unused on a non-networked Citadel.
+
+THE MESSAGE STORE
+-----------------
+This is where all message text is stored. It's indexed by message number:
+give it a number, get back a message. Messages are numbered sequentially, and
+the message numbers are never reused.
+
+We also keep a "metadata" record for each message. This record is also stored
+in the msgmain table, using the index (0 - msgnum). We keep in the metadata
+record, among other things, a reference count for each message. Since a
+message may exist in more than one room, it's important to keep this reference
+count up to date, and to delete the message from disk when the reference count
+reaches zero.
+
+# Here's the format for the message itself:
+
+ - Each message begins with an 0xFF 'start of message' byte.
+
+ - The next byte denotes whether this is an anonymous message. The codes
+ available are `MES_NORMAL`, `MES_ANON`, or `MES_AN2` (defined in `citadel.h`).
+
+ - The third byte is a "message type" code. The following codes are defined:
+ - 0 - "Traditional" Citadel format. Message is to be displayed "formatted."
+ - 1 - Plain pre-formatted ASCII text (otherwise known as text/plain)
+ - 4 - MIME formatted message. The text of the message which follows is
+ expected to begin with a "Content-type:" header.
+
+ - After these three opening bytes, the remainder of
+ the message consists of a sequence of character strings. Each string
+ begins with a type byte indicating the meaning of the string and is
+ ended with a null. All strings are printable ASCII: in particular,
+ all numbers are in ASCII rather than binary. This is for simplicity,
+ both in implementing the system and in implementing other code to
+ work with the system. For instance, a database driven off Citadel archives
+ can do wildcard matching without worrying about unpacking binary data such
+ as message ID's first. To provide later downward compatability
+ all software should be written to IGNORE fields not currently defined.
+
+
+# The type bytes currently defined are:
+
+
+ | BYTE | Enum | NW | Mnemonic | Enum / Comments
+ |-------|-------------------|------|----------------|---------------------------------------------------------
+ | A | eAuthor | from | Author | The display name of the Author of the message.
+ | B | eBig_message | | Big message | This is a flag which indicates that the message is
+ | | | | | big, and Citadel is storing the body in a separate
+ | | | | | record. You will never see this field because the
+ | | | | | internal API handles it.
+ | E | eExclusiveID | exti | Exclusive ID | A persistent alphanumeric Message ID used for
+ | | | | | replication control. When a message arrives that
+ | | | | | contains an Exclusive ID, any existing messages which
+ | | | | | contain the same Exclusive ID and are *older* than this
+ | | | | | message should be deleted. If there exist any messages
+ | | | | | with the same Exclusive ID that are *newer*, then this
+ | | | | | message should be dropped.
+ | F | erFc822Addr | rfca | rFc822 address | email address or user principal name of the message
+ | | | | | author.
+ | I | emessageId | msgn | Message ID | An RFC822-compatible message ID for this message.
+ | | | | |
+ | J | eJournal | jrnl | Journal | The presence of this field indicates that the message
+ | | | | | is disqualified from being journaled, perhaps because
+ | | | | | it is itself a journalized message and we wish to
+ | | | | | avoid double journaling.
+ | K | eReplyTo | rep2 | Reply-To | the Reply-To header for mailinglist outbound messages
+ | L | eListID | list | List-ID | Mailing list identification, as per RFC 2919
+ | M | eMesageText | text | Message Text | Normal ASCII, newlines seperated by CR's or LF's,
+ | | | | | null terminated as always.
+ | O | eOriginalRoom | room | Room | Room of origin.
+ | P | eMessagePath | path | Path | Complete path of message, as in the UseNet news
+ | | | | | standard. A user should be able to send Internet mail
+ | | | | | to this path. (Note that your system name will not be
+ | | | | | tacked onto this until you're sending the message to
+ | | | | | someone else)
+ | R | eRecipient | rcpt | Recipient | Only present in Mail messages.
+ | T | eTimestamp | time | date/Time | Unix timestamp containing the creation date/time of
+ | | | | | the message.
+ | U | eMsgSubject | subj | sUbject | Message subject. Optional.
+ | | | | | Developers may choose whether they wish to
+ | | | | | generate or display subject fields.
+ | V | eenVelopeTo | nvto | enVelope-to | The recipient specified in incoming SMTP messages.
+ | W | eWeferences | wefw | Wefewences | Previous message ID's for conversation threading. When
+ | | | | | converting from RFC822 we use References: if present, or
+ | | | | | In-Reply-To: otherwise.
+ | | | | | (Who in extnotify spool messages which don't need to know
+ | | | | | other message ids)
+ | Y | eCarbonCopY | cccc | carbon copY | Carbon copy (CC) recipients.
+ | | | | | Optional, and only in Mail messages.
+ | % | eHeaderOnly | nhdr | oNlyHeader | we will just be sending headers. for the Wire protocol only.
+ | % | eFormatType | type | type | type of citadel message: (Wire protocol only)
+ | | | | | FMT\_CITADEL 0 Citadel vari-format (proprietary)
+ | | | | | FMT\_FIXED 1 Fixed format (proprietary)
+ | | | | | FMT\_RFC822 4 Standard (headers are in M field)
+ | % | eMessagePart | part | emessagePart | eMessagePart is the id of this part in the mime hierachy
+ | % | eSubFolder | suff | eSubFolder | descend into a mime sub container
+ | % | ePevious | pref | ePevious | exit a mime sub container
+ | 0 | eErrorMsg | | Error | This field is typically never found in a message on
+ | | | | | disk or in transit. Message scanning modules are
+ | | | | | expected to fill in this field when rejecting a message
+ | | | | | with an explanation as to what happened (virus found,
+ | | | | | message looks like spam, etc.)
+ | 1 | eSuppressIdx | | suppress index | The presence of this field indicates that the message is
+ | | | | | disqualified from being added to the full text index.
+ | 2 | eExtnotify | | extnotify | Used internally by the serv_extnotify module.
+ | 3 | eVltMsgNum | | msgnum | Used internally to pass the local message number in the
+ | | | | | database to after-save hooks. Discarded afterwards.
+ | | | locl | | The presence of this field indicates that the message
+ | | | | | is believed to have originated on the local Citadel node,
+ | | | | | not as an inbound email or some other outside source.
+
+EXAMPLE
+-------
+Let `<FF>` be a `0xFF` byte, and `<0>` be a null `(0x00)` byte. Then a message
+which prints as...
+
+ Apr 12, 1988 23:16 From Test User In Network Test> @lifesys (Life Central)
+ Have a nice day!
+
+might be stored as...
+
+ <FF><40><0>I12345<0>Pneighbor!lifesys!test_user<0>T576918988<0> (continued)
+ -----------|Mesg ID#|--Message Path---------------|--Date------
+
+ AThe Test User<0>ONetwork Test<0>Nlifesys<0>HLife Central<0>MHave a nice day!<0>
+ |-----Author-----|-Room name-----|-nodename-|Human Name-|--Message text-----
+
+Weird things can happen if fields are missing, especially if you use the
+networker. But basically, the date, author, room, and nodename may be in any
+order. But the leading fields and the message text must remain in the same
+place. The H field looks better when it is placed immediately after the N
+field.
+
+
+EUID (EXCLUSIVE MESSAGE ID'S)
+-----------------------------
+This is where the groupware magic happens. Any message in any room may have
+a field called the Exclusive message *ID*, or *EUID*. We keep an index in the
+table `CDB_EUIDINDEX` which knows the message number of any item that has an
+*EUID*. This allows us to do two things:
+
+ - If a subsequent message arrives with the same *EUID*, it automatically
+ *deletes* the existing one, because the new one is considered a replacement
+ for the existing one.
+ - If we know the *EUID* of the item we're looking for, we can fetch it by *EUID*
+ and get the most up-to-date version, even if it's been updated several times.
+
+This functionality is made more useful by server-side hooks. For example,
+when we save a vCard to an address book room, or an iCalendar item to a
+calendar room, our server modules detect this condition, and automatically set
+the *EUID* of the message to the *UUID* of the *vCard* or *iCalendar* item.
+Therefore when you save an updated version of an address book entry or
+a calendar item, the old one is automatically deleted.
+
+NETWORKING (REPLICATION)
+------------------------
+Citadel nodes network by sharing one or more rooms. Any Citadel node
+can choose to share messages with any other Citadel node, through the sending
+of spool files. The sending system takes all messages it hasn't sent yet, and
+spools them to the recieving system, which posts them in the rooms.
+
+The *EUID* discussion above is extremely relevant, because *EUID* is carried over
+the network as well, and the replacement rules are followed over the network
+as well. Therefore, when a message containing an *EUID* is saved in a networked
+room, it replaces any existing message with the same *EUID* *on every node in
+the network*.
+
+Complexities arise primarily from the possibility of densely connected
+networks: one does not wish to accumulate multiple copies of a given
+message, which can easily happen. Nor does one want to see old messages
+percolating indefinitely through the system.
+
+This problem is handled by keeping track of the path a message has taken over
+the network, like the UseNet news system does. When a system sends out a
+message, it adds its own name to the bang-path in the *<P>* field of the
+message. If no path field is present, it generates one.
+
+With the path present, all the networker has to do to assure that it doesn't
+send another system a message it's already received is check the <P>ath field
+for that system's name somewhere in the bang path. If it's present, the system
+has already seen the message, so we don't send it.
+
+We also keep a small database, called the "use table," containing the ID's of
+all messages we've seen recently. If the same message arrives a second or
+subsequent time, we will find its ID in the use table, indicating that we
+already have a copy of that message. It will therefore be discarded.
+
+The above discussion should make the function of the fields reasonably clear:
+
+ o Travelling messages need to carry original message-id, system of origin,
+ date of origin, author, and path with them, to keep reproduction and
+ cycling under control.
+
+(Uncoincidentally) the format used to transmit messages for networking
+purposes is precisely that used on disk, serialized. The current
+distribution includes serv_network.c, which is basically a database replicator;
+please see network.txt on its operation and functionality (if any).
+
+PORTABILITY ISSUES
+------------------
+Citadel is 32/64 bit clean and architecture-independent. The software is
+developed and primarily run on the Linux operating system (which uses the
+Linux kernel) but it should compile and run on any reasonably POSIX
+compliant system.
+
+On the client side, it's also POSIX compliant. The client even seems to
+build ok on non-POSIX systems with porting libraries (such as Cygwin and
+WSL).
+
+SUPPORTING PRIVATE MAIL
+-----------------------
+Can one have an elegant kludge? This must come pretty close.
+
+Private mail is sent and recieved in the `Mail>` room, which otherwise
+behaves pretty much as any other room. To make this work, we have a
+separate Mail> room for each user behind the scenes. The actual room name
+in the database looks like `0000001234.Mail` (where `1234` is the user
+number) and it's flagged with the `QR_MAILBOX` flag. The user number is
+stripped off by the server before the name is presented to the client. This
+provides the ability to give each user a separate namespace for mailboxes
+and personal rooms.
+
+This requires a little fiddling to get things just right. For example,
+`make_message()` has to be kludged to ask for the name of the recipient
+of the message whenever a message is entered in `Mail>`. But basically
+it works pretty well, keeping the code and user interface simple and
+regular.
+
+PASSWORDS AND NAME VALIDATION
+-----------------------------
+This has changed a couple of times over the course of Citadel's history. At
+this point it's very simple, again due to the fact that record managers are
+used for everything. The user file (user) is indexed using the user's
+name, converted to all lower-case. Searching for a user, then, is easy. We
+just lowercase the name we're looking for and query the database. If no
+match is found, it is assumed that the user does not exist.
+
+This makes it difficult to forge messages from an existing user. (Fine
+point: nonprinting characters are converted to printing characters, and
+leading, trailing, and double blanks are deleted.)
+++ /dev/null
-The totally incomplete guide to Citadel internals
------------------------------------------------------
-
-Citadel has evolved quite a bit since its early days, and the data structures
-have evolved with it. This document provides a rough overview of how the
-system works internally. For details you're going to have to dig through the
-code, but this'll get you started.
-
-
-DATABASE TABLES
----------------
-As you probably already know by now, Citadel uses a group of tables stored
-with a record manager (usually Berkeley DB). Since we're using a record
-manager rather than a relational database, all record structures are managed
-by Citadel. Here are some of the tables we keep on disk:
-
-
-USER RECORDS
-------------
-This table contains all user records. It's indexed by
-user name (translated to lower case for indexing purposes). The records in
-this file look something like this:
-
-struct ctdluser { /* User record */
- int version; /* Cit vers. which created this rec */
- uid_t uid; /* Associate with a unix account? */
- char password[32]; /* password (for Citadel-only users)*/
- unsigned flags; /* See US_ flags below */
- long timescalled; /* Total number of logins */
- long posted; /* Number of messages posted (ever) */
- CIT_UBYTE axlevel; /* Access level */
- long usernum; /* User number (never recycled) */
- time_t lastcall; /* Last time the user called */
- int USuserpurge; /* Purge time (in days) for user */
- char fullname[64]; /* Name for Citadel messages & mail */
-};
-
- Most fields here should be fairly self-explanatory. The ones that might
-deserve some attention are:
-
- - *uid* -- if uid is not the same as the *unix uid* Citadel is running as, then the
- account is assumed to belong to the user on the underlying Unix system with
- that uid. This allows us to require the user's OS password instead of having
- a separate Citadel password.
-
- - *usernum* -- these are assigned sequentially, and **NEVER REUSED**. This is
- important because it allows us to use this number in other data structures
- without having to worry about users being added/removed later on, as you'll
- see later in this document.
-
-
-ROOM RECORDS
-------------
-These are room records. There is a room record for every room on the
-system, public or private or mailbox. It's indexed by room name (also in
-lower case for easy indexing) and it contains records which look like this:
-
- struct ctdlroom {
- char QRname[ROOMNAMELEN]; /* Name of room */
- char QRpasswd[10]; /* Only valid if it's a private rm */
- long QRroomaide; /* User number of room aide */
- long QRhighest; /* Highest message NUMBER in room */
- time_t QRgen; /* Generation number of room */
- unsigned QRflags; /* See flag values below */
- char QRdirname[15]; /* Directory name, if applicable */
- long QRinfo; /* Info file update relative to msgs*/
- char QRfloor; /* Which floor this room is on */
- time_t QRmtime; /* Date/time of last post */
- struct ExpirePolicy QRep; /* Message expiration policy */
- long QRnumber; /* Globally unique room number */
- char QRorder; /* Sort key for room listing order */
- unsigned QRflags2; /* Additional flags */
- int QRdefaultview; /* How to display the contents */
- };
-
-Again, mostly self-explanatory. Here are the interesting ones:
-
-*QRnumber* is a globally unique room ID, while QRgen is the "generation number"
-of the room (it's actually a timestamp). The two combined produce a unique
-value which identifies the room. The reason for two separate fields will be
-explained below when we discuss the visit table. For now just remember that
-*QRnumber* remains the same for the duration of the room's existence, and QRgen
-is timestamped once during room creation but may be restamped later on when
-certain circumstances exist.
-
-FLOORTAB
---------
-Floors. This is so simplistic it's not worth going into detail about, except
-to note that we keep a reference count of the number of rooms on each floor.
-
-MSGLISTS
---------
-Each record in this table consists of a bunch of message numbers
-which represent the contents of a room. A message can exist in more than one
-room (for example, a mail message with multiple recipients -- 'single instance
-store'). This table is never, ever traversed in its entirety. When you do
-any type of read operation, it fetches the msglist for the room you're in
-(using the room's ID as the index key) and then you can go ahead and read
-those messages one by one.
-
-Each room is basically just a list of message numbers. Each time
-we enter a new message in a room, its message number is appended to the end
-of the list. If an old message is to be expired, we must delete it from the
-message base. Reading a room is just a matter of looking up the messages
-one by one and sending them to the client for display, printing, or whatever.
-
-
-VISIT
------
-This is the tough one. Put on your thinking cap and grab a fresh cup of
-coffee before attempting to grok the visit table.
-
-This table contains records which establish the relationship between users
-and rooms. Its index is a hash of the user and room combination in question.
-When looking for such a relationship, the record in this table can tell the
-server things like "this user has zapped this room," "this user has access to
-this private room," etc. It's also where we keep track of which messages
-the user has marked as "old" and which are "new" (which are not necessarily
-contiguous; contrast with older Citadel implementations which simply kept a
-"last read" pointer).
-
-
-Here's what the records look like:
-
- struct visit {
- long v_roomnum;
- long v_roomgen;
- long v_usernum;
- long v_lastseen;
- unsigned int v_flags;
- char v_seen[SIZ];
- int v_view;
- };
-
- #define V_FORGET 1 /* User has zapped this room */
- #define V_LOCKOUT 2 /* User is locked out of this room */
- #define V_ACCESS 4 /* Access is granted to this room */
-
-This table is indexed by a concatenation of the first three fields. Whenever
-we want to learn the relationship between a user and a room, we feed that
-data to a function which looks up the corresponding record. The record is
-designed in such a way that an "all zeroes" record (which is what you get if
-the record isn't found) represents the default relationship.
-
-With this data, we now know which private rooms we're allowed to visit: if
-the *V_ACCESS* bit is set, the room is one which the user knows, and it may
-appear in his/her known rooms list. Conversely, we also know which rooms the
-user has zapped: if the *V_FORGET* flag is set, we relegate the room to the
-zapped list and don't bring it up during new message searches. It's also
-worth noting that the *V_LOCKOUT* flag works in a similar way to administratively
-lock users out of rooms.
-
-Implementing the "cause all users to forget room" command, then, becomes very
-simple: we simply change the generation number of the room by putting a new
-timestamp in the *QRgen* field. This causes all relevant visit records to
-become irrelevant, because they appear to point to a different room. At the
-same time, we don't lose the messages in the room, because the msglists table
-is indexed by the room number (*QRnumber*), which never changes.
-
-*v_seen* contains a string which represents the set of messages in this room
-which the user has read (marked as 'seen' or 'old'). It follows the same
-syntax used by IMAP and NNTP. When we search for new messages, we simply
-return any messages that are in the room that are **not** represented by this
-set. Naturally, when we do want to mark more messages as seen (or unmark
-them), we change this string. Citadel BBS client implementations are naive
-and think linearly in terms of "everything is old up to this point," but IMAP
-clients want to have more granularity.
-
-
-DIRECTORY
----------
-This table simply maps Internet e-mail addresses to Citadel network addresses
-for quick lookup. It is generated from data in the Global Address Book room.
-
-USETABLE
---------
-This table keeps track of message ID's of messages arriving over a network,
-to prevent duplicates from being posted if someone misconfigures the network
-and a loop is created. This table goes unused on a non-networked Citadel.
-
-THE MESSAGE STORE
------------------
-This is where all message text is stored. It's indexed by message number:
-give it a number, get back a message. Messages are numbered sequentially, and
-the message numbers are never reused.
-
-We also keep a "metadata" record for each message. This record is also stored
-in the msgmain table, using the index (0 - msgnum). We keep in the metadata
-record, among other things, a reference count for each message. Since a
-message may exist in more than one room, it's important to keep this reference
-count up to date, and to delete the message from disk when the reference count
-reaches zero.
-
-#Here's the format for the message itself:
-
- - Each message begins with an 0xFF 'start of message' byte.
-
- - The next byte denotes whether this is an anonymous message. The codes
- available are *MES_NORMAL*, *MES_ANON*, or *MES_AN2* (defined in citadel.h).
-
- - The third byte is a "message type" code. The following codes are defined:
- - 0 - "Traditional" Citadel format. Message is to be displayed "formatted."
- - 1 - Plain pre-formatted ASCII text (otherwise known as text/plain)
- - 4 - MIME formatted message. The text of the message which follows is
- expected to begin with a "Content-type:" header.
-
- - After these three opening bytes, the remainder of
- the message consists of a sequence of character strings. Each string
- begins with a type byte indicating the meaning of the string and is
- ended with a null. All strings are printable ASCII: in particular,
- all numbers are in ASCII rather than binary. This is for simplicity,
- both in implementing the system and in implementing other code to
- work with the system. For instance, a database driven off Citadel archives
- can do wildcard matching without worrying about unpacking binary data such
- as message ID's first. To provide later downward compatability
- all software should be written to IGNORE fields not currently defined.
-
-
-#The type bytes currently defined are:
-
-
-| BYTE | Enum | NW | Mnemonic | Enum / Comments
-|-------|-------------------|------|----------------|---------------------------------------------------------
-| A | eAuthor | from | Author | The display name of the Author of the message.
-| B | eBig_message | | Big message | This is a flag which indicates that the message is
-| | | | | big, and Citadel is storing the body in a separate
-| | | | | record. You will never see this field because the
-| | | | | internal API handles it.
-| E | eExclusiveID | exti | Exclusive ID | A persistent alphanumeric Message ID used for
-| | | | | replication control. When a message arrives that
-| | | | | contains an Exclusive ID, any existing messages which
-| | | | | contain the same Exclusive ID and are *older* than this
-| | | | | message should be deleted. If there exist any messages
-| | | | | with the same Exclusive ID that are *newer*, then this
-| | | | | message should be dropped.
-| F | erFc822Addr | rfca | rFc822 address | email address or user principal name of the message
-| | | | | author.
-| I | emessageId | msgn | Message ID | An RFC822-compatible message ID for this message.
-| | | | |
-| J | eJournal | jrnl | Journal | The presence of this field indicates that the message
-| | | | | is disqualified from being journaled, perhaps because
-| | | | | it is itself a journalized message and we wish to
-| | | | | avoid double journaling.
-| K | eReplyTo | rep2 | Reply-To | the Reply-To header for mailinglist outbound messages
-| L | eListID | list | List-ID | Mailing list identification, as per RFC 2919
-| M | eMesageText | text | Message Text | Normal ASCII, newlines seperated by CR's or LF's,
-| | | | | null terminated as always.
-| O | eOriginalRoom | room | Room | Room of origin.
-| P | eMessagePath | path | Path | Complete path of message, as in the UseNet news
-| | | | | standard. A user should be able to send Internet mail
-| | | | | to this path. (Note that your system name will not be
-| | | | | tacked onto this until you're sending the message to
-| | | | | someone else)
-| R | eRecipient | rcpt | Recipient | Only present in Mail messages.
-| T | eTimestamp | time | date/Time | Unix timestamp containing the creation date/time of
-| | | | | the message.
-| U | eMsgSubject | subj | sUbject | Message subject. Optional.
-| | | | | Developers may choose whether they wish to
-| | | | | generate or display subject fields.
-| V | eenVelopeTo | nvto | enVelope-to | The recipient specified in incoming SMTP messages.
-| W | eWeferences | wefw | Wefewences | Previous message ID's for conversation threading. When
-| | | | | converting from RFC822 we use References: if present, or
-| | | | | In-Reply-To: otherwise.
-| | | | | (Who in extnotify spool messages which don't need to know
-| | | | | other message ids)
-| Y | eCarbonCopY | cccc | carbon copY | Carbon copy (CC) recipients.
-| | | | | Optional, and only in Mail messages.
-| % | eHeaderOnly | nhdr | oNlyHeader | we will just be sending headers. for the Wire protocol only.
-| % | eFormatType | type | type | type of citadel message: (Wire protocol only)
-| | | | | FMT\_CITADEL 0 Citadel vari-format (proprietary)
-| | | | | FMT\_FIXED 1 Fixed format (proprietary)
-| | | | | FMT\_RFC822 4 Standard (headers are in M field)
-| % | eMessagePart | part | emessagePart | eMessagePart is the id of this part in the mime hierachy
-| % | eSubFolder | suff | eSubFolder | descend into a mime sub container
-| % | ePevious | pref | ePevious | exit a mime sub container
-| 0 | eErrorMsg | | Error | This field is typically never found in a message on
-| | | | | disk or in transit. Message scanning modules are
-| | | | | expected to fill in this field when rejecting a message
-| | | | | with an explanation as to what happened (virus found,
-| | | | | message looks like spam, etc.)
-| 1 | eSuppressIdx | | suppress index | The presence of this field indicates that the message is
-| | | | | disqualified from being added to the full text index.
-| 2 | eExtnotify | | extnotify | Used internally by the serv_extnotify module.
-| 3 | eVltMsgNum | | msgnum | Used internally to pass the local message number in the
-| | | | | database to after-save hooks. Discarded afterwards.
-| | | locl | | The presence of this field indicates that the message
-| | | | | is believed to have originated on the local Citadel node,
-| | | | | not as an inbound email or some other outside source.
-
-EXAMPLE
--------
-Let *<FF>* be a *0xFF* byte, and *<0>* be a null *(0x00)* byte. Then a message
-which prints as...
-
- Apr 12, 1988 23:16 From Test User In Network Test> @lifesys (Life Central)
- Have a nice day!
-
-might be stored as...
-
- <FF><40><0>I12345<0>Pneighbor!lifesys!test_user<0>T576918988<0> (continued)
- -----------|Mesg ID#|--Message Path---------------|--Date------
-
- AThe Test User<0>ONetwork Test<0>Nlifesys<0>HLife Central<0>MHave a nice day!<0>
- |-----Author-----|-Room name-----|-nodename-|Human Name-|--Message text-----
-
-Weird things can happen if fields are missing, especially if you use the
-networker. But basically, the date, author, room, and nodename may be in any
-order. But the leading fields and the message text must remain in the same
-place. The H field looks better when it is placed immediately after the N
-field.
-
-
-EUID (EXCLUSIVE MESSAGE ID'S)
------------------------------
-This is where the groupware magic happens. Any message in any room may have
-a field called the Exclusive message *ID*, or *EUID*. We keep an index in the
-table *CDB_EUIDINDEX* which knows the message number of any item that has an
-*EUID*. This allows us to do two things:
-
- - If a subsequent message arrives with the same *EUID*, it automatically
- *deletes* the existing one, because the new one is considered a replacement
- for the existing one.
- - If we know the *EUID* of the item we're looking for, we can fetch it by *EUID*
- and get the most up-to-date version, even if it's been updated several times.
-
-This functionality is made more useful by server-side hooks. For example,
-when we save a vCard to an address book room, or an iCalendar item to a
-calendar room, our server modules detect this condition, and automatically set
-the *EUID* of the message to the *UUID* of the *vCard* or *iCalendar* item.
-Therefore when you save an updated version of an address book entry or
-a calendar item, the old one is automatically deleted.
-
-NETWORKING (REPLICATION)
-------------------------
-Citadel nodes network by sharing one or more rooms. Any Citadel node
-can choose to share messages with any other Citadel node, through the sending
-of spool files. The sending system takes all messages it hasn't sent yet, and
-spools them to the recieving system, which posts them in the rooms.
-
-The *EUID* discussion above is extremely relevant, because *EUID* is carried over
-the network as well, and the replacement rules are followed over the network
-as well. Therefore, when a message containing an *EUID* is saved in a networked
-room, it replaces any existing message with the same *EUID* *on every node in
-the network*.
-
-Complexities arise primarily from the possibility of densely connected
-networks: one does not wish to accumulate multiple copies of a given
-message, which can easily happen. Nor does one want to see old messages
-percolating indefinitely through the system.
-
-This problem is handled by keeping track of the path a message has taken over
-the network, like the UseNet news system does. When a system sends out a
-message, it adds its own name to the bang-path in the *<P>* field of the
-message. If no path field is present, it generates one.
-
-With the path present, all the networker has to do to assure that it doesn't
-send another system a message it's already received is check the <P>ath field
-for that system's name somewhere in the bang path. If it's present, the system
-has already seen the message, so we don't send it.
-
-We also keep a small database, called the "use table," containing the ID's of
-all messages we've seen recently. If the same message arrives a second or
-subsequent time, we will find its ID in the use table, indicating that we
-already have a copy of that message. It will therefore be discarded.
-
-The above discussion should make the function of the fields reasonably clear:
-
- o Travelling messages need to carry original message-id, system of origin,
- date of origin, author, and path with them, to keep reproduction and
- cycling under control.
-
-(Uncoincidentally) the format used to transmit messages for networking
-purposes is precisely that used on disk, serialized. The current
-distribution includes serv_network.c, which is basically a database replicator;
-please see network.txt on its operation and functionality (if any).
-
-PORTABILITY ISSUES
-------------------
-Citadel is 64-bit clean and architecture-independent. The software is
-developed and primarily run on the Linux operating system (which uses the
-Linux kernel) but it should compile and run on any reasonably POSIX
-compliant system.
-
-On the client side, it's also POSIX compliant. The client even seems to
-build ok on non-POSIX systems with porting libraries (such as Cygwin and
-WSL).
-
-SUPPORTING PRIVATE MAIL
------------------------
-Can one have an elegant kludge? This must come pretty close.
-
-Private mail is sent and recieved in the *Mail>* room, which otherwise
-behaves pretty much as any other room. To make this work, we have a
-separate Mail> room for each user behind the scenes. The actual room name
-in the database looks like *"0000001234.Mail"* (where *'1234'* is the user
-number) and it's flagged with the *QR_MAILBOX* flag. The user number is
-stripped off by the server before the name is presented to the client. This
-provides the ability to give each user a separate namespace for mailboxes
-and personal rooms.
-
-This requires a little fiddling to get things just right. For example,
-*make_message()* has to be kludged to ask for the name of the recipient
-of the message whenever a message is entered in *Mail>*. But basically
-it works pretty well, keeping the code and user interface simple and
-regular.
-
-PASSWORDS AND NAME VALIDATION
------------------------------
-This has changed a couple of times over the course of Citadel's history. At
-this point it's very simple, again due to the fact that record managers are
-used for everything. The user file (user) is indexed using the user's
-name, converted to all lower-case. Searching for a user, then, is easy. We
-just lowercase the name we're looking for and query the database. If no
-match is found, it is assumed that the user does not exist.
-
-This makes it difficult to forge messages from an existing user. (Fine
-point: nonprinting characters are converted to printing characters, and
-leading, trailing, and double blanks are deleted.)
--- /dev/null
+How "views" work in Citadel
+---------------------------
+
+There's no need to be rigid and stupid about how different rooms are presented
+in a Citadel client. And we don't enforce things either. But there's a need
+to make things look the way the user wants to see them. For example, we might
+always choose to see a room full of private mail as a summary (one line per
+message) rather than always dumping out the entire contents like we do on a
+typical message room. An address book room might look better as a tabbed view
+or something, rather than as a bunch of messages with vCards attached to them.
+
+This is why we define "views" for a room. It gives the client software a
+hint as to how to display the contents of a room. This is kept on a per-user
+basis by storing it in the `visit` record for a particular room/user
+combination. It is `visit.v_view` and is an integer. Naturally, there also
+needs to be a default, for users who have never visited the room before. This
+is in the room record as `room.QRdefaultview` (and is also an integer).
+
+In recent versions of Citadel, the view for a room also defines when and how
+it is indexed. For example, mailboxes and bulletin boards don't need to have
+an euid index, but address books and calendars do.
+
+The values currently defined are:
+
+ #define VIEW_BBS 0 /* Bulletin board view */
+ #define VIEW_MAILBOX 1 /* Mailbox summary */
+ #define VIEW_ADDRESSBOOK 2 /* Address book view */
+ #define VIEW_CALENDAR 3 /* Calendar view */
+ #define VIEW_TASKS 4 /* Tasks view */
+ #define VIEW_NOTES 5 /* Notes view */
+ #define VIEW_WIKI 6 /* Wiki view */
+
+++ /dev/null
-How "views" work in Citadel
----------------------------
-
- There's no need to be rigid and stupid about how different rooms are presented
-in a Citadel client. And we don't enforce things either. But there's a need
-to make things look the way the user wants to see them. For example, we might
-always choose to see a room full of private mail as a summary (one line per
-message) rather than always dumping out the entire contents like we do on a
-typical message room. An address book room might look better as a tabbed view
-or something, rather than as a bunch of messages with vCards attached to them.
-
- This is why we define "views" for a room. It gives the client software a
-hint as to how to display the contents of a room. This is kept on a per-user
-basis by storing it in the 'visit' record for a particular room/user
-combination. It is visit.v_view and is an integer. Naturally, there also
-needs to be a default, for users who have never visited the room before. This
-is in the room record as room.QRdefaultview (and is also an integer).
-
- In recent versions of Citadel, the view for a room also defines when and how
-it is indexed. For example, mailboxes and bulletin boards don't need to have
-an euid index, but address books and calendars do.
-
- The values currently defined are:
-
-#define VIEW_BBS 0 /* Bulletin board view */
-#define VIEW_MAILBOX 1 /* Mailbox summary */
-#define VIEW_ADDRESSBOOK 2 /* Address book view */
-#define VIEW_CALENDAR 3 /* Calendar view */
-#define VIEW_TASKS 4 /* Tasks view */
-#define VIEW_NOTES 5 /* Notes view */
-#define VIEW_WIKI 6 /* Wiki view */
-
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