<title>Fossil File Formats</title>

The global state of a fossil repository is kept simple so that it can
endure in useful form for decades or centuries.
A fossil repository is intended to be readable,
searchable, and extensible by people not yet born.

The global state of a fossil repository is an unordered
set of <i>artifacts</i>.
An artifact might be a source code file, the text of a wiki page,
part of a trouble ticket, a description of a check-in including all
the files in that check-in with the check-in comment and so forth.
Artifacts are broadly grouped into two types: content artifacts and
structural artifacts.  Content artifacts are the raw project source-code
files that are checked into the repository.  Structural artifacts have
special formatting rules and are used to show the relationships between
other artifacts in the repository.  It is possible for an artifact to
be both a structure artifact and a content artifact, though this is
rare. Artifacts can be text or binary.

In addition to the global state,
each fossil repository also contains local state.
The local state consists of web-page formatting
preferences, authorized users, ticket display and reporting formats,
and so forth.  The global state is shared in common among all
repositories for the same project, whereas the local state is often
different in separate repositories.
The local state is not versioned and is not synchronized
with the global state.
The local state is not composed of artifacts and is not intended to be enduring.
This document is concerned with global state only.  Local state is only
mentioned here in order to distinguish it from global state.

<h2 id="names">1.0 Artifact Names</h2>

Each artifact in the repository is named by a hash of its content.
No prefixes, suffixes, or other information is added to an artifact before
the hash is computed.  The artifact name is just the (lower-case
hexadecimal) hash of the raw artifact.

Fossil currently computes artifact names using either SHA1 or SHA3-256.  It
is relatively easy to add new algorithms in the future, but there are no
plans to do so at this time.

When referring to artifacts in using tty commands or webpage URLs, it is
sufficient to specify a unique prefix for the artifact name.  If the input
prefix is not unique, Fossil will show an error.  Within a structural
artifact, however, all references to other artifacts must be the complete
hash.

Prior to Fossil version 2.0, all names were formed from the SHA1 hash of
the artifact.  The key innovation in Fossil 2.0 was adding support for
alternative hash algorithms.

<h2 id="structural">2.0 Structural Artifacts</h2>

A structural artifact is an artifact with a particular format
that is used to define the relationships between other artifacts in the
repository.
Fossil recognizes the following kinds of structural
artifacts:

<ul>
<li> [#manifest | Manifests] </li>
<li> [#cluster | Clusters] </li>
<li> [#ctrl | Control Artifacts] </li>
<li> [#wikichng | Wiki Pages] </li>
<li> [#tktchng | Ticket Changes] </li>
<li> [#attachment | Attachments] </li>
<li> [#event | TechNotes] </li>
<li> [#forum | Forum Posts] </li>
</ul>

These eight structural artifact types are described in subsections below.

Structural artifacts are UTF-8 text.  The artifact may be PGP clearsigned.
After removal of the PGP clearsign header and suffix (if any) a structural
artifact consists of one or more "cards" separated by a single newline
(ASCII: 0x0a) character. Each card begins with a single
character "card type".  Zero or more arguments may follow
the card type.  All arguments are separated from each other
and from the card-type character by a single space
character.  There is no surplus white space between arguments
and no leading or trailing whitespace except for the newline
character that acts as the card separator.  All cards must be in strict
lexicographical order (except for an
[./fileformat.wiki#outofordercards|historical bug compatibility]).
There may not be any duplicate cards.

In the current implementation (as of 2017-02-27) the artifacts that
make up a fossil repository are stored as delta- and zlib-compressed
blobs in an <a href="http://www.sqlite.org/">SQLite</a> database.  This
is an implementation detail and might change in a future release.  For
the purpose of this article "file format" means the format of the artifacts,
not how the artifacts are stored on disk.  It is the artifact format that
is intended to be enduring.  The specifics of how artifacts are stored on
disk, though stable, is not intended to live as long as the
artifact format.

<h3 id="manifest">2.1 The Manifest</h3>

A manifest defines a check-in.
A manifest contains a list of artifacts for
each file in the project and the corresponding filenames, as
well as information such as parent check-ins, the username of the
programmer who created the check-in, the date and time when
the check-in was created, and any check-in comments associated
with the check-in.

Allowed cards in the manifest are as follows:

<div class="indent">
<b>B</b> <i>baseline-manifest</i><br>
<b>C</b> <i>checkin-comment</i><br>
<b>D</b> <i>time-and-date-stamp</i><br>
<b>F</b> <i>filename</i> ?<i>hash</i>? ?<i>permissions</i>? ?<i>old-name</i>?<br>
<b>N</b> <i>mimetype</i><br>
<b>P</b> <i>artifact-hash</i>+<br>
<b>Q</b> (<b>+</b>|<b>-</b>)<i>artifact-hash</i> ?<i>artifact-hash</i>?<br>
<b>R</b> <i>repository-checksum</i><br>
<b>T</b> (<b>+</b>|<b>-</b>|<b>*</b>)<i>tag-name</i> <b>*</b> ?<i>value</i>?<br>
<b>U</b> <i>user-login</i><br>
<b>Z</b> <i>manifest-checksum</i>
</div>

A manifest may optionally have a single <b>B</b> card.  The <b>B</b> card specifies
another manifest that serves as the "baseline" for this manifest.  A
manifest that has a <b>B</b> card is called a delta-manifest and a manifest
that omits the <b>B</b> card is a baseline-manifest.  The other manifest
identified by the argument of the <b>B</b> card must be a baseline-manifest.
A baseline-manifest records the complete contents of a check-in.
A delta-manifest records only changes from its baseline.

A manifest must have exactly one <b>C</b> card.  The sole argument to
the <b>C</b> card is a check-in comment that describes the check-in that
the manifest defines.  The check-in comment is text.  The following
escape sequences are applied to the text:
A space (ASCII 0x20) is represented as "\s" (ASCII 0x5C, 0x73).  A
newline (ASCII 0x0a) is "\n" (ASCII 0x5C, x6E).  A backslash
(ASCII 0x5C) is represented as two backslashes "\\".  Apart from
space and newline, no other whitespace characters are allowed in
the check-in comment.  Nor are any unprintable characters allowed
in the comment.

A manifest must have exactly one <b>D</b> card.  The sole argument to
the <b>D</b> card is a date-time stamp in the ISO8601 format.  The
date and time should be in coordinated universal time (UTC).
The format one of:

<pre class="indent"><i>YYYY-MM-DD<b>T</b>HH:MM:SS
YYYY-MM-DD<b>T</b>HH:MM:SS.SSS</i></pre>

A manifest has zero or more <b>F</b> cards.  Each <b>F</b> card identifies a file
that is part of the check-in.  There are one, two, three, or four
arguments.  The first argument is the pathname of the file in the
check-in relative to the root of the project file hierarchy.  No ".."
or "." directories are allowed within the filename.  Space characters
are escaped as in <b>C</b> card comment text.  Backslash characters and
newlines are not allowed within filenames.  The directory separator
character is a forward slash (ASCII 0x2F).  The second argument to the
<b>F</b> card is the lower-case hexadecimal artifact hash of
the content artifact.  The second argument is required for baseline
manifests but is optional for delta manifests.  When the second
argument to the <b>F</b> card is omitted, it means that the file has been
deleted relative to the baseline (files removed in baseline manifests
versions are <em>not</em> added as <b>F</b> cards). The optional 3rd argument
defines any special access permissions associated with the file.  This
can be defined as "x" to mean that the file is executable or "l"
(small letter ell) to mean a symlink.  All files are always readable
and writable.  This can be expressed by "w" permission if desired but
is optional.  The file format might be extended with new permission
letters in the future.  The optional 4th argument is the name of the
same file as it existed in the parent check-in.  If the name of the
file is unchanged from its parent, then the 4th argument is omitted.

A manifest has zero or one <b>N</b> cards.  The <b>N</b> card specifies the mimetype for the
text in the comment of the <b>C</b> card.  If the <b>N</b> card is omitted, a default mimetype
is used.

A manifest has zero or one <b>P</b> cards.  Most manifests have one <b>P</b> card.
The <b>P</b> card has a varying number of arguments that
define other manifests from which the current manifest
is derived.  Each argument is a lowercase
hexadecimal artifact hash of a predecessor manifest.  All arguments
to the <b>P</b> card must be unique within that card.
The first argument is the artifact hash of the direct ancestor of the manifest.
Other arguments define manifests with which the first was
merged to yield the current manifest.  Most manifests have
a <b>P</b> card with a single argument.  The first manifest in the
project has no ancestors and thus has no <b>P</b> card or (depending
on the Fossil version) an empty <b>P</b> card (no arguments).

A manifest has zero or more <b>Q</b> cards.  A <b>Q</b> card is similar to a <b>P</b> card
in that it defines a predecessor to the current check-in.  But
whereas a <b>P</b> card defines the immediate ancestor or a merge
ancestor, the <b>Q</b> card is used to identify a single check-in or a small
range of check-ins which were cherry-picked for inclusion in or
exclusion from the current manifest.  The first argument of
the <b>Q</b> card is the artifact ID of another manifest (the "target")
which has had its changes included or excluded in the current manifest.
The target is preceded by "+" or "-" to show inclusion or
exclusion, respectively.  The optional second argument to the
<b>Q</b> card is another manifest artifact ID which is the "baseline"
for the cherry-pick.  If omitted, the baseline is the primary
parent of the target.  The
changes included or excluded consist of all changes moving from
the baseline to the target.

The <b>Q</b> card was added to the interface specification on 2011-02-26.
Older versions of Fossil will reject manifests that contain <b>Q</b> cards.

A manifest may optionally have a single <b>R</b> card.  The <b>R</b> card has
a single argument which is the MD5 checksum of all files in
the check-in except the manifest itself.  The checksum is expressed
as 32 characters of lowercase hexadecimal.   The checksum is
computed as follows:  For each file in the check-in (except for
the manifest itself) in strict sorted lexicographical order,
take the pathname of the file relative to the root of the
repository, append a single space (ASCII 0x20), the
size of the file in ASCII decimal, a single newline
character (ASCII 0x0A), and the complete text of the file.
Compute the MD5 checksum of the result.

A manifest might contain one or more <b>T</b> cards used to set
[./branching.wiki#tags | tags or properties]
on the check-in.  The format of the <b>T</b> card is the same as
described in <i>Control Artifacts</i> section below, except that the
second argument is the single character "<b>*</b>" instead of an
artifact ID.  The <b>*</b> in place of the artifact ID indicates that
the tag or property applies to the current artifact.  It is not
possible to encode the current artifact ID as part of an artifact,
since the act of inserting the artifact ID would change the artifact ID,
hence a <b>*</b> is used to represent "self".  <b>T</b> cards are typically
added to manifests in order to set the <b>branch</b> property and a
symbolic name when the check-in is intended to start a new branch.

Each manifest has a single <b>U</b> card.  The argument to the <b>U</b> card is
the login of the user who created the manifest.  The login name
is encoded using the same character escapes as is used for the
check-in comment argument to the <b>C</b> card.

A manifest must have a single <b>Z</b> card as its last line.  The argument
to the <b>Z</b> card is a 32-character lowercase hexadecimal MD5 hash
of all prior lines of the manifest up to and including the newline
character that immediately precedes the "Z", excluding any PGP
clear-signing prefix.  The <b>Z</b> card is
a sanity check to prove that the manifest is well-formed and
consistent.

A sample manifest from Fossil itself can be seen
[/artifact/28987096ac | here].

<h3 id="cluster">2.2 Clusters</h3>

A cluster is an artifact that declares the existence of other artifacts.
Clusters are used during repository synchronization to help
reduce network traffic.  As such, clusters are an optimization and
may be removed from a repository without loss or damage to the
underlying project code.

Allowed cards in the cluster are as follows:

<div class="indent">
<b>M</b> <i>artifact-id</i><br />
<b>Z</b> <i>checksum</i>
</div>

A cluster contains one or more <b>M</b> cards followed by a single <b>Z</b> card.
Each <b>M</b> card has a single argument which is the artifact ID of
another artifact in the repository.  The <b>Z</b> card works exactly like
the <b>Z</b> card of a manifest.  The argument to the <b>Z</b> card is the
lower-case hexadecimal representation of the MD5 checksum of all
prior cards in the cluster.  The <b>Z</b> card is required.

An example cluster from Fossil can be seen
[/artifact/d03dbdd73a2a8 | here].

<h3 id="ctrl">2.3 Control Artifacts</h3>

Control artifacts are used to assign properties to other artifacts
within the repository.
Allowed cards in a control artifact are as follows:

<div class="indent">
<b>D</b> <i>time-and-date-stamp</i><br />
<b>T</b> (<b>+</b>|<b>-</b>|<b>*</b>)<i>tag-name</i> <i>artifact-id</i> ?<i>value</i>?<br />
<b>U</b> <i>user-name</i><br />
<b>Z</b> <i>checksum</i><br />
</div>

A control artifact must have one <b>D</b> card, one <b>U</b> card, one <b>Z</b> card and
one or more <b>T</b> cards.  No other cards or other text is
allowed in a control artifact.  Control artifacts might be PGP
clearsigned.

The <b>D</b> card and the <b>Z</b> card of a control artifact are the same
as in a manifest.

The <b>T</b> card represents a [./branching.wiki#tags | tag or property]
that is applied to
some other artifact.  The <b>T</b> card has two or three values.  The
second argument is the lowercase artifact ID of the artifact
to which the tag is to be applied. The
first value is the tag name.  The first character of the tag
is either "+", "-", or "*".  The "+" means the tag should be added
to the artifact.  The "-" means the tag should be removed.
The "*" character means the tag should be added to the artifact
and all direct descendants (but not descendants through a merge) down
to but not including the first descendant that contains a
more recent "-", "*", or "+" tag with the same name.
The optional third argument is the value of the tag.  A tag
without a value is a Boolean.

When two or more tags with the same name are applied to the
same artifact, the tag with the latest (most recent) date is
used.

Some tags have special meaning.  The "comment" tag when applied
to a check-in will override the check-in comment of that check-in
for display purposes.  The "user" tag overrides the name of the
check-in user.  The "date" tag overrides the check-in date.
The "branch" tag sets the name of the branch that at check-in
belongs to.  Symbolic tags begin with the "sym-" prefix.

The <b>U</b> card is the name of the user that created the control
artifact.  The <b>Z</b> card is the usual required artifact checksum.

An example control artifact can be seen [/info/9d302ccda8 | here].


<h3 id="wikichng">2.4 Wiki Pages</h3>

A wiki artifact defines a single version of a
single wiki page.
Wiki artifacts accept
the following card types:

<div class="indent">
<b>C</b> <i>change-comment</i><br>
<b>D</b> <i>time-and-date-stamp</i><br />
<b>L</b> <i>wiki-title</i><br />
<b>N</b> <i>mimetype</i><br />
<b>P</b> <i>parent-artifact-id</i>+<br />
<b>U</b> <i>user-name</i><br />
<b>W</b> <i>size</i> <b>\n</b> <i>text</i> <b>\n</b><br />
<b>Z</b> <i>checksum</i>
</div>

The <b>D</b> card is the date and time when the wiki page was edited.
The <b>P</b> card specifies the parent wiki pages, if any.  The <b>L</b> card
gives the name of the wiki page.  The optional <b>N</b> card specifies
the mimetype of the wiki text.  If the <b>N</b> card is omitted, the
mimetype is assumed to be text/x-fossil-wiki.
The <b>U</b> card specifies the login
of the user who made this edit to the wiki page.  The <b>Z</b> card is
the usual checksum over the entire artifact and is required.

The <b>W</b> card is used to specify the text of the wiki page.  The
argument to the <b>W</b> card is an integer which is the number of bytes
of text in the wiki page.  That text follows the newline character
that terminates the <b>W</b> card.  The wiki text is always followed by one
extra newline.

The <b>C</b> card on a wiki page is optional.  The argument is a comment
that explains why the changes was made.  The ability to have a <b>C</b>
card on a wiki page artifact was added on 2019-12-02 at the suggestion
of user George Krivov and is not currently used or generated by the 
implementation. Older versions of Fossil will reject a wiki-page
artifact that includes a <b>C</b> card.

An example wiki artifact can be seen
[/artifact?name=7b2f5fd0e0&txt=1 | here].

<h3 id="tktchng">2.5 Ticket Changes</h3>

A ticket-change artifact represents a change to a trouble ticket.
The following cards are allowed on a ticket change artifact:

<div class="indent">
<b>D</b> <i>time-and-date-stamp</i><br />
<b>J</b> ?<b>+</b>?<i>name</i> ?<i>value</i>?<br />
<b>K</b> <i>ticket-id</i><br />
<b>U</b> <i>user-name</i><br />
<b>Z</b> <i>checksum</i>
</div>

The <b>D</b> card is the usual date and time stamp and represents the point
in time when the change was entered.  The <b>U</b> card is the login of the
programmer who entered this change.  The <b>Z</b> card is the required checksum over
the entire artifact.

Every ticket has a distinct ticket-id:
40-character lower-case hexadecimal number.
The ticket-id is given in the <b>K</b> card.  A ticket exists if it contains one or
more changes.  The first "change" to a ticket is what brings the
ticket into existence.

<b>J</b> cards specify changes to the "value" of "fields" in the ticket.
If the <i>value</i> parameter of the <b>J</b> card is omitted, then the
field is set to an empty string.
Each fossil server has a ticket configuration which specifies the fields its
understands.  The ticket configuration is part of the local state for
the repository and thus can vary from one repository to another.
Hence a <b>J</b> card might specify a <i>field</i> that do not exist in the
local ticket configuration.  If a <b>J</b> card specifies a <i>field</i> that
is not in the local configuration, then that <b>J</b> card
is simply ignored.

The first argument of the <b>J</b> card is the field name.  The second
value is the field value.  If the field name begins with "+" then
the value is appended to the prior value.  Otherwise, the value
on the <b>J</b> card replaces any previous value of the field.
The field name and value are both encoded using the character
escapes defined for the <b>C</b> card of a manifest.

An example ticket-change artifact can be seen
[/artifact/91f1ec6af053 | here].

<h3 id="attachment">2.6 Attachments</h3>

An attachment artifact associates some other artifact that is the
attachment (the source artifact) with a ticket or wiki page or
technical note to which
the attachment is connected (the target artifact).
The following cards are allowed on an attachment artifact:

<div class="indent">
<b>A</b> <i>filename target</i> ?<i>source</i>?<br />
<b>C</b> <i>comment</i><br />
<b>D</b> <i>time-and-date-stamp</i><br />
<b>N</b> <i>mimetype</i><br />
<b>U</b> <i>user-name</i><br />
<b>Z</b> <i>checksum</i>
</div>

The <b>A</b> card specifies a filename for the attachment in its first argument.
The second argument to the <b>A</b> card is the name of the wiki page or
ticket or technical note to which the attachment is connected.  The
third argument is either missing or else it is the lower-case artifact
ID of the attachment itself.  A missing third argument means that the
attachment should be deleted.

The <b>C</b> card is an optional comment describing what the attachment is about.
The <b>C</b> card is optional, but there can only be one.

A single <b>D</b> card is required to give the date and time when the attachment
was applied.

There may be zero or one <b>N</b> cards.  The <b>N</b> card specifies the mimetype of the
comment text provided in the <b>C</b> card.  If the <b>N</b> card is omitted, the <b>C</b> card
mimetype is taken to be text/plain.

A single <b>U</b> card gives the name of the user who added the attachment.
If an attachment is added anonymously, then the <b>U</b> card may be omitted.

The <b>Z</b> card is the usual checksum over the rest of the attachment artifact.
The <b>Z</b> card is required.


<h3 id="event">2.7 Technical Notes</h3>

A technical note or "technote" artifact (formerly known as an "event" artifact)
associates a timeline comment and a page of text
(similar to a wiki page) with a point in time.  Technotes can be used
to record project milestones, release notes, blog entries, process
checkpoints, or news articles.
The following cards are allowed on an technote artifact:

<div class="indent">
<b>C</b> <i>comment</i><br>
<b>D</b> <i>time-and-date-stamp</i><br />
<b>E</b> <i>technote-time</i> <i>technote-id</i><br />
<b>N</b> <i>mimetype</i><br />
<b>P</b> <i>parent-artifact-id</i>+<br />
<b>T</b> <b>+</b><i>tag-name</i> <b>*</b> ?<i>value</i>?<br />
<b>U</b> <i>user-name</i><br />
<b>W</b> <i>size</i> <b>\n</b> <i>text</i> <b>\n</b><br />
<b>Z</b> <i>checksum</i>
</div>

The <b>C</b> card contains text that is displayed on the timeline for the
technote.  The <b>C</b> card is optional, but there can only be one.

A single <b>D</b> card is required to give the date and time when the
technote artifact was created.  This is different from the time at which
the technote appears on the timeline.

A single <b>E</b> card gives the time of the technote (the point on the timeline
where the technote is displayed) and a unique identifier for the technote.
When there are multiple artifacts with the same technote-id, the one with
the most recent <b>D</b> card is the only one used.  The technote-id must be a
40-character lower-case hexadecimal string.

The optional <b>N</b> card specifies the mimetype of the text of the technote
that is contained in the <b>W</b> card.  If the <b>N</b> card is omitted, then the
<b>W</b> card text mimetype is assumed to be text/x-fossil-wiki, which is the
Fossil wiki format.

The optional <b>P</b> card specifies a prior technote with the same technote-id
from which the current technote is an edit.  The <b>P</b> card is a hint to the
system that it might be space efficient to store one technote as a delta of
the other.

A technote might contain one or more <b>T</b> cards used to set
[./branching.wiki#tags | tags or properties]
on the technote.  The format of the <b>T</b> card is the same as
described in [#ctrl | Control Artifacts] section above, except that the
second argument is the single character "<b>*</b>" instead of an
artifact ID and the name is always prefaced by "<b>+</b>".
The <b>*</b> in place of the artifact ID indicates that
the tag or property applies to the current artifact.  It is not
possible to encode the current artifact ID as part of an artifact,
since the act of inserting the artifact ID would change the artifact ID,
hence a <b>*</b> is used to represent "self".  The "<b>+</b>" on the
name means that tags can only be add and they can only be non-propagating
tags.  In a technote, <b>T</b> cards are normally used to set the background
display color for timelines.

The optional <b>U</b> card gives name of the user who entered the technote.

A single <b>W</b> card provides wiki text for the document associated with the
technote.  The format of the <b>W</b> card is exactly the same as for a
[#wikichng | wiki artifact].

The <b>Z</b> card is the required checksum over the rest of the artifact.

<h3 id="forum">2.8 Forum Posts</h3>

Forum posts are intended as a mechanism for users and developers to
discuss a project.  Forum posts are like messages on a mailing list.

The following cards are allowed on an forum post artifact:

<div class="indent">
<b>D</b> <i>time-and-date-stamp</i><br />
<b>G</b> <i>thread-root</i><br />
<b>H</b> <i>thread-title</i><br />
<b>I</b> <i>in-reply-to</i><br />
<b>N</b> <i>mimetype</i><br />
<b>P</b> <i>parent-artifact-id</i><br />
<b>U</b> <i>user-name</i><br />
<b>W</b> <i>size</i> <b>\n</b> <i>text</i> <b>\n</b><br />
<b>Z</b> <i>checksum</i>
</div>

Every forum post must have either one <b>I</b> card and one <b>G</b> card
or one <b>H</b> card.
Forum posts are organized into topic threads.  The initial
post for a thread (the root post) has an <b>H</b> card giving the title or
subject for that thread.  The argument to the <b>H</b> card is a string
in the same format as a comment string in a <b>C</b> card.
All follow-up posts have an <b>I</b> card that
indicates which prior post in the same thread the current forum
post is replying to, and a <b>G</b> card specifying the root post for
the entire thread.  The argument to <b>G</b> and <b>I</b> cards is the
artifact hash for the prior forum post to which the card refers.

In theory, it is sufficient for follow-up posts to have only an
<b>I</b> card, since the <b>G</b> card value could be computed by following a
chain of <b>I</b> cards.  However, the <b>G</b> card is required in order to
associate the artifact with a forum thread in the case where an
intermediate artifact in the <b>I</b> card chain is shunned or otherwise
becomes unreadable.

A single <b>D</b> card is required to give the date and time when the
forum post was created.

The optional <b>N</b> card specifies the mimetype of the text of the technote
that is contained in the <b>W</b> card.  If the <b>N</b> card is omitted, then the
<b>W</b> card text mimetype is assumed to be text/x-fossil-wiki, which is the
Fossil wiki format.

The optional <b>P</b> card specifies a prior forum post for which this
forum post is an edit.  For display purposes, only the child post
is shown, though the historical post is retained as a record.
If <b>P</b> cards are used and there exist multiple versions of the same
forum post, then <b>I</b> cards for other artifacts refer to whichever
version of the post was current at the time the reply was made,
but <b>G</b> cards refer to the initial, unedited root post for the thread.
Thus, following the chain of <b>I</b> cards back to the root of the thread
may land on a different post than the one given in the <b>G</b> card.
However, following the chain of <b>I</b> cards back to the thread root,
then following <b>P</b> cards back to the initial version of the thread
root must give the same artifact as is provided by the <b>G</b> card,
otherwise the artifact containing the <b>G</b> card is considered invalid
and should be ignored.

In general, <b>P</b> cards may contain multiple arguments, indicating a
merge.  But since forum posts cannot be merged, the
<b>P</b> card of a forum post may only contain a single argument.

The <b>U</b> card gives name of the user who entered the forum post.

A single <b>W</b> card provides wiki text for the forum post.
The format of the <b>W</b> card is exactly the same as for a
[#wikichng | wiki artifact].

The <b>Z</b> card is the required checksum over the rest of the artifact.


<h2 id="summary">3.0 Card Summary</h2>

The following table summarizes the various kinds of cards that appear
on Fossil artifacts. A blank entry means that combination of card and
artifact is not legal. A number or range of numbers indicates the number
of times a card may (or must) appear in the corresponding artifact type.
e.g. a value of 1 indicates a required unique card and 1+ indicates that one
or more such cards are required.

<table>
<tr>
<th>⇩ Card Format / Used By ⇨</th>
<th>Manifest</th>
<th>Cluster</th>
<th>Control</th>
<th>Wiki</th>
<th>Ticket</th>
<th>Attachment</th>
<th>Technote</th>
<th>Forum</th>
</tr>
<tr>
<td><b>A</b> <i>filename</i> <i>target</i> ?<i>source</i>?</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td align=center><b>1</b></td>
<td>&nbsp;</td>
<td>&nbsp;</td>
</tr>
<tr>
<td><b>B</b> <i>baseline</i></td>
<td align=center><b>0-1</b></td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
</tr>
<tr>
<td><b>C</b> <i>comment-text</i></td>
<td align=center><b>1</b></td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td align=center><b>0-1</b></td>
<td>&nbsp;</td>
<td align=center><b>0-1</b></td>
<td align=center><b>0-1</b></td>
<td>&nbsp;</td>
</tr>
<tr>
<td><b>D</b> <i>date-time-stamp</i></td>
<td align=center><b>1</b></td>
<td>&nbsp;</td>
<td align=center><b>1</b></td>
<td align=center><b>1</b></td>
<td align=center><b>1</b></td>
<td align=center><b>1</b></td>
<td align=center><b>1</b></td>
<td align=center><b>1</b></td>
</tr>
<tr>
<td><b>E</b> <i>technote-time technote-id</i></td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td align=center><b>1</b></td>
<td>&nbsp;</td>
</tr>
<tr>
<td><b>F</b> <i>filename</i> ?<i>uuid</i>? ?<i>permissions</i>? ?<i>oldname</i>?</td>
<td align=center><b>0+</b></td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
</tr>
<tr>
<td><b>G</b> <i>thread-root</i></td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td align=center><b>0-1</b></td>
</tr>
<tr>
<td><b>H</b> <i>thread-title</i></td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td align=center><b>0-1</b><sup><nowiki>[4]</nowiki></sup></td>
</tr>
<tr>
<td><b>I</b> <i>in-reply-to</i></td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td align=center><b>0-1</b><sup><nowiki>[4]</nowiki></sup></td>
</tr>
<tr>
<td><b>J</b> <i>name</i> ?<i>value</i>?</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td align=center><b>1+</b></td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
</tr>
<tr>
<td><b>K</b> <i>ticket-uuid</i></td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td align=center><b>1</b></td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
</tr>
<tr>
<td><b>L</b> <i>wiki-title</i></td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td align=center><b>1</b></td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
</tr>
<tr>
<td><b>M</b> <i>uuid</i></td>
<td>&nbsp;</td>
<td align=center><b>1+</b></td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
</tr>
<tr>
<td><b>N</b> <i>mimetype</i></td>
<td align=center><b>0-1</b></td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td align=center><b>0-1</b></td>
<td>&nbsp;</td>
<td align=center><b>0-1</b></td>
<td align=center><b>0-1</b></td>
<td align=center><b>0-1</b></td>
</tr>
<tr>
<td><b>P</b> <i>uuid ...</i></td>
<td align=center><b>0-1</b></td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td align=center><b>0-1</b></td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td align=center><b>0-1</b></td>
<td align=center><b>0-1</b><sup><nowiki>[5]</nowiki></sup></td>
</tr>
<tr>
<td><b>Q</b> (<b>+</b>|<b>-</b>)<i>uuid</i> ?<i>uuid</i>?</td>
<td align=center><b>0+</b></td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
</tr>
<tr>
<td><b>R</b> <i>md5sum</i></td>
<td align=center><b>0-1</b></td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td><b>T</b> (<b>+</b>|<b>*</b>|<b>-</b>)<i>tagname</i> <i>uuid</i> ?<i>value</i>?<sup><nowiki>[1]</nowiki></sup></td>
<td align=center><b>0+</b></td>
<td>&nbsp;</td>
<td align=center><b>1+</b><sup><nowiki>[2]</nowiki></sup></td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td align=center><b>0+</b><sup><nowiki>[3]</nowiki></sup></td>
<td>&nbsp;</td>
</tr>
<tr>
<td><b>U</b> <i>username</i></td>
<td align=center><b>1</b></td>
<td>&nbsp;</td>
<td align=center><b>1</b></td>
<td align=center><b>1</b></td>
<td align=center><b>1</b></td>
<td align=center><b>0-1</b></td>
<td align=center><b>0-1</b></td>
<td align=center><b>1</b></td>
</tr>
<tr>
<td><b>W</b> <i>size</i> <b>\n</b> <i>text</i> <b>\n</b></td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td align=center><b>1</b></td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td align=center><b>1</b></td>
<td align=center><b>1</b></td>
</tr>
<tr>
<td><b>Z</b> <i>md5sum</i></td>
<td align=center><b>1</b></td>
<td align=center><b>1</b></td>
<td align=center><b>1</b></td>
<td align=center><b>1</b></td>
<td align=center><b>1</b></td>
<td align=center><b>1</b></td>
<td align=center><b>1</b></td>
<td align=center><b>1</b></td>
</tr>
</table>

Footnotes:

1) T-card names may not be made up of only hexadecimal characters, as
   they would be indistinguishable from a hash prefix.

2) Tags in [#ctrl | Control Artifacts] may not be
   self-referential. i.e. their target hash may not be <tt>*</tt>.

3) Tags in [#event | Technotes] must be self-referential. i.e. their
   target hash must be <tt>*</tt>. Similarly, technote tags may only
   be non-propagating "add" tags. i.e. their name prefix must be
   <tt>+</tt>.

4) [#forum | Forum Posts] must have either one H-card or one
   I-card, not both.

5) [#forum | Forum Post] P-cards may have only a single parent
   hash. i.e. they may not have merge parents.

<h2 id="addenda">4.0 Addenda</h2>

This section contains additional information which may be useful when
implementing algorithms described above.

<h3 id="outofordercards">4.1 Relaxed Card Ordering Due To An Historical Bug</h3>

All cards of a structural artifact should be in lexicographical order.
The Fossil implementation verifies this and rejects any structural
artifact which has out-of-order cards.  Futhermore, when Fossil is
generating new structural artifacts, it runs the generated artifact
through the parser to confirm that all cards really are in the correct
order before committing the transaction.  In this way, Fossil prevents
bugs in the code from accidentally inserting misformatted artifacts.
The test parse of newly created artifacts is part of the
[./selfcheck.wiki|self-check strategy] of Fossil.  It takes a
few more CPU cycles to double check each artifact before inserting it.
The developers consider those CPU cycles well-spent.

However, the card-order safety check was accidentally disabled due to
[15d04de574383d61|a bug].
And while that bug was lurking undetected in the code,
[5e67a7f4041a36ad|another bug] caused the N cards of Technical Notes
to occur after the P card rather than before.
Thus for a span of several years, Technical Note artifacts were being
inserted into Fossil repositories that had their N and P cards in the
wrong order.

Both bugs have now been fixed.  However, to prevent historical
Technical Note artifacts that were inserted by users in good faith
from being rejected by newer Fossil builds, the card ordering
requirement is relaxed slightly.  The actual implementation is this:

<p class=blockquote>
"All cards must be in strict lexicographic order, except that the
N and P cards of a Technical Note artifact are allowed to be
interchanged."
</p>

Future versions of Fossil might strengthen this slightly to only allow
the out of order N and P cards for Technical Notes entered before
a certain date.

<h3>4.2 R-Card Hash Calculation</h3>

Given a manifest file named <tt>MF</tt>, the following Bash shell code
demonstrates how to compute the value of the <b>R</b> card in that manifest.
This example uses manifest [28987096ac]. Lines starting with <tt>#</tt> are
shell input and other lines are output. This demonstration assumes that the
file versions represented by the input manifest are checked out
under the current directory.

<nowiki><pre>
# head MF
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

C Make\sthe\s"clearsign"\sPGP\ssigning\sdefault\sto\soff.
D 2010-02-23T15:33:14
F BUILD.txt 4f7988767e4e48b29f7eddd0e2cdea4555b9161c
F COPYRIGHT-GPL2.txt 06877624ea5c77efe3b7e39b0f909eda6e25a4ec
...

# grep '^R ' MF
R c0788982781981c96a0d81465fec7192

# for i in $(awk '/^F /{print $2}' MF); do \
  echo $i $(stat -c '%s' $i); \
  cat $i; \
done | md5sum
c0788982781981c96a0d81465fec7192  -
</pre></nowiki>

Minor caveats: the above demonstration will work only when none of the
filenames in the manifest are "fossilized" (encoded) because they contain
spaces. In that case the shell-generated hash would differ because the
<tt>stat</tt> calls will fail to find such files (which are output in encoded
form here). That approach also won't work for delta manifests. Calculating
the <b>R</b> card for delta manifests requires traversing both the delta and its baseline in
lexical order of the files, preferring the delta's copy if both contain
a given file.
