<title>Fossil File Formats</title>
<h1 align="center">
Fossil File Formats
</h1>

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, or one of several special artifacts
used to show the relationships between other artifacts within the
project.  Each artifact is normally represented on disk as a separate
file.  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

Each artifact in the repository is named by its SHA1 hash.
No prefixes or meta information is added to an artifact before
its hash is computed.  The name of an artifact in the repository
is exactly the same SHA1 hash that is computed by sha1sum 
on the file as it exists in your source tree.</p>
















In the current implementation (as of 2015-12-23) 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.

All of the artifacts can be extracted from a Fossil repository using
the "fossil deconstruct" command.

<h2>1.0 Special Artifacts</h2>

Some artifacts have a particular format which gives them special
meaning to fossil.  Fossil recognizes:

<ul>
<li> [#manifest | Manifests] </li>
<li> [#directory | Directories] </li>
<li> [#cluster | Clusters] </li>
<li> [#ctrl | Tags] </li>
<li> [#wikichng | Wiki Pages] </li>
<li> [#tktchng | Ticket Changes] </li>
<li> [#attachment | Attachments] </li>
<li> [#event | TechNotes] </li>
</ul>

Any artifact is not one of the above eight special artifacts is a
"content" artifact.  Every distinct version of every file under 
management is a content artifact, as are attachments to wiki pages
and tickets.

Any artifact that follows the appropriate syntactic rules is a special
artifact.  It is possible for the same artifact to be used as both
a special artifact and a content artifact, thought this is rare and 
probably undesirable.  (Future versions of Fossil might restrict attempts
to check-in special artifacts as content files.)
To prevent accidental occurrences of the same artifact being used as both
a special artifact and a content artifact, the syntactic rules for
special artifacts are very strict.

All special artifacts are pure UTF8 text. Newline characters
(ASCII 0x0a) separate the artifact into "cards".
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 (ASCII 0x20).  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 of a special artifact occur in strict sorted lexicographical order.
No card may be duplicated.
Some special artifacts (example: [#manifest|manifests])
may be PGP clear-signed, but otherwise special artifacts
may contain no additional text or data.


<a name="manifest"></a>
<h2>1.1 The Manifest Artifact</h2>

A manifest defines a check-in or version of the project
source tree.  The 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 name 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:

<blockquote>
<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>SHA1-hash</i>? ?<i>permissions</i>? ?<i>old-name</i>?<br>

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 has zero or one N-cards.  The N-card specifies the mimetype for the
text in the comment of the C-card.  If the N-card is omitted, a default mimetype
is used.

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

<blockquote>
<i>YYYY</i><b>-</b><i>MM</i><b>-</b><i>DD</i><b>T</b><i>HH</i><b>:</b><i>MM</i><b>:</b><i>SS</i><br>
<i>YYYY</i><b>-</b><i>MM</i><b>-</b><i>DD</i><b>T</b><i>HH</i><b>:</b><i>MM</i><b>:</b><i>SS</i><b>.</b><i>SSS</i>
</blockquote>

A manifest has zero or more F-cards.  Each F-card identifies a file or
subdirectory
that is part of the check-in.  There are one, two, three, or four
arguments.  The first argument is the pathname of the file or
subdirectory 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 C-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
F-card is the full 40-character lower-case hexadecimal SHA1 hash of
the content artifact, or of the [#directory|directory artifact] if
the "d" permission is present.  The second argument is required for baseline
manifests but is optional for delta manifests.  When the second
argument to the F-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 F-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 or "d" to mean the entry describes
a subdirectory rather than a file.  All files and subdirectories 
are always readable and writable.  This can be expressed by "w" 
permission if desired but the "w" permission is optional and is ignored
by Fossil.  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.

Manifests may be either flat or hierarchical.  A flat manifest lists
all files in the check-in, including all files in subdirectories.  A
flat manifest may not include F-cards with the "d" permission.  An
heirarchical manifest only lists the files or subdirectories at the
top-level of the check-in.  An heirarchical manifest may not include
an F-card entries that have a directory separator character ("/").  
An heirarchical manifest may not be a delta-manifest (it may not have
a B-card) nor may it be used as a baseline-manifest by some other
delta-manifest.  Hierarchical manifests
are only recognized by Fossil versions 1.35 and later.  Repositories
that contain hierarchical manifests will cause problems for earlier
versions of Fossil.

When an F-card refers to a subdirectory (that is to say, when the
F-card is part of an hierarchical manifest and contains the "d"
permission) then the referenced directory artifact must be a 
[#directory|well-formed directory artifact] that contains a
G-card that exactly matches the name of the subdirectory as assigned
by the F-card.  If these conditions are not met, then the artifact is
not a valid manifest.

A manifest has zero or one P-cards.  Most manifests have one P-card.
The P-card has a varying number of arguments that
defines other manifests from which the current manifest
is derived.  Each argument is an 40-character lowercase 
hexadecimal SHA1 of the predecessor manifest.  All arguments
to the P-card must be unique to that line.

of all prior lines of the manifest up to and including the newline 
character that immediately precedes the "Z".  The Z-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].

<a name="directory"></a>
<h3>1.2 Directory Artifacts</h3>

A directory artifact describes the files and subdirectories within a
single directory of an hierarchical manifest.  Directory artifacts
are only recognized by Fossil version 1.35 and later (circa 2015-12-23).

Directory artifacts contain zero or more F-cards and exactly one Z-card,
in the same format as a manifest.  A directory artifact also contains
exactly one G-card with a single argument that is the pathname
of the directory relative to the root of the repository.
The format of the directory name in a G-card is
the same as the format of a filename in an F-card.

The F-cards in a directory artifact may not contain directory separator
characters.  The content of subdirectories must be expressed using
additional directory artifacts referenced by F-cards with the "d"
permission.  All F-cards in a directory artifact must contain at least
two arguments.

When an F-card X of directory artifact Y refers to 
subdirectory Z (that is to say, when F-card X contains
the "d" permission and the second argument on X is the SHA1
hash of directory artifact Z) then the G-card of Z must
be the concatenation of the G-card on artifact Y, the
directory separator character "/" and the first argument to
the F-card X.  Otherwise, the artifact Y is not a valid
directory artifact.

<a name="cluster"></a>
<h3>1.3 Clusters Artifacts</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.  Clusters may not be PGP clearsigned.
















Allowed cards in the cluster are as follows:

<blockquote>
<b>M</b> <i>artifact-id</i><br />
<b>Z</b> <i>checksum</i>
</blockquote>

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

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

<a name="ctrl"></a>
<h3>1.4 Tag Artifacts</h3>

Tag artifacts are used to assign properties to other artifacts
within the repository.  Tag artifacts where called "control artifacts"
in an earlier version of this document.  Though their name has changed
in the documentation, their function has not.




Allowed cards in a tag artifact are as follows:

<blockquote>
<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 />
</blockquote>

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

The D card and the Z card of a tag artifact are the same
as in a manifest.

The T card represents a [./branching.wiki#tags | tag or property]
that is applied to
some other artifact.  The T card has two or three values.  The
second argument is the 40 character lowercase artifact ID of the artifact
to which the tag is to be applied. 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 U card is the name of the user that created the control 
artifact.  The Z card is the usual required artifact checksum.

An example tag artifacts can be seen [/info/9d302ccda8 | here].


<a name="wikichng"></a>
<h3>1.5 Wiki Pages</h3>

A wiki artifact defines a single version of a single wiki


page.  Wiki artifacts accept
the following card types:

<blockquote>
<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 />

that terminates the W card.  The wiki text is always followed by one
extra newline.

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

<a name="tktchng"></a>
<h3>1.6 Ticket Changes</h3>

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

<blockquote>
<b>D</b> <i>time-and-date-stamp</i><br />
<b>J</b> ?<b>+</b>?<i>name</i> ?<i>value</i>?<br />

The field name and value are both encoded using the character
escapes defined for the C card of a manifest.

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

<a name="attachment"></a>
<h3>1.7 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:

If an attachment is added anonymously, then the U card may be omitted.

The Z card is the usual checksum over the rest of the attachment artifact.
The Z card is required.


<a name="event"></a>
<h3>1.8 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:

from which the current technote is an edit.  The P 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 T-cards used to set
[./branching.wiki#tags | tags or properties]
on the technote.  The format of the T-card is the same as
described in [#ctrl | Tag 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

technote.  The format of the W card is exactly the same as for a 
[#wikichng | wiki artifact].

The Z card is the required checksum over the rest of the artifact.


<a name="summary"></a>
<h2>2.0 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 border=1 width="100%">
<tr>
<th rowspan=2 valign=bottom>Card Format</th>
<th colspan=8>Used By</th>
</tr>
<tr>
<th>Manifest</th>
<th>Directory</th>
<th>Cluster</th>
<th>Tag</th>
<th>Wiki</th>
<th>Ticket</th>
<th>Attachment</th>
<th>Technote</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>&nbsp;</td>
<td align=center><b>1</b></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>&nbsp;</td><td colspan='8'>* = Required for delta manifests,
Disallowed for hierarchical manifests.</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>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td align=center><b>0-1</b></td>
<td align=center><b>0-1</b></td>
</tr>
<tr>
<td><b>D</b> <i>date-time-stamp</i></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>
<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>&nbsp;</td>
<td align=center><b>1</b></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 align=center><b>0+</b></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>fileame</i>
<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>J</b> <i>name</i> ?<i>value</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>K</b> <i>ticket-uuid</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>L</b> <i>wiki-title</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>M</b> <i>uuid</i></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>
<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>&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>
</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>&nbsp;</td>
<td align=center><b>0-1</b></td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td align=center><b>0-1</b></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>?</td>
<td align=center><b>0+</b></td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td align=center><b>1+</b></td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td align=center><b>0+</b></td>
</tr>
<tr>
<td><b>U</b> <i>username</i></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>
<td align=center><b>1</b></td>
<td align=center><b>0-1</b></td>
<td align=center><b>0-1</b></td>
</tr>
<tr>
<td><b>W</b> <i>size</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 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>


<a name="addenda"></a>
<h2>3.0 Addenda</h2>

This section contains additional information about the low-level artifact
formats of Fossil.

<h3>3.1 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 R 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.

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 R-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.

<h3>3.2 Different Kinds Of Manifest Artifacts</h3>

The original (1.0) version of Fossil only supported flat baseline
manifests.  That means that all the files of a check-in had to be
listed in every manifest.  Because manifests are delta-encoded, there
is not a storage space issue.  Fossil was originally designed
specifically to support the SQLite project, and as SQLite has fewer
than 2000 files on any give version, a flat baseline manifest design
worked well there and was simple to implement.

However, some project (ex: NetBSD) contain a huge number of files in
every version, and even though the manifests compressed will using
delta-compression, many CPU cycles had to be spent to decompress those
manifests.  To help make Fossil more efficient for large projects like
NetBSD, the concept of a delta-manifest was added.  This helped a lot
but was not a perfect solution.

Later, the concept of an hierarchical manifest was added.  By breaking
up each manifest into many separate subdirectories it is hoped that
the processing of projects with many files can be better optimized.
The hierarchical manifest design also more closely resembles the low-level
file format used by Git, thus making pull and clone from Git repositories
easier.

In retrospect, it would have been better if Fossil had only
hierarchical manifests.  But as there are many legacy repositories
that use flat manifests and delta manifests, all three forms must
be supported moving forward.