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This document describes the current and future design of the bzr bundle facility.
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Bundles are intended to be a compact binary representation of the changes done within
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a branch for transmission between users. Bundles should be able to be used
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easily and seamlessly - we want to avoid having a parallel set of commands to
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get data from within a bundle.
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A related concept is **merge directives** which are used to transmit bzr merge
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and merge-like operations from one user to another in such a way that the
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recipient can be sure they get the correct data the initiator desired.
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* A bundle should be able to substitute for the entire branch in any bzr
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command that operates on branches in a read only fashion.
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* Bundles should be as small as possible without losing data to keep them
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feasible for including in emails.
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Not formally documented, the current released implementation can be found
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in bzrlib.bundle.serializer. One key element is that this design included
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parts of the branch data as human readable diffs; which were then subject
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to corruption by transports such as email.
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Bundles will be implemented as a 'Shallow Branch' with the branch and
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repository data combined into a single file. This removes the need to
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special case bundle handling for all command which read from branches.
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Bundles will be encoded using the bzr pack format. Within the pack the
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branch metadata will be serialised as a BzrMetaDir1 branch entry. The
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Repository data added by the revisions contained in the bundle will be
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encoded using multi parent diffs as they are the most pithy diffs we are
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able to create today in the presence of merges. XXX More details needed?
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Ideally we can reuse our BzrMetaDir based branch formats directly within a
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Bundle by layering a Transport interface on top of the pack - or just
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copying the data out into a readonly memory transport when we read the
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pack. This suggests we will have a pack specific Control instance,
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replacing the usual 'BzrDir' instance, but use the Branch class as-is.
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For the Repository access, we will create a composite Repository using the
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planned Repository Stacking API, and a minimal Repository implementation
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that can work with the multi parent diffs within the bundle.
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We will need access to a branch that has the basis revision of the bundle
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to be able to construct revisions from within it - this is a requirement
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for Shallow Branches too, so hopefully we can define a single mechanism at
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the Branch level to gain access to that.
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doc/developers/bundles.txt
