view mercurial/help/internals/censor.txt @ 37653:b2fa1591fb44

wireproto: add media type to version 2 capabilities response

This is useful to advertise because servers reject unsupported
media types. A client may wish to speak multiple media types and
choose the one the server supports.

I doubt we'll ever use multiple media types or negotiation in core.
But during the course of developing this protocol, I may end up
making extensions that backport and forward port protocol support
as needed to support Mercurial deploys in the wild. e.g. I may
deploy support for an older protocol on a server so old clients
can continue using it.

It's worth pursuing changing the SSH protocol's upgrade mechanism
to support multiple media types as well...

Differential Revision: https://phab.mercurial-scm.org/D3299

The censor system allows retroactively removing content from
files. Actually censoring a node requires using the censor extension,
but the functionality for handling censored nodes is partially in core.

Censored nodes in a filelog have the flag ``REVIDX_ISCENSORED`` set,
and the contents of the censored node are replaced with a censor
tombstone. For historical reasons, the tombstone is packed in the
filelog metadata field ``censored``. This allows censored nodes to be
(mostly) safely transmitted through old formats like changegroup
versions 1 and 2. When using changegroup formats older than 3, the
receiver is required to re-add the ``REVIDX_ISCENSORED`` flag when
storing the revision. This depends on the ``censored`` metadata key
never being used for anything other than censoring revisions, which is
true as of January 2017. Note that the revlog flag is the
authoritative marker of a censored node: the tombstone should only be
consulted when looking for a reason a node was censored or when revlog
flags are unavailable as mentioned above.

The tombstone data is a free-form string. It's expected that users of
censor will want to record the reason for censoring a node in the
tombstone. Censored nodes must be able to fit in the size of the
content being censored.