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                           DRAFT FOR REVIEW
                       The X Resource Extension
                             Version 1.2
                             Rami Ylimäki
                        rami.ylimaki@vincit.fi

                             ❧❧❧❧❧❧❧❧❧❧❧

1. Introduction

The protocol description of X Resource Extension version 1.1 has been
either lost or has never been written. This specification documents
version 1.0 based on reverse engineered library and server
code. Version 1.1 has been accidentally released from the version
control and while it doesn't have differences to version 1.0, this
version is labeled 1.2 in order to remove the risk of confusion. In
addition to the 1.0 description, this document introduces a new 1.2
version of the extension.

Version 1.2 is a minor release and therefore the changes are
compatible with the previous version. Main enhancements over version
1.0 are:

- Client identification is now possible. For example, servers
  supporting version 1.2 may report PID of local clients.

- Size of any resource can be queried from the server. Servers may not
  necessarily support size calculation for every resource. However,
  clients have now at least the chance to let the server do resource
  size estimation for them.

                             ❧❧❧❧❧❧❧❧❧❧❧

2. Notations used in this document

Notation for data types and requests follows the guidelines set in
sections 2-4 of X Window System Protocol standard.

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3. Interoperability between version 1.1 and 1.2

Version 1.2 only introduces two new requests. However, these requests
could be seen as generalized versions of existing requests. Even
though we aren't deprecating any old requests, libraries could
implement some old requests using the new ones.

The new XResQueryClientIds request could be used instead of
XResQueryClients.

The new XResQueryResourceBytes request could be used instead of
XResQueryClientPixmapBytes.

Using the old requests is still acceptable because we don't want to
change the semantics of existing requests between version 1.1 and 1.2.

                             ❧❧❧❧❧❧❧❧❧❧❧

4. Data types

4.1 Types in version 1.0

CLIENTXIDRANGE [ resource_base: CARD32
                 resource_mask: CARD32 ]

This type is used for reply of XResQueryClients in version 1.1. It
represents the range of resource allocated for a client and can be
also used for client identification.

resource_base
    First resource ID reserved for a client. Used also to identify the
    clients themselves.
resource_mask
    Mask that can be used to identify a client from some resource
    ID. Just zero the bits indicated by this mask from any resource ID
    to identify the client that owns the resource.

CLIENTXID [ client: XID ]

This type identifies a single client by a resource owned by that
client or by the first resource ID allocated for the client
(resource_base of CLIENTXIDRANGE). Whenever a resource ID is used, it
is masked by resource_mask of CLIENTXIDRANGE to find out the client
that owns the resource.

CLIENTRESOURCETYPECOUNT [ resource_type: ATOM
                          count:         CARD32 ]

This type is used for reply of XResQueryClientResources in version
1.1. It represents the number of certain type of resources that are
owned by some client.

resource_type
    Atom specifying the type of a resource.
count
    Number of resources of the given type owned by a client.

4.2 Types in version 1.2

4.2.1 Types used by XResQueryClientIds

CLIENTIDMASK { ClientXid = 0x1, LocalClientPid = 0x2 }

A bitmask specifying a client identification method. Currently only
the PID of local clients is supported in the form of
LocalClientPid. ClientXid is provided for backward compatibility with
version 1.0 so that the new 1.2 requests (XResQueryClientIds) can be
used in place of the older ones (XResQueryClients).

CLIENTIDSPEC [ client:	CLIENTXID or None
               mask:	SETofCLIENTIDMASK or None ]

A data structure for selecting client IDs.

client
    ID of a resource allocated for some client. Only the part
    identifying a client is actually used. The resource_base of
    CLIENTXIDRANGE can be used if the client doesn't own any
    resources. However, any resource ID is accepted because that makes
    identifying the owners of existing resources easy. The null
    resource None can be used to select all clients.
mask
    Collection of identification methods that should be applied on the
    client. The special value None can be used to apply all supported
    identification methods.

CLIENTIDVALUE [ spec:   CLIENTIDSPEC
                length: CARD32
                value:  LISTofCARD32 ]

A data structure specifying a single client ID.

spec
    A unique identifier for a specific ID of some client. Wildcards
    such as None and bitmask unions aren't allowed. The data structure
    must always identify a single client and single ID type. However,
    the client doesn't have to be specified as the resource_base of
    CLIENTXIDRANGE and can be any resource owned by the client.
length
    Specifies the length of an ID in units of CARD32. The length
    depends on the ID type. In version 1.2 the lengths are 0 for
    ClientXid and 4 for LocalClientPid. The length of ClientXid is 0
    because that is already stored in the spec field.
value
    Actual ID data. In version 1.2 this is missing for ClientXid and
    consists of a single CARD32 for LocalClientPid.

4.2.2 Types used by XResQueryResourceBytes

To better understand how resources are related to each other, it's
useful to introduce the concepts of main resource and cross
reference. By main resource we just mean a normal resource that has a
valid XID. By cross reference we mean a resource that is used by some
other resource.

The same resource may have both of these roles depending on the
context. For example, there could be an ordinary pixmap resource. When
we talk about this resource in isolation the term main resource is
used. We call the exact same resource a cross reference when we are
concentrating on some higher level resource, such as window or
graphics context, that is using the lower level resource. Cross
references may also be internal server resources that don't have a
valid XID.

RESOURCEIDSPEC [ resource: XID or None
                 type:     ATOM or None/AnyPropertyType ]

A data structure for selecting or identifying resources. The
interpretation of fields changes depending on the context. The
differences in interpretation are described below.

resource
    An XID of a resource. The null resource None can be used to select
    all resources matching some type if the data structure is used in
    XResQueryResourceBytes request. The null resource None can be used
    to mark private server resources if the data structure is used in
    a cross reference of XResQueryResourceBytes reply.
type
    An atom identifying the resource type. The null atom
    None/AnyPropertyType can be used to select all resource types
    matching some resource ID if the data structure is used in
    XResQueryResourceBytes request.

RESOURCESIZESPEC [ spec:      RESOURCEIDSPEC
                   bytes:     CARD32
                   ref_count: CARD32
                   use_count: CARD32 ]

A data structure specifying the size of a single resource.

spec
    Uniquely identifies a single resource. Wildcards such as None and
    AnyPropertyType aren't allowed for main resources. In cross
    references, None is used to mark internal server resources.
bytes
    Number of bytes allocated for the resource. The size of a resource
    is never divided by a reference count. This is the number of bytes
    released in server when there are no more references left to the
    resource.
ref_count
    Number of total users of the resource. Typically the reference
    count is 1 but for pixmaps and other resources used from different
    contexts the count may be larger.
use_count
    Number of times the resource is used by some other resource. For
    main resources this is typically 1, because a resource doesn't
    usually use itself recursively. For cross references this is the
    number of times the resource is used and is also 1 usually.

RESOURCESIZEVALUE [ size:                 RESOURCESIZESPEC
                    num_cross_references: CARD32
                    cross_references:     LISTofRESOURCESIZESPEC ]

A data structure specifying sizes of cross references to other
resources in addition to the main resource size.

size
    Size of a main resource.
num_cross_references
    Number of cross references to other resources from the main
    resource. Currently resources can only have pixmaps as cross
    references but this can be extended to other types in the
    future. For simple resources this field is therefore 0 and the
    cross_references list is missing.
cross_references:
    Size specifications for cross references. Note that cross
    references may contain resources that don't have a valid XID. For
    example, a DRI2 drawable might have a cross reference to a private
    pixmap that is used internally in the server only. These private
    cross references are contained in this list also. This makes it
    possible to emulate XResGetClientPixmapBytes with
    XResGetResourceBytes.

                             ❧❧❧❧❧❧❧❧❧❧❧

5. Requests

5.1 Requests in version 1.0

┌───
    XResQueryVersion
    client_major: CARD8
    client_minor: CARD8
    server_major: CARD16
    server_minor: CARD16
└───

The client sends the highest supported version to the server and the
server sends the highest version it supports, but no higher than the
requested version. Major version changes can introduce
incompatibilities in existing functionality, minor version changes
introduce only backward compatible changes. It is the client's
responsibility to ensure that the server supports a version which is
compatible with its expectations.

client_major
    Major X Resource Extension version supported by client.
client_minor
    Minor X Resource Extension version supported by client.
server_major
    Highest version supported by server that is compatible with
    client.
server_minor
    Highest version supported by server that is compatible with
    client.

┌───
    XResQueryClients
    num_clients: CARD32
    clients:     LISTofCLIENTXIDRANGE
└───

The request asks X server to return the list of all currently
connected clients.

num_clients
    Number of currently connected clients.
clients
    List of XID ranges allocated for the connected clients.

┌───
    XResQueryClientResources
    client:    CLIENTXID
    num_types: CARD32
    types:     LISTofCLIENTRESOURCETYPECOUNT

    Errors:    Value
└───

This request can be used to ask the number of resources owned by a
client. The server will return the counts of each type of resource.

client
    An XID in the resource range of a client. This identifies the
    client and not some specific resource.
num_types
    Number of different resource types owned by the client.
types
    A list of counts for each resource type.

A value error is generated if invalid resource or client XID is given
in the request.

┌───
    XResQueryClientPixmapBytes
    client:         CLIENTXID
    bytes:          CARD32
    bytes_overflow: CARD32

    Errors:         Value
└───

This request is used to get the pixmap usage of some client. The
returned number is a sum of memory usage of each pixmap that can be
attributed to the given client. Ideally the server goes through all
pixmaps and divides each pixmap size by the pixmap reference count to
get a pixmap reference size. The reference size is then added to the
returned sum if the client happens to be referencing that pixmap. In
practice some pixmap references may be missed, because it would be too
difficult to keep track of all pixmap references. However, the server
will check the most important client resources that are using pixmaps
and tries to estimate the pixmap usage as well as is possible. In
other words, the server need only make a best-effort attempt to
calculate resource source, so actual resource size may differ from
that reported in practice.

client
    Identifies a client by an ID in its resource ID range.
bytes:
    Number of bytes attributed to pixmap references from the client
    resources.
bytes_overflow:
    Higher order word for the bytes field in case the sum of pixmap
    reference sizes doesn't fit in CARD32.

A value error is generated if invalid resource or client XID is given
in the request.

5.2 Requests in version 1.2

┌───
    XResQueryClientIds
    num_specs:    CARD32
    client_specs: LISTofCLIENTIDSPEC
    num_ids:      CARD32
    client_ids:   LISTofCLIENTIDVALUE

    Errors:       Value
└───

XResQueryClientIds can be used to identify a given set of clients with
some identification method. The request sends a list of specifiers
that select clients and identification methods to server. The server
then tries to identify the chosen clients using the identification
methods specified for each client. The server returns IDs for those
clients that were successfully identified. It's not an error condition
if some identification method couldn't be applied to a client. If the
server is unable to identify some clients, they simply aren't included
in the returned list.

The request supports wildcards in the client specifications so that in
the most general case all IDs of all clients can be queried with a
single CLIENTIDSPEC.

The CLIENTIDSPEC of request and CLIENTIDSPEC of CLIENTIDVALUE in reply
usually match each other. For example, if a request selected a client
by a resource ID owned by the client, then the client is identified by
the same resource ID in the reply. This has been done so that it would
be easy to identify an owner of some resource.

However, the CLIENTIDSPEC of returned CLIENTIDVALUE never contains any
wildcards. If the request used a wildcard to specify all clients in a
single CLIENTIDSPEC, then the reply has expanded the wildcard and
returns separate CLIENTIDVALUE records for each client. In this case
wildcarded clients are identified by resource_base of CLIENTXIDRANGE.

The LocalClientPid type of IDs are included in the reply list only if
the client executing the request asked for it and was also a local
client itself. It doesn't make sense for remote clients to ask PIDs of
local clients.

num_specs
    Number of client ID specifications.
client_specs
    A list specifying identification methods for clients. Supports
    multiple identification methods and clients in a single
    specification. See CLIENTIDSPEC for details.
num_ids
    Number of IDs that were successfully determined. Can be different
    from num_specs or even zero if the server didn't support any
    identification methods for the given clients.
client_ids
    A list specifying ID information for successfully identified
    clients. If wildcards were used in a single CLIENTIDSPEC of
    client_specs, then multiple CLIENTIDVALUE records may be returned
    for that CLIENTIDSPEC. See CLIENTIDVALUE for details.

A Value error is returned if the request specifies an invalid client
XID or invalid identification method type.

┌───
    XResQueryResourceBytes
    client:         CLIENTXID or None
    num_specs:      CARD32
    resource_specs: LISTofRESOURCEIDSPEC
    num_sizes:      CARD32
    sizes:          LISTofRESOURCESIZEVALUE

    Errors:         Atom, Value
└───

XResQueryResourceBytes can be used to ask the sizes of resources from
X server. The request sends a list of specifiers that selects
resources for size calculation. The server tries to calculate the
sizes of chosen resources and returns an estimate for a resource only
if the size could be determined. It's not an error condition if a size
couldn't be calculated. In that case the resources simply aren't
included in the returned list.

The request supports wildcards so that in the most general case sizes
of all resources of all clients can be queried with a single
RESOURCEIDSPEC. However, the reply has all wildcards expanded and
reports a size of a single resource in each RESOURCESIZEVALUE.

client
    An ID of a client can be given to limit the query to resources of
    that client. Just like in CLIENTIDSPEC, any resource ID can be
    given to identify a client and None can be used if the query
    shouldn't be limited to a specific client. Note that in some cases
    this field is redundant because resource_specs already fully
    determines which resources are selected. If the client ID doesn't
    match the owner of any resource in resource_specs, no sizes are
    returned and no error is generated.
num_specs
    Number of resource specifications.
resource_specs
    A list of resource specifications. Each specification can either
    uniquely identify a single resource or multiple resources if
    wildcarding is used. See RESOURCEIDSPEC for details.
num_sizes
    Number of resources whose size could be determined. Can be
    different from num_specs or even zero if the server didn't support
    size calculation for the given resources.
sizes
    A list of resource sizes. Each resource size is linked to a unique
    resource. Wildcards are never used in the returned size
    records. For example, it's not possible to receive a single
    RESOURCESIZEVALUE that would specify the size of all pixmaps if
    the sizes of pixmap type resources were asked. Instead, a single
    RESOURCESIZEVALUE would be returned for each pixmap in that case.

An Atom error is returned if the request specifies an invalid resource
type. A Value error is returned if the request specifies an invalid
XID for a client or a resource.

                             ❧❧❧❧❧❧❧❧❧❧❧