Commit e6f903a0 authored by Stephen Morris's avatar Stephen Morris
Browse files

[3635] Remove references to DNS servers in the Hooks Developer's Guide.

parent ae405fc3
......@@ -387,9 +387,9 @@ allocates an address to the client. A callout may decide to allocate
special addresses for certain clients, in which case it needs to tell
the server not to allocate an address in this case.
- Drop the packet and continue with the next request. A possible scenario
is a DNS server where a callout inspects the source address of an incoming
packet and compares it against a black list; if the address is on it,
the callout notifies the server to drop the packet.
is a server where a callout inspects the hardware address of the client
sending the packet and compares it against a black list; if the address
is on it, the callout notifies the server to drop the packet.
To handle these common cases, the CalloutHandle has a "skip" flag.
This is set by a callout when it wishes the server to skip normal
......@@ -420,26 +420,25 @@ later in the list are able to examine (and modify) the settings of earlier ones.
@subsubsection hooksdgCalloutContext Per-Request Context
Although many of the Kea modules can be characterised as handling
singles packet - e.g. the DHCPv4 server receives a DISCOVER packet,
processes it and responds with an OFFER, this is not true in all cases.
The principal exception is the recursive DNS resolver: this receives a
packet from a client but that packet may itself generate multiple packets
being sent to upstream servers. To avoid possible confusion the rest of
this section uses the term "request" to indicate a request by a client
for some information or action.
Although the Kea modules can be characterised as handling a single
packet at a time - e.g. the DHCPv4 server receives a DISCOVER packet,
processes it and responds with an OFFER, this may not always be true.
Future developments may have the server processing multiple packets
simultaneously, or to suspend processing on a packet and resume it at
a later time after other packets have been processed.
As well as argument information, the CalloutHandle object can be used by
callouts to attach information to a request being handled by the server.
callouts to attach information to a packet being handled by the server.
This information (known as "context") is not used by the server: its purpose
is to allow callouts to pass information between one another on a
per-request basis.
per-packet basis.
Context only exists only for the duration of the request: when a request
is completed, the context is destroyed. A new request starts with no
context information. Context is particularly useful in servers that may
be processing multiple requests simultaneously: callouts can effectively
attach data to a request that follows the request around the system.
Context associated with a packet only exists only for the duration of the
processing of that packet: when processing is completed, the context is
destroyed. A new packet starts with a new (empty) context. Context is
particularly useful in servers that may be processing multiple packets
simultaneously: callouts can effectively attach data to a packet that
follows the packet around the system.
Context information is held as name/value pairs in the same way
as arguments, being accessed by the pair of methods setContext and
......@@ -603,9 +602,8 @@ for details.
installed Kea.
- The list of libraries that need to be included in the command line
depends on the functionality used by the hook code and the module to
which they are attached (e.g. hook code for DNS will need to link against
the libkea-dns++ library). Depending on operating system, you may also need
to explicitly list libraries on which the Kea libraries depend.
which they are attached. Depending on operating system, you may also need
to explicitly list libraries on which the Kea libraries you link against depend.
@subsection hooksdgConfiguration Configuring the Hooks Library
......
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