+++ /dev/null
-<!--
-Copyright (C) Internet Systems Consortium, Inc. ("ISC")
-
-SPDX-License-Identifier: MPL-2.0
-
-This Source Code Form is subject to the terms of the Mozilla Public
-License, v. 2.0. If a copy of the MPL was not distributed with this
-file, you can obtain one at https://mozilla.org/MPL/2.0/.
-
-See the COPYRIGHT file distributed with this work for additional
-information regarding copyright ownership.
--->
-
- Name Compression
-
-Overview.
-
- BIND 4.x and BIND 8.x only had one methods of compression to deal
- with 14 bit compression. BIND 9 has 3 methods of compression
- to deal with 14 bit, 16 bit and local compression (14 and 16 bit).
-
- In addition to this the allowed compression methods vary across
- types and across client revisions thanks to EDNS.
-
- To be able to compress a domain name you need to some or all of
- the following pieces of information.
-
- 1. where the message starts.
- 2. where the current rdata starts in the message (local compression).
- 3. what the current owner name is (local compression).
- 4. existing global 14 bit compression targets.
- 5. existing global 16 bit compression targets.
- 6. existing local compression targets.
- 7. the current domain name.
- 8. what are allowable compression methods, these are not constant
- across a message.
-
- BIND 4.x and BIND 8.x used a table of existing 14 bit compression
- targets.
-
- The implicit assumption is that we will use compression whenever
- possible and when ever there are multiple alternatives available
- we will choose the one that minimises the size of the message.
-
- We will need functions that determine the allowable compression
- methods, find the "best" match among the available compression
- targets, add new compression targets.
-
- We need to be able to back out any changes made to the compression
- targets if we are unable to add a complete RR (RRset?). This is
- only a problem for the global compression targets.
-
-Implementation:
-
- We will maintain two RBT, one for local compression targets and
- one for global compression targets. The data for these RBT will
- be the offset values. The local compression RBT only needs to
- be maintained when local compression is possible. The global
- compression RBT is maintained regardless. Unless there is a
- perfect match (or the name is ".") we will add the name to the
- compression RBTs provide the offset would not be too large for
- the valid compression methods of the RBT. All nodes of the RBT
- will have an offset excluding the root node.
-
- The local compression RBT will be initialised with the owner name
- and the start of the rdata will be recorded.
-
- We will use deepest partial match to find the potential
- compression targets.
-
- We only need to maintain one global RBT as 16 bit compression
- pointers are either valid or invalid for the whole message.
-
- dns_rdata_towire() will set the allowed methods based on the
- edns version.
-
-Functions:
-
- dns_result_t
- dns_compress_init(dns_compress_t *cctx, int edns, isc_mem_t *mctx);
-
- Initialises cctx to empty and sets whether 16 bit global
- compression targets are to be added to the global RBT based on the
- edns value.
-
- dns_result_t
- dns_compress_localinit(dns_compress_t *cctx, dns_name_t *owner,
- isc_buffer_t *target);
-
- Initialise a RBT for local compression, freeing and existing RBT.
- Record current offset.
-
- dns_compress_invalidate(dns_compress_t *cctx);
-
- Free any RBT's and make empty.
-
- dns_compress_localinvalidate(dns_compress_t *cctx);
-
- Free the local RBT.
-
- void
- dns_compress_setmethods(dns_compress_t *cctx, unsigned int allowed);
-
- unsigned int
- dns_compress_getmethods(dns_compress_t *cctx);
-
- int
- dns_compress_getedns(dns_compress_t *cctx);
-
- dns_result_t
- dns_name_towire(dns_name_t *name, dns_compress_t *cctx,
- isc_buffer_t *target);
-
- 'name' contains the current name to be added to the message 'target'.
- 'target' is assumed to only contain the message.
- 'cctx' contains the compression context and has to hold all the
- information required that cannot be obtained from 'name' or 'target'.
-
- struct dns_compress {
- unsigned int allowed; /* Allowed methods. */
- unsigned int rdata; /* Start of local rdata */
- bool global16; /* 16 bit offsets allowed */
- dns_rbt_t *local; /* Local RBT */
- dns_rbt_t *global; /* Global RBT */
- isc_mem_t *mctx; /* Required by RBT */
- };
-
- sets allowed based on the value of edns.
-
- bool
- dns_compress_findglobal(dns_compress_t *cctx, dns_name_t *name,
- dns_name_t *prefix, dns_name_t *suffix,
- uint16_t *offset, isc_buffer_t *workspace);
-
- bool
- dns_compress_findlocal(dns_compress_t *cctx, dns_name_t *name,
- dns_name_t *prefix, dns_name_t *suffix,
- uint16_t *offset, isc_buffer_t *workspace);
-
- Find the best best match in the global / local RBT. Returns prefix,
- suffix and offset of the bestmatch. Findglobal(), findlocal()
- requires as workspace as it may be necessary to spit a bit stream
- label. The result prefix will be such that it can be added to the
- wire format followed by a compression pointer pointing to offset.
- Suffix is returned so that it is possible to add the compression
- pointers via dns_compress_add().
-
- void
- dns_compress_add(dns_compress_t *cctx, dns_name_t *prefix,
- dns_name_t *suffix, uint16_t offset);
-
- Add compression pointers pointing to lebels (if any) in prefix.
- The offset to the first label is passed in offset.
-
-Dependency:
-
- Requires RBT deepest match.
- Requires the ability to walk the RBT and remove any node which
- meets the removal condition.
+++ /dev/null
-<!--
-Copyright (C) Internet Systems Consortium, Inc. ("ISC")
-
-SPDX-License-Identifier: MPL-2.0
-
-This Source Code Form is subject to the terms of the Mozilla Public
-License, v. 2.0. If a copy of the MPL was not distributed with this
-file, you can obtain one at https://mozilla.org/MPL/2.0/.
-
-See the COPYRIGHT file distributed with this work for additional
-information regarding copyright ownership.
--->
-
- Name Decompression
-
-Overview.
-
- There are 4 type of compression: global 14 bit, global 16 bit,
- local 14 bit and local 16 bit.
-
- In general the resolver / nameserver should accept any compression
- method at any time regardless of whether it was legal to
- send it. This fits with the principle of being liberal with
- what you accept and strict with what you send.
-
- There are a few cases where it does not make sense to accept
- compression pointers of a given type. i.e. the first domain name
- in a message, local compression pointers in the ownername of a RR
- or in a question.
-
- When performing regression testing however we should be as strict
- as possible. Hence we need to be able modify the behaviour of the
- decompression routines.
-
- To be able to decompress a domain name we need some or all of the
- following pieces of information.
-
- 1. where the message starts.
- 2. where the current rdata starts in the message (local compression).
- 3. what the current owner name is (local compression).
- 4. where the domainname we are decompressing starts.
- 5. what are allowable decompression method. These vary across type
- and edn version.
-
-Implementation:
-
- dns_rdata_fromwire will set the allowed decompression methods allowed
- by looking at edns, strict and the type values.
-
-Types:
- struct dns_decompress {
- unsigned int magic;
- unsigned int allowed;
- int edns;
- dns_name_t owner_name;
- unsigned int rdata;
- bool strict;
- }
-
-Functions:
-
- void
- dns_decompress_init(dns_decompress_t *dctx, int edns,
- bool strict);
- initialise dctx
- dctx->ownername is invalidated
-
- void
- dns_decompress_localinit(dns_decompress_t *dctx, dns_name_t *name,
- isc_buffer_t *source);
- initialise dctx->ownername
- record source->current to dctx->rdata
-
- void
- dns_decompress_invalidate(dns_decompress_t *dctx);
-
- invalidate dctx
-
- void
- dns_decompress_localinvalidate(dns_decompress_t *dctx);
-
- invalidate dctx->ownername
-
- void
- dns_decompress_setmethods(dns_decompress_t *dctx, unsigned int allowed);
-
- sets dctx->allowed
-
- unsigned int
- dns_decompress_getmethods(dns_decompress_t *dctx);
-
- returns dctx->allowed
-
- int
- dns_decompress_edns(dns_decompress_t *dctx);
-
- returns dctx->edns
-
- bool
- dns_decompress_strict(dns_decompress_t *dctx);
-
- returns dctx->strict
-
- dns_result_t
- dns_name_fromwire(dns_name_t *name, isc_buffer_t *source,
- dns_decompress_t *dctx, bool downcase,
- isc_buffer_t *target)
projects / thirdparty / bind9.git / commitdiff
