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//! Building a new message. //! //! DNS messages consist of five sections. The first, the *header section* //! contain, among other things, the number of entries in the following four //! section which then contain these entries without any further //! delimitation. In order to safely build a correct message, it thus needs //! to be assembled step by step, entry by entry. This module provides four //! types, each responsible for assembling one of the entry sections. //! //! You start out with a [`MessageBuilder`] which you can either create from //! an existing [`Composer`] or, as a shortcut, either completely [`new()`] //! or from an existing bytes vector via [`from_vec()`]. Like all of these //! type, the [`MessageBuilder`] allows access to the header section. In //! addition, it is used for building the *question section* of the message. //! This section contains [`Question`]s to be asked of a name server, //! normally exactly one. You can add questions using the //! [`push()`](struct.MessageBuilder.html#method.push) method. //! //! Once you are happy with the question section, you can proceed to the //! next section, the *answer section,* by calling the //! [`answer()`](struct.MessageBuilder.html#method.answer) method. In a //! response, this section contains those resource records that answer the //! question. The section is represented by the [`AnswerBuilder`] type. //! It, too, has a [`push()`](struct.AnswerBuilder.html#method.push) method, //! but for [`Record`]s. //! //! A call to [`authority()`](struct.AnswerBuilder.html#method.authority) //! moves on to the *authority section*. It contains resource records that //! point to the name servers that serve authoritative for the question. //! Like with the answer section, //! [`push()`](struct.AuthorityBuilder.html#method.push) adds records to this //! section. //! //! The final section is the *additional section.* Here a name server can add //! information it believes will help the client to get to the answer it //! really wants. Which these are depends on the question and is generally //! given in RFCs that define the record types. Unsurprisingly, you will //! arrive at a [`AdditionalBuilder`] by calling the //! [`additional()`](struct.AuthorityBuilder.html#method.additional) method //! once you are done with the authority section. //! //! Once you are done with the additional section, too, you call //! [`finish()`](struct.AdditionalBuilder.html#method.finish) to retrieve //! the bytes vector with the assembled message data. //! //! Since at least some of the sections are empty in many messages, for //! instance, a simple request only contains a single question, there are //! shortcuts in place to skip over sections. Each type can go to any later //! section through the methods named above. Each type also has a `finish()` //! method to arrive at the final data quickly. //! //! //! # Example //! //! To summarize all of this, here is an example that builds a //! response to an A query for example.com that contains two A records and //! nothing else. //! //! ``` //! use std::str::FromStr; //! use domain::bits::{ComposeMode, DNameBuf, MessageBuilder, Question}; //! use domain::iana::Rtype; //! use domain::rdata::A; //! //! let name = DNameBuf::from_str("example.com.").unwrap(); //! let mut msg = MessageBuilder::new(ComposeMode::Limited(512), //! true).unwrap(); //! msg.header_mut().set_rd(true); //! msg.push((&name, Rtype::A)); //! let mut msg = msg.answer(); //! msg.push((&name, 86400, A::from_octets(192, 0, 2, 1))).unwrap(); //! msg.push((&name, 86400, A::from_octets(192, 0, 2, 2))).unwrap(); //! let _ = msg.finish(); // get the Vec<u8> //! ``` //! //! [`AdditionalBuilder`]: struct.AdditionalBuilder.html //! [`AnswerBuilder`]: struct.AnswerBuilder.html //! [`AuthorityBuilder`]: struct.AuthorityBuilder.html //! [`Composer`]: ../compose/Composer.html //! [`MessageBuilder`]: struct.MessageBuilder.html //! [`Question`]: ../question/struct.Question.html //! [`Record`]: ../record/struct.Record.html //! [`new()`]: struct.MessageBuilder.html#method.new //! [`from_vec()`]: struct.MessageBuilder.html#method.from_vec use std::mem; use ::iana::{Class, OptRcode, Rtype}; use super::{Composer, ComposeError, ComposeMode, ComposeResult, ComposeSnapshot, DName, DNameSlice, HeaderSection, Header, HeaderCounts, Message, Question, Record, RecordData}; use super::record::RecordBuilder; use super::opt::OptData; //------------ MessageBuilder ----------------------------------------------- /// A type for building the question section of a DNS message. /// /// This type starts building a DNS message and allows adding questions to /// its question section. See the [module documentation] for details. /// /// [module documentation]: index.html #[derive(Clone, Debug)] pub struct MessageBuilder { target: MessageTarget, } /// # Creation /// impl MessageBuilder { /// Creates a new empty DNS message. /// /// The `mode` argument decides whether the message will have a size /// limit and whether it should include the length prefix for use with /// stream transports. If `compress` is `true`, name compression will /// be enabled for the message. /// /// This function may fail if the size limit in `mode` is too small to /// even add the header section. pub fn new(mode: ComposeMode, compress: bool) -> ComposeResult<Self> { Self::from_composer(Composer::new(mode, compress)) } /// Creates a new DNS message appended to the content of a bytes vector. /// /// The `mode` argument decides whether the message will have a size /// limit and whether it should include the length prefix for use with /// stream transports. If `compress` is `true`, name compression will /// be enabled for the message. /// /// This function may fail if the size limit in `mode` is too small to /// even add the header section. pub fn from_vec(vec: Vec<u8>, mode: ComposeMode, compress: bool) -> ComposeResult<Self> { Self::from_composer(Composer::from_vec(vec, mode, compress)) } /// Creates a new DNS message atop an existing composer. /// /// This doesn’t reset the composer but starts off after whatever is in /// there already. As this may result in invalid message, user discretion /// is advised. pub fn from_composer(mut composer: Composer) -> ComposeResult<Self> { try!(composer.compose_empty(mem::size_of::<HeaderSection>())); Ok(MessageBuilder{target: MessageTarget::new(composer)}) } } /// # Building /// impl MessageBuilder { /// Returns a reference to the message’s header. pub fn header(&self) -> &Header { self.target.header() } /// Returns a mutable reference to the message’s header. pub fn header_mut(&mut self) -> &mut Header { self.target.header_mut() } /// Appends a new question to the message. /// /// This function is generic over anything that can be converted into a /// [`Question`]. In particular, triples of a domain name, a record type, /// and a class as well as pairs of just a domain name and a record type /// fulfill this requirement with the class assumed to be `Class::In` in /// the latter case. /// /// [`Question`]: ../question/struct.Question.html pub fn push<N: DName, Q: Into<Question<N>>>(&mut self, question: Q) -> ComposeResult<()> { self.target.push(|target| question.into().compose(target), |counts| counts.inc_qdcount(1)) } /// Rewinds to the beginning of the question section. /// /// This drops all previously assembled questions. pub fn rewind(&mut self) { self.target.rewind(|counts| counts.set_qdcount(0)); } /// Proceeds to building the answer section. pub fn answer(self) -> AnswerBuilder { AnswerBuilder::new(self.target.commit()) } /// Proceeds to building the authority section, skipping the answer. pub fn authority(self) -> AuthorityBuilder { self.answer().authority() } /// Proceeds to building the additonal section. /// /// Leaves the answer and additional sections empty. pub fn additional(self) -> AdditionalBuilder { self.answer().authority().additional() } /// Returns a reference to the message assembled so far. /// /// This method requires a `&mut self` since it may need to update some /// length values to return a valid message. /// /// In case the builder was created from a vector with previous content, /// the returned reference is for the full content of this vector. pub fn preview(&mut self) -> &[u8] { self.target.preview() } /// Finishes the message and returns the underlying target. /// /// This will result in a message with all three record sections empty. pub fn finish(self) -> Vec<u8> { self.target.finish() } } //------------ AnswerBuilder ------------------------------------------------- /// A type for building the answer section of a DNS message. /// /// This type is typically constructed by calling [`answer()`] on a /// [`MessageBuilder`]. See the [module documentation] for details. /// /// [`answer()`]: struct.MessageBuilder.html#method.answer /// [`MessageBuilder`]: struct.MessageBuilder.html /// [module documentation]: index.html #[derive(Clone, Debug)] pub struct AnswerBuilder { target: MessageTarget, } impl AnswerBuilder { /// Creates a new answer builder from a compser. fn new(composer: Composer) -> Self { AnswerBuilder { target: MessageTarget::new(composer) } } /// Returns a reference to the messages header. pub fn header(&self) -> &Header { self.target.header() } /// Returns a mutable reference to the messages header. pub fn header_mut(&mut self) -> &mut Header { self.target.header_mut() } /// Appends a new resource record to the answer section. /// /// This method is generic over anything that can be converted into a /// [`Record`]. In particular, you can use four-tuples consisting of /// a domain name, class, TTL, and record data or triples leaving out /// the class which will then be assumed to be `Class::In`. /// /// [`Record`]: ../record/struct.Record.html pub fn push<N, D, R>(&mut self, record: R) -> ComposeResult<()> where N: DName, D: RecordData, R: Into<Record<N, D>> { self.target.push(|target| record.into().compose(target), |counts| counts.inc_ancount(1)) } /// Rewinds to the beginning of the answer section. /// /// This drops all previously assembled answer records. pub fn rewind(&mut self) { self.target.rewind(|counts| counts.set_ancount(0)) } /// Proceeds to building the authority section. pub fn authority(self) -> AuthorityBuilder { AuthorityBuilder::new(self.target.commit()) } /// Proceeds to building the additional section, skipping authority. pub fn additional(self) -> AdditionalBuilder { self.authority().additional() } /// Returns a reference to the message assembled so far. /// /// This method requires a `&mut self` since it may need to update some /// length values to return a valid message. /// /// In case the builder was created from a vector with previous content, /// the returned reference is for the full content of this vector. pub fn preview(&mut self) -> &[u8] { self.target.preview() } /// Finishes the message. /// /// The resulting message will have empty authority and additional /// sections. pub fn finish(self) -> Vec<u8> { self.target.finish() } } //------------ AuthorityBuilder --------------------------------------------- /// A type for building the authority section of a DNS message. /// /// This type can be constructed by calling `authority()` on a /// [`MessageBuilder`] or [`AnswerBuilder`]. See the [module documentation] /// for details. /// /// [`AnswerBuilder`]: struct.AnswerBuilder.html /// [`MessageBuilder`]: struct.MessageBuilder.html /// [module documentation]: index.html #[derive(Clone, Debug)] pub struct AuthorityBuilder { target: MessageTarget, } impl AuthorityBuilder { /// Creates a new authority builder from a compser. fn new(composer: Composer) -> Self { AuthorityBuilder { target: MessageTarget::new(composer) } } /// Returns a reference to the messages header. pub fn header(&self) -> &Header { self.target.header() } /// Returns a mutable reference to the messages header. pub fn header_mut(&mut self) -> &mut Header { self.target.header_mut() } /// Appends a new resource record to the authority section. /// /// This method is generic over anything that can be converted into a /// [`Record`]. In particular, you can use four-tuples consisting of /// a domain name, class, TTL, and record data or triples leaving out /// the class which will then be assumed to be `Class::In`. /// /// [`Record`]: ../record/struct.Record.html pub fn push<N, D, R>(&mut self, record: R) -> ComposeResult<()> where N: DName, D: RecordData, R: Into<Record<N, D>> { self.target.push(|target| record.into().compose(target), |counts| counts.inc_nscount(1)) } /// Rewinds to the beginning of the authority section. /// /// This drops all previously assembled authority records. pub fn rewind(&mut self) { self.target.rewind(|counts| counts.set_nscount(0)) } /// Proceeds to building the additional section. pub fn additional(self) -> AdditionalBuilder { AdditionalBuilder::new(self.target.commit()) } /// Returns a reference to the message assembled so far. /// /// This method requires a `&mut self` since it may need to update some /// length values to return a valid message. /// /// In case the builder was created from a vector with previous content, /// the returned reference is for the full content of this vector. pub fn preview(&mut self) -> &[u8] { self.target.preview() } /// Finishes the message. /// /// The resulting message will have an empty additional section. pub fn finish(self) -> Vec<u8> { self.target.finish() } } //------------ AdditionalBuilder -------------------------------------------- /// A type for building the additional section of a DNS message. /// /// This type can be constructed by calling `additional()` on a /// [`MessageBuilder`], [`AnswerBuilder`], or [`AuthorityBuilder`]. See the /// [module documentation] for details. /// /// [`AnswerBuilder`]: struct.AnswerBuilder.html /// [`AuthorityBuilder`]: struct.AuthorityBuilder.html /// [`MessageBuilder`]: struct.MessageBuilder.html /// [module documentation]: index.html #[derive(Clone, Debug)] pub struct AdditionalBuilder { target: MessageTarget, } impl AdditionalBuilder { /// Creates a new additional builder from a compser. fn new(composer: Composer) -> Self { AdditionalBuilder { target: MessageTarget::new(composer) } } /// Returns a reference to the messages header. pub fn header(&self) -> &Header { self.target.header() } /// Returns a mutable reference to the messages header. pub fn header_mut(&mut self) -> &mut Header { self.target.header_mut() } /// Appends a new resource record to the additional section. /// /// This method is generic over anything that can be converted into a /// [`Record`]. In particular, you can use four-tuples consisting of /// a domain name, class, TTL, and record data or triples leaving out /// the class which will then be assumed to be `Class::In`. /// /// [`Record`]: ../record/struct.Record.html pub fn push<N, D, R>(&mut self, record: R) -> ComposeResult<()> where N: DName, D: RecordData, R: Into<Record<N, D>> { self.target.push(|target| record.into().compose(target), |counts| counts.inc_arcount(1)) } /// Starts appending an OPT record to the section. /// /// The method expects the values of the OPT record that are encoded in /// various fields of the record header. /// /// The *payload_size* field contains /// the maximum size of UDP payload a requestor can assemble and process. /// /// The `rcode` argument should contain the Rcode used for a response /// or `OptRcode::NoError` for a message. Only the upper eight bits are /// used here, the lower for bits go into the message header’s rcode /// field. /// /// The `dnssec_ok` flag indicates whether a sender is prepared to /// receive and process DNSSEC-related resource records in a response. /// In a response it must be equal to its value in a request. /// /// This method trades in the additional section builder for an OPT /// record builder. Once the record is finished, it can be traded back /// to continue building the additional section. pub fn build_opt(self, payload_size: u16, rcode: OptRcode, dnssec_ok: bool) -> ComposeResult<OptBuilder> { OptBuilder::new(self, payload_size, rcode, dnssec_ok) } /// Rewinds to the beginning of the additional section. /// /// This drops all previously assembled additonal records. pub fn rewind(&mut self) { self.target.rewind(|counts| counts.set_arcount(0)) } /// Returns a reference to the message assembled so far. /// /// This method requires a `&mut self` since it may need to update some /// length values to return a valid message. /// /// In case the builder was created from a vector with previous content, /// the returned reference is for the full content of this vector. pub fn preview(&mut self) -> &[u8] { self.target.preview() } /// Finishes the message. pub fn finish(self) -> Vec<u8> { self.target.finish() } } impl AsRef<Message> for AdditionalBuilder { fn as_ref(&self) -> &Message { self.target.as_ref() } } //------------ OptBuilder ---------------------------------------------------- /// A type for building an OPT record on the fly. /// /// The OPT record is part of the additional section. You can therefore get /// hold of a value of this type through the `AdditionalBuilder::build_opt()` /// method. /// /// You use this value to add options to the record via the `push()` method. /// Once you are done, call `complete()` to finish up the record and get the /// additional builder back. #[derive(Clone, Debug)] pub struct OptBuilder { builder: RecordBuilder<ComposeSnapshot>, } impl OptBuilder { /// Creates a new OPT builder from an additional builder fn new(builder: AdditionalBuilder, payload_size: u16, rcode: OptRcode, dnssec_ok: bool) -> ComposeResult<Self> { let mut ttl = (rcode.ext() as u32) << 24; if dnssec_ok { ttl |= 0x8000 } let builder = RecordBuilder::new(builder.target.composer, &DNameSlice::root(), Class::Int(payload_size), Rtype::Opt, ttl)?; Ok(OptBuilder { builder }) } /// Pushes an option to the OPT record. pub fn push<O: OptData>(&mut self, option: O) -> ComposeResult<()> { option.compose(&mut self.builder) } /// Completes the OPT record and returns the additional section builder. pub fn complete(self) -> ComposeResult<AdditionalBuilder> { let mut target = MessageTarget { composer: self.builder.finish()? }; target.counts_mut().inc_arcount(1)?; Ok(AdditionalBuilder { target }) } } //------------ MessageTarget ------------------------------------------------- /// Underlying data for constructing a DNS message. /// /// This private type does all the heavy lifting for constructing messages. #[derive(Clone, Debug)] struct MessageTarget { composer: ComposeSnapshot, } impl MessageTarget { /// Creates a new message target atop a given composer. fn new(composer: Composer) -> Self { MessageTarget{composer: composer.snapshot()} } /// Returns a reference to the message’s header. fn header(&self) -> &Header { Header::from_message(self.composer.so_far()) } /// Returns a mutable reference to the message’s header. fn header_mut(&mut self) -> &mut Header { Header::from_message_mut(self.composer.so_far_mut()) } /// Returns a mutable reference to the message’s header counts. fn counts_mut(&mut self) -> &mut HeaderCounts { HeaderCounts::from_message_mut(self.composer.so_far_mut()) } /// Pushes something to the end of the message. /// /// There’s two closures here. The first one, `composeop` actually /// writes the data. The second, `incop` increments the counter in the /// messages header to reflect the new element. fn push<O, I>(&mut self, composeop: O, incop: I) -> ComposeResult<()> where O: FnOnce(&mut Composer) -> ComposeResult<()>, I: FnOnce(&mut HeaderCounts) -> ComposeResult<()> { if !self.composer.is_truncated() { self.composer.mark_checkpoint(); match composeop(&mut self.composer) { Ok(()) => { try!(incop(self.counts_mut())); Ok(()) } Err(ComposeError::SizeExceeded) => Ok(()), Err(error) => Err(error) } } else { Ok(()) } } /// Returns a reference to the message assembled so far. fn preview(&mut self) -> &[u8] { self.composer.preview() } /// Finishes the message building and extracts the underlying vector. fn finish(mut self) -> Vec<u8> { let tc = self.composer.is_truncated(); self.header_mut().set_tc(tc); self.composer.commit().finish() } /// Rewinds the compose snapshots and allows updating the header counts. fn rewind<F>(&mut self, op: F) where F: FnOnce(&mut HeaderCounts) { op(self.counts_mut()); self.composer.rewind() } /// Commit the compose snapshot. fn commit(self) -> Composer { self.composer.commit() } } impl AsRef<Message> for MessageTarget { fn as_ref(&self) -> &Message { unsafe { Message::from_bytes_unsafe(self.composer.so_far()) } } }