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//! The header of a DNS message. //! //! Each DNS message starts with a twelve octet long header section //! containing some general information related to the message as well as //! the number of records in each of its four sections. Its content and //! format are defined in section 4.1.1 of [RFC 1035]. //! //! In order to reflect the fact that changing the section counts may //! invalidate the rest of the message whereas the other elements of the //! header section can safely be modified, the header section has been split //! into two separate types: [`Header`] contains the ‘safe’ part at the //! beginning of the section and [`HeaderCounts`] contains the section //! counts. In addition, the [`HeaderSection`] type wraps both of them into //! a single type. //! //! [`Header`]: struct.Header.html //! [`HeaderCounts`]: struct.HeaderCounts.html //! [`HeaderSection`]: struct.HeaderSection.html //! [RFC 1035]: https://tools.ietf.org/html/rfc1035 use std::mem; use byteorder::{BigEndian, ByteOrder}; use ::iana::{Opcode, Rcode}; use super::compose::{ComposeError, ComposeResult}; //------------ Header -------------------------------------------------- /// The first part of the header of a DNS message. /// /// This type represents the information contained in the first four bytes of /// the header: the message ID, opcode, rcode, and the various flags. /// /// The header is layed out like this: /// /// ```text /// 1 1 1 1 1 1 /// 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 /// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /// | ID | /// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /// |QR| Opcode |AA|TC|RD|RA|Z |AD|CD| RCODE | /// +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /// ``` /// /// Methods are available for each of accessing each of these fields. /// See [Field Access] below. /// /// Most of this is defined in [RFC 1035], except for the AD and CD flags, /// which are defined in [RFC 4035]. /// /// [Field Access]: #field-access /// [RFC 1035]: https://tools.ietf.org/html/rfc1035 /// [RFC 4035]: https://tools.ietf.org/html/rfc4035 #[derive(Clone, Debug, Default, PartialEq)] pub struct Header { /// The actual header in its wire format representation. /// /// This means that the ID field is in big endian. inner: [u8; 4] } /// # Creation and Conversion /// impl Header { /// Creates a new header. /// /// The new header has all fields as either zero or false. Thus, the /// opcode will be `Opcode::Query` and the response code will be /// `Rcode::NoError`. /// pub fn new() -> Header { Header { inner: [0; 4] } } /// Creates a header reference from a bytes slice of a message. /// /// # Panics /// /// This function panics if the bytes slice is too short. pub fn from_message(s: &[u8]) -> &Header { assert!(s.len() >= mem::size_of::<Header>()); unsafe { &*(s.as_ptr() as *const Header) } } /// Creates a mutable header reference from a bytes slice of a message. /// /// # Panics /// /// This function panics if the bytes slice is too short. pub fn from_message_mut(s: &mut [u8]) -> &mut Header { assert!(s.len() >= mem::size_of::<Header>()); unsafe { &mut *(s.as_ptr() as *mut Header) } } /// Returns a reference to the underlying bytes slice. pub fn as_bytes(&self) -> &[u8] { &self.inner } } /// # Field Access /// impl Header { /// Returns the value of the ID field. /// /// The ID field is an identifier chosen by whoever created a query /// and is copied into a response. It serves to match incoming responses /// to their request. pub fn id(&self) -> u16 { BigEndian::read_u16(&self.inner) } /// Sets the value of the ID field. pub fn set_id(&mut self, value: u16) { BigEndian::write_u16(&mut self.inner, value) } /// Sets the value of the ID field to a randomly chosen number. pub fn set_random_id(&mut self) { self.set_id(::rand::random()) } /// Returns whether the QR bit is set. /// /// The QR bit specifies whether this message is a query (`false`) or /// a response (`true`). In other words, this bit is actually stating /// whether the message is *not* a query. pub fn qr(&self) -> bool { self.get_bit(2, 7) } /// Sets the value of the QR bit. /// pub fn set_qr(&mut self, set: bool) { self.set_bit(2, 7, set) } /// Returns the value of the Opcode field. /// /// This field specifies the kind of query this message contains. See /// the [`Opcode`] type for more information on the possible values and /// their meaning. Normal queries have the variant [`Opcode::Query`] /// which is also the value set when creating a new header. /// /// [`Opcode`]: ../../iana/opcode/enum.Opcode.html /// [`Opcode::Query`]: ../../iana/opcode/enum.Opcode.html#variant.Query pub fn opcode(&self) -> Opcode { Opcode::from_int((self.inner[2] >> 3) & 0x0F) } /// Sets the value of the opcode field. pub fn set_opcode(&mut self, opcode: Opcode) { self.inner[2] = self.inner[2] & 0x87 | (opcode.to_int() << 3); } /// Returns whether the AA bit is set. /// /// Using this bit, a name server generating a response states whether /// it is authoritative for the requested domain name, ie., whether this /// response is an *authoritative answer.* The field has no meaning in /// a query. pub fn aa(&self) -> bool { self.get_bit(2, 2) } /// Sets the value of the AA bit. pub fn set_aa(&mut self, set: bool) { self.set_bit(2, 2, set) } /// Returns whether the TC bit is set. /// /// The *truncation* bit is set if there was more data available then /// fit into the message. This is typically used when employing /// datagram transports such as UDP to signal to try again using a /// stream transport such as TCP. pub fn tc(&self) -> bool { self.get_bit(2, 1) } /// Sets the value of the TC bit. pub fn set_tc(&mut self, set: bool) { self.set_bit(2, 1, set) } /// Returns whether the RD bit is set. /// /// The *recursion desired* bit may be set in a query to ask the name /// server to try and recursively gather a response if it doesn’t have /// the data available locally. The bit’s value is copied into the /// response. pub fn rd(&self) -> bool { self.get_bit(2, 0) } /// Sets the value of the RD bit. pub fn set_rd(&mut self, set: bool) { self.set_bit(2, 0, set) } /// Returns whether the RA bit is set. /// /// In a response, the *recursion available* bit denotes whether the /// responding name server supports recursion. It has no meaning in /// a query. pub fn ra(&self) -> bool { self.get_bit(3, 7) } /// Sets the value of the RA bit. pub fn set_ra(&mut self, set: bool) { self.set_bit(3, 7, set) } /// Returns whether the reserved bit is set. /// /// This bit must be `false` in all queries and responses. pub fn z(&self) -> bool { self.get_bit(3, 6) } /// Sets the value of the reserved bit. pub fn set_z(&mut self, set: bool) { self.set_bit(3, 6, set) } /// Returns whether the AD bit is set. /// /// The *authentic data* bit is used by security-aware recursive name /// servers to indicate that it considers all RRsets in its response to /// be authentic. pub fn ad(&self) -> bool { self.get_bit(3, 5) } /// Sets the value of the AD bit. pub fn set_ad(&mut self, set: bool) { self.set_bit(3, 5, set) } /// Returns whether the CD bit is set. /// /// The *checking disabled* bit is used by security-aware resolvers /// to indicate that it does not want upstream name servers to perform /// verification but rather would like to verify everything itself. pub fn cd(&self) -> bool { self.get_bit(3, 4) } /// Sets the value of the CD bit. pub fn set_cd(&mut self, set: bool) { self.set_bit(3, 4, set) } /// Returns the value of the RCODE field. /// /// The *response code* is used in a response to indicate what happened /// when processing the query. See the [`Rcode`] type for information on /// possible values and their meaning. /// /// [`Rcode`]: ../../iana/rcode/enum.Rcode.html pub fn rcode(&self) -> Rcode { Rcode::from_int(self.inner[3] & 0x0F) } /// Sets the value of the RCODE field. pub fn set_rcode(&mut self, rcode: Rcode) { self.inner[3] = self.inner[3] & 0xF0 | (rcode.to_int() & 0x0F); } //--- Internal helpers /// Returns the value of the bit at the given position. /// /// The argument `offset` gives the byte offset of the underlying bytes /// slice and `bit` gives the number of the bit with the most significant /// bit being 7. fn get_bit(&self, offset: usize, bit: usize) -> bool { self.inner[offset] & (1 << bit) != 0 } /// Sets or resets the given bit. fn set_bit(&mut self, offset: usize, bit: usize, set: bool) { if set { self.inner[offset] |= 1 << bit } else { self.inner[offset] &= !(1 << bit) } } } //------------ HeaderCounts ------------------------------------------------- /// The section count part of the header section of a DNS message. /// /// This part consists of four 16 bit counters for the number of entries in /// the four sections of a DNS message. /// /// The counters are arranged in the same order as the sections themselves: /// QDCOUNT for the question section, ANCOUNT for the answer section, /// NSCOUNT for the authority section, and ARCOUNT for the additional section. /// These are defined in [RFC 1035]. /// /// [RFC 2136] defines the UPDATE method and reuses the four section for /// different purposes. Here the counters are ZOCOUNT for the zone section, /// PRCOUNT for the prerequisite section, UPCOUNT for the update section, /// and ADCOUNT for the additional section. The type has convenience methods /// for these fields as well so you don’t have to remember which is which. /// /// For each field there are three methods for getting, setting, and /// incrementing. /// /// [RFC 1035]: https://tools.ietf.org/html/rfc1035 /// [RFC 2136]: https://tools.ietf.org/html/rfc2136 #[derive(Clone, Debug, Default, PartialEq)] pub struct HeaderCounts { /// The actual headers in their wire-format representation. /// /// Ie., all values are stored big endian. inner: [u8; 8] } /// # Creation and Conversion /// impl HeaderCounts { /// Creates a new value with all counters set to zero. pub fn new() -> HeaderCounts { HeaderCounts { inner: [0; 8] } } /// Creates a reference from the bytes slice of a message (!). /// /// # Panics /// /// This function panics if the bytes slice is too short. pub fn from_message(s: &[u8]) -> &HeaderCounts { assert!(s.len() >= mem::size_of::<HeaderSection>()); unsafe { &*((s[mem::size_of::<Header>()..].as_ptr()) as *const HeaderCounts) } } /// Creates a mutable reference from the bytes slice of a message. /// /// # Panics /// /// This function panics if the bytes slice is too short. pub fn from_message_mut(s: &mut [u8]) -> &mut HeaderCounts { assert!(s.len() >= mem::size_of::<HeaderSection>()); unsafe { &mut *((s[mem::size_of::<Header>()..].as_ptr()) as *mut HeaderCounts) } } /// Returns a reference to the underlying bytes slice. pub fn as_bytes(&self) -> &[u8] { &self.inner } } /// # Field Access /// impl HeaderCounts { //--- Count fields in regular messages /// Returns the value of the QDCOUNT field. /// /// This field contains the number of questions in the first /// section of the message, normally the question section. pub fn qdcount(&self) -> u16 { self.get_u16(0) } /// Sets the value of the QDCOUNT field. pub fn set_qdcount(&mut self, value: u16) { self.set_u16(0, value) } /// Increase the value of the QDCOUNT field. pub fn inc_qdcount(&mut self, inc: u16) -> ComposeResult<()> { self.inc_u16(0, inc) } /// Returns the value of the ANCOUNT field. /// /// This field contains the number of resource records in the second /// section of the message, normally the answer section. pub fn ancount(&self) -> u16 { self.get_u16(2) } /// Sets the value of the ANCOUNT field. pub fn set_ancount(&mut self, value: u16) { self.set_u16(2, value) } /// Increases the value of the ANCOUNT field. pub fn inc_ancount(&mut self, inc: u16) -> ComposeResult<()> { self.inc_u16(2, inc) } /// Returns the value of the NSCOUNT field. /// /// This field contains the number of resource records in the third /// section of the message, normally the authority section. pub fn nscount(&self) -> u16 { self.get_u16(4) } /// Sets the value of the NSCOUNT field. pub fn set_nscount(&mut self, value: u16) { self.set_u16(4, value) } /// Increases the value of the NSCOUNT field. pub fn inc_nscount(&mut self, inc: u16) -> ComposeResult<()> { self.inc_u16(4, inc) } /// Returns the value of the ARCOUNT field. /// /// This field contains the number of resource records in the fourth /// section of the message, normally the additional section. pub fn arcount(&self) -> u16 { self.get_u16(6) } /// Sets the value of the ARCOUNT field. pub fn set_arcount(&mut self, value: u16) { self.set_u16(6, value) } /// Increases the value of the ARCOUNT field. pub fn inc_arcount(&mut self, inc: u16) -> ComposeResult<()> { self.inc_u16(6, inc) } //--- Count fields in UPDATE messages /// Returns the value of the ZOCOUNT field. /// /// This is the same as the `qdcount()`. It is used in UPDATE queries /// where the first section is the zone section. pub fn zocount(&self) -> u16 { self.get_u16(0) } /// Sets the value of the ZOCOUNT field. pub fn set_zocount(&mut self, value: u16) { self.set_u16(0, value) } /// Increments the value of the ZOCOUNT field. pub fn inc_zocount(&mut self, inc: u16) -> ComposeResult<()> { self.inc_u16(0, inc) } /// Returns the value of the PRCOUNT field. /// /// This is the same as the `ancount()`. It is used in UPDATE queries /// where the first section is the prerequisite section. pub fn prcount(&self) -> u16 { self.get_u16(2) } /// Sete the value of the PRCOUNT field. pub fn set_prcount(&mut self, value: u16) { self.set_u16(2, value) } /// Increments the value of the PRCOUNT field, pub fn inc_prcount(&mut self, inc: u16) -> ComposeResult<()> { self.inc_u16(2, inc) } /// Returns the value of the UPCOUNT field. /// /// This is the same as the `nscount()`. It is used in UPDATE queries /// where the first section is the update section. pub fn upcount(&self) -> u16 { self.get_u16(4) } /// Sets the value of the UPCOUNT field. pub fn set_upcount(&mut self, value: u16) { self.set_u16(4, value) } /// Increments the value of the UPCOUNT field. pub fn inc_upcount(&mut self, inc: u16) -> ComposeResult<()> { self.inc_u16(4, inc) } /// Returns the value of the ADCOUNT field. /// /// This is the same as the `arcount()`. It is used in UPDATE queries /// where the first section is the additional section. pub fn adcount(&self) -> u16 { self.get_u16(6) } /// Sets the value of the ADCOUNT field. pub fn set_adcount(&mut self, value: u16) { self.set_u16(6, value) } /// Increments the value of the ADCOUNT field. pub fn inc_adcount(&mut self, inc: u16) -> ComposeResult<()> { self.inc_u16(6, inc) } //--- Internal helpers /// Returns the value of the 16 bit integer starting at a given offset. fn get_u16(&self, offset: usize) -> u16 { BigEndian::read_u16(&self.inner[offset..]) } /// Sets the value of the 16 bit integer starting at a given offset. fn set_u16(&mut self, offset: usize, value: u16) { BigEndian::write_u16(&mut self.inner[offset..], value) } /// Increments the value of the 16 bit integer starting at a given offset. fn inc_u16(&mut self, offset: usize, inc: u16) -> ComposeResult<()> { let value = match self.get_u16(offset).checked_add(inc) { Some(value) => value, None => return Err(ComposeError::Overflow), }; self.set_u16(offset, value); Ok(()) } } //------------ HeaderSection ------------------------------------------------- /// The complete header section of a DNS message. /// /// Consists of a `Header` and a `HeaderCounts`. #[derive(Clone, Debug, Default, PartialEq)] pub struct HeaderSection { inner: [u8; 12] } /// # Creation and Conversion /// impl HeaderSection { /// Creates a new empty header section. pub fn new() -> HeaderSection { HeaderSection { inner: [0; 12] } } /// Creates a reference from the bytes slice of a message. /// /// # Panics /// /// This function panics if the size of the bytes slice is smaller than /// the header section. pub fn from_message(s: &[u8]) -> &HeaderSection { assert!(s.len() >= mem::size_of::<HeaderSection>()); unsafe { &*(s.as_ptr() as *const HeaderSection) } } /// Creates a mutable reference from the bytes slice of a message. /// /// # Panics /// /// This function panics if the size of the bytes slice is smaller than /// the header section. pub fn from_message_mut(s: &mut [u8]) -> &mut HeaderSection { assert!(s.len() >= mem::size_of::<HeaderSection>()); unsafe { &mut *(s.as_ptr() as *mut HeaderSection) } } /// Returns a reference to the underlying bytes slice. pub fn as_bytes(&self) -> &[u8] { &self.inner } } /// # Access to Header and Counts /// impl HeaderSection { /// Returns a reference to the header. pub fn header(&self) -> &Header { Header::from_message(&self.inner) } /// Returns a mutable reference to the header. pub fn header_mut(&mut self) -> &mut Header { Header::from_message_mut(&mut self. inner) } /// Returns a reference to the header counts. pub fn counts(&self) -> &HeaderCounts { HeaderCounts::from_message(&self.inner) } /// Returns a mutable reference to the header counts. pub fn counts_mut(&mut self) -> &mut HeaderCounts { HeaderCounts::from_message_mut(&mut self.inner) } } //============ Testing ====================================================== #[cfg(test)] mod test { use super::*; use iana::{Opcode, Rcode}; macro_rules! test_field { ($get:ident, $set:ident, $default:expr, $($value:expr),*) => { $({ let mut h = Header::new(); assert_eq!(h.$get(), $default); h.$set($value); assert_eq!(h.$get(), $value); })* } } #[test] #[should_panic] fn short_header() { Header::from_message(b"134"); } #[test] #[should_panic] fn short_header_counts() { HeaderCounts::from_message(b"12345678"); } #[test] #[should_panic] fn short_header_section() { HeaderSection::from_message(b"1234"); } #[test] fn header() { test_field!(id, set_id, 0, 0x1234); test_field!(qr, set_qr, false, true, false); test_field!(opcode, set_opcode, Opcode::Query, Opcode::Notify); test_field!(aa, set_aa, false, true, false); test_field!(tc, set_tc, false, true, false); test_field!(rd, set_rd, false, true, false); test_field!(ra, set_ra, false, true, false); test_field!(z, set_z, false, true, false); test_field!(ad, set_ad, false, true, false); test_field!(cd, set_cd, false, true, false); test_field!(rcode, set_rcode, Rcode::NoError, Rcode::Refused); } #[test] fn counts() { let mut c = HeaderCounts { inner: [ 1, 2, 3, 4, 5, 6, 7, 8 ] }; assert_eq!(c.qdcount(), 0x0102); assert_eq!(c.ancount(), 0x0304); assert_eq!(c.nscount(), 0x0506); assert_eq!(c.arcount(), 0x0708); c.inc_qdcount(1).unwrap(); c.inc_ancount(1).unwrap(); c.inc_nscount(0x0100).unwrap(); c.inc_arcount(0x0100).unwrap(); assert_eq!(c.inner, [ 1, 3, 3, 5, 6, 6, 8, 8 ]); c.set_qdcount(0x0807); c.set_ancount(0x0605); c.set_nscount(0x0403); c.set_arcount(0x0201); assert_eq!(c.inner, [ 8, 7, 6, 5, 4, 3, 2, 1 ]); } #[test] fn update_counts() { let mut c = HeaderCounts { inner: [ 1, 2, 3, 4, 5, 6, 7, 8 ] }; assert_eq!(c.zocount(), 0x0102); assert_eq!(c.prcount(), 0x0304); assert_eq!(c.upcount(), 0x0506); assert_eq!(c.adcount(), 0x0708); c.inc_zocount(1).unwrap(); c.inc_prcount(1).unwrap(); c.inc_upcount(0x0100).unwrap(); c.inc_adcount(0x0100).unwrap(); assert_eq!(c.inner, [ 1, 3, 3, 5, 6, 6, 8, 8 ]); c.set_zocount(0x0807); c.set_prcount(0x0605); c.set_upcount(0x0403); c.set_adcount(0x0201); assert_eq!(c.inner, [ 8, 7, 6, 5, 4, 3, 2, 1 ]); } }