Struct Header

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pub struct Header { /* private fields */ }

Expand description

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 type’s data contains such a header in its wire format which is layed out like this:

                                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 accessing each of these fields. See Field Access below.

The basic structure and most of the fields re defined in RFC 1035, except for the AD and CD flags, which are defined in RFC 4035.

Implementations§

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impl Header

§Creation and Conversion

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pub fn new() -> Self

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.

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pub fn for_message_slice(s: &[u8]) -> &Header

Creates a header reference from a byte slice of a message.

§Panics

This function panics if the byte slice is too short.

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pub fn for_message_slice_mut(s: &mut [u8]) -> &mut Header

Creates a mutable header reference from a byte slice of a message.

§Panics

This function panics if the byte slice is too short.

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pub fn as_slice(&self) -> &[u8] ⓘ

Returns a reference to the underlying bytes slice.

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impl Header

§Field Access

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pub fn id(self) -> u16

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 by a server. It allows matching incoming responses to their queries.

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pub fn set_id(&mut self, value: u16)

Sets the value of the ID field.

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pub fn set_random_id(&mut self)

Sets the value of the ID field to a randomly chosen number.

This uses rand::random which may not be good enough.

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pub fn qr(self) -> bool

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. So, perhaps it might be good to read ‘QR’ as ‘query response.’

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pub fn set_qr(&mut self, set: bool)

Sets the value of the QR bit.

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pub fn opcode(self) -> Opcode

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.

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pub fn set_opcode(&mut self, opcode: Opcode)

Sets the value of the opcode field.

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pub fn aa(self) -> bool

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.

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pub fn set_aa(&mut self, set: bool)

Sets the value of the AA bit.

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pub fn tc(self) -> bool

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.

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pub fn set_tc(&mut self, set: bool)

Sets the value of the TC bit.

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pub fn rd(self) -> bool

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.

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pub fn set_rd(&mut self, set: bool)

Sets the value of the RD bit.

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pub fn ra(self) -> bool

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.

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pub fn set_ra(&mut self, set: bool)

Sets the value of the RA bit.

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pub fn z(self) -> bool

Returns whether the reserved bit is set.

This bit must be false in all queries and responses.

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pub fn set_z(&mut self, set: bool)

Sets the value of the reserved bit.

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pub fn ad(self) -> bool

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.

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pub fn set_ad(&mut self, set: bool)

Sets the value of the AD bit.

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pub fn cd(self) -> bool

Returns whether the CD bit is set.

The checking disabled bit is used by a security-aware resolver to indicate that it does not want upstream name servers to perform verification but rather would like to verify everything itself.

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pub fn set_cd(&mut self, set: bool)

Sets the value of the CD bit.

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pub fn rcode(self) -> Rcode

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.

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