[−][src]Module deku::attributes
A documentation-only module for #[deku] attributes
List of attributes
Attribute | Scope | Description |
---|---|---|
endian | top-level, field | Set the endianness |
magic | top-level | A magic value that must be present at the start of this struct/enum |
assert | field | Assert a condition |
assert_eq | field | Assert equals on the field |
bits | field | Set the bit-size of the field |
bytes | field | Set the byte-size of the field |
count | field | Set the field representing the element count of a container |
bits_read | field | Set the field representing the number of bits to read into a container |
bytes_read | field | Set the field representing the number of bytes to read into a container |
until | field | Set a predicate returning when to stop reading elements into a container |
update | field | Apply code over the field when .update() is called |
temp | field | Read the field but exclude it from the struct/enum |
skip | field | Skip the reading/writing of a field |
pad_bytes_before | field | Skip bytes before reading, pad before writing |
pad_bits_before | field | Skip bits before reading, pad before writing |
pad_bytes_after | field | Skip bytes after reading, pad after writing |
pad_bits_after | field | Skip bits after reading, pad after writing |
cond | field | Conditional expression for the field |
default | field | Provide default value. Used with skip or cond |
map | field | Apply a function over the result of reading |
reader | variant, field | Custom reader code |
writer | variant, field | Custom writer code |
ctx | top-level, field | Context list for context sensitive parsing |
ctx_default | top-level, field | Default context values |
enum: id | top-level, variant | enum or variant id value |
enum: id_pat | variant | variant id match pattern |
enum: type | top-level | Set the type of the variant id |
enum: bits | top-level | Set the bit-size of the variant id |
enum: bytes | top-level | Set the byte-size of the variant id |
endian
Set to read/write bytes in a specific byte order.
Values: big
, little
or an expression which returns a Endian
Precedence: field > top-level > system endianness (default)
Example:
// #[deku(endian = "little")] // top-level, defaults to system endianness struct DekuTest { #[deku(endian = "big")] // field-level override field_be: u16, field_default: u16, // defaults to top-level } let data: Vec<u8> = vec![0xAB, 0xCD, 0xAB, 0xCD]; let value = DekuTest::try_from(data.as_ref()).unwrap(); assert_eq!( DekuTest { field_be: 0xABCD, field_default: 0xCDAB, }, value ); let value: Vec<u8> = value.try_into().unwrap(); assert_eq!(data, value);
Note: The endian
is passed as a context argument to sub-types
Example:
#[deku(endian = "endian", ctx = "endian: deku::ctx::Endian")] // context passed from `DekuTest` top-level endian struct Child { field_a: u16 } #[deku(endian = "little")] // top-level, defaults to system endianness struct DekuTest { #[deku(endian = "big")] // field-level override field_be: u16, field_default: u16, // defaults to top-level // because a top-level endian is specified, // it is passed as a context field_child: Child, } let data: Vec<u8> = vec![0xAB, 0xCD, 0xAB, 0xCD, 0xEF, 0xBE]; let value = DekuTest::try_from(data.as_ref()).unwrap(); assert_eq!( DekuTest { field_be: 0xABCD, field_default: 0xCDAB, field_child: Child { field_a: 0xBEEF } }, value ); let value: Vec<u8> = value.try_into().unwrap(); assert_eq!(data, value);
magic
Sets a "magic" value that must be present in the data at the start of a struct/enum when reading, and that is written out of the start of that type's data when writing.
Example:
#[deku(magic = b"deku")] struct DekuTest { data: u8 } let data: Vec<u8> = vec![b'd', b'e', b'k', b'u', 50]; let value = DekuTest::try_from(data.as_ref()).unwrap(); assert_eq!( DekuTest { data: 50 }, value ); let value: Vec<u8> = value.try_into().unwrap(); assert_eq!(data, value);
assert
Assert a condition after reading and before writing a field
Example:
struct DekuTest { #[deku(assert = "*data >= 8")] data: u8 } let data: Vec<u8> = vec![0x00, 0x01, 0x02]; let value = DekuTest::try_from(data.as_ref()); assert_eq!( Err(DekuError::Assertion("field 'data' failed assertion: * data >= 8".into())), value );
assert_eq
Assert equals after reading and before writing a field
Example:
struct DekuTest { #[deku(assert_eq = "0x01")] data: u8, } let data: Vec<u8> = vec![0x01]; let mut value = DekuTest::try_from(data.as_ref()).unwrap(); assert_eq!( DekuTest { data: 0x01 }, value ); value.data = 0x02; let value: Result<Vec<u8>, DekuError> = value.try_into(); assert_eq!( Err(DekuError::Assertion("field 'data' failed assertion: data == 0x01".into())), value );
bits
Set the bit-size of the field
Note: Cannot be used in combination with bytes
Example:
struct DekuTest { #[deku(bits = 2)] field_a: u8, #[deku(bits = 6)] field_b: u8, field_c: u8, // defaults to size_of<u8>*8 } let data: Vec<u8> = vec![0b11_101010, 0xFF]; let value = DekuTest::try_from(data.as_ref()).unwrap(); assert_eq!( DekuTest { field_a: 0b11, field_b: 0b101010, field_c: 0xFF, }, value ); let value: Vec<u8> = value.try_into().unwrap(); assert_eq!(data, value);
bytes
Set the byte-size of the field
Note: Cannot be used in combination with bits
Example:
struct DekuTest { #[deku(bytes = 2)] field_a: u32, field_b: u8, // defaults to size_of<u8> } let data: Vec<u8> = vec![0xAB, 0xCD, 0xFF]; let value = DekuTest::try_from(data.as_ref()).unwrap(); assert_eq!( DekuTest { field_a: 0xCDAB, field_b: 0xFF, }, value ); let value: Vec<u8> = value.try_into().unwrap(); assert_eq!(data, value);
count
Specify the field representing the length of the container, i.e. a Vec
Example:
struct DekuTest { #[deku(update = "self.items.len()")] count: u8, #[deku(count = "count")] items: Vec<u8>, } let data: Vec<u8> = vec![0x02, 0xAB, 0xCD]; let value = DekuTest::try_from(data.as_ref()).unwrap(); assert_eq!( DekuTest { count: 0x02, items: vec![0xAB, 0xCD], }, value ); let value: Vec<u8> = value.try_into().unwrap(); assert_eq!(data, value);
Note: See update for more information on the attribute!
bytes_read
Specify the field representing the total number of bytes to read into a container
See the following example, where InnerDekuTest
is 2 bytes, so setting bytes_read
to
4 will read 2 items into the container:
struct InnerDekuTest { field_a: u8, field_b: u8 } struct DekuTest { #[deku(update = "(self.items.len() / 2)")] bytes: u8, #[deku(bytes_read = "bytes")] items: Vec<InnerDekuTest>, } let data: Vec<u8> = vec![0x04, 0xAB, 0xBC, 0xDE, 0xEF]; let value = DekuTest::try_from(data.as_ref()).unwrap(); assert_eq!( DekuTest { bytes: 0x04, items: vec![ InnerDekuTest{field_a: 0xAB, field_b: 0xBC}, InnerDekuTest{field_a: 0xDE, field_b: 0xEF}], }, value ); let value: Vec<u8> = value.try_into().unwrap(); assert_eq!(data, value);
Note: See update for more information on the attribute!
bits_read
This is equivalent to bytes_read, however specifies the bit limit instead of a byte limit
until
Specifies a predicate which sets when to stop reading values into the container.
Note: The last value which matches the predicate is read
The predicate is given a borrow to each item as it is read, and must return a boolean as to whether this should be the last item or not. If it returns true, then reading stops.
A good example of this is to read a null-terminated string:
struct DekuTest { #[deku(until = "|v: &u8| *v == 0")] string: Vec<u8> } let data: Vec<u8> = vec![b'H', b'e', b'l', b'l', b'o', 0]; let value = DekuTest::try_from(data.as_ref()).unwrap(); assert_eq!( DekuTest { string: CString::new(b"Hello".to_vec()).unwrap().into_bytes_with_nul() }, value );
update
Specify custom code to run on the field when .update()
is called on the struct/enum
Example:
use deku::prelude::*; use std::convert::{TryInto, TryFrom}; #[derive(Debug, PartialEq, DekuRead, DekuWrite)] struct DekuTest { #[deku(update = "self.items.len()")] count: u8, #[deku(count = "count")] items: Vec<u8>, } let data: Vec<u8> = vec![0x02, 0xAB, 0xCD]; // `mut` so it can be updated let mut value = DekuTest::try_from(data.as_ref()).unwrap(); assert_eq!( DekuTest { count: 0x02, items: vec![0xAB, 0xCD] }, value ); // push a new item to the vec value.items.push(0xFF); // update it, this will update the `count` field value.update().unwrap(); assert_eq!( DekuTest { count: 0x03, items: vec![0xAB, 0xCD, 0xFF] }, value ); let value: Vec<u8> = value.try_into().unwrap(); assert_eq!(vec![0x03, 0xAB, 0xCD, 0xFF], value);
temp
A temporary field
Included in the reading of the struct/enum but not stored
Note: Struct/enum must be derived with #[deku_derive(...)]
to derive
DekuRead
and/or DekuWrite
, not with #[derive(...)]
. This is because the
struct/enum needs to be modified at compile time.
Example:
#[deku_derive(DekuRead, DekuWrite)] #[derive(Debug, PartialEq)] struct DekuTest { #[deku(temp)] num_items: u8, #[deku(count = "num_items", endian = "big")] items: Vec<u16>, } let data: Vec<u8> = vec![0x01, 0xBE, 0xEF]; let value = DekuTest::try_from(data.as_ref()).unwrap(); assert_eq!( DekuTest { items: vec![0xBEEF] }, value ); let value: Vec<u8> = value.try_into().unwrap(); assert_eq!(vec![0xBE, 0xEF], value);
skip
Skip the reading/writing of a field.
Defaults value to default
Note: Can be paired with cond to have conditional skipping
Example:
#[derive(PartialEq, Debug, DekuRead, DekuWrite)] struct DekuTest { field_a: u8, #[deku(skip)] field_b: Option<u8>, field_c: u8, } let data: Vec<u8> = vec![0x01, 0x02]; let value = DekuTest::try_from(data.as_ref()).unwrap(); assert_eq!( DekuTest { field_a: 0x01, field_b: None, field_c: 0x02 }, value );
pad_bytes_before
Skip a number of bytes before reading, pad with 0x00s before writing
Example:
#[derive(PartialEq, Debug, DekuRead, DekuWrite)] pub struct DekuTest { pub field_a: u8, #[deku(pad_bytes_before = "2")] pub field_b: u8, } let data: Vec<u8> = vec![0xAA, 0xBB, 0xCC, 0xDD]; let value = DekuTest::try_from(data.as_ref()).unwrap(); assert_eq!( DekuTest { field_a: 0xAA, field_b: 0xDD, }, value ); let value: Vec<u8> = value.try_into().unwrap(); assert_eq!(vec![0xAA, 0x00, 0x00, 0xDD], value);
pad_bits_before
Skip a number of bytes before reading, pad with 0s before writing
Example:
#[derive(PartialEq, Debug, DekuRead, DekuWrite)] struct DekuTest { #[deku(bits = 2)] field_a: u8, #[deku(pad_bits_before = "2", bits = 4)] field_b: u8, } let data: Vec<u8> = vec![0b10_01_1001]; let value = DekuTest::try_from(data.as_ref()).unwrap(); assert_eq!( DekuTest { field_a: 0b10, field_b: 0b1001, }, value ); let value: Vec<u8> = value.try_into().unwrap(); assert_eq!(vec![0b10_00_1001], value);
pad_bytes_after
Skip a number of bytes after reading, pad with 0x00s after writing
Example:
#[derive(PartialEq, Debug, DekuRead, DekuWrite)] pub struct DekuTest { #[deku(pad_bytes_after = "2")] pub field_a: u8, pub field_b: u8, } let data: Vec<u8> = vec![0xAA, 0xBB, 0xCC, 0xDD]; let value = DekuTest::try_from(data.as_ref()).unwrap(); assert_eq!( DekuTest { field_a: 0xAA, field_b: 0xDD, }, value ); let value: Vec<u8> = value.try_into().unwrap(); assert_eq!(vec![0xAA, 0x00, 0x00, 0xDD], value);
pad_bits_after
Skip a number of bytes after reading, pad with 0s after writing
Example:
#[derive(PartialEq, Debug, DekuRead, DekuWrite)] struct DekuTest { #[deku(bits = 2, pad_bits_after = "2")] field_a: u8, #[deku(bits = 4)] field_b: u8, } let data: Vec<u8> = vec![0b10_01_1001]; let value = DekuTest::try_from(data.as_ref()).unwrap(); assert_eq!( DekuTest { field_a: 0b10, field_b: 0b1001, }, value ); let value: Vec<u8> = value.try_into().unwrap(); assert_eq!(vec![0b10_00_1001], value);
cond
Specify a condition to parse or skip a field
Note: Can be paired with default
Example:
#[derive(PartialEq, Debug, DekuRead, DekuWrite)] struct DekuTest { field_a: u8, #[deku(cond = "*field_a == 0x01")] field_b: Option<u8>, #[deku(cond = "*field_b == Some(0xFF)", default = "Some(0x05)")] field_c: Option<u8>, #[deku(skip, cond = "*field_a == 0x01", default = "Some(0x06)")] field_d: Option<u8>, } let data: Vec<u8> = vec![0x01, 0x02]; let value = DekuTest::try_from(data.as_ref()).unwrap(); assert_eq!( DekuTest { field_a: 0x01, field_b: Some(0x02), field_c: Some(0x05), field_d: Some(0x06)}, value ); assert_eq!( vec![0x01, 0x02, 0x05], value.to_bytes().unwrap(), )
default
Default code tokens used with skip or cond
Defaults to Default::default()
Example:
#[derive(PartialEq, Debug, DekuRead, DekuWrite)] struct DekuTest { field_a: u8, #[deku(skip, default = "Some(*field_a)")] field_b: Option<u8>, field_c: u8, } let data: Vec<u8> = vec![0x01, 0x02]; let value = DekuTest::try_from(data.as_ref()).unwrap(); assert_eq!( DekuTest { field_a: 0x01, field_b: Some(0x01), field_c: 0x02 }, value );
map
Specify a function or lambda to apply to the result of the read
Example:
Read a u8
and apply a function to convert it to a String
.
#[derive(PartialEq, Debug, DekuRead)] struct DekuTest { #[deku(map = "|field: u8| -> Result<_, DekuError> { Ok(field.to_string()) }")] field_a: String, #[deku(map = "DekuTest::map_field_b")] field_b: String, } impl DekuTest { fn map_field_b(field_b: u8) -> Result<String, DekuError> { Ok(field_b.to_string()) } } let data: Vec<u8> = vec![0x01, 0x02]; let value = DekuTest::try_from(data.as_ref()).unwrap(); assert_eq!( DekuTest { field_a: "1".to_string(), field_b: "2".to_string() }, value );
reader/writer
Specify custom reader or writer tokens for reading a field or variant
Example:
struct DekuTest { #[deku( reader = "DekuTest::read(deku::rest)", writer = "DekuTest::write(deku::output, &self.field_a)" )] field_a: String, } impl DekuTest { /// Read and convert to String fn read( rest: &BitSlice<Msb0, u8>, ) -> Result<(&BitSlice<Msb0, u8>, String), DekuError> { let (rest, value) = u8::read(rest, ())?; Ok((rest, value.to_string())) } /// Parse from String to u8 and write fn write(output: &mut BitVec<Msb0, u8>, field_a: &str) -> Result<(), DekuError> { let value = field_a.parse::<u8>().unwrap(); value.write(output, ()) } } let data: Vec<u8> = vec![0x01]; let value = DekuTest::try_from(data.as_ref()).unwrap(); assert_eq!( DekuTest { field_a: "1".to_string() }, value ); let value: Vec<u8> = value.try_into().unwrap(); assert_eq!(data, value);
ctx
This attribute allows sending and receiving context (variables/values) to sub-parsers/writers
Note: endian
, bytes
, bits
, count
attributes use ctx
internally, see examples below
top-level: The value of a ctx attribute is a function argument list,
for example #[deku(ctx = "a: u8, b: String")]
field-level: The value of the ctx attribute is a list of expressions,
for example #[deku("a, b")]
Visibility: The following can be accessed:
- All former fields which have been parsed (given as a reference).
endian
,bytes
,bits
attributes declared on the top-level- These are prepended to the list of ctx variables
Example
#[derive(DekuRead, DekuWrite)] #[deku(ctx = "a: u8")] struct Subtype { #[deku(map = "|b: u8| -> Result<_, DekuError> { Ok(b + a) }")] b: u8 } #[derive(DekuRead, DekuWrite)] struct Test { a: u8, #[deku(ctx = "*a")] // pass `a` to `SubType`, `a` is a reference sub: Subtype } let data: Vec<u8> = vec![0x01, 0x02]; let (rest, value) = Test::from_bytes((&data[..], 0)).unwrap(); assert_eq!(value.a, 0x01); assert_eq!(value.sub.b, 0x01 + 0x02)
Note: In addition, endian
, bytes
and bits
use the ctx
concept internally, examples below are equivalent:
Example:
struct Type1 { #[deku(endian = "big", bits = "1")] field: u8, } // is equivalent to struct Type1 { #[deku(ctx = "Endian::Big, Size::Bits(1)")] field: u8, }
Example: Adding context
#[deku(endian = "big")] struct Type1 { field_a: u16, #[deku(bits = "5", ctx = "*field_a")] field_b: SubType, } // is equivalent to struct Type1 { #[deku(ctx = "Endian::Big")] field_a: u16, #[deku(ctx = "Endian::Big, Size::Bits(5), *field_a")] // endian is prepended field_b: SubType, }
ctx_default
When paired with the ctx
attribute, ctx_default
provides default
values for the context
Example:
#[derive(DekuRead, DekuWrite)] #[deku(ctx = "a: u8", ctx_default = "1")] // Defaults `a` to 1 struct Subtype { #[deku(map = "|b: u8| -> Result<_, DekuError> { Ok(b + a) }")] b: u8 } #[derive(DekuRead, DekuWrite)] struct Test { a: u8, #[deku(ctx = "*a")] // pass `a` to `SubType`, `a` is a reference sub: Subtype } let data: Vec<u8> = vec![0x01, 0x02]; // Use with context from `Test` let (rest, value) = Test::from_bytes((&data[..], 0)).unwrap(); assert_eq!(value.a, 0x01); assert_eq!(value.sub.b, 0x01 + 0x02); // Use as a stand-alone container, using defaults // Note: `from_bytes` is now available on `SubType` let data: Vec<u8> = vec![0x02]; let (rest, value) = Subtype::from_bytes((&data[..], 0)).unwrap(); assert_eq!(value.b, 0x01 + 0x02)
id
id (top-level)
Specify the enum id
This is useful in cases when the enum id
is already consumed or is given externally
Example:
#[derive(PartialEq, Debug, DekuRead, DekuWrite)] struct DekuTest { my_id: u8, data: u8, #[deku(ctx = "*my_id")] enum_from_id: MyEnum, } #[derive(PartialEq, Debug, DekuRead, DekuWrite)] #[deku(ctx = "my_id: u8", id = "my_id")] enum MyEnum { #[deku(id = "1")] VariantA(u8), #[deku(id = "2")] VariantB, } let data: Vec<u8> = vec![0x01_u8, 0xff, 0xab]; let ret_read = DekuTest::try_from(data.as_ref()).unwrap(); assert_eq!( DekuTest { my_id: 0x01, data: 0xff, enum_from_id: MyEnum::VariantA(0xab), }, ret_read ); let ret_write: Vec<u8> = ret_read.try_into().unwrap(); assert_eq!(ret_write, data)
id (variant)
Specify the identifier of the enum variant, must be paired with type or id (top-level)
Note:
- If no id
is specified, it is defaulted to the discriminant value.
- The discriminant value is retreived using the as
keyword.
Example:
#[deku(type = "u8")] enum DekuTest { #[deku(id = "0x01")] VariantA(u8), #[deku(id = "0x02")] VariantB(u8, u16), } let data: Vec<u8> = vec![0x01, 0xFF, 0x02, 0xAB, 0xEF, 0xBE]; let (rest, value) = DekuTest::from_bytes((data.as_ref(), 0)).unwrap(); assert_eq!( DekuTest::VariantA(0xFF), value ); let variant_bytes: Vec<u8> = value.try_into().unwrap(); assert_eq!(vec![0x01, 0xFF], variant_bytes); let (rest, value) = DekuTest::from_bytes(rest).unwrap(); assert_eq!( DekuTest::VariantB(0xAB, 0xBEEF), value ); let variant_bytes: Vec<u8> = value.try_into().unwrap(); assert_eq!(vec![0x02, 0xAB, 0xEF, 0xBE], variant_bytes);
Example discriminant
#[deku(type = "u8")] enum DekuTest { VariantA = 0x01, VariantB, } let data: Vec<u8> = vec![0x01, 0x02]; let (rest, value) = DekuTest::from_bytes((data.as_ref(), 0)).unwrap(); assert_eq!( DekuTest::VariantA, value ); let variant_bytes: Vec<u8> = value.try_into().unwrap(); assert_eq!(vec![0x01], variant_bytes); let (rest, value) = DekuTest::from_bytes(rest).unwrap(); assert_eq!( DekuTest::VariantB, value ); let variant_bytes: Vec<u8> = value.try_into().unwrap(); assert_eq!(vec![0x02], variant_bytes);
id_pat
Specify the identifier in the form of a match pattern for the enum variant.
The enum variant must have space to store the identifier for proper writing.
Example:
#[deku(type = "u8")] enum DekuTest { #[deku(id = "0x01")] VariantA(u8), #[deku(id_pat = "0x02..=0x06")] VariantB { id: u8 }, #[deku(id_pat = "_")] VariantC(u8), } let data: Vec<u8> = vec![0x03, 0xFF]; let (rest, value) = DekuTest::from_bytes((data.as_ref(), 0)).unwrap(); assert_eq!( DekuTest::VariantB { id: 0x03 }, value ); let variant_bytes: Vec<u8> = value.try_into().unwrap(); assert_eq!(vec![0x03], variant_bytes); let (rest, value) = DekuTest::from_bytes(rest).unwrap(); assert_eq!( DekuTest::VariantC(0xFF), value ); let variant_bytes: Vec<u8> = value.try_into().unwrap(); assert_eq!(vec![0xFF], variant_bytes);
type
Specify the type of the enum variant id to consume, see example
bits
Set the bit size of the enum variant id
Note: Cannot be used in combination with bytes
Example:
#[deku(type = "u8", bits = "4")] enum DekuTest { #[deku(id = "0b1001")] VariantA( #[deku(bits = "4")] u8, u8), } let data: Vec<u8> = vec![0b1001_0110, 0xFF]; let (rest, value) = DekuTest::from_bytes((&data, 0)).unwrap(); assert_eq!( DekuTest::VariantA(0b0110, 0xFF), value ); let value: Vec<u8> = value.try_into().unwrap(); assert_eq!(data, value);
bytes
Set the byte size of the enum variant id
Note: Cannot be used in combination with bits
Example:
#[deku(type = "u32", bytes = "2")] enum DekuTest { #[deku(id = "0xBEEF")] VariantA(u8), } let data: Vec<u8> = vec![0xEF, 0xBE, 0xFF]; let value = DekuTest::try_from(data.as_ref()).unwrap(); assert_eq!( DekuTest::VariantA(0xFF), value ); let value: Vec<u8> = value.try_into().unwrap(); assert_eq!(data, value);