[−][src]Trait scroll::ctx::TryFromCtx

pub trait TryFromCtx<'a, Ctx: Copy = (), This: ?Sized = [u8]> where
    Self: 'a + Sized, {
    type Error;
    fn try_from_ctx(
        from: &'a This, 
        ctx: Ctx
    ) -> Result<(Self, usize), Self::Error>;
}

Tries to read Self from This using the context Ctx

Implementing Your Own Reader

If you want to implement your own reader for a type Foo from some kind of buffer (say [u8]), then you need to implement this trait

use scroll::{self, ctx, Pread};
#[derive(Debug, PartialEq, Eq)]
pub struct Foo(u16);

impl<'a> ctx::TryFromCtx<'a, scroll::Endian> for Foo {
     type Error = scroll::Error;
     fn try_from_ctx(this: &'a [u8], le: scroll::Endian) -> Result<(Self, usize), Self::Error> {
         if this.len() < 2 { return Err((scroll::Error::Custom("whatever".to_string())).into()) }
         let n = this.pread_with(0, le)?;
         Ok((Foo(n), 2))
     }
}

let bytes: [u8; 4] = [0xde, 0xad, 0, 0];
let foo = bytes.pread_with::<Foo>(0, scroll::LE).unwrap();
assert_eq!(Foo(0xadde), foo);

let foo2 = bytes.pread_with::<Foo>(0, scroll::BE).unwrap();
assert_eq!(Foo(0xdeadu16), foo2);

Advanced: Using Your Own Error in TryFromCtx

 use scroll::{self, ctx, Pread};
 use std::error;
 use std::fmt::{self, Display};
 // make some kind of normal error which also can transformed from a scroll error
 #[derive(Debug)]
 pub struct ExternalError {}

 impl Display for ExternalError {
     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
         write!(fmt, "ExternalError")
     }
 }

 impl error::Error for ExternalError {
     fn description(&self) -> &str {
         "ExternalError"
     }
     fn cause(&self) -> Option<&error::Error> { None}
 }

 impl From<scroll::Error> for ExternalError {
     fn from(err: scroll::Error) -> Self {
         match err {
             _ => ExternalError{},
         }
     }
 }
 #[derive(Debug, PartialEq, Eq)]
 pub struct Foo(u16);

 impl<'a> ctx::TryFromCtx<'a, scroll::Endian> for Foo {
     type Error = ExternalError;
     fn try_from_ctx(this: &'a [u8], le: scroll::Endian) -> Result<(Self, usize), Self::Error> {
         if this.len() <= 2 { return Err((ExternalError {}).into()) }
         let offset = &mut 0;
         let n = this.gread_with(offset, le)?;
         Ok((Foo(n), *offset))
     }
 }

let bytes: [u8; 4] = [0xde, 0xad, 0, 0];
let foo: Result<Foo, ExternalError> = bytes.pread(0);

Associated Types

type Error

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Required methods

fn try_from_ctx(from: &'a This, ctx: Ctx) -> Result<(Self, usize), Self::Error>

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Implementations on Foreign Types

impl<'a> TryFromCtx<'a, Endian, [u8]> for u8 where
    u8: FromCtx<Endian>, [src]

type Error = Error

impl<'a, T> TryFromCtx<'a, Endian, T> for u8 where
    u8: FromCtx<Endian, T>,
    T: AsRef<[u8]>, [src]

type Error = Error

impl<'a> TryFromCtx<'a, Endian, [u8]> for i8 where
    i8: FromCtx<Endian>, [src]

type Error = Error

impl<'a, T> TryFromCtx<'a, Endian, T> for i8 where
    i8: FromCtx<Endian, T>,
    T: AsRef<[u8]>, [src]

type Error = Error

impl<'a> TryFromCtx<'a, Endian, [u8]> for u16 where
    u16: FromCtx<Endian>, [src]

type Error = Error

impl<'a, T> TryFromCtx<'a, Endian, T> for u16 where
    u16: FromCtx<Endian, T>,
    T: AsRef<[u8]>, [src]

type Error = Error

impl<'a> TryFromCtx<'a, Endian, [u8]> for i16 where
    i16: FromCtx<Endian>, [src]

type Error = Error

impl<'a, T> TryFromCtx<'a, Endian, T> for i16 where
    i16: FromCtx<Endian, T>,
    T: AsRef<[u8]>, [src]

type Error = Error

impl<'a> TryFromCtx<'a, Endian, [u8]> for u32 where
    u32: FromCtx<Endian>, [src]

type Error = Error

impl<'a, T> TryFromCtx<'a, Endian, T> for u32 where
    u32: FromCtx<Endian, T>,
    T: AsRef<[u8]>, [src]

type Error = Error

impl<'a> TryFromCtx<'a, Endian, [u8]> for i32 where
    i32: FromCtx<Endian>, [src]

type Error = Error

impl<'a, T> TryFromCtx<'a, Endian, T> for i32 where
    i32: FromCtx<Endian, T>,
    T: AsRef<[u8]>, [src]

type Error = Error

impl<'a> TryFromCtx<'a, Endian, [u8]> for u64 where
    u64: FromCtx<Endian>, [src]

type Error = Error

impl<'a, T> TryFromCtx<'a, Endian, T> for u64 where
    u64: FromCtx<Endian, T>,
    T: AsRef<[u8]>, [src]

type Error = Error

impl<'a> TryFromCtx<'a, Endian, [u8]> for i64 where
    i64: FromCtx<Endian>, [src]

type Error = Error

impl<'a, T> TryFromCtx<'a, Endian, T> for i64 where
    i64: FromCtx<Endian, T>,
    T: AsRef<[u8]>, [src]

type Error = Error

impl<'a> TryFromCtx<'a, Endian, [u8]> for u128 where
    u128: FromCtx<Endian>, [src]

type Error = Error

impl<'a, T> TryFromCtx<'a, Endian, T> for u128 where
    u128: FromCtx<Endian, T>,
    T: AsRef<[u8]>, [src]

type Error = Error

impl<'a> TryFromCtx<'a, Endian, [u8]> for i128 where
    i128: FromCtx<Endian>, [src]

type Error = Error

impl<'a, T> TryFromCtx<'a, Endian, T> for i128 where
    i128: FromCtx<Endian, T>,
    T: AsRef<[u8]>, [src]

type Error = Error

impl<'a> TryFromCtx<'a, Endian, [u8]> for f32 where
    f32: FromCtx<Endian>, [src]

type Error = Error

impl<'a> TryFromCtx<'a, Endian, [u8]> for f64 where
    f64: FromCtx<Endian>, [src]

type Error = Error

impl<'a> TryFromCtx<'a, StrCtx, [u8]> for &'a str[src]

type Error = Error

fn try_from_ctx(
    src: &'a [u8],
    ctx: StrCtx
) -> Result<(Self, usize), Self::Error>[src]

Read a &str from src using delimiter

impl<'a, T> TryFromCtx<'a, StrCtx, T> for &'a str where
    T: AsRef<[u8]>, [src]

type Error = Error

impl<'a> TryFromCtx<'a, Endian, [u8]> for usize where
    usize: FromCtx<Endian>, [src]

type Error = Error

impl<'a> TryFromCtx<'a, usize, [u8]> for &'a [u8][src]

type Error = Error

impl<'a> TryFromCtx<'a, (), [u8]> for &'a CStr[src]

type Error = Error

impl<'a> TryFromCtx<'a, (), [u8]> for CString[src]

type Error = Error

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Implementors

impl<'a> TryFromCtx<'a, (), [u8]> for Sleb128[src]

type Error = Error

impl<'a> TryFromCtx<'a, (), [u8]> for Uleb128[src]

type Error = Error

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