Trait rocket::request::FromParam

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pub trait FromParam<'a>: Sized {
    type Error: Debug;

    // Required method
    fn from_param(param: &'a str) -> Result<Self, Self::Error>;
}
Expand description

Trait to convert a dynamic path segment string to a concrete value.

This trait is used by Rocket’s code generation facilities to parse dynamic path segment string values into a given type. That is, when a path contains a dynamic segment <param> where param has some type T that implements FromParam, T::from_param will be called.

§Forwarding

If the conversion fails, the incoming request will be forwarded to the next matching route, if any. For instance, consider the following route and handler for the dynamic "/<id>" path:

#[get("/<id>")]
fn hello(id: usize) -> String {
    ...
}

If usize::from_param returns an Ok(usize) variant, the encapsulated value is used as the id function parameter. If not, the request is forwarded to the next matching route. Since there are no additional matching routes, this example will result in a 404 error for requests with invalid id values.

§Catching Errors

Sometimes, a forward is not desired, and instead, we simply want to know that the dynamic path segment could not be parsed into some desired type T. In these cases, types of Option<T>, Result<T, T::Error>, or Either<A, B> can be used, which implement FromParam themselves.

  • Option<T> where T: FromParam

    Always returns successfully.

    If the conversion to T fails, None is returned. If the conversion succeeds, Some(value) is returned.

  • Result<T, T::Error> where T: FromParam

    Always returns successfully.

    If the conversion to T fails, Err(error) is returned. If the conversion succeeds, Ok(value) is returned.

  • Either<A, B> where A: FromParam and B: FromParam

    Fails only when both A::from_param and B::from_param fail. If one of the two succeeds, the successful value is returned in Either::Left(A) or Either::Right(B) variant, respectively. If both fail, the error values from both calls are returned in a tuple in the Err variant.

Either<A, B> is particularly useful with a B type of &str, allowing you to retrieve the invalid path segment. Because &str’s implementation of FromParam always succeeds, the Right variant of the Either will always contain the path segment in case of failure.

For instance, consider the following route and handler:

use rocket::either::{Either, Left, Right};

#[get("/<id>")]
fn hello(id: Either<usize, &str>) -> String {
    match id {
        Left(id_num) => format!("usize: {}", id_num),
        Right(string) => format!("Not a usize: {}", string)
    }
}

In the above example, if the dynamic path segment cannot be parsed into a usize, the raw path segment is returned in the Right variant of the Either<usize, &str> value.

§Provided Implementations

Rocket implements FromParam for several standard library types. Their behavior is documented here.

    • Primitive types: f32, f64, isize, i8, i16, i32, i64, i128, usize, u8, u16, u32, u64, u128, bool
    • IpAddr and SocketAddr types: IpAddr, Ipv4Addr, Ipv6Addr, SocketAddrV4, SocketAddrV6, SocketAddr
    • NonZero* types: NonZeroI8, NonZeroI16, NonZeroI32, NonZeroI64, NonZeroI128, NonZeroIsize, NonZeroU8, NonZeroU16, NonZeroU32, NonZeroU64, NonZeroU128, NonZeroUsize

    A value is parsed successfully if the from_str method from the given type returns successfully. Otherwise, the raw path segment is returned in the Err value.

  • &str, String

    This implementation always returns successfully.

    Returns the percent-decoded path segment with invalid UTF-8 byte sequences replaced by � U+FFFD.

  • Option<T> where T: FromParam

    This implementation always returns successfully.

    The path segment is parsed by T’s FromParam implementation. If the parse succeeds, a Some(parsed_value) is returned. Otherwise, a None is returned.

  • Result<T, T::Error> where T: FromParam

    This implementation always returns successfully.

    The path segment is parsed by T’s FromParam implementation. The returned Result value is returned.

§Example

Say you want to parse a segment of the form:

[a-zA-Z]+:[0-9]+

into the following structure, where the string before the : is stored in key and the number after the colon is stored in value:

struct MyParam<'r> {
    key: &'r str,
    value: usize
}

The following implementation accomplishes this:

use rocket::request::FromParam;

impl<'r> FromParam<'r> for MyParam<'r> {
    type Error = &'r str;

    fn from_param(param: &'r str) -> Result<Self, Self::Error> {
        // We can convert `param` into a `str` since we'll check every
        // character for safety later.
        let (key, val_str) = match param.find(':') {
            Some(i) if i > 0 => (&param[..i], &param[(i + 1)..]),
            _ => return Err(param)
        };

        if !key.chars().all(|c| c.is_ascii_alphabetic()) {
            return Err(param);
        }

        val_str.parse()
            .map(|value| MyParam { key, value })
            .map_err(|_| param)
    }
}

With the implementation, the MyParam type can be used as the target of a dynamic path segment:

#[get("/<key_val>")]
fn hello(key_val: MyParam) -> String {
    ...
}

Required Associated Types§

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type Error: Debug

The associated error to be returned if parsing/validation fails.

Required Methods§

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

Parses and validates an instance of Self from a path parameter string or returns an Error if parsing or validation fails.

Object Safety§

This trait is not object safe.

Implementations on Foreign Types§

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impl<'a> FromParam<'a> for &'a str

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type Error = Empty

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fn from_param(param: &'a str) -> Result<&'a str, Self::Error>

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impl<'a> FromParam<'a> for IpAddr

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type Error = <IpAddr as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for SocketAddr

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type Error = <SocketAddr as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for bool

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type Error = <bool as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for f32

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type Error = <f32 as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for f64

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type Error = <f64 as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for i8

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type Error = <i8 as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for i16

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type Error = <i16 as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for i32

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type Error = <i32 as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for i64

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type Error = <i64 as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for i128

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type Error = <i128 as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for isize

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type Error = <isize as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for u8

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type Error = <u8 as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for u16

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type Error = <u16 as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for u32

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type Error = <u32 as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for u64

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type Error = <u64 as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for u128

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type Error = <u128 as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for usize

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type Error = <usize as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for Ipv4Addr

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type Error = <Ipv4Addr as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for Ipv6Addr

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type Error = <Ipv6Addr as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for SocketAddrV4

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type Error = <SocketAddrV4 as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for SocketAddrV6

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type Error = <SocketAddrV6 as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for PathBuf

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type Error = PathError

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for NonZeroI8

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type Error = <NonZero<i8> as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for NonZeroI16

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type Error = <NonZero<i16> as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for NonZeroI32

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type Error = <NonZero<i32> as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for NonZeroI64

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type Error = <NonZero<i64> as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for NonZeroI128

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type Error = <NonZero<i128> as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for NonZeroIsize

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type Error = <NonZero<isize> as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for NonZeroU8

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type Error = <NonZero<u8> as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for NonZeroU16

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type Error = <NonZero<u16> as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for NonZeroU32

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type Error = <NonZero<u32> as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for NonZeroU64

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type Error = <NonZero<u64> as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for NonZeroU128

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type Error = <NonZero<u128> as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'a> FromParam<'a> for NonZeroUsize

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type Error = <NonZero<usize> as FromStr>::Err

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fn from_param(param: &'a str) -> Result<Self, Self::Error>

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impl<'v, A: FromParam<'v>, B: FromParam<'v>> FromParam<'v> for Either<A, B>

Implements FromParam for Either<A, B>, where A and B both implement FromParam. If A::from_param returns Ok(a), Either::Left(a) is returned. If B::from_param returns Ok(b), Either::Right(b) is returned. If both A::from_param and B::from_param return Err(a) and Err(b), respectively, then Err((a, b)) is returned.

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type Error = (<A as FromParam<'v>>::Error, <B as FromParam<'v>>::Error)

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fn from_param(param: &'v str) -> Result<Self, Self::Error>

Implementors§

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impl<'a> FromParam<'a> for String

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type Error = Empty

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impl<'a> FromParam<'a> for Uuid

Available on crate feature uuid only.
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type Error = Error

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impl<'a, T: FromParam<'a>> FromParam<'a> for Option<T>

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impl<'a, T: FromParam<'a>> FromParam<'a> for Result<T, T::Error>