1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108

//! Helper types for converting types to `Result<T, FieldError<E>>`.
//!
//! Used in `#[graphql_subscription]` macros to convert result type aliases on
//! subscription handlers to a concrete return type.

use futures::Stream;

use crate::{FieldError, GraphQLValue, IntoFieldError, ScalarValue};

/// Trait for wrapping [`Stream`] into [`Ok`] if it's not [`Result`].
///
/// Used in subscription macros when user can provide type alias for [`Stream`] or
/// `Result<Stream, _>` and then a function on [`Stream`] should be called.
pub trait IntoFieldResult<T, S> {
    /// Type of items yielded by this [`Stream`].
    type Item;

    /// Turns current [`Stream`] type into a generic [`Result`].
    fn into_result(self) -> Result<T, FieldError<S>>;
}

impl<T, E, S> IntoFieldResult<T, S> for Result<T, E>
where
    T: IntoFieldResult<T, S>,
    E: IntoFieldError<S>,
{
    type Item = T::Item;

    fn into_result(self) -> Result<T, FieldError<S>> {
        self.map_err(E::into_field_error)
    }
}

impl<T, S> IntoFieldResult<T, S> for T
where
    T: Stream,
{
    type Item = T::Item;

    fn into_result(self) -> Result<T, FieldError<S>> {
        Ok(self)
    }
}

/// This struct is used in `ExtractTypeFromStream` implementation for streams
/// of values.
pub struct StreamItem;

/// This struct is used in `ExtractTypeFromStream` implementation for results
/// with streams of values inside.
pub struct StreamResult;

/// This struct is used in `ExtractTypeFromStream` implementation for streams
/// of results of values inside.
pub struct ResultStreamItem;

/// This struct is used in `ExtractTypeFromStream` implementation for results
/// with streams of results of values inside.
pub struct ResultStreamResult;

/// This trait is used in `juniper::graphql_subscription` macro to get stream's
/// item type that implements `GraphQLValue` from type alias provided
/// by user.
pub trait ExtractTypeFromStream<T, S>
where
    S: ScalarValue,
{
    /// Stream's return Value that will be returned if
    /// no errors occured. Is used to determine field type in
    /// `#[juniper::graphql_subscription]`
    type Item: GraphQLValue<S>;
}

impl<T, I, S> ExtractTypeFromStream<StreamItem, S> for T
where
    T: futures::Stream<Item = I>,
    I: GraphQLValue<S>,
    S: ScalarValue,
{
    type Item = I;
}

impl<Ty, T, E, S> ExtractTypeFromStream<StreamResult, S> for Ty
where
    Ty: futures::Stream<Item = Result<T, E>>,
    T: GraphQLValue<S>,
    S: ScalarValue,
{
    type Item = T;
}

impl<T, I, E, S> ExtractTypeFromStream<ResultStreamItem, S> for Result<T, E>
where
    T: futures::Stream<Item = I>,
    I: GraphQLValue<S>,
    S: ScalarValue,
{
    type Item = I;
}

impl<T, E, I, ER, S> ExtractTypeFromStream<ResultStreamResult, S> for Result<T, E>
where
    T: futures::Stream<Item = Result<I, ER>>,
    I: GraphQLValue<S>,
    S: ScalarValue,
{
    type Item = I;
}