Add Cursor scalar (#48)

* Add Cursor scalar

src/types/connection/connection_type.rs

@@ -1,3 +1,4 @@
+use crate::types::connection::cursor::Cursor;
 use crate::types::connection::edge::Edge;
 use crate::types::connection::page_info::PageInfo;
 use crate::{
@@ -18,7 +19,7 @@ use std::collections::HashMap;
 pub struct Connection<T, E: ObjectType + Sync + Send = EmptyEdgeFields> {
     total_count: Option<usize>,
     page_info: PageInfo,
-    nodes: Vec<(String, E, T)>,
+    nodes: Vec<(Cursor, E, T)>,
 }
 
 impl<T, E: ObjectType + Sync + Send> Connection<T, E> {
@@ -27,7 +28,7 @@ impl<T, E: ObjectType + Sync + Send> Connection<T, E> {
         total_count: Option<usize>,
         has_previous_page: bool,
         has_next_page: bool,
-        nodes: Vec<(String, E, T)>,
+        nodes: Vec<(Cursor, E, T)>,
     ) -> Self {
         Connection {
             total_count,

src/types/connection/cursor.rs

@@ -0,0 +1,66 @@
+use crate::{Result, ScalarType, Value};
+use async_graphql_derive::Scalar;
+use std::ops::{Deref, DerefMut};
+
+/// Cursor scalar
+///
+/// A custom scalar that serializes as a string.
+/// https://relay.dev/graphql/connections.htm#sec-Cursor
+#[derive(Clone, Ord, PartialOrd, Eq, PartialEq, Hash, Debug)]
+pub struct Cursor(String);
+
+impl std::fmt::Display for Cursor {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}
+
+impl Deref for Cursor {
+    type Target = String;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl DerefMut for Cursor {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
+    }
+}
+
+impl From<String> for Cursor {
+    fn from(value: String) -> Self {
+        Cursor(value)
+    }
+}
+
+impl<'a> From<&'a str> for Cursor {
+    fn from(value: &'a str) -> Self {
+        Cursor(value.to_string())
+    }
+}
+
+impl From<usize> for Cursor {
+    fn from(value: usize) -> Self {
+        Cursor(value.to_string())
+    }
+}
+
+#[Scalar(internal)]
+impl ScalarType for Cursor {
+    fn type_name() -> &'static str {
+        "Cursor"
+    }
+
+    fn parse(value: &Value) -> Option<Self> {
+        match value {
+            Value::String(s) => Some(Cursor(s.into())),
+            _ => None,
+        }
+    }
+
+    fn to_json(&self) -> Result<serde_json::Value> {
+        Ok(self.0.to_string().into())
+    }
+}

src/types/connection/mod.rs

@@ -1,4 +1,5 @@
 mod connection_type;
+mod cursor;
 mod edge;
 mod page_info;
 mod slice;
@@ -6,6 +7,7 @@ mod slice;
 use crate::{Context, FieldResult, ObjectType};
 
 pub use connection_type::Connection;
+pub use cursor::Cursor;
 
 /// Connection query operation
 pub enum QueryOperation<'a> {
@@ -77,7 +79,7 @@ pub struct EmptyEdgeFields;
 ///             }
 ///         };
 ///
-///         let nodes = (start..end).into_iter().map(|n| (base64::encode(n.to_be_bytes()), DiffFields {diff: n - 1000}, n)).collect();
+///         let nodes = (start..end).into_iter().map(|n| (base64::encode(n.to_be_bytes()).into(), DiffFields {diff: n - 1000}, n)).collect();
 ///         Ok(Connection::new(None, true, true, nodes))
 ///     }
 /// }

src/types/connection/page_info.rs

@@ -1,10 +1,11 @@
+use crate::types::connection::cursor::Cursor;
 use async_graphql_derive::Object;
 
 pub struct PageInfo {
     pub has_previous_page: bool,
     pub has_next_page: bool,
-    pub start_cursor: Option<String>,
-    pub end_cursor: Option<String>,
+    pub start_cursor: Option<Cursor>,
+    pub end_cursor: Option<Cursor>,
 }
 
 #[Object(internal)]
@@ -20,12 +21,12 @@ impl PageInfo {
     }
 
     #[field(desc = "When paginating backwards, the cursor to continue.")]
-    async fn start_cursor(&self) -> &Option<String> {
+    async fn start_cursor(&self) -> &Option<Cursor> {
         &self.start_cursor
     }
 
     #[field(desc = "When paginating forwards, the cursor to continue.")]
-    async fn end_cursor(&self) -> &Option<String> {
+    async fn end_cursor(&self) -> &Option<Cursor> {
         &self.end_cursor
     }
 }

src/types/connection/slice.rs

@@ -35,7 +35,7 @@ impl<'a, T: Sync> DataSource for &'a [T] {
         let mut nodes = Vec::with_capacity(end - start);
         for (idx, item) in self[start..end].iter().enumerate() {
             nodes.push((
-                base64::encode((idx as u32).to_be_bytes()),
+                base64::encode((idx as u32).to_be_bytes()).into(),
                 EmptyEdgeFields,
                 item,
             ));

src/types/mod.rs

@@ -7,7 +7,7 @@ mod optional;
 mod query_root;
 mod upload;
 
-pub use connection::{Connection, DataSource, EmptyEdgeFields, QueryOperation};
+pub use connection::{Connection, Cursor, DataSource, EmptyEdgeFields, QueryOperation};
 pub use empty_mutation::EmptyMutation;
 pub use empty_subscription::EmptySubscription;
 pub use query_root::QueryRoot;