activitypub-federation-rust/src/protocol/context.rs

//! Wrapper for federated structs which handles `@context` field.
//!
//! This wrapper can be used when sending Activitypub data, to automatically add `@context`. It
//! avoids having to repeat the `@context` property on every struct, and getting multiple contexts
//! in nested structs.
//!
//! ```
//! # use activitypub_federation::protocol::context::WithContext;
//! #[derive(serde::Serialize)]
//! struct Note {
//!     content: String
//! }
//! let note = Note {
//!     content: "Hello world".to_string()
//! };
//! let note_with_context = WithContext::new_default(note);
//! let serialized = serde_json::to_string(&note_with_context)?;
//! assert_eq!(serialized, r#"{"@context":["https://www.w3.org/ns/activitystreams"],"content":"Hello world"}"#);
//! Ok::<(), serde_json::error::Error>(())
//! ```

use crate::{
    config::RequestData,
    protocol::helpers::deserialize_one_or_many,
    traits::ActivityHandler,
};
use serde::{Deserialize, Serialize};
use serde_json::Value;
use url::Url;

/// Default context used in Activitypub
const DEFAULT_CONTEXT: &str = "https://www.w3.org/ns/activitystreams";

/// Wrapper for federated structs which handles `@context` field.
#[derive(Serialize, Deserialize, Debug)]
pub struct WithContext<T> {
    #[serde(rename = "@context")]
    #[serde(deserialize_with = "deserialize_one_or_many")]
    context: Vec<Value>,
    #[serde(flatten)]
    inner: T,
}

impl<T> WithContext<T> {
    /// Create a new wrapper with the default Activitypub context.
    pub fn new_default(inner: T) -> WithContext<T> {
        let context = vec![Value::String(DEFAULT_CONTEXT.to_string())];
        WithContext::new(inner, context)
    }

    /// Create new wrapper with custom context. Use this in case you are implementing extensions.
    pub fn new(inner: T, context: Vec<Value>) -> WithContext<T> {
        WithContext { context, inner }
    }

    /// Returns the inner `T` object which this `WithContext` object is wrapping
    pub fn inner(&self) -> &T {
        &self.inner
    }
}

#[async_trait::async_trait]
impl<T> ActivityHandler for WithContext<T>
where
    T: ActivityHandler + Send,
{
    type DataType = <T as ActivityHandler>::DataType;
    type Error = <T as ActivityHandler>::Error;

    fn id(&self) -> &Url {
        self.inner.id()
    }

    fn actor(&self) -> &Url {
        self.inner.actor()
    }

    async fn receive(self, data: &RequestData<Self::DataType>) -> Result<(), Self::Error> {
        self.inner.receive(data).await
    }
}