Improvements to ID generation

src/ap/mod.rs

@@ -3,7 +3,7 @@
 use futures::prelude::*;
 use serde::Serialize;
 
-use crate::{ Id, Activity, err, Result, Error, sign, ctx::Context, db::{Post, Privacy} };
+use crate::{ Id, Activity, err, Result, Error, sign, ctx::Context, db::{ Post, Privacy } };
 
 /// Represents the creation of an object.
 ///
@@ -132,11 +132,15 @@ impl Activity {
 
 	/// Get all delivery targets as urls.
 	async fn delivery_targets (&self) -> Result<Vec<reqwest::Url>> {
-		todo!()
+    	let unId = |Id (x)| x;
+    	Ok (self.to().chain(self.cc()).map(unId).collect())
 	}
 
 	/// Perform the activity.
-	pub async fn perform <S> (self, ctx: &mut Context<S>) -> Result<()> where S: sign::Sign {
+	pub async fn perform <S> (self, _: &mut Context<S>) -> Result<()>
+	where
+    	S: sign::Sign
+	{
 		todo!()
 	}
 

src/db/mod.rs

@@ -2,6 +2,7 @@
 
 use std::borrow::Borrow;
 use std::pin::Pin;
+use std::sync::Arc;
 
 use crate::ap::Note;
 use crate::{ Id, Result, ap::Actor, err };
@@ -9,6 +10,9 @@ use futures::prelude::*;
 
 use sqlx::{pool::PoolConnection, database::HasArguments};
 use sqlx::{ FromRow, Either::Right };
+use tokio::sync::{Mutex, mpsc};
+
+use std::collections::HashSet as Set;
 
 pub (crate) use self::data::*;
 
@@ -57,6 +61,7 @@ impl Default for Config {
 pub struct Client {
 	/// The internal connection pool.
 	pool: sqlx::Pool<Database>,
+	reserved: Arc<Mutex<Set<Id>>>,
 }
 
 impl Client {
@@ -109,6 +114,33 @@ impl Client {
     		.await
 	}
 
+    /// Determine if an [`Id`] is already taken.
+	pub async fn verify_unique (&self, id: Id) -> Result<Option<Id>> {
+
+    	let mut r = self.reserved.lock().await;
+
+		// First check the set of reserved ids.
+    	if r.contains(&id) {
+			return Ok (None)
+    	}
+
+		// If not, determine if it is taken in the database.
+		let is_taken: bool = self
+    		.with_conn(|_| async {
+        		todo!()
+    		})
+    		.await?;
+
+		// Reserve the id if it is not taken. This should prevent most race
+		// conditions in id generation.
+		Ok (if is_taken {
+    		None
+		} else {
+			r.insert(id.clone());
+    		Some (id)
+		})
+
+	}
 	
 }
 
@@ -226,7 +258,7 @@ pub mod data {
 	//! and in that case conversions between the two are needed.
     
     use sqlx::{ Type, FromRow };
-    use crate::{Id, ap::{Note, Create}, Result, Error};
+    use crate::{ Id, ap::Create };
 
     /// Encodes the status of a follow request.
     #[derive(Clone, Debug, Type)]

src/error.rs

@@ -24,6 +24,8 @@ pub enum Error {
 	Url (url::ParseError),
 	/// An error in converting between models.
 	Invalid (ap::Invalid),
+	/// Generic "timed out" error.
+	Timeout,
 }
 
 /// Trivial conversion function for use in `map_err` functions.

src/lib.rs

@@ -10,7 +10,7 @@ use serde::Serialize;
 
 // Expose the `Id` type in the crate root
 pub use id::Id;
-pub use ctx::Context;
+pub use ctx::{ Dereferencer, IdGenerator, Context };
 
 // Module imports
 pub mod conf;
@@ -44,7 +44,7 @@ mod id {
     use crate::db;
 
 	/// An ActivityPub identifier.
-    #[derive(PartialEq, Eq, Clone, Debug, Serialize, Deserialize)]
+    #[derive(PartialEq, Eq, Hash, Clone, Debug, Serialize, Deserialize)]
     #[serde(transparent)]
     pub struct Id (reqwest::Url);
 
@@ -98,7 +98,7 @@ mod ctx {
     use rand::{Rng, prelude::StdRng, SeedableRng};
     use serde_json::{Value, to_value};
 
-    use crate::{ conf::Config, db, Result, sign::Sign, ap, Activity, Id, err };
+    use crate::{ conf::Config, db, Result, sign::Sign, ap, Activity, Id, err, Error };
 
 	/// The context of a thread/task.
 	///
@@ -183,9 +183,10 @@ mod ctx {
             todo!()
         }
 
-        pub fn id_gen (&self) -> IdGenerator<StdRng> {
+		/// Get an [`IdGenerator`].
+        pub fn id_gen (&self) -> IdGenerator<'_, StdRng> {
 			IdGenerator {
-    			hostname: self.config.host.clone(),
+    			hostname: &self.config.host,
     			rng: StdRng::from_entropy(),
     			db: self.client.clone(),
 			}
@@ -213,11 +214,6 @@ mod ctx {
     		}
     	}
 
-		/// Get the inner database client.
-    	fn db_client (&self) -> &db::Client {
-    		&self.db
-    	}
-
        	/// Get the inner web client.
     	fn web_client (&self) -> &reqwest::Client {
         	&self.web
@@ -293,35 +289,55 @@ mod ctx {
 
     }
 
+	/// How many bytes to generate for an ID.
     const ID_LEN: usize = 64;
 
     /// Generates [`Id`]s.
-    pub struct IdGenerator <R> {
-        hostname: String,
+    pub struct IdGenerator <'h, R> {
+        hostname: &'h str,
         db: db::Client,
         rng: R,
     }
 
-    impl<R> IdGenerator<R>
+    impl<R> IdGenerator<'_, R>
     where
     	R: Rng
     {
-    	pub fn gen (&mut self, prefix: &str) -> Option<Id> {
+        /// Generate an [`Id`] with the given prefix.
+    	pub async fn gen (&mut self, prefix: &str) -> Result<Id> {
 
         	let IdGenerator { rng, db, hostname } = self;
 
-        	// Generate a random suffix
-        	let suffix = {
-            	let mut buf = [0; ID_LEN];
-            	rng.fill(&mut buf);
-            	base64::encode_block(&buf)
-                	.replace("=", "-")
-                	.replace("+", "_")
-        	};
+        	// Give up after 200 failed attempts.
+        	let mut tries = 200;
 
-        	let id = format!("https://{hostname}/{prefix}/{suffix}").parse().ok()?;
+			loop {
 
-        	Some (id)
+            	// Generate a random suffix and encode it as base64.
+            	let suffix = {
+                	let mut buf = [0; ID_LEN];
+                	rng.fill(&mut buf);
+                	base64::encode_block(&buf)
+                    	.replace("=", "-")
+                    	.replace("+", "_")
+            	};
+
+				// Create an actual `Id` with the generated garbage.
+            	let id = format!("https://{hostname}/{prefix}/{suffix}").parse()?;
+
+				// Basic check to see if the given id exists. This reserves the id.
+				// If the id is already taken, it is consumed.
+            	if let Some (id) = db.verify_unique(id).await? {
+                	break Ok (id)
+            	}
+
+            	tries -= 1;
+            	if tries == 0 {
+                	// After our tries are exhausted, give up.
+                	break Err (Error::Timeout)
+            	}
+
+			}
 
     	}
     }