From 96480b6fb9057becbe6abf4f6fa6b2e1238c63f8 Mon Sep 17 00:00:00 2001
From: Aleksei Voronov <despawn@gmail.com>
Date: Mon, 25 Sep 2023 12:49:01 +0200
Subject: [PATCH] Add proper error handling to the web service

Return 500 when shit happens.
Return 404 when the feed is not found
---
 README.md                                     |  2 +-
 src/processes/feed_server.rs                  |  1 +
 .../endpoints/get_feed_skeleton.rs            | 24 ++++++++--------
 src/processes/feed_server/errors.rs           | 28 +++++++++++++++++++
 4 files changed, 41 insertions(+), 14 deletions(-)
 create mode 100644 src/processes/feed_server/errors.rs

diff --git a/README.md b/README.md
index 667492e..31b7f7e 100644
--- a/README.md
+++ b/README.md
@@ -13,7 +13,7 @@ Heavily WIP. Doesn't work yet at all, but does read the stream of posts as they
 - [x] Keep subscription state to not lose messages
 - [x] Serve the feed
 - [x] Handle deleting of posts
-- [ ] Handle errors in the web service gracefully
+- [x] Handle errors in the web service gracefully
 - [x] Handle missing profiles in the profile classifier
 - [ ] Add a way to mark a profile as being from a certain country manually
 - [ ] Handle reconnecting to websocket somehow
diff --git a/src/processes/feed_server.rs b/src/processes/feed_server.rs
index 86187ee..e55d94c 100644
--- a/src/processes/feed_server.rs
+++ b/src/processes/feed_server.rs
@@ -1,5 +1,6 @@
 mod endpoints;
 mod server;
 mod state;
+mod errors;
 
 pub use server::FeedServer;
diff --git a/src/processes/feed_server/endpoints/get_feed_skeleton.rs b/src/processes/feed_server/endpoints/get_feed_skeleton.rs
index bf6171c..833916a 100644
--- a/src/processes/feed_server/endpoints/get_feed_skeleton.rs
+++ b/src/processes/feed_server/endpoints/get_feed_skeleton.rs
@@ -1,4 +1,4 @@
-use anyhow::{anyhow, Result};
+use anyhow::anyhow;
 use atrium_api::app::bsky::feed::defs::SkeletonFeedPost;
 use atrium_api::app::bsky::feed::get_feed_skeleton::{
     Output as FeedSkeleton, Parameters as FeedSkeletonQuery,
@@ -8,29 +8,27 @@ use axum::Json;
 use chrono::{DateTime, TimeZone, Utc};
 
 use crate::processes::feed_server::state::FeedServerState;
+use crate::processes::feed_server::errors::AppError;
 
 pub async fn get_feed_skeleton(
     State(state): State<FeedServerState>,
     query: Query<FeedSkeletonQuery>,
-) -> Json<FeedSkeleton> {
+) -> Result<Json<FeedSkeleton>, AppError> {
     let algo = state
         .algos
         .get_by_name(&query.feed)
-        .ok_or_else(|| anyhow!("Feed {} not found", query.feed))
-        .unwrap(); // TODO: handle error
+        .ok_or_else(|| AppError::FeedNotFound(query.feed.clone()))?;
 
     let limit = query.limit.unwrap_or(20);
     let earlier_than = query
         .cursor
         .as_deref()
         .map(parse_cursor)
-        .transpose()
-        .unwrap(); // TODO: handle error
+        .transpose()?;
 
     let posts = algo
         .fetch_posts(&state.database, limit, earlier_than)
-        .await
-        .unwrap(); // TODO: handle error
+        .await?;
 
     let feed = posts
         .iter()
@@ -42,21 +40,21 @@ pub async fn get_feed_skeleton(
 
     let cursor = posts.last().map(|p| make_cursor(&p.indexed_at, &p.cid));
 
-    Json(FeedSkeleton { cursor, feed })
+    Ok(Json(FeedSkeleton { cursor, feed }))
 }
 
 fn make_cursor(date: &DateTime<Utc>, cid: &str) -> String {
     format!("{}::{}", date.timestamp() * 1000, cid)
 }
 
-fn parse_cursor(cursor: &str) -> Result<(DateTime<Utc>, &str)> {
+fn parse_cursor(cursor: &str) -> anyhow::Result<(DateTime<Utc>, &str)> {
     let mut parts = cursor.split("::");
 
-    let indexed_at = parts.next().ok_or_else(|| anyhow!("Malformed cursor"))?;
-    let cid = parts.next().ok_or_else(|| anyhow!("Malformed cursor"))?;
+    let indexed_at = parts.next().ok_or_else(|| anyhow!("Malformed cursor: {cursor}"))?;
+    let cid = parts.next().ok_or_else(|| anyhow!("Malformed cursor: {cursor}"))?;
 
     if parts.next().is_some() {
-        return Err(anyhow!("Malformed cursor"));
+        return Err(anyhow!("Malformed cursor: {cursor}"));
     }
 
     let indexed_at: i64 = indexed_at.parse()?;
diff --git a/src/processes/feed_server/errors.rs b/src/processes/feed_server/errors.rs
new file mode 100644
index 0000000..db6992c
--- /dev/null
+++ b/src/processes/feed_server/errors.rs
@@ -0,0 +1,28 @@
+use axum::response::{Response, IntoResponse};
+use axum::http::StatusCode;
+
+pub enum AppError {
+    FeedNotFound(String),
+    Other(anyhow::Error),
+}
+
+impl IntoResponse for AppError {
+    fn into_response(self) -> Response {
+        match self {
+            Self::FeedNotFound(name) => (StatusCode::NOT_FOUND, format!("Feed not found: {}", name)),
+            Self::Other(e) => (
+                StatusCode::INTERNAL_SERVER_ERROR,
+                format!("Something went wrong: {}", e),
+            )
+        }.into_response()
+    }
+}
+
+impl<E> From<E> for AppError
+where
+    E: Into<anyhow::Error>,
+{
+    fn from(err: E) -> Self {
+        Self::Other(err.into())
+    }
+}