Return an iterator over ResourceDiff items

Rather than returning a Receiver<Bytes>, instead return a ResourceStream
struct that implements the Iterator trait so callers can simply iterate
over the ResourceDiff items received.

crates/rdsys-backend/Cargo.toml

@@ -9,5 +9,7 @@ edition = "2021"
 serde_json = "1"
 futures-util = { version = "0.3"}
 serde = { version = "1", features = ["derive"]}
+bytes = "1"
+tokio = "1"
 
 reqwest = { version = "0.11", features = ["stream"]}

crates/rdsys-backend/src/http.rs

@@ -1,6 +1,9 @@
-use reqwest::Client;
+use bytes::{self, Buf, Bytes};
 use futures_util::StreamExt;
-use std::io;
+use reqwest::Client;
+use std::io::{self, BufRead};
+use std::sync::mpsc;
+use tokio;
 
 #[derive(Debug)]
 pub enum Error {
@@ -27,7 +30,141 @@ impl From<io::Error> for Error {
     }
 }
 
-pub async fn start_stream(api_endpoint: String, name: String, token: String, resource_types: Vec<String> ) -> Result<(), Error> {
+pub struct ResourceStream {
+    rx: mpsc::Receiver<Bytes>,
+    buf: Vec<u8>,
+    partial: Option<bytes::buf::Reader<Bytes>>,
+}
+
+impl Iterator for ResourceStream {
+    type Item = crate::ResourceDiff;
+    fn next(&mut self) -> Option<Self::Item> {
+        let mut parse =
+            |buffer: &mut bytes::buf::Reader<Bytes>| -> Result<Option<Self::Item>, Error> {
+                match buffer.read_until(b'\r', &mut self.buf) {
+                    Ok(_) => match self.buf.pop() {
+                        Some(b'\r') => match serde_json::from_slice(&self.buf) {
+                            Ok(diff) => {
+                                self.buf.clear();
+                                return Ok(Some(diff));
+                            }
+                            Err(e) => return Err(Error::JSON(e)),
+                        },
+                        Some(n) => {
+                            self.buf.push(n);
+                            return Ok(None);
+                        }
+                        None => return Ok(None),
+                    },
+                    Err(e) => Err(Error::Io(e)),
+                }
+            };
+
+        if let Some(p) = &mut self.partial {
+            match parse(p) {
+                Ok(Some(diff)) => return Some(diff),
+                Ok(None) => self.partial = None,
+                Err(_) => return None,
+            }
+        }
+        for chunk in &self.rx {
+            let mut buffer = chunk.reader();
+            match parse(&mut buffer) {
+                Ok(Some(diff)) => {
+                    self.partial = Some(buffer);
+                    return Some(diff);
+                }
+                Ok(None) => continue,
+                Err(_) => return None,
+            };
+        }
+        None
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn parse_resource() {
+        let chunk = Bytes::from_static(
+            b"{\"new\": null,\"changed\": null,\"gone\": null,\"full_update\": true}\r",
+        );
+        let (tx, rx) = mpsc::channel();
+        tx.send(chunk).unwrap();
+        let mut diffs = ResourceStream {
+            rx: rx,
+            partial: None,
+            buf: vec![],
+        };
+        let res = diffs.next();
+        assert_ne!(res, None);
+        if let Some(diff) = res {
+            assert_eq!(diff.new, None);
+            assert_eq!(diff.full_update, true);
+        }
+    }
+
+    #[test]
+    fn parse_across_chunks() {
+        let chunk1 = Bytes::from_static(b"{\"new\": null,\"changed\": null,");
+        let chunk2 = Bytes::from_static(b"\"gone\": null,\"full_update\": true}\r");
+        let (tx, rx) = mpsc::channel();
+        tx.send(chunk1).unwrap();
+        tx.send(chunk2).unwrap();
+        let mut diffs = ResourceStream {
+            rx: rx,
+            partial: None,
+            buf: vec![],
+        };
+        let res = diffs.next();
+        assert_ne!(res, None);
+        if let Some(diff) = res {
+            assert_eq!(diff.new, None);
+            assert_eq!(diff.full_update, true);
+        }
+    }
+
+    #[test]
+    fn parse_multi_diff_partial_chunks() {
+        let chunk1 = Bytes::from_static(b"{\"new\": null,\"changed\": null,");
+        let chunk2 =
+            Bytes::from_static(b"\"gone\": null,\"full_update\": true}\r{\"new\": null,\"changed");
+        let chunk3 = Bytes::from_static(b"\": null,\"gone\": null,\"full_update\": true}");
+        let chunk4 = Bytes::from_static(b"\r");
+        let (tx, rx) = mpsc::channel();
+        tx.send(chunk1).unwrap();
+        tx.send(chunk2).unwrap();
+        tx.send(chunk3).unwrap();
+        tx.send(chunk4).unwrap();
+        let mut diffs = ResourceStream {
+            rx: rx,
+            partial: None,
+            buf: vec![],
+        };
+        let mut res = diffs.next();
+        assert_ne!(res, None);
+        if let Some(diff) = res {
+            assert_eq!(diff.new, None);
+            assert_eq!(diff.full_update, true);
+        }
+        res = diffs.next();
+        assert_ne!(res, None);
+        if let Some(diff) = res {
+            assert_eq!(diff.new, None);
+            assert_eq!(diff.full_update, true);
+        }
+    }
+}
+
+pub async fn start_stream(
+    api_endpoint: String,
+    name: String,
+    token: String,
+    resource_types: Vec<String>,
+) -> Result<ResourceStream, Error> {
+    let (tx, rx) = mpsc::channel();
 
     let req = crate::ResourceRequest {
         request_origin: name,
@@ -38,15 +175,29 @@ pub async fn start_stream(api_endpoint: String, name: String, token: String, res
     let auth_value = format!("Bearer {}", token);
 
     let client = Client::new();
-    let mut stream = client.get(api_endpoint)
+
+    let mut stream = client
+        .get(api_endpoint)
         .header("Authorization", &auth_value)
         .body(json)
         .send()
         .await?
         .bytes_stream();
 
+    tokio::spawn(async move {
         while let Some(chunk) = stream.next().await {
-        println!("Chunk: {:?}", chunk?);
-    };
-    Ok(())
+            let bytes = match chunk {
+                Ok(b) => b,
+                Err(_e) => {
+                    return;
+                }
+            };
+            tx.send(bytes).unwrap();
+        }
+    });
+    Ok(ResourceStream {
+        rx: rx,
+        buf: vec![],
+        partial: None,
+    })
 }

crates/rdsys-backend/src/lib.rs

@@ -189,4 +189,17 @@ mod tests {
         };
         assert_eq!(diff, empty_diff);
     }
+
+    #[test]
+    fn deserialize_empty_condensed_diff() {
+        let data = "{\"new\": null,\"changed\": null,\"gone\": null,\"full_update\": true}";
+        let diff: ResourceDiff = serde_json::from_str(data).unwrap();
+        let empty_diff = ResourceDiff {
+            new: None,
+            changed: None,
+            gone: None,
+            full_update: true,
+        };
+        assert_eq!(diff, empty_diff);
+    }
 }