Add parser module for index loading

src/main.rs

@@ -1,6 +1,7 @@
 //! Main module.
 
 pub mod error;
+pub mod parser;
 pub mod story;
 
 fn main() {

src/parser.rs

@@ -0,0 +1,83 @@
+//! Index parser.
+
+use std::io::BufRead;
+use std::sync::mpsc::{channel, Receiver};
+use std::thread::spawn;
+
+use serde_json::from_str;
+
+use crate::error::{Error, Result};
+use crate::story::Story;
+
+const TRIM: &'static [char] = &['"', ',', ' ', '\t', '\n', '\r'];
+
+pub fn parse(reader: impl BufRead) -> Result<Vec<Story>> {
+    use Error::*;
+
+    let (tx, rx) = channel();
+    let rx = spawn_parser(rx);
+
+    for line in reader.lines() {
+        let line = line.map_err(|e| match e {
+            _ => SourceError("Could not read index line."),
+        })?;
+
+        if 3 < line.len() {
+            tx.send(line).unwrap();
+        }
+    }
+
+    drop(tx);
+
+    rx.recv().unwrap()
+}
+
+fn spawn_parser(stream: Receiver<String>) -> Receiver<Result<Vec<Story>>> {
+    let (tx, rx) = channel();
+
+    spawn(move || {
+        let mut stories = Vec::with_capacity(250_000);
+
+        while let Ok(line) = stream.recv() {
+            match deserialize(line) {
+                Ok(story) => stories.push(story),
+                Err(e) => return tx.send(Err(e)).unwrap(),
+            };
+        }
+
+        stories.shrink_to_fit();
+        stories.sort_by_key(|story| story.id);
+
+        tx.send(Ok(stories)).unwrap();
+    });
+
+    rx
+}
+
+fn deserialize(line: String) -> Result<Story> {
+    use Error::*;
+
+    let split = line
+        .splitn(2, ':')
+        .map(|value| value.trim_matches(TRIM))
+        .collect::<Vec<&str>>();
+
+    let (skey, json) = match split[..] {
+        [skey, json] => Ok((skey, json)),
+        _ => Err(SourceError("Invalid line format.")),
+    }?;
+
+    let key: i64 = skey.parse().map_err(|e| match e {
+        _ => SourceError("Invalid meta key."),
+    })?;
+
+    let story: Story = from_str(json).map_err(|e| match e {
+        _ => SourceError("Invalid meta value."),
+    })?;
+
+    if key != story.id {
+        return Err(SourceError("Meta key mismatch."));
+    }
+
+    Ok(story)
+}