Use struct for error handling

src/archive/fetcher.rs

@@ -1,6 +1,7 @@
 //! Archive fetcher.
 
 use std::fs::File;
+use std::io::ErrorKind as IoErrorKind;
 use std::io::{BufReader, Read, Seek};
 use std::path::Path;
 use std::sync::Mutex;
@@ -8,9 +9,9 @@ use std::sync::Mutex;
 use zip::read::ZipArchive;
 use zip::result::ZipError;
 
-use crate::error::{Error, Result};
 use super::parser::parse;
 use super::story::Story;
+use crate::error::{Error, Result};
 
 pub struct Fetcher<T>
 where
@@ -22,10 +23,11 @@ where
 
 impl Fetcher<BufReader<File>> {
     pub fn from(path: impl AsRef<Path>) -> Result<Self> {
-        use Error::*;
+        use IoErrorKind::*;
 
-        let file = File::open(path).map_err(|e| match e {
-            _ => SourceError("Could not open archive file."),
+        let file = File::open(path).map_err(|e| match e.kind() {
+            NotFound => Error::archive("File not found"),
+            _ => Error::archive("Could not open file"),
         })?;
 
         Self::from_reader(BufReader::with_capacity(8_000_000, file))
@@ -45,26 +47,24 @@ where
     }
 
     fn open(archive: T) -> Result<ZipArchive<T>> {
-        use Error::*;
         use ZipError::*;
 
         ZipArchive::new(archive).map_err(|e| match e {
-            InvalidArchive(e) => SourceError(e),
-            UnsupportedArchive(e) => SourceError(e),
-            _ => SourceError("Could not read archive."),
+            InvalidArchive(e) => Error::archive(e),
+            UnsupportedArchive(e) => Error::archive(e),
+            _ => Error::archive("Unknown ZIP-file issue"),
         })
     }
 
     fn load(archive: &mut ZipArchive<T>) -> Result<Vec<Story>> {
-        use Error::*;
         use ZipError::*;
 
         let file = archive.by_name("index.json").map_err(|e| match e {
-            FileNotFound => SourceError("Missing archive index."),
-            _ => SourceError("Could not open archive index."),
+            FileNotFound => Error::archive("Missing story index"),
+            _ => Error::archive("Could not open story index"),
         })?;
 
-        parse(BufReader::with_capacity(8_000_000, file))
+        parse(BufReader::with_capacity(8_000_000, file)).map_err(Error::index)
     }
 
     pub fn fetch(&self, key: i64) -> Option<&Story> {
@@ -75,23 +75,23 @@ where
     }
 
     pub fn read(&self, path: &str) -> Result<Vec<u8>> {
-        use Error::*;
         use ZipError::*;
 
         let mut archive = self.archive.lock().map_err(|e| match e {
-            _ => SourceError("Could not acquire archive lock."),
+            _ => Error::archive("Could not acquire fetcher lock"),
         })?;
 
         let mut file = archive.by_name(path).map_err(|e| match e {
-            FileNotFound => SourceError("File not found."),
-            _ => SourceError("Could not open file."),
+            FileNotFound => Error::archive("Missing story data"),
+            _ => Error::archive("Could not open story data"),
         })?;
 
         let size = file.size() as usize;
         let mut buf = Vec::with_capacity(size);
 
-        file.read_to_end(&mut buf)
-            .map_err(|_| SourceError("Could not read file."))?;
+        file.read_to_end(&mut buf).map_err(|e| match e {
+            _ => Error::archive("Could not read story data"),
+        })?;
 
         Ok(buf)
     }

src/archive/parser.rs

@@ -4,22 +4,21 @@ use std::io::BufRead;
 use std::sync::mpsc::{channel, Receiver};
 use std::thread::spawn;
 
+use serde::de::Error;
+use serde_json::error::Result;
 use serde_json::from_str;
 
-use crate::error::{Error, Result};
 use super::story::Story;
 
 const TRIM: &[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."),
+            _ => Error::custom("Could not read line"),
         })?;
 
         if tx.send(line).is_ok() {
@@ -27,8 +26,8 @@ pub fn parse(reader: impl BufRead) -> Result<Vec<Story>> {
         }
 
         return Err(match rx.recv() {
-            Err(_) => SourceError("Parser disappeared unexpectedly."),
-            Ok(Ok(_)) => SourceError("Parser returned unexpectedly."),
+            Err(_) => Error::custom("Parser disappeared unexpectedly"),
+            Ok(Ok(_)) => Error::custom("Parser returned unexpectedly"),
             Ok(Err(error)) => error,
         });
     }
@@ -36,13 +35,11 @@ pub fn parse(reader: impl BufRead) -> Result<Vec<Story>> {
     drop(tx);
 
     rx.recv().map_err(|e| match e {
-        _ => SourceError("Missing parser result."),
+        _ => Error::custom("Missing parser result"),
     })?
 }
 
 fn spawn_parser(stream: Receiver<String>) -> Receiver<Result<Vec<Story>>> {
-    use Error::*;
-
     let (tx, rx) = channel();
 
     spawn(move || {
@@ -68,11 +65,11 @@ fn spawn_parser(stream: Receiver<String>) -> Receiver<Result<Vec<Story>>> {
         stories.shrink_to_fit();
 
         if wrappers != "{}" {
-            return tx.send(Err(SourceError("Invalid index structure.")));
+            return tx.send(Err(Error::custom("Invalid file structure")));
         }
 
         if count != stories.len() {
-            return tx.send(Err(SourceError("Index contains duplicates.")));
+            return tx.send(Err(Error::custom("Found duplicate story")));
         }
 
         tx.send(Ok(stories))
@@ -82,8 +79,6 @@ fn spawn_parser(stream: Receiver<String>) -> Receiver<Result<Vec<Story>>> {
 }
 
 fn deserialize(line: String) -> Result<Story> {
-    use Error::*;
-
     let split = line
         .splitn(2, ':')
         .map(|value| value.trim_matches(TRIM))
@@ -91,19 +86,17 @@ fn deserialize(line: String) -> Result<Story> {
 
     let (skey, json) = match split[..] {
         [skey, json] => Ok((skey, json)),
-        _ => Err(SourceError("Invalid line format.")),
+        _ => Err(Error::custom("Invalid line format")),
     }?;
 
-    let key: i64 = skey.parse().map_err(|e| match e {
-        _ => SourceError("Invalid meta key."),
-    })?;
+    let story: Story = from_str(json)?;
 
-    let story: Story = from_str(json).map_err(|e| match e {
-        _ => SourceError("Invalid meta value."),
+    let key: i64 = skey.parse().map_err(|e| match e {
+        _ => Error::custom("Invalid line key"),
     })?;
 
     if key != story.id {
-        return Err(SourceError("Meta key mismatch."));
+        return Err(Error::custom("Line key mismatch"));
     }
 
     Ok(story)

src/archive/story.rs

@@ -182,10 +182,10 @@ where
         Ok(value.as_i64().unwrap())
     } else if value.is_string() {
         value.as_str().unwrap().parse().map_err(|e| match e {
-            _ => Error::custom("Could not parse ID string."),
+            _ => Error::custom("Could not parse ID string"),
         })
     } else {
-        Err(Error::custom("Invalid type for ID value."))
+        Err(Error::custom("Invalid type for ID value"))
     }
 }
 
@@ -199,15 +199,15 @@ impl<'de> Deserialize<'de> for Color {
         let text = object
             .get("hex")
             .and_then(|value| value.as_str())
-            .ok_or_else(|| Error::custom("Color is missing hex value."))?;
+            .ok_or_else(|| Error::custom("Color is missing hex value"))?;
 
         let array = hex::decode(text).map_err(|e| match e {
-            _ => Error::custom("Color hex has invalid value."),
+            _ => Error::custom("Color hex has invalid value"),
         })?;
 
         match array[..] {
             [red, green, blue] => Ok(Color { red, green, blue }),
-            _ => Err(Error::custom("Color hex has invalid length.")),
+            _ => Err(Error::custom("Color hex has invalid length")),
         }
     }
 }

src/error.rs

@@ -1,10 +1,126 @@
 //! Error types.
 
-#[derive(Debug)]
-pub enum Error {
-    InvalidStory(),
-    SourceError(&'static str),
-    UserError(&'static str),
+use std::error::Error as StdError;
+use std::fmt::Result as FmtResult;
+use std::fmt::{Display, Formatter};
+use std::result::Result as StdResult;
+
+use serde_json::error::Error as SerdeError;
+
+use self::ErrorKind::*;
+
+pub type Result<T> = StdResult<T, Error>;
+
+#[derive(Clone, Debug)]
+pub enum ErrorKind {
+    ArchiveError,
+    IndexError,
+    InvalidStory,
+    UsageError,
 }
 
-pub type Result<T> = std::result::Result<T, Error>;
+#[derive(Debug)]
+pub struct Error {
+    kind: ErrorKind,
+    message: Option<String>,
+    source: Option<Box<dyn StdError + 'static>>,
+}
+
+pub struct ErrorBuilder(Error);
+
+impl ErrorBuilder {
+    pub fn new(kind: ErrorKind) -> Self {
+        ErrorBuilder(Error {
+            kind,
+            message: None,
+            source: None,
+        })
+    }
+
+    pub fn message(mut self, message: impl ToString) -> Self {
+        self.0.message = Some(message.to_string());
+        self
+    }
+
+    pub fn source(mut self, source: impl StdError + 'static) -> Self {
+        self.0.source = Some(Box::new(source));
+        self
+    }
+
+    pub fn build(self) -> Error {
+        self.0
+    }
+}
+
+impl Error {
+    pub fn archive(message: impl ToString) -> Self {
+        ErrorBuilder::new(ArchiveError).message(message).build()
+    }
+
+    pub fn index(error: SerdeError) -> Self {
+        ErrorBuilder::new(IndexError)
+            .message(&error)
+            .source(error)
+            .build()
+    }
+
+    pub fn invalid() -> Self {
+        ErrorBuilder::new(InvalidStory).build()
+    }
+
+    pub fn usage(message: impl ToString) -> Self {
+        ErrorBuilder::new(UsageError).message(message).build()
+    }
+
+    pub fn kind(&self) -> ErrorKind {
+        self.kind.clone()
+    }
+
+    pub fn message(&self) -> Option<&String> {
+        self.message.as_ref()
+    }
+}
+
+fn lower(message: &str) -> String {
+    let mut chars = message.chars();
+
+    let head: String = match chars.next() {
+        Some(c) => c.to_lowercase().collect(),
+        None => return String::from(message),
+    };
+
+    format!("{}{}", head, chars.as_str())
+}
+
+impl Display for ErrorKind {
+    fn fmt(&self, f: &mut Formatter) -> FmtResult {
+        let message = match self {
+            ArchiveError => "Archive error",
+            IndexError => "Index error",
+            InvalidStory => "Invalid story",
+            UsageError => "Usage error",
+        };
+
+        write!(f, "{}", message)
+    }
+}
+
+impl Display for Error {
+    fn fmt(&self, f: &mut Formatter) -> FmtResult {
+        let message = match &self.message {
+            Some(message) => message,
+            None => "Unknown cause",
+        };
+
+        let kind = self.kind();
+        let info = lower(message);
+
+        write!(f, "{}, {}.", kind, info)
+    }
+}
+
+impl StdError for Error {
+    fn source(&self) -> Option<&(dyn StdError + 'static)> {
+        self.source.as_ref().map(Box::as_ref)
+    }
+}

src/main.rs

@@ -7,26 +7,30 @@ use std::env::args;
 use std::time::Instant;
 
 use crate::archive::Fetcher;
-use crate::error::{Error, Result};
+use crate::error::Error;
 
-fn main() -> Result<()> {
-    use Error::*;
+fn exit(error: Error) -> ! {
+    eprintln!("{}", error);
 
+    std::process::exit(1)
+}
+
+fn main() {
     let argv = args().collect::<Vec<String>>();
 
-    let path = match argv.len() {
-        2 => Ok(argv.get(1).unwrap()),
-        _ => Err(UserError("Usage: fimfareader <ARCHIVE>")),
-    }?;
+    if argv.len() != 2 {
+        eprintln!("Usage: fimfareader <ARCHIVE>");
+        std::process::exit(1);
+    }
 
     println!("Hellopaca, World!");
 
     let start = Instant::now();
-    let fetcher = Fetcher::from(path)?;
+    let result = Fetcher::from(&argv[1]);
     let finish = Instant::now() - start;
 
+    let fetcher = result.map_err(exit).unwrap();
+
     println!("Finished loading in {} milliseconds.", finish.as_millis());
     println!("The archive contains {} stories.", fetcher.iter().count());
-
-    Ok(())
 }