feat(export): handler with custom error type

examples/custom_handler.rs

@@ -1,26 +1,53 @@
-use std::env::args;
-use std::fs::File;
-use std::io::{Cursor, Read, Result, Write};
-
 use orgize::export::*;
 use orgize::headline::Headline;
 use slugify::slugify;
+use std::convert::From;
+use std::env::args;
+use std::fs::File;
+use std::io::{Cursor, Error as IOError, Read, Write};
+use std::string::FromUtf8Error;
 
 struct CustomHtmlHandler;
 
-impl<W: Write> HtmlHandler<W> for CustomHtmlHandler {
-    fn handle_headline_beg(&mut self, w: &mut W, hdl: Headline) -> Result<()> {
-        write!(
-            w,
-            r##"<h{0}><a class="anchor" href="#{1}">{2}</a></h{0}>"##,
-            if hdl.level <= 6 { hdl.level } else { 6 },
-            slugify!(hdl.title),
-            hdl.title,
-        )
+#[derive(Debug)]
+enum Error {
+    IO(IOError),
+    Heading,
+    Utf8(FromUtf8Error),
+}
+
+// From<std::io::Error> trait is required
+impl From<IOError> for Error {
+    fn from(err: IOError) -> Error {
+        Error::IO(err)
     }
 }
 
-fn main() -> Result<()> {
+impl From<FromUtf8Error> for Error {
+    fn from(err: FromUtf8Error) -> Error {
+        Error::Utf8(err)
+    }
+}
+
+type Result = std::result::Result<(), Error>;
+
+impl<W: Write> HtmlHandler<W, Error> for CustomHtmlHandler {
+    fn handle_headline_beg(&mut self, w: &mut W, hdl: Headline) -> Result {
+        if hdl.level > 6 {
+            Err(Error::Heading)
+        } else {
+            Ok(write!(
+                w,
+                r##"<h{0}><a class="anchor" href="#{1}">{2}</a></h{0}>"##,
+                hdl.level,
+                slugify!(hdl.title),
+                hdl.title,
+            )?)
+        }
+    }
+}
+
+fn main() -> Result {
     let args: Vec<_> = args().collect();
 
     if args.len() < 2 {
@@ -39,10 +66,7 @@ fn main() -> Result<()> {
 
         render.render()?;
 
-        println!(
-            "{}",
-            String::from_utf8(cursor.into_inner()).expect("invalid utf-8")
-        );
+        println!("{}", String::from_utf8(cursor.into_inner())?);
     }
 
     Ok(())