From 5d03cf3d42303ebe4a07c33cb67cc1f88915a80b Mon Sep 17 00:00:00 2001
From: Richard Dodd <richard.o.dodd@gmail.com>
Date: Mon, 1 Jul 2019 14:20:35 +0100
Subject: [PATCH] Make program exit gracefully when binding fails.

Also give good error message when address is in use.
---
 src/main.rs | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/src/main.rs b/src/main.rs
index 988f0c2..85d0c43 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -65,7 +65,8 @@ fn run() -> Result<()> {
     info!("root dir: {}", config.root_dir.display());
     info!("extensions: {}", config.use_extensions);
 
-    let server = Server::bind(&config.addr)
+    let server = Server::try_bind(&config.addr)
+        .map_err(|e| translate_bind_error(e, config.addr))?
         .serve(move || {
             let config = config.clone();
             service_fn(move |req| {
@@ -114,6 +115,19 @@ pub struct Config {
     use_extensions: bool,
 }
 
+/// Translate a hyper error into our error for binding
+fn translate_bind_error(e: hyper::Error, addr: SocketAddr) -> Error {
+    if let Some(os_error) = e
+        .source()
+        .and_then(|source| source.downcast_ref::<io::Error>())
+    {
+        if os_error.kind() == io::ErrorKind::AddrInUse {
+            return Error::AddrInUse(addr);
+        }
+    }
+    Error::BindWithHyper(e)
+}
+
 /// The function that returns a future of an HTTP response for each hyper
 /// Request that is received. Errors are turned into an Error response (404 or
 /// 500), and never propagated upward for hyper to deal with.
@@ -413,6 +427,12 @@ pub enum Error {
     #[display(fmt = "failed to parse IP address")]
     AddrParse(std::net::AddrParseError),
 
+    #[display(fmt = "the address \"{}\" is already in use", _0)]
+    AddrInUse(SocketAddr),
+
+    #[display(fmt = "failed to bind server to socket")]
+    BindWithHyper(hyper::Error),
+
     #[display(fmt = "markdown is not UTF-8")]
     MarkdownUtf8,
 
@@ -437,6 +457,8 @@ impl StdError for Error {
             Http(e) => Some(e),
             Io(e) => Some(e),
             AddrParse(e) => Some(e),
+            AddrInUse(_) => None,
+            BindWithHyper(e) => Some(e),
             MarkdownUtf8 => None,
             StripPrefixInDirList(e) => Some(e),
             TemplateRender(e) => Some(e),