From 8652f276cdef5f888f7292ce926f23b71995c056 Mon Sep 17 00:00:00 2001
From: utam0k <k0ma@utam0k.jp>
Date: Sun, 6 Jun 2021 18:40:37 +0900
Subject: [PATCH] add handling of WouldBlock error.

---
 src/process/child.rs  | 18 ++++++++++++++----
 src/process/parent.rs | 21 +++++++++++++++++++--
 2 files changed, 33 insertions(+), 6 deletions(-)

diff --git a/src/process/child.rs b/src/process/child.rs
index 52f393dd2..2bdca4931 100644
--- a/src/process/child.rs
+++ b/src/process/child.rs
@@ -1,13 +1,15 @@
-use super::{MAX_EVENTS, WAIT_FOR_INIT};
+use std::io::ErrorKind;
+use std::io::Read;
+use std::io::Write;
+
 use anyhow::{bail, Result};
 use mio::unix::pipe;
 use mio::unix::pipe::Receiver;
 use mio::unix::pipe::Sender;
 use mio::{Events, Interest, Poll, Token};
 use nix::unistd::Pid;
-use std::io::Read;
-use std::io::Write;
 
+use super::{MAX_EVENTS, WAIT_FOR_INIT};
 use crate::process::message::Message;
 
 // Token is used to identify which socket generated an event
@@ -97,7 +99,15 @@ impl ChildProcess {
             if let CHILD = event.token() {
                 // read message from the init process
                 let mut buf = [0; 1];
-                receiver.read_exact(&mut buf)?;
+                match receiver.read_exact(&mut buf) {
+                    // This error simply means that there are no more incoming connections waiting to be accepted at this point.
+                    Err(ref e) if e.kind() == ErrorKind::WouldBlock => (),
+                    Err(e) => bail!(
+                        "Failed to receive a message from the child process. {:?}",
+                        e
+                    ),
+                    _ => (),
+                }
                 match Message::from(u8::from_be_bytes(buf)) {
                     Message::InitReady => return Ok(()),
                     msg => bail!("receive unexpected message {:?} in child process", msg),
diff --git a/src/process/parent.rs b/src/process/parent.rs
index ea003a64b..3ff941794 100644
--- a/src/process/parent.rs
+++ b/src/process/parent.rs
@@ -1,3 +1,4 @@
+use std::io::ErrorKind;
 use std::io::Read;
 
 use super::{MAX_EVENTS, WAIT_FOR_CHILD};
@@ -47,13 +48,29 @@ impl ParentProcess {
             if let PARENT = event.token() {
                 // read data from pipe
                 let mut buf = [0; 1];
-                self.receiver.read_exact(&mut buf)?;
+                match self.receiver.read_exact(&mut buf) {
+                    // This error simply means that there are no more incoming connections waiting to be accepted at this point.
+                    Err(ref e) if e.kind() == ErrorKind::WouldBlock => (),
+                    Err(e) => bail!(
+                        "Failed to receive a message from the child process. {:?}",
+                        e
+                    ),
+                    _ => (),
+                };
                 // convert to Message wrapper
                 match Message::from(u8::from_be_bytes(buf)) {
                     Message::ChildReady => {
                         // read pid of init process forked by child, 4 bytes as the type is i32
                         let mut buf = [0; 4];
-                        self.receiver.read_exact(&mut buf)?;
+                        match self.receiver.read_exact(&mut buf) {
+                            // This error simply means that there are no more incoming connections waiting to be accepted at this point.
+                            Err(ref e) if e.kind() == ErrorKind::WouldBlock => (),
+                            Err(e) => bail!(
+                                "Failed to receive a message from the child process. {:?}",
+                                e
+                            ),
+                            _ => (),
+                        }
                         return Ok(i32::from_be_bytes(buf));
                     }
                     msg => bail!("receive unexpected message {:?} in parent process", msg),