From 7c4e5e97cfca92e193dc79b3241dc24e7f9e7279 Mon Sep 17 00:00:00 2001
From: Yves Fischer <yvesf-git@xapek.org>
Date: Tue, 29 Jan 2019 01:00:12 +0100
Subject: Improve error handling

---
 src/main.rs | 52 ++++++++++++++++++++++++++++++++--------------------
 1 file changed, 32 insertions(+), 20 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index 112b7a5..dbf2a81 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -10,61 +10,73 @@ const PATH_ENERGY_NOW: &str = "/sys/class/power_supply/BAT0/energy_now";
 const PATH_ENERGY_FULL: &str = "/sys/class/power_supply/BAT0/energy_full_design";
 const PATH_LIGHT: &str = "/sys/devices/platform/thinkpad_acpi/leds/tpacpi::power/brightness";
 
+fn error(msg: &str) -> Error {
+    Error::new(ErrorKind::Other, msg)
+}
+
+macro_rules! mytry {
+    ($expr : expr, $msg : expr) => (match $expr {
+        Ok(val) => val,
+        Err(err) => {
+            return Err(Error::new(ErrorKind::Other, format!("{}: {:?}", $msg, err)))
+        }
+    });
+}
+
 fn file_read_integer<P: AsRef<Path>>(path: P) -> Result<u64> {
     let mut buf = [0; 20];
-    let mut file = OpenOptions::new().read(true).open(path.as_ref())?;
-    let len = file.read(&mut buf)?;
+    let mut file = mytry!(OpenOptions::new().read(true).open(path.as_ref()),
+        "Failed to open file");
+    let len = mytry!(file.read(&mut buf), "Failed to read from file");
     if len < 1 {
-        return Err(Error::new(ErrorKind::Other, "Empty file"));
-    };
+        return Err(error("Failed to read value, file is empty"));
+    }
 
-    let s = str::from_utf8(&buf[0..len])
-        .map_err(|e| Error::new(ErrorKind::Other, e))?;
-    s.trim().parse()
-        .map_err(|err| Error::new(ErrorKind::Other, format!("String parse failed: {}", err)))
+    let s = mytry!(str::from_utf8(&buf[0..len]), "UTF-8 error when reading file");
+    Ok(mytry!(s.trim().parse(), "Failed to parse String"))
 }
 
 fn read_battery_percentage() -> Result<u32> {
-    let now = file_read_integer(PATH_ENERGY_NOW)?;
-    let full = file_read_integer(PATH_ENERGY_FULL)?;
+    let now = mytry!(file_read_integer(PATH_ENERGY_NOW), "Failed to read energy_now");
+    let full = mytry!(file_read_integer(PATH_ENERGY_FULL), "Failed to read energy_full");
     Ok(((now * 100) / full) as u32)
 }
 
 fn write_brightness(level: u8) -> Result<()> {
     let string = format!("{}\n", level);
-    let mut file = OpenOptions::new().write(true).open(PATH_LIGHT)?;
-    if file.write(string.as_bytes())? == string.len() {
+    let mut file = mytry!(OpenOptions::new().write(true).open(PATH_LIGHT), "Failed to open PATH_LIGHT");
+    let bytes_written = mytry!(file.write(string.as_bytes()), "Failed to write brightness file");
+    if bytes_written == string.len() {
         Ok(())
     } else {
-        Err(Error::new(ErrorKind::Other, "Failed to write brightness"))
+        Err(error("Failed to write all bytes to brightness file"))
     }
 }
 
 fn read_brightness() -> Result<u8> {
-    let level = file_read_integer(PATH_LIGHT)?;
+    let level = mytry!(file_read_integer(PATH_LIGHT), "Failed to read PATH_LIGHT");
     Ok(level as u8)
 }
 
 fn indicate_battery_level(level: u32) -> Result<()> {
-    let led_state = read_brightness()?;
+    let led_state = mytry!(read_brightness(), "Reading brightness failed");
     let flashing_time: u32 = 10000;
     let offtime: u32 = 40;
     let ontime: u32 = 20;
     let n = flashing_time / (level * offtime + level * ontime);
     for _ in 0..n {
-        write_brightness(0)?;
+        mytry!(write_brightness(0), "Failed to switch off brightness");
         sleep(Duration::from_millis(u64::from(level * offtime)));
-        write_brightness(1)?;
+        mytry!(write_brightness(1), "Failed to switch on brightness");
         sleep(Duration::from_millis(u64::from(level * ontime)));
     }
-    write_brightness(led_state)?;
+    mytry!(write_brightness(led_state), "Failed to re-set brightness");
     Ok(())
 }
 
 fn main() {
     loop {
-        let p = read_battery_percentage();
-        match p {
+        match read_battery_percentage() {
             Ok(level) => {
                 if level < 20 {
                     if let Err(e) = indicate_battery_level(level) {
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