Move trace file opening into TraceDump::new

Moves the responsibility of opening the trace file into TraceDump::new, so that
it doesn't need to be repeated at every call site.

components/profile/time.rs

@@ -15,10 +15,8 @@ use std::borrow::ToOwned;
 use std::cmp::Ordering;
 use std::collections::BTreeMap;
 use std::error::Error;
-use std::fs;
 use std::fs::File;
 use std::io::{self, Write};
-use std::path;
 use std::path::Path;
 use std::time::Duration;
 use std_time::precise_time_ns;
@@ -178,9 +176,7 @@ impl Profiler {
                 let outputoption = option.clone();
                 thread::Builder::new().name("Time profiler".to_owned()).spawn(move || {
                     let trace = file_path.as_ref()
-                        .map(path::Path::new)
-                        .map(fs::File::create)
-                        .map(|res| TraceDump::new(res.unwrap()));
+                        .and_then(|p| TraceDump::new(p).ok());
                     let mut profiler = Profiler::new(port, trace, Some(outputoption));
                     profiler.start();
                 }).expect("Thread spawning failed");
@@ -207,9 +203,7 @@ impl Profiler {
                     // Spawn the time profiler
                     thread::Builder::new().name("Time profiler".to_owned()).spawn(move || {
                         let trace = file_path.as_ref()
-                            .map(path::Path::new)
-                            .map(fs::File::create)
-                            .map(|res| TraceDump::new(res.unwrap()));
+                            .and_then(|p| TraceDump::new(p).ok());
                         let mut profiler = Profiler::new(port, trace, None);
                         profiler.start();
                     }).expect("Thread spawning failed");

components/profile/trace_dump.rs

@@ -7,7 +7,8 @@
 use profile_traits::time::{ProfilerCategory, TimerMetadata};
 use serde_json;
 use std::fs;
-use std::io::Write;
+use std::io::{self, Write};
+use std::path;
 
 /// An RAII class for writing the HTML trace dump.
 #[derive(Debug)]
@@ -36,9 +37,12 @@ struct TraceEntry {
 impl TraceDump {
     /// Create a new TraceDump and write the prologue of the HTML file out to
     /// disk.
-    pub fn new(mut file: fs::File) -> TraceDump {
-        write_prologue(&mut file);
-        TraceDump { file: file }
+    pub fn new<P>(trace_file_path: P) -> io::Result<TraceDump>
+        where P: AsRef<path::Path>
+    {
+        let mut file = fs::File::create(trace_file_path)?;
+        write_prologue(&mut file)?;
+        Ok(TraceDump { file: file })
     }
 
     /// Write one trace to the trace dump file.
@@ -63,18 +67,18 @@ impl Drop for TraceDump {
     /// Write the epilogue of the trace dump HTML file out to disk on
     /// destruction.
     fn drop(&mut self) {
-        write_epilogue(&mut self.file);
+        write_epilogue(&mut self.file).unwrap();
     }
 }
 
-fn write_prologue(file: &mut fs::File) {
-    writeln!(file, "{}", include_str!("./trace-dump-prologue-1.html")).unwrap();
-    writeln!(file, "{}", include_str!("./trace-dump.css")).unwrap();
-    writeln!(file, "{}", include_str!("./trace-dump-prologue-2.html")).unwrap();
+fn write_prologue(file: &mut fs::File) -> io::Result<()> {
+    writeln!(file, "{}", include_str!("./trace-dump-prologue-1.html"))?;
+    writeln!(file, "{}", include_str!("./trace-dump.css"))?;
+    writeln!(file, "{}", include_str!("./trace-dump-prologue-2.html"))
 }
 
-fn write_epilogue(file: &mut fs::File) {
-    writeln!(file, "{}", include_str!("./trace-dump-epilogue-1.html")).unwrap();
-    writeln!(file, "{}", include_str!("./trace-dump.js")).unwrap();
-    writeln!(file, "{}", include_str!("./trace-dump-epilogue-2.html")).unwrap();
+fn write_epilogue(file: &mut fs::File) -> io::Result<()> {
+    writeln!(file, "{}", include_str!("./trace-dump-epilogue-1.html"))?;
+    writeln!(file, "{}", include_str!("./trace-dump.js"))?;
+    writeln!(file, "{}", include_str!("./trace-dump-epilogue-2.html"))
 }