From e9fdee8818f5c089013b9c8604e183b1cbd816ad Mon Sep 17 00:00:00 2001 From: Matt Brubeck Date: Wed, 17 Jan 2018 08:37:03 -0800 Subject: [PATCH] Use File::metadata instead of fs::metadata to choose buffer size This replaces a `stat` syscall with `fstat` or similar, which can be faster. Fixes #47519. --- src/libstd/fs.rs | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-) diff --git a/src/libstd/fs.rs b/src/libstd/fs.rs index 51cb9609120e3..1325ca464c4da 100644 --- a/src/libstd/fs.rs +++ b/src/libstd/fs.rs @@ -211,12 +211,12 @@ pub struct DirBuilder { recursive: bool, } -/// How large a buffer to pre-allocate before reading the entire file at `path`. -fn initial_buffer_size>(path: P) -> usize { +/// How large a buffer to pre-allocate before reading the entire file. +fn initial_buffer_size(file: &File) -> usize { // Allocate one extra byte so the buffer doesn't need to grow before the // final `read` call at the end of the file. Don't worry about `usize` // overflow because reading will fail regardless in that case. - metadata(path).map(|m| m.len() as usize + 1).unwrap_or(0) + file.metadata().map(|m| m.len() as usize + 1).unwrap_or(0) } /// Read the entire contents of a file into a bytes vector. @@ -254,8 +254,9 @@ fn initial_buffer_size>(path: P) -> usize { /// ``` #[unstable(feature = "fs_read_write", issue = "46588")] pub fn read>(path: P) -> io::Result> { - let mut bytes = Vec::with_capacity(initial_buffer_size(&path)); - File::open(path)?.read_to_end(&mut bytes)?; + let mut file = File::open(path)?; + let mut bytes = Vec::with_capacity(initial_buffer_size(&file)); + file.read_to_end(&mut bytes)?; Ok(bytes) } @@ -295,8 +296,9 @@ pub fn read>(path: P) -> io::Result> { /// ``` #[unstable(feature = "fs_read_write", issue = "46588")] pub fn read_string>(path: P) -> io::Result { - let mut string = String::with_capacity(initial_buffer_size(&path)); - File::open(path)?.read_to_string(&mut string)?; + let mut file = File::open(path)?; + let mut string = String::with_capacity(initial_buffer_size(&file)); + file.read_to_string(&mut string)?; Ok(string) }