From 291b6f16bb03c92fb383dfa12b8849808bace801 Mon Sep 17 00:00:00 2001 From: Tobias Bucher Date: Mon, 18 Jul 2016 14:31:26 +0200 Subject: [PATCH] Comment on the casts in the `seek` implementations on files --- src/libstd/sys/unix/fs.rs | 10 ++++++---- src/libstd/sys/windows/fs.rs | 2 ++ 2 files changed, 8 insertions(+), 4 deletions(-) diff --git a/src/libstd/sys/unix/fs.rs b/src/libstd/sys/unix/fs.rs index b315e6762633b..3b132744f7055 100644 --- a/src/libstd/sys/unix/fs.rs +++ b/src/libstd/sys/unix/fs.rs @@ -27,7 +27,7 @@ use sys_common::{AsInner, FromInner}; #[cfg(any(target_os = "linux", target_os = "emscripten"))] use libc::{stat64, fstat64, lstat64, off64_t, ftruncate64, lseek64, dirent64, readdir64_r, open64}; #[cfg(target_os = "android")] -use libc::{stat as stat64, fstat as fstat64, lstat as lstat64, off64_t, lseek64, +use libc::{stat as stat64, fstat as fstat64, lstat as lstat64, lseek64, dirent as dirent64, open as open64}; #[cfg(not(any(target_os = "linux", target_os = "emscripten", @@ -485,9 +485,11 @@ impl File { pub fn seek(&self, pos: SeekFrom) -> io::Result { let (whence, pos) = match pos { - SeekFrom::Start(off) => (libc::SEEK_SET, off as off64_t), - SeekFrom::End(off) => (libc::SEEK_END, off as off64_t), - SeekFrom::Current(off) => (libc::SEEK_CUR, off as off64_t), + // Casting to `i64` is fine, too large values will end up as + // negative which will cause an error in `lseek64`. + SeekFrom::Start(off) => (libc::SEEK_SET, off as i64), + SeekFrom::End(off) => (libc::SEEK_END, off), + SeekFrom::Current(off) => (libc::SEEK_CUR, off), }; let n = cvt(unsafe { lseek64(self.0.raw(), pos, whence) })?; Ok(n as u64) diff --git a/src/libstd/sys/windows/fs.rs b/src/libstd/sys/windows/fs.rs index 2683e57256dc7..4e6cef9a28d8f 100644 --- a/src/libstd/sys/windows/fs.rs +++ b/src/libstd/sys/windows/fs.rs @@ -324,6 +324,8 @@ impl File { pub fn seek(&self, pos: SeekFrom) -> io::Result { let (whence, pos) = match pos { + // Casting to `i64` is fine, `SetFilePointerEx` reinterprets this + // integer as `u64`. SeekFrom::Start(n) => (c::FILE_BEGIN, n as i64), SeekFrom::End(n) => (c::FILE_END, n), SeekFrom::Current(n) => (c::FILE_CURRENT, n),