Auto merge of #62987 - Thomasdezeeuw:ioslice-advance, r=Thomasdezeeuw

Add {IoSlice, IoSliceMut}::advance

API inspired by the [`Buf::advance`](https://docs.rs/bytes/0.4.12/bytes/trait.Buf.html#tymethod.advance) method found in the [bytes](https://docs.rs/bytes) crate.

Closes #62726.

8 files changed, 152 insertions, 0 deletions

diff --git a/src/libstd/sys/cloudabi/io.rs b/src/libstd/sys/cloudabi/io.rs
index 4b423a5cbc1..976e122463d 100644
--- a/src/libstd/sys/cloudabi/io.rs
+++ b/src/libstd/sys/cloudabi/io.rs
@@ -1,3 +1,5 @@
+use crate::mem;
+
 pub struct IoSlice<'a>(&'a [u8]);
 
 impl<'a> IoSlice<'a> {
@@ -7,6 +9,11 @@ impl<'a> IoSlice<'a> {
     }
 
     #[inline]
+    pub fn advance(&mut self, n: usize) {
+        self.0 = &self.0[n..]
+    }
+
+    #[inline]
     pub fn as_slice(&self) -> &[u8] {
         self.0
     }
@@ -21,6 +28,13 @@ impl<'a> IoSliceMut<'a> {
     }
 
     #[inline]
+    pub fn advance(&mut self, n: usize) {
+        let slice = mem::replace(&mut self.0, &mut []);
+        let (_, remaining) = slice.split_at_mut(n);
+        self.0 = remaining;
+    }
+
+    #[inline]
     pub fn as_slice(&self) -> &[u8] {
         self.0
     }
diff --git a/src/libstd/sys/redox/io.rs b/src/libstd/sys/redox/io.rs
index 4b423a5cbc1..976e122463d 100644
--- a/src/libstd/sys/redox/io.rs
+++ b/src/libstd/sys/redox/io.rs
@@ -1,3 +1,5 @@
+use crate::mem;
+
 pub struct IoSlice<'a>(&'a [u8]);
 
 impl<'a> IoSlice<'a> {
@@ -7,6 +9,11 @@ impl<'a> IoSlice<'a> {
     }
 
     #[inline]
+    pub fn advance(&mut self, n: usize) {
+        self.0 = &self.0[n..]
+    }
+
+    #[inline]
     pub fn as_slice(&self) -> &[u8] {
         self.0
     }
@@ -21,6 +28,13 @@ impl<'a> IoSliceMut<'a> {
     }
 
     #[inline]
+    pub fn advance(&mut self, n: usize) {
+        let slice = mem::replace(&mut self.0, &mut []);
+        let (_, remaining) = slice.split_at_mut(n);
+        self.0 = remaining;
+    }
+
+    #[inline]
     pub fn as_slice(&self) -> &[u8] {
         self.0
     }
diff --git a/src/libstd/sys/sgx/io.rs b/src/libstd/sys/sgx/io.rs
index 4b423a5cbc1..976e122463d 100644
--- a/src/libstd/sys/sgx/io.rs
+++ b/src/libstd/sys/sgx/io.rs
@@ -1,3 +1,5 @@
+use crate::mem;
+
 pub struct IoSlice<'a>(&'a [u8]);
 
 impl<'a> IoSlice<'a> {
@@ -7,6 +9,11 @@ impl<'a> IoSlice<'a> {
     }
 
     #[inline]
+    pub fn advance(&mut self, n: usize) {
+        self.0 = &self.0[n..]
+    }
+
+    #[inline]
     pub fn as_slice(&self) -> &[u8] {
         self.0
     }
@@ -21,6 +28,13 @@ impl<'a> IoSliceMut<'a> {
     }
 
     #[inline]
+    pub fn advance(&mut self, n: usize) {
+        let slice = mem::replace(&mut self.0, &mut []);
+        let (_, remaining) = slice.split_at_mut(n);
+        self.0 = remaining;
+    }
+
+    #[inline]
     pub fn as_slice(&self) -> &[u8] {
         self.0
     }
diff --git a/src/libstd/sys/unix/io.rs b/src/libstd/sys/unix/io.rs
index bc854e772e1..a3a72919176 100644
--- a/src/libstd/sys/unix/io.rs
+++ b/src/libstd/sys/unix/io.rs
@@ -22,6 +22,18 @@ impl<'a> IoSlice<'a> {
     }
 
     #[inline]
+    pub fn advance(&mut self, n: usize) {
+        if self.vec.iov_len < n {
+            panic!("advancing IoSlice beyond its length");
+        }
+
+        unsafe {
+            self.vec.iov_len -= n;
+            self.vec.iov_base = self.vec.iov_base.add(n);
+        }
+    }
+
+    #[inline]
     pub fn as_slice(&self) -> &[u8] {
         unsafe {
             slice::from_raw_parts(self.vec.iov_base as *mut u8, self.vec.iov_len)
@@ -48,6 +60,18 @@ impl<'a> IoSliceMut<'a> {
     }
 
     #[inline]
+    pub fn advance(&mut self, n: usize) {
+        if self.vec.iov_len < n {
+            panic!("advancing IoSliceMut beyond its length");
+        }
+
+        unsafe {
+            self.vec.iov_len -= n;
+            self.vec.iov_base = self.vec.iov_base.add(n);
+        }
+    }
+
+    #[inline]
     pub fn as_slice(&self) -> &[u8] {
         unsafe {
             slice::from_raw_parts(self.vec.iov_base as *mut u8, self.vec.iov_len)
diff --git a/src/libstd/sys/vxworks/io.rs b/src/libstd/sys/vxworks/io.rs
index 72954ff20ef..8cd11cbf5df 100644
--- a/src/libstd/sys/vxworks/io.rs
+++ b/src/libstd/sys/vxworks/io.rs
@@ -22,6 +22,18 @@ impl<'a> IoSlice<'a> {
     }
 
     #[inline]
+    pub fn advance(&mut self, n: usize) {
+        if self.vec.iov_len < n {
+            panic!("advancing IoSlice beyond its length");
+        }
+
+        unsafe {
+            self.vec.iov_len -= n;
+            self.vec.iov_base = self.vec.iov_base.add(n);
+        }
+    }
+
+    #[inline]
     pub fn as_slice(&self) -> &[u8] {
         unsafe {
             slice::from_raw_parts(self.vec.iov_base as *mut u8, self.vec.iov_len)
@@ -47,6 +59,18 @@ impl<'a> IoSliceMut<'a> {
     }
 
     #[inline]
+    pub fn advance(&mut self, n: usize) {
+        if self.vec.iov_len < n {
+            panic!("advancing IoSliceMut beyond its length");
+        }
+
+        unsafe {
+            self.vec.iov_len -= n;
+            self.vec.iov_base = self.vec.iov_base.add(n);
+        }
+    }
+
+    #[inline]
     pub fn as_slice(&self) -> &[u8] {
         unsafe {
             slice::from_raw_parts(self.vec.iov_base as *mut u8, self.vec.iov_len)
diff --git a/src/libstd/sys/wasi/io.rs b/src/libstd/sys/wasi/io.rs
index a5bddad708b..ffecca5d1b6 100644
--- a/src/libstd/sys/wasi/io.rs
+++ b/src/libstd/sys/wasi/io.rs
@@ -22,6 +22,18 @@ impl<'a> IoSlice<'a> {
     }
 
     #[inline]
+    pub fn advance(&mut self, n: usize) {
+        if self.vec.buf_len < n {
+            panic!("advancing IoSlice beyond its length");
+        }
+
+        unsafe {
+            self.vec.buf_len -= n;
+            self.vec.buf = self.vec.buf.add(n);
+        }
+    }
+
+    #[inline]
     pub fn as_slice(&self) -> &[u8] {
         unsafe {
             slice::from_raw_parts(self.vec.buf as *const u8, self.vec.buf_len)
@@ -48,6 +60,18 @@ impl<'a> IoSliceMut<'a> {
     }
 
     #[inline]
+    pub fn advance(&mut self, n: usize) {
+        if self.vec.buf_len < n {
+            panic!("advancing IoSlice beyond its length");
+        }
+
+        unsafe {
+            self.vec.buf_len -= n;
+            self.vec.buf = self.vec.buf.add(n);
+        }
+    }
+
+    #[inline]
     pub fn as_slice(&self) -> &[u8] {
         unsafe {
             slice::from_raw_parts(self.vec.buf as *const u8, self.vec.buf_len)
diff --git a/src/libstd/sys/wasm/io.rs b/src/libstd/sys/wasm/io.rs
index 4b423a5cbc1..976e122463d 100644
--- a/src/libstd/sys/wasm/io.rs
+++ b/src/libstd/sys/wasm/io.rs
@@ -1,3 +1,5 @@
+use crate::mem;
+
 pub struct IoSlice<'a>(&'a [u8]);
 
 impl<'a> IoSlice<'a> {
@@ -7,6 +9,11 @@ impl<'a> IoSlice<'a> {
     }
 
     #[inline]
+    pub fn advance(&mut self, n: usize) {
+        self.0 = &self.0[n..]
+    }
+
+    #[inline]
     pub fn as_slice(&self) -> &[u8] {
         self.0
     }
@@ -21,6 +28,13 @@ impl<'a> IoSliceMut<'a> {
     }
 
     #[inline]
+    pub fn advance(&mut self, n: usize) {
+        let slice = mem::replace(&mut self.0, &mut []);
+        let (_, remaining) = slice.split_at_mut(n);
+        self.0 = remaining;
+    }
+
+    #[inline]
     pub fn as_slice(&self) -> &[u8] {
         self.0
     }
diff --git a/src/libstd/sys/windows/io.rs b/src/libstd/sys/windows/io.rs
index f0da2323f4f..e44dcbe164d 100644
--- a/src/libstd/sys/windows/io.rs
+++ b/src/libstd/sys/windows/io.rs
@@ -22,6 +22,18 @@ impl<'a> IoSlice<'a> {
     }
 
     #[inline]
+    pub fn advance(&mut self, n: usize) {
+        if (self.vec.len as usize) < n {
+            panic!("advancing IoSlice beyond its length");
+        }
+
+        unsafe {
+            self.vec.len -= n as c::ULONG;
+            self.vec.buf = self.vec.buf.add(n);
+        }
+    }
+
+    #[inline]
     pub fn as_slice(&self) -> &[u8] {
         unsafe {
             slice::from_raw_parts(self.vec.buf as *mut u8, self.vec.len as usize)
@@ -49,6 +61,18 @@ impl<'a> IoSliceMut<'a> {
     }
 
     #[inline]
+    pub fn advance(&mut self, n: usize) {
+        if (self.vec.len as usize) < n {
+            panic!("advancing IoSliceMut beyond its length");
+        }
+
+        unsafe {
+            self.vec.len -= n as c::ULONG;
+            self.vec.buf = self.vec.buf.add(n);
+        }
+    }
+
+    #[inline]
     pub fn as_slice(&self) -> &[u8] {
         unsafe {
             slice::from_raw_parts(self.vec.buf as *mut u8, self.vec.len as usize)