Merging upstream version 1.75.0+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 74 insertions, 0 deletions

diff --git a/library/std/src/io/copy.rs b/library/std/src/io/copy.rs
index eafd078a7..4d51a719f 100644
--- a/library/std/src/io/copy.rs
+++ b/library/std/src/io/copy.rs
@@ -1,5 +1,7 @@
 use super::{BorrowedBuf, BufReader, BufWriter, Read, Result, Write, DEFAULT_BUF_SIZE};
 use crate::alloc::Allocator;
+use crate::cmp;
+use crate::cmp::min;
 use crate::collections::VecDeque;
 use crate::io::IoSlice;
 use crate::mem::MaybeUninit;
@@ -254,6 +256,78 @@ impl<I: Write + ?Sized> BufferedWriterSpec for BufWriter<I> {
     }
 }
 
+impl<A: Allocator> BufferedWriterSpec for Vec<u8, A> {
+    fn buffer_size(&self) -> usize {
+        cmp::max(DEFAULT_BUF_SIZE, self.capacity() - self.len())
+    }
+
+    fn copy_from<R: Read + ?Sized>(&mut self, reader: &mut R) -> Result<u64> {
+        let mut bytes = 0;
+
+        // avoid inflating empty/small vecs before we have determined that there's anything to read
+        if self.capacity() < DEFAULT_BUF_SIZE {
+            let stack_read_limit = DEFAULT_BUF_SIZE as u64;
+            bytes = stack_buffer_copy(&mut reader.take(stack_read_limit), self)?;
+            // fewer bytes than requested -> EOF reached
+            if bytes < stack_read_limit {
+                return Ok(bytes);
+            }
+        }
+
+        // don't immediately offer the vec's whole spare capacity, otherwise
+        // we might have to fully initialize it if the reader doesn't have a custom read_buf() impl
+        let mut max_read_size = DEFAULT_BUF_SIZE;
+
+        loop {
+            self.reserve(DEFAULT_BUF_SIZE);
+            let mut initialized_spare_capacity = 0;
+
+            loop {
+                let buf = self.spare_capacity_mut();
+                let read_size = min(max_read_size, buf.len());
+                let mut buf = BorrowedBuf::from(&mut buf[..read_size]);
+                // SAFETY: init is either 0 or the init_len from the previous iteration.
+                unsafe {
+                    buf.set_init(initialized_spare_capacity);
+                }
+                match reader.read_buf(buf.unfilled()) {
+                    Ok(()) => {
+                        let bytes_read = buf.len();
+
+                        // EOF
+                        if bytes_read == 0 {
+                            return Ok(bytes);
+                        }
+
+                        // the reader is returning short reads but it doesn't call ensure_init()
+                        if buf.init_len() < buf.capacity() {
+                            max_read_size = usize::MAX;
+                        }
+                        // the reader hasn't returned short reads so far
+                        if bytes_read == buf.capacity() {
+                            max_read_size *= 2;
+                        }
+
+                        initialized_spare_capacity = buf.init_len() - bytes_read;
+                        bytes += bytes_read as u64;
+                        // SAFETY: BorrowedBuf guarantees all of its filled bytes are init
+                        // and the number of read bytes can't exceed the spare capacity since
+                        // that's what the buffer is borrowing from.
+                        unsafe { self.set_len(self.len() + bytes_read) };
+
+                        // spare capacity full, reserve more
+                        if self.len() == self.capacity() {
+                            break;
+                        }
+                    }
+                    Err(e) if e.is_interrupted() => continue,
+                    Err(e) => return Err(e),
+                }
+            }
+        }
+    }
+}
+
 fn stack_buffer_copy<R: Read + ?Sized, W: Write + ?Sized>(
     reader: &mut R,
     writer: &mut W,