From c3e1276229b9b29b0f830193707aba9b4e551acd Mon Sep 17 00:00:00 2001
From: "Jeong, YunWon" <69878+youknowone@users.noreply.github.com>
Date: Tue, 13 Oct 2026 10:33:55 +0900
Subject: [PATCH] Release unused capacity after more short reads (#9089)

Call shrink_to_fit on the result buffer in os.pread, os.getrandom,
WindowsConsoleIO.read, _winapi.PeekNamedPipe, _winapi.ReadFile,
_multiprocessing.recv and the openssl MemoryBIO.read.

Assisted-by: Claude:claude-opus-5-5
Assisted-by: Grok:grok-4.7
---
 crates/stdlib/src/multiprocessing.rs | 7 +++++--
 crates/stdlib/src/openssl.rs         | 1 +
 crates/vm/src/stdlib/_io.rs          | 1 +
 crates/vm/src/stdlib/_winapi.rs      | 6 ++++--
 crates/vm/src/stdlib/posix.rs        | 2 ++
 5 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/crates/stdlib/src/multiprocessing.rs b/crates/stdlib/src/multiprocessing.rs
index 5c3356495..c992f90f7 100644
--- a/crates/stdlib/src/multiprocessing.rs
+++ b/crates/stdlib/src/multiprocessing.rs
@@ -408,8 +408,11 @@ mod _multiprocessing {
 
     #[pyfunction]
     fn recv(socket: usize, size: usize, vm: &VirtualMachine) -> PyResult<Vec<u8>> {
-        host_multiprocessing::recv_socket(socket as host_multiprocessing::RawSocket, size)
-            .map_err(|_| vm.new_last_os_error())
+        let mut buf =
+            host_multiprocessing::recv_socket(socket as host_multiprocessing::RawSocket, size)
+                .map_err(|_| vm.new_last_os_error())?;
+        buf.shrink_to_fit();
+        Ok(buf)
     }
 
     #[pyfunction]
diff --git a/crates/stdlib/src/openssl.rs b/crates/stdlib/src/openssl.rs
index 5470f7884..bba64f702 100644
--- a/crates/stdlib/src/openssl.rs
+++ b/crates/stdlib/src/openssl.rs
@@ -3706,6 +3706,7 @@ mod _ssl {
                 }
 
                 buf.truncate(nbytes as usize);
+                buf.shrink_to_fit();
                 Ok(buf)
             }
         }
diff --git a/crates/vm/src/stdlib/_io.rs b/crates/vm/src/stdlib/_io.rs
index 9bf3b3cfb..6c1fa064a 100644
--- a/crates/vm/src/stdlib/_io.rs
+++ b/crates/vm/src/stdlib/_io.rs
@@ -6949,6 +6949,7 @@ mod winconsoleio {
             }
 
             buf.truncate(read_len);
+            buf.shrink_to_fit();
             Ok(vm.ctx.new_bytes(buf).into())
         }
 
diff --git a/crates/vm/src/stdlib/_winapi.rs b/crates/vm/src/stdlib/_winapi.rs
index c47ea6823..6f495299a 100644
--- a/crates/vm/src/stdlib/_winapi.rs
+++ b/crates/vm/src/stdlib/_winapi.rs
@@ -768,7 +768,8 @@ mod _winapi {
         if size > 0 {
             let result = host_winapi::peek_named_pipe(handle.0, Some(size as u32))
                 .map_err(|e| e.to_pyexception(vm))?;
-            let buf = result.data.unwrap_or_default();
+            let mut buf = result.data.unwrap_or_default();
+            buf.shrink_to_fit();
             let bytes: PyObjectRef = vm.ctx.new_bytes(buf).into();
             Ok(vm
                 .ctx
@@ -886,9 +887,10 @@ mod _winapi {
             return Ok(result.into());
         }
 
-        let result = vm
+        let mut result = vm
             .allow_threads(|| host_winapi::read_file(handle.0, size))
             .map_err(|e| e.to_pyexception(vm))?;
+        result.data.shrink_to_fit();
         Ok(vm
             .ctx
             .new_tuple(vec![
diff --git a/crates/vm/src/stdlib/posix.rs b/crates/vm/src/stdlib/posix.rs
index 388771acb..26371c87e 100644
--- a/crates/vm/src/stdlib/posix.rs
+++ b/crates/vm/src/stdlib/posix.rs
@@ -1214,6 +1214,7 @@ pub mod module {
             match vm.allow_threads(|| rustpython_host_env::posix::pread(fd, &mut buffer, offset)) {
                 Ok(n) => {
                     buffer.truncate(n);
+                    buffer.shrink_to_fit();
                     return Ok(vm.ctx.new_bytes(buffer));
                 }
                 Err(err) if err.raw_os_error() == Some(libc::EINTR) => {
@@ -2976,6 +2977,7 @@ pub mod module {
             .map_err(|_| vm.new_last_os_error())?;
             buf.set_len(len);
         }
+        buf.shrink_to_fit();
         Ok(buf)
     }