refactor(http1): use MaybeUninit for parsing with uninitialized headers (#2545)

Closes #2532

src/proto/h1/role.rs

@@ -1,9 +1,5 @@
-// `mem::uninitialized` replaced with `mem::MaybeUninit`,
-// can't upgrade yet
-#![allow(deprecated)]
-
 use std::fmt::{self, Write};
-use std::mem;
+use std::mem::{self, MaybeUninit};
 
 #[cfg(any(test, feature = "server", feature = "ffi"))]
 use bytes::Bytes;
@@ -115,17 +111,23 @@ impl Http1Transaction for Server {
         // but we *never* read any of it until after httparse has assigned
         // values into it. By not zeroing out the stack memory, this saves
         // a good ~5% on pipeline benchmarks.
-        let mut headers_indices: [HeaderIndices; MAX_HEADERS] = unsafe { mem::uninitialized() };
+        let mut headers_indices: [MaybeUninit<HeaderIndices>; MAX_HEADERS] = unsafe {
+            // SAFETY: We can go safely from MaybeUninit array to array of MaybeUninit
+            MaybeUninit::uninit().assume_init()
+        };
         {
-            let mut headers: [httparse::Header<'_>; MAX_HEADERS] = unsafe { mem::uninitialized() };
+            /* SAFETY: it is safe to go from MaybeUninit array to array of MaybeUninit */
+            let mut headers: [MaybeUninit<httparse::Header<'_>>; MAX_HEADERS] = unsafe {
+                MaybeUninit::uninit().assume_init()
+            };
             trace!(
                 "Request.parse([Header; {}], [u8; {}])",
                 headers.len(),
                 buf.len()
             );
-            let mut req = httparse::Request::new(&mut headers);
+            let mut req = httparse::Request::new(&mut []);
             let bytes = buf.as_ref();
-            match req.parse(bytes) {
+            match req.parse_with_uninit_headers(bytes, &mut headers) {
                 Ok(httparse::Status::Complete(parsed_len)) => {
                     trace!("Request.parse Complete({})", parsed_len);
                     len = parsed_len;
@@ -194,6 +196,8 @@ impl Http1Transaction for Server {
         headers.reserve(headers_len);
 
         for header in &headers_indices[..headers_len] {
+            // SAFETY: array is valid up to `headers_len`
+            let header = unsafe { &*header.as_ptr() };
             let name = header_name!(&slice[header.name.0..header.name.1]);
             let value = header_value!(slice.slice(header.value.0..header.value.1));
 
@@ -867,18 +871,24 @@ impl Http1Transaction for Client {
         // Loop to skip information status code headers (100 Continue, etc).
         loop {
             // Unsafe: see comment in Server Http1Transaction, above.
-            let mut headers_indices: [HeaderIndices; MAX_HEADERS] = unsafe { mem::uninitialized() };
+            let mut headers_indices: [MaybeUninit<HeaderIndices>; MAX_HEADERS] = unsafe {
+                // SAFETY: We can go safely from MaybeUninit array to array of MaybeUninit
+                MaybeUninit::uninit().assume_init()
+            };
             let (len, status, reason, version, headers_len) = {
-                let mut headers: [httparse::Header<'_>; MAX_HEADERS] =
+                // SAFETY: We can go safely from MaybeUninit array to array of MaybeUninit
-                    unsafe { mem::uninitialized() };
+                let mut headers: [MaybeUninit<httparse::Header<'_>>; MAX_HEADERS] =
+                    unsafe { MaybeUninit::uninit().assume_init() };
                 trace!(
                     "Response.parse([Header; {}], [u8; {}])",
                     headers.len(),
                     buf.len()
                 );
-                let mut res = httparse::Response::new(&mut headers);
+                let mut res = httparse::Response::new(&mut []);
                 let bytes = buf.as_ref();
-                match ctx.h1_parser_config.parse_response(&mut res, bytes) {
+                match ctx.h1_parser_config
+                    .parse_response_with_uninit_headers(&mut res, bytes, &mut headers)
+                {
                     Ok(httparse::Status::Complete(len)) => {
                         trace!("Response.parse Complete({})", len);
                         let status = StatusCode::from_u16(res.code.unwrap())?;
@@ -934,6 +944,8 @@ impl Http1Transaction for Client {
 
             headers.reserve(headers_len);
             for header in &headers_indices[..headers_len] {
+                // SAFETY: array is valid up to `headers_len`
+                let header = unsafe { &*header.as_ptr() };
                 let name = header_name!(&slice[header.name.0..header.name.1]);
                 let value = header_value!(slice.slice(header.value.0..header.value.1));
 
@@ -1288,7 +1300,7 @@ struct HeaderIndices {
 fn record_header_indices(
     bytes: &[u8],
     headers: &[httparse::Header<'_>],
-    indices: &mut [HeaderIndices],
+    indices: &mut [MaybeUninit<HeaderIndices>],
 ) -> Result<(), crate::error::Parse> {
     let bytes_ptr = bytes.as_ptr() as usize;
 
@@ -1299,10 +1311,19 @@ fn record_header_indices(
         }
         let name_start = header.name.as_ptr() as usize - bytes_ptr;
         let name_end = name_start + header.name.len();
-        indices.name = (name_start, name_end);
         let value_start = header.value.as_ptr() as usize - bytes_ptr;
         let value_end = value_start + header.value.len();
-        indices.value = (value_start, value_end);
+
+        // FIXME(maybe_uninit_extra)
+        // FIXME(addr_of)
+        // Currently we don't have `ptr::addr_of_mut` in stable rust or
+        // MaybeUninit::write, so this is some way of assigning into a MaybeUninit
+        // safely
+        let new_header_indices = HeaderIndices {
+            name: (name_start, name_end),
+            value: (value_start, value_end),
+        };
+        *indices = MaybeUninit::new(new_header_indices);
     }
 
     Ok(())