removes raw indexing from streamer (#19183)

Raw indexing is verbose and error-prone. This same code had an indexing
bug causing validator nodes panic just a few months ago:
https://github.com/solana-labs/solana/commit/482b8c6be

streamer/src/sendmmsg.rs

@@ -1,5 +1,12 @@
 //! The `sendmmsg` module provides sendmmsg() API implementation
 
+#[cfg(target_os = "linux")]
+use {
+    itertools::izip,
+    libc::{iovec, mmsghdr, sockaddr_in, sockaddr_in6, sockaddr_storage},
+    nix::sys::socket::InetAddr,
+    std::os::unix::io::AsRawFd,
+};
 use {
     std::{
         borrow::Borrow,
@@ -41,78 +48,50 @@ where
     }
 }
 
-#[cfg(target_os = "linux")]
-use libc::{iovec, mmsghdr, sockaddr_in, sockaddr_in6, sockaddr_storage};
-
 #[cfg(target_os = "linux")]
 fn mmsghdr_for_packet(
     packet: &[u8],
     dest: &SocketAddr,
-    iovs: &mut Vec<iovec>,
-    addrs: &mut Vec<sockaddr_storage>,
-    hdrs: &mut Vec<mmsghdr>,
+    iov: &mut iovec,
+    addr: &mut sockaddr_storage,
+    hdr: &mut mmsghdr,
 ) {
-    use libc::c_void;
-    use nix::sys::socket::InetAddr;
-    use std::mem;
+    const SIZE_OF_SOCKADDR_IN: usize = std::mem::size_of::<sockaddr_in>();
+    const SIZE_OF_SOCKADDR_IN6: usize = std::mem::size_of::<sockaddr_in6>();
 
-    const SIZE_OF_SOCKADDR_IN: usize = mem::size_of::<sockaddr_in>();
-    const SIZE_OF_SOCKADDR_IN6: usize = mem::size_of::<sockaddr_in6>();
-
-    let index = hdrs.len();
-
-    debug_assert!(index < hdrs.capacity());
-    debug_assert!(index < addrs.capacity());
-    debug_assert!(index < iovs.capacity());
-    debug_assert_eq!(hdrs.len(), addrs.len());
-    debug_assert_eq!(hdrs.len(), iovs.len());
-
-    iovs.push(iovec {
-        iov_base: packet.as_ptr() as *mut c_void,
+    *iov = iovec {
+        iov_base: packet.as_ptr() as *mut libc::c_void,
         iov_len: packet.len(),
-    });
-
-    let hdr: mmsghdr = unsafe { mem::zeroed() };
-    hdrs.push(hdr);
-
-    let addr_storage: sockaddr_storage = unsafe { mem::zeroed() };
-    addrs.push(addr_storage);
-
-    debug_assert!(index < hdrs.len());
-
-    hdrs[index].msg_hdr.msg_iov = &mut iovs[index];
-    hdrs[index].msg_hdr.msg_iovlen = 1;
+    };
+    hdr.msg_hdr.msg_iov = iov;
+    hdr.msg_hdr.msg_iovlen = 1;
+    hdr.msg_hdr.msg_name = addr as *mut _ as *mut _;
 
     match InetAddr::from_std(dest) {
-        InetAddr::V4(addr) => {
+        InetAddr::V4(dest) => {
             unsafe {
-                core::ptr::write(&mut addrs[index] as *mut _ as *mut _, addr);
+                std::ptr::write(addr as *mut _ as *mut _, dest);
             }
-            hdrs[index].msg_hdr.msg_name = &mut addrs[index] as *mut _ as *mut _;
-            hdrs[index].msg_hdr.msg_namelen = SIZE_OF_SOCKADDR_IN as u32;
+            hdr.msg_hdr.msg_namelen = SIZE_OF_SOCKADDR_IN as u32;
         }
-        InetAddr::V6(addr) => {
+        InetAddr::V6(dest) => {
             unsafe {
-                core::ptr::write(&mut addrs[index] as *mut _ as *mut _, addr);
+                std::ptr::write(addr as *mut _ as *mut _, dest);
             }
-            hdrs[index].msg_hdr.msg_name = &mut addrs[index] as *mut _ as *mut _;
-            hdrs[index].msg_hdr.msg_namelen = SIZE_OF_SOCKADDR_IN6 as u32;
+            hdr.msg_hdr.msg_namelen = SIZE_OF_SOCKADDR_IN6 as u32;
         }
     };
 }
 
 #[cfg(target_os = "linux")]
 fn sendmmsg_retry(sock: &UdpSocket, hdrs: &mut Vec<mmsghdr>) -> Result<(), SendPktsError> {
-    use libc::sendmmsg;
-    use std::os::unix::io::AsRawFd;
-
     let sock_fd = sock.as_raw_fd();
     let mut total_sent = 0;
     let mut erropt = None;
 
     let mut pkts = &mut hdrs[..];
     while !pkts.is_empty() {
-        let npkts = match unsafe { sendmmsg(sock_fd, &mut pkts[0], pkts.len() as u32, 0) } {
+        let npkts = match unsafe { libc::sendmmsg(sock_fd, &mut pkts[0], pkts.len() as u32, 0) } {
             -1 => {
                 if erropt.is_none() {
                     erropt = Some(io::Error::last_os_error());
@@ -143,22 +122,14 @@ where
     S: Borrow<SocketAddr>,
     T: AsRef<[u8]>,
 {
-    // The vectors are allocated with capacity, as later code inserts elements
-    // at specific indices, and uses the address of the vector index in hdrs
-    let mut iovs: Vec<iovec> = Vec::with_capacity(packets.len());
-    let mut addrs: Vec<sockaddr_storage> = Vec::with_capacity(packets.len());
-    let mut hdrs: Vec<mmsghdr> = Vec::with_capacity(packets.len());
-
-    for (pkt, dest) in packets.iter() {
-        mmsghdr_for_packet(
-            pkt.as_ref(),
-            dest.borrow(),
-            &mut iovs,
-            &mut addrs,
-            &mut hdrs,
-        );
+    let size = packets.len();
+    #[allow(clippy::uninit_assumed_init)]
+    let mut iovs = vec![unsafe { std::mem::MaybeUninit::uninit().assume_init() }; size];
+    let mut addrs = vec![unsafe { std::mem::zeroed() }; size];
+    let mut hdrs = vec![unsafe { std::mem::zeroed() }; size];
+    for ((pkt, dest), hdr, iov, addr) in izip!(packets, &mut hdrs, &mut iovs, &mut addrs) {
+        mmsghdr_for_packet(pkt.as_ref(), dest.borrow(), iov, addr, hdr);
     }
-
     sendmmsg_retry(sock, &mut hdrs)
 }