Auto merge of rust-lang#3609 - tiif:feat/socketpair, r=RalfJung

Add socketpair shim

Fixes rust-lang#3442
Design proposal: https://hackmd.io/`@tiif/Skhc1t0-C`

src/tools/miri/src/shims/unix/socket.rs

@@ -1,15 +1,38 @@
+use std::cell::RefCell;
+use std::collections::VecDeque;
 use std::io;
+use std::io::{Error, ErrorKind, Read};
+use std::rc::{Rc, Weak};
 
 use crate::shims::unix::*;
-use crate::*;
+use crate::{concurrency::VClock, *};
 
 use self::fd::FileDescriptor;
 
+/// The maximum capacity of the socketpair buffer in bytes.
+/// This number is arbitrary as the value can always
+/// be configured in the real system.
+const MAX_SOCKETPAIR_BUFFER_CAPACITY: usize = 212992;
+
 /// Pair of connected sockets.
-///
-/// We currently don't allow sending any data through this pair, so this can be just a dummy.
 #[derive(Debug)]
-struct SocketPair;
+struct SocketPair {
+    // By making the write link weak, a `write` can detect when all readers are
+    // gone, and trigger EPIPE as appropriate.
+    writebuf: Weak<RefCell<Buffer>>,
+    readbuf: Rc<RefCell<Buffer>>,
+    is_nonblock: bool,
+}
+
+#[derive(Debug)]
+struct Buffer {
+    buf: VecDeque<u8>,
+    clock: VClock,
+    /// Indicates if there is at least one active writer to this buffer.
+    /// If all writers of this buffer are dropped, buf_has_writer becomes false and we
+    /// indicate EOF instead of blocking.
+    buf_has_writer: bool,
+}
 
 impl FileDescription for SocketPair {
     fn name(&self) -> &'static str {
@@ -20,17 +43,102 @@ impl FileDescription for SocketPair {
         self: Box<Self>,
         _communicate_allowed: bool,
     ) -> InterpResult<'tcx, io::Result<()>> {
+        // This is used to signal socketfd of other side that there is no writer to its readbuf.
+        // If the upgrade fails, there is no need to update as all read ends have been dropped.
+        if let Some(writebuf) = self.writebuf.upgrade() {
+            writebuf.borrow_mut().buf_has_writer = false;
+        };
         Ok(Ok(()))
     }
+
+    fn read<'tcx>(
+        &mut self,
+        _communicate_allowed: bool,
+        bytes: &mut [u8],
+        ecx: &mut MiriInterpCx<'tcx>,
+    ) -> InterpResult<'tcx, io::Result<usize>> {
+        let request_byte_size = bytes.len();
+        let mut readbuf = self.readbuf.borrow_mut();
+
+        // Always succeed on read size 0.
+        if request_byte_size == 0 {
+            return Ok(Ok(0));
+        }
+
+        if readbuf.buf.is_empty() {
+            if !readbuf.buf_has_writer {
+                // Socketpair with no writer and empty buffer.
+                // 0 bytes successfully read indicates end-of-file.
+                return Ok(Ok(0));
+            } else {
+                if self.is_nonblock {
+                    // Non-blocking socketpair with writer and empty buffer.
+                    // https://linux.die.net/man/2/read
+                    // EAGAIN or EWOULDBLOCK can be returned for socket,
+                    // POSIX.1-2001 allows either error to be returned for this case.
+                    // Since there is no ErrorKind for EAGAIN, WouldBlock is used.
+                    return Ok(Err(Error::from(ErrorKind::WouldBlock)));
+                } else {
+                    // Blocking socketpair with writer and empty buffer.
+                    // FIXME: blocking is currently not supported
+                    throw_unsup_format!("socketpair read: blocking isn't supported yet");
+                }
+            }
+        }
+
+        // Synchronize with all previous writes to this buffer.
+        // FIXME: this over-synchronizes; a more precise approach would be to
+        // only sync with the writes whose data we will read.
+        ecx.acquire_clock(&readbuf.clock);
+        // Do full read / partial read based on the space available.
+        // Conveniently, `read` exists on `VecDeque` and has exactly the desired behavior.
+        let actual_read_size = readbuf.buf.read(bytes).unwrap();
+        return Ok(Ok(actual_read_size));
+    }
+
+    fn write<'tcx>(
+        &mut self,
+        _communicate_allowed: bool,
+        bytes: &[u8],
+        ecx: &mut MiriInterpCx<'tcx>,
+    ) -> InterpResult<'tcx, io::Result<usize>> {
+        let write_size = bytes.len();
+        // Always succeed on write size 0.
+        // ("If count is zero and fd refers to a file other than a regular file, the results are not specified.")
+        if write_size == 0 {
+            return Ok(Ok(0));
+        }
+
+        let Some(writebuf) = self.writebuf.upgrade() else {
+            // If the upgrade from Weak to Rc fails, it indicates that all read ends have been
+            // closed.
+            return Ok(Err(Error::from(ErrorKind::BrokenPipe)));
+        };
+        let mut writebuf = writebuf.borrow_mut();
+        let data_size = writebuf.buf.len();
+        let available_space = MAX_SOCKETPAIR_BUFFER_CAPACITY.checked_sub(data_size).unwrap();
+        if available_space == 0 {
+            if self.is_nonblock {
+                // Non-blocking socketpair with a full buffer.
+                return Ok(Err(Error::from(ErrorKind::WouldBlock)));
+            } else {
+                // Blocking socketpair with a full buffer.
+                throw_unsup_format!("socketpair write: blocking isn't supported yet");
+            }
+        }
+        // Remember this clock so `read` can synchronize with us.
+        if let Some(clock) = &ecx.release_clock() {
+            writebuf.clock.join(clock);
+        }
+        // Do full write / partial write based on the space available.
+        let actual_write_size = write_size.min(available_space);
+        writebuf.buf.extend(&bytes[..actual_write_size]);
+        return Ok(Ok(actual_write_size));
+    }
 }
 
 impl<'tcx> EvalContextExt<'tcx> for crate::MiriInterpCx<'tcx> {}
 pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
-    /// Currently this function this function is a stub. Eventually we need to
-    /// properly implement an FD type for sockets and have this function create
-    /// two sockets and associated FDs such that writing to one will produce
-    /// data that can be read from the other.
-    ///
     /// For more information on the arguments see the socketpair manpage:
     /// <https://linux.die.net/man/2/socketpair>
     fn socketpair(
@@ -42,17 +150,80 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
     ) -> InterpResult<'tcx, Scalar> {
         let this = self.eval_context_mut();
 
-        let _domain = this.read_scalar(domain)?.to_i32()?;
-        let _type_ = this.read_scalar(type_)?.to_i32()?;
-        let _protocol = this.read_scalar(protocol)?.to_i32()?;
+        let domain = this.read_scalar(domain)?.to_i32()?;
+        let mut type_ = this.read_scalar(type_)?.to_i32()?;
+        let protocol = this.read_scalar(protocol)?.to_i32()?;
         let sv = this.deref_pointer(sv)?;
 
-        // FIXME: fail on unsupported inputs
+        let mut is_sock_nonblock = false;
+
+        // Parse and remove the type flags that we support. If type != 0 after removing,
+        // unsupported flags are used.
+        if type_ & this.eval_libc_i32("SOCK_STREAM") == this.eval_libc_i32("SOCK_STREAM") {
+            type_ &= !(this.eval_libc_i32("SOCK_STREAM"));
+        }
+
+        // SOCK_NONBLOCK only exists on Linux.
+        if this.tcx.sess.target.os == "linux" {
+            if type_ & this.eval_libc_i32("SOCK_NONBLOCK") == this.eval_libc_i32("SOCK_NONBLOCK") {
+                is_sock_nonblock = true;
+                type_ &= !(this.eval_libc_i32("SOCK_NONBLOCK"));
+            }
+            if type_ & this.eval_libc_i32("SOCK_CLOEXEC") == this.eval_libc_i32("SOCK_CLOEXEC") {
+                type_ &= !(this.eval_libc_i32("SOCK_CLOEXEC"));
+            }
+        }
+
+        // Fail on unsupported input.
+        // AF_UNIX and AF_LOCAL are synonyms, so we accept both in case
+        // their values differ.
+        if domain != this.eval_libc_i32("AF_UNIX") && domain != this.eval_libc_i32("AF_LOCAL") {
+            throw_unsup_format!(
+                "socketpair: Unsupported domain {:#x} is used, only AF_UNIX \
+                                 and AF_LOCAL are allowed",
+                domain
+            );
+        } else if type_ != 0 {
+            throw_unsup_format!(
+                "socketpair: Unsupported type {:#x} is used, only SOCK_STREAM, \
+                                 SOCK_CLOEXEC and SOCK_NONBLOCK are allowed",
+                type_
+            );
+        } else if protocol != 0 {
+            throw_unsup_format!(
+                "socketpair: Unsupported socket protocol {protocol} is used, \
+                                 only 0 is allowed",
+            );
+        }
+
+        let buffer1 = Rc::new(RefCell::new(Buffer {
+            buf: VecDeque::new(),
+            clock: VClock::default(),
+            buf_has_writer: true,
+        }));
+
+        let buffer2 = Rc::new(RefCell::new(Buffer {
+            buf: VecDeque::new(),
+            clock: VClock::default(),
+            buf_has_writer: true,
+        }));
+
+        let socketpair_0 = SocketPair {
+            writebuf: Rc::downgrade(&buffer1),
+            readbuf: Rc::clone(&buffer2),
+            is_nonblock: is_sock_nonblock,
+        };
+
+        let socketpair_1 = SocketPair {
+            writebuf: Rc::downgrade(&buffer2),
+            readbuf: Rc::clone(&buffer1),
+            is_nonblock: is_sock_nonblock,
+        };
 
         let fds = &mut this.machine.fds;
-        let sv0 = fds.insert_fd(FileDescriptor::new(SocketPair));
+        let sv0 = fds.insert_fd(FileDescriptor::new(socketpair_0));
         let sv0 = Scalar::try_from_int(sv0, sv.layout.size).unwrap();
-        let sv1 = fds.insert_fd(FileDescriptor::new(SocketPair));
+        let sv1 = fds.insert_fd(FileDescriptor::new(socketpair_1));
         let sv1 = Scalar::try_from_int(sv1, sv.layout.size).unwrap();
 
         this.write_scalar(sv0, &sv)?;

src/tools/miri/tests/fail-dep/libc/socketpair_read_blocking.rs

@@ -0,0 +1,12 @@
+//@ignore-target-windows: no libc socketpair on Windows
+
+// This is temporarily here because blocking on fd is not supported yet.
+// When blocking is eventually supported, this will be moved to pass-dep/libc/libc-socketpair
+
+fn main() {
+    let mut fds = [-1, -1];
+    let _ = unsafe { libc::socketpair(libc::AF_UNIX, libc::SOCK_STREAM, 0, fds.as_mut_ptr()) };
+    // The read below will be blocked because the buffer is empty.
+    let mut buf: [u8; 3] = [0; 3];
+    let _res = unsafe { libc::read(fds[1], buf.as_mut_ptr().cast(), buf.len() as libc::size_t) }; //~ERROR: blocking isn't supported
+}

src/tools/miri/tests/fail-dep/libc/socketpair_read_blocking.stderr

@@ -0,0 +1,14 @@
+error: unsupported operation: socketpair read: blocking isn't supported yet
+  --> $DIR/socketpair_read_blocking.rs:LL:CC
+   |
+LL |     let _res = unsafe { libc::read(fds[1], buf.as_mut_ptr().cast(), buf.len() as libc::size_t) };
+   |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ socketpair read: blocking isn't supported yet
+   |
+   = help: this is likely not a bug in the program; it indicates that the program performed an operation that Miri does not support
+   = note: BACKTRACE:
+   = note: inside `main` at $DIR/socketpair_read_blocking.rs:LL:CC
+
+note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
+
+error: aborting due to 1 previous error
+

src/tools/miri/tests/fail-dep/libc/socketpair_write_blocking.rs

@@ -0,0 +1,16 @@
+//@ignore-target-windows: no libc socketpair on Windows
+// This is temporarily here because blocking on fd is not supported yet.
+// When blocking is eventually supported, this will be moved to pass-dep/libc/libc-socketpair
+fn main() {
+    let mut fds = [-1, -1];
+    let _ = unsafe { libc::socketpair(libc::AF_UNIX, libc::SOCK_STREAM, 0, fds.as_mut_ptr()) };
+    // Write size > buffer capacity
+    // Used up all the space in the buffer.
+    let arr1: [u8; 212992] = [1; 212992];
+    let _ = unsafe { libc::write(fds[0], arr1.as_ptr() as *const libc::c_void, 212992) };
+    let data = "abc".as_bytes().as_ptr();
+    // The write below will be blocked as the buffer is full.
+    let _ = unsafe { libc::write(fds[0], data as *const libc::c_void, 3) }; //~ERROR: blocking isn't supported
+    let mut buf: [u8; 3] = [0; 3];
+    let _res = unsafe { libc::read(fds[1], buf.as_mut_ptr().cast(), buf.len() as libc::size_t) };
+}

src/tools/miri/tests/fail-dep/libc/socketpair_write_blocking.stderr

@@ -0,0 +1,14 @@
+error: unsupported operation: socketpair write: blocking isn't supported yet
+  --> $DIR/socketpair_write_blocking.rs:LL:CC
+   |
+LL |     let _ = unsafe { libc::write(fds[0], data as *const libc::c_void, 3) };
+   |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ socketpair write: blocking isn't supported yet
+   |
+   = help: this is likely not a bug in the program; it indicates that the program performed an operation that Miri does not support
+   = note: BACKTRACE:
+   = note: inside `main` at $DIR/socketpair_write_blocking.rs:LL:CC
+
+note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
+
+error: aborting due to 1 previous error
+