bring socket logic back together and fix logic bug

Author: RalfJung

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

@@ -96,26 +96,7 @@ impl FileDescription for AnonSocket {
         dest: &MPlaceTy<'tcx>,
         ecx: &mut MiriInterpCx<'tcx>,
     ) -> InterpResult<'tcx> {
-        // Always succeed on read size 0.
-        if len == 0 {
-            return ecx.return_read_success(ptr, &[], 0, dest);
-        }
-
-        let Some(readbuf) = &self.readbuf else {
-            // FIXME: This should return EBADF, but there's no nice way to do that as there's no
-            // corresponding ErrorKind variant.
-            throw_unsup_format!("reading from the write end of a pipe");
-        };
-
-        if readbuf.borrow().buf.is_empty() && 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 ecx.set_last_error_and_return(ErrorKind::WouldBlock, dest);
-        }
-        anonsocket_read(self_ref.downgrade(), len, ptr, dest.clone(), ecx)
+        anonsocket_read(self_ref, len, ptr, dest, ecx)
     }
 
     fn write<'tcx>(
@@ -127,31 +108,7 @@ impl FileDescription for AnonSocket {
         dest: &MPlaceTy<'tcx>,
         ecx: &mut MiriInterpCx<'tcx>,
     ) -> InterpResult<'tcx> {
-        // 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 len == 0 {
-            return ecx.return_write_success(0, dest);
-        }
-
-        // We are writing to our peer's readbuf.
-        let Some(peer_fd) = self.peer_fd().upgrade() else {
-            // If the upgrade from Weak to Rc fails, it indicates that all read ends have been
-            // closed.
-            return ecx.set_last_error_and_return(ErrorKind::BrokenPipe, dest);
-        };
-
-        let Some(writebuf) = &peer_fd.downcast::<AnonSocket>().unwrap().readbuf else {
-            // FIXME: This should return EBADF, but there's no nice way to do that as there's no
-            // corresponding ErrorKind variant.
-            throw_unsup_format!("writing to the reading end of a pipe");
-        };
-        let available_space =
-            MAX_SOCKETPAIR_BUFFER_CAPACITY.strict_sub(writebuf.borrow().buf.len());
-        if available_space == 0 && self.is_nonblock {
-            // Non-blocking socketpair with a full buffer.
-            return ecx.set_last_error_and_return(ErrorKind::WouldBlock, dest);
-        }
-        anonsocket_write(self_ref.downgrade(), ptr, len, dest.clone(), ecx)
+        anonsocket_write(self_ref, ptr, len, dest, ecx)
     }
 
     fn as_unix(&self) -> &dyn UnixFileDescription {
@@ -161,50 +118,66 @@ impl FileDescription for AnonSocket {
 
 /// Write to AnonSocket based on the space available and return the written byte size.
 fn anonsocket_write<'tcx>(
-    weak_self_ref: WeakFileDescriptionRef,
+    self_ref: &FileDescriptionRef,
     ptr: Pointer,
     len: usize,
-    dest: MPlaceTy<'tcx>,
+    dest: &MPlaceTy<'tcx>,
     ecx: &mut MiriInterpCx<'tcx>,
 ) -> InterpResult<'tcx> {
-    let Some(self_ref) = weak_self_ref.upgrade() else {
-        // FIXME:  We should raise a deadlock error if the self_ref upgrade failed.
-        throw_unsup_format!("This will be a deadlock error in future")
-    };
     let self_anonsocket = self_ref.downcast::<AnonSocket>().unwrap();
+
+    // 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 len == 0 {
+        return ecx.return_write_success(0, dest);
+    }
+
+    // We are writing to our peer's readbuf.
     let Some(peer_fd) = self_anonsocket.peer_fd().upgrade() else {
         // If the upgrade from Weak to Rc fails, it indicates that all read ends have been
-        // closed.
-        return ecx.set_last_error_and_return(ErrorKind::BrokenPipe, &dest);
+        // closed. It is an error to write even if there would be space.
+        return ecx.set_last_error_and_return(ErrorKind::BrokenPipe, dest);
     };
+
     let Some(writebuf) = &peer_fd.downcast::<AnonSocket>().unwrap().readbuf else {
-        // FIXME: This should return EBADF, but there's no nice way to do that as there's no
-        // corresponding ErrorKind variant.
-        throw_unsup_format!("writing to the reading end of a pipe")
+        // Writing to the read end of a pipe.
+        return ecx.set_last_error_and_return(IoError::LibcError("EBADF"), dest);
     };
 
+    // Let's see if we can write.
     let available_space = MAX_SOCKETPAIR_BUFFER_CAPACITY.strict_sub(writebuf.borrow().buf.len());
-
     if available_space == 0 {
-        // Blocking socketpair with a full buffer.
-        let dest = dest.clone();
-        self_anonsocket.blocked_write_tid.borrow_mut().push(ecx.active_thread());
-        ecx.block_thread(
-            BlockReason::UnnamedSocket,
-            None,
-            callback!(
-                @capture<'tcx> {
-                    weak_self_ref: WeakFileDescriptionRef,
-                    ptr: Pointer,
-                    len: usize,
-                    dest: MPlaceTy<'tcx>,
-                }
-                @unblock = |this| {
-                    anonsocket_write(weak_self_ref, ptr, len, dest, this)
-                }
-            ),
-        );
+        if self_anonsocket.is_nonblock {
+            // Non-blocking socketpair with a full buffer.
+            return ecx.set_last_error_and_return(ErrorKind::WouldBlock, dest);
+        } else {
+            // Blocking socketpair with a full buffer.
+            // Block the current thread; only keep a weak ref for this.
+            let weak_self_ref = self_ref.downgrade();
+            let dest = dest.clone();
+            self_anonsocket.blocked_write_tid.borrow_mut().push(ecx.active_thread());
+            ecx.block_thread(
+                BlockReason::UnnamedSocket,
+                None,
+                callback!(
+                    @capture<'tcx> {
+                        weak_self_ref: WeakFileDescriptionRef,
+                        ptr: Pointer,
+                        len: usize,
+                        dest: MPlaceTy<'tcx>,
+                    }
+                    @unblock = |this| {
+                        let Some(self_ref) = weak_self_ref.upgrade() else {
+                            // FIXME:  We should raise a deadlock error if the self_ref upgrade failed.
+                            throw_unsup_format!("This will be a deadlock error in future")
+                        };
+                        anonsocket_write(&self_ref, ptr, len, &dest, this)
+                    }
+                ),
+            );
+        }
     } else {
+        // There is space to write!
         let mut writebuf = writebuf.borrow_mut();
         // Remember this clock so `read` can synchronize with us.
         ecx.release_clock(|clock| {
@@ -229,25 +202,26 @@ fn anonsocket_write<'tcx>(
             ecx.unblock_thread(thread_id, BlockReason::UnnamedSocket)?;
         }
 
-        return ecx.return_write_success(actual_write_size, &dest);
+        return ecx.return_write_success(actual_write_size, dest);
     }
     interp_ok(())
 }
 
 /// Read from AnonSocket and return the number of bytes read.
 fn anonsocket_read<'tcx>(
-    weak_self_ref: WeakFileDescriptionRef,
+    self_ref: &FileDescriptionRef,
     len: usize,
     ptr: Pointer,
-    dest: MPlaceTy<'tcx>,
+    dest: &MPlaceTy<'tcx>,
     ecx: &mut MiriInterpCx<'tcx>,
 ) -> InterpResult<'tcx> {
-    let Some(self_ref) = weak_self_ref.upgrade() else {
-        // FIXME:  We should raise a deadlock error if the self_ref upgrade failed.
-        throw_unsup_format!("This will be a deadlock error in future")
-    };
     let self_anonsocket = self_ref.downcast::<AnonSocket>().unwrap();
 
+    // Always succeed on read size 0.
+    if len == 0 {
+        return ecx.return_read_success(ptr, &[], 0, dest);
+    }
+
     let Some(readbuf) = &self_anonsocket.readbuf else {
         // FIXME: This should return EBADF, but there's no nice way to do that as there's no
         // corresponding ErrorKind variant.
@@ -258,10 +232,19 @@ fn anonsocket_read<'tcx>(
         if self_anonsocket.peer_fd().upgrade().is_none() {
             // Socketpair with no peer and empty buffer.
             // 0 bytes successfully read indicates end-of-file.
-            return ecx.return_read_success(ptr, &[], 0, &dest);
+            return ecx.return_read_success(ptr, &[], 0, dest);
+        } else if self_anonsocket.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 ecx.set_last_error_and_return(ErrorKind::WouldBlock, dest);
         } else {
             // Blocking socketpair with writer and empty buffer.
-            let weak_self_ref = weak_self_ref.clone();
+            // Block the current thread; only keep a weak ref for this.
+            let weak_self_ref = self_ref.downgrade();
+            let dest = dest.clone();
             self_anonsocket.blocked_read_tid.borrow_mut().push(ecx.active_thread());
             ecx.block_thread(
                 BlockReason::UnnamedSocket,
@@ -274,12 +257,17 @@ fn anonsocket_read<'tcx>(
                         dest: MPlaceTy<'tcx>,
                     }
                     @unblock = |this| {
-                        anonsocket_read(weak_self_ref, len, ptr, dest, this)
+                        let Some(self_ref) = weak_self_ref.upgrade() else {
+                            // FIXME:  We should raise a deadlock error if the self_ref upgrade failed.
+                            throw_unsup_format!("This will be a deadlock error in future")
+                        };
+                        anonsocket_read(&self_ref, len, ptr, &dest, this)
                     }
                 ),
             );
         }
     } else {
+        // There's data to be read!
         let mut bytes = vec![0; len];
         let mut readbuf = readbuf.borrow_mut();
         // Synchronize with all previous writes to this buffer.
@@ -313,7 +301,7 @@ fn anonsocket_read<'tcx>(
             }
         };
 
-        return ecx.return_read_success(ptr, &bytes, actual_read_size, &dest);
+        return ecx.return_read_success(ptr, &bytes, actual_read_size, dest);
     }
     interp_ok(())
 }