libs/binder/rust/src/parcel/file_descriptor.rs

/*
 * Copyright (C) 2020 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

use super::{
    BorrowedParcel, Deserialize, DeserializeArray, DeserializeOption, Serialize, SerializeArray,
    SerializeOption,
};
use crate::binder::AsNative;
use crate::error::{status_result, Result, StatusCode};
use crate::sys;

use std::fs::File;
use std::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd, RawFd};

/// Rust version of the Java class android.os.ParcelFileDescriptor
#[derive(Debug)]
pub struct ParcelFileDescriptor(File);

impl ParcelFileDescriptor {
    /// Create a new `ParcelFileDescriptor`
    pub fn new(file: File) -> Self {
        Self(file)
    }
}

impl AsRef<File> for ParcelFileDescriptor {
    fn as_ref(&self) -> &File {
        &self.0
    }
}

impl From<ParcelFileDescriptor> for File {
    fn from(file: ParcelFileDescriptor) -> File {
        file.0
    }
}

impl AsRawFd for ParcelFileDescriptor {
    fn as_raw_fd(&self) -> RawFd {
        self.0.as_raw_fd()
    }
}

impl IntoRawFd for ParcelFileDescriptor {
    fn into_raw_fd(self) -> RawFd {
        self.0.into_raw_fd()
    }
}

impl PartialEq for ParcelFileDescriptor {
    // Since ParcelFileDescriptors own the FD, if this function ever returns true (and it is used to
    // compare two different objects), then it would imply that an FD is double-owned.
    fn eq(&self, other: &Self) -> bool {
        self.as_raw_fd() == other.as_raw_fd()
    }
}

impl Eq for ParcelFileDescriptor {}

impl Serialize for ParcelFileDescriptor {
    fn serialize(&self, parcel: &mut BorrowedParcel<'_>) -> Result<()> {
        let fd = self.0.as_raw_fd();
        let status = unsafe {
            // Safety: `Parcel` always contains a valid pointer to an
            // `AParcel`. Likewise, `ParcelFileDescriptor` always contains a
            // valid file, so we can borrow a valid file
            // descriptor. `AParcel_writeParcelFileDescriptor` does NOT take
            // ownership of the fd, so we need not duplicate it first.
            sys::AParcel_writeParcelFileDescriptor(parcel.as_native_mut(), fd)
        };
        status_result(status)
    }
}

impl SerializeArray for ParcelFileDescriptor {}

impl SerializeOption for ParcelFileDescriptor {
    fn serialize_option(this: Option<&Self>, parcel: &mut BorrowedParcel<'_>) -> Result<()> {
        if let Some(f) = this {
            f.serialize(parcel)
        } else {
            let status = unsafe {
                // Safety: `Parcel` always contains a valid pointer to an
                // `AParcel`. `AParcel_writeParcelFileDescriptor` accepts the
                // value `-1` as the file descriptor to signify serializing a
                // null file descriptor.
                sys::AParcel_writeParcelFileDescriptor(parcel.as_native_mut(), -1i32)
            };
            status_result(status)
        }
    }
}

impl DeserializeOption for ParcelFileDescriptor {
    fn deserialize_option(parcel: &BorrowedParcel<'_>) -> Result<Option<Self>> {
        let mut fd = -1i32;
        unsafe {
            // Safety: `Parcel` always contains a valid pointer to an
            // `AParcel`. We pass a valid mutable pointer to an i32, which
            // `AParcel_readParcelFileDescriptor` assigns the valid file
            // descriptor into, or `-1` if deserializing a null file
            // descriptor. The read function passes ownership of the file
            // descriptor to its caller if it was non-null, so we must take
            // ownership of the file and ensure that it is eventually closed.
            status_result(sys::AParcel_readParcelFileDescriptor(parcel.as_native(), &mut fd))?;
        }
        if fd < 0 {
            Ok(None)
        } else {
            let file = unsafe {
                // Safety: At this point, we know that the file descriptor was
                // not -1, so must be a valid, owned file descriptor which we
                // can safely turn into a `File`.
                File::from_raw_fd(fd)
            };
            Ok(Some(ParcelFileDescriptor::new(file)))
        }
    }
}

impl Deserialize for ParcelFileDescriptor {
    type UninitType = Option<Self>;
    fn uninit() -> Self::UninitType {
        Self::UninitType::default()
    }
    fn from_init(value: Self) -> Self::UninitType {
        Some(value)
    }

    fn deserialize(parcel: &BorrowedParcel<'_>) -> Result<Self> {
        Deserialize::deserialize(parcel).transpose().unwrap_or(Err(StatusCode::UNEXPECTED_NULL))
    }
}

impl DeserializeArray for ParcelFileDescriptor {}