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    //! Envelope encryption.
    //!
    //! # Example
    //!
    //! ```rust
    //!
    //! extern crate openssl;
    //!
    //! use openssl::rsa::Rsa;
    //! use openssl::envelope::Seal;
    //! use openssl::pkey::PKey;
    //! use openssl::symm::Cipher;
    //!
    //! fn main() {
    //!     let rsa = Rsa::generate(2048).unwrap();
    //!     let key = PKey::from_rsa(rsa).unwrap();
    //!
    //!     let cipher = Cipher::aes_256_cbc();
    //!     let mut seal = Seal::new(cipher, &[key]).unwrap();
    //!
    //!     let secret = b"My secret message";
    //!     let mut encrypted = vec![0; secret.len() + cipher.block_size()];
    //!
    //!     let mut enc_len = seal.update(secret, &mut encrypted).unwrap();
    //!     enc_len += seal.finalize(&mut encrypted[enc_len..]).unwrap();
    //!     encrypted.truncate(enc_len);
    //! }
    //! ```
    use error::ErrorStack;
    use ffi;
    use foreign_types::{ForeignType, ForeignTypeRef};
    use libc::c_int;
    use pkey::{HasPrivate, HasPublic, PKey, PKeyRef};
    use std::cmp;
    use std::ptr;
    use symm::Cipher;
    use {cvt, cvt_p};

    /// Represents an EVP_Seal context.
    pub struct Seal {
        ctx: *mut ffi::EVP_CIPHER_CTX,
        block_size: usize,
        iv: Option<Vec<u8>>,
        enc_keys: Vec<Vec<u8>>,
    }

    impl Seal {
        /// Creates a new `Seal`.
        pub fn new<T>(cipher: Cipher, pub_keys: &[PKey<T>]) -> Result<Seal, ErrorStack>
        where
            T: HasPublic,
        {
            unsafe {
                assert!(pub_keys.len() <= c_int::max_value() as usize);

                let ctx = cvt_p(ffi::EVP_CIPHER_CTX_new())?;
                let mut enc_key_ptrs = vec![];
                let mut pub_key_ptrs = vec![];
                let mut enc_keys = vec![];
                for key in pub_keys {
                    let mut enc_key = vec![0; key.size()];
                    let enc_key_ptr = enc_key.as_mut_ptr();
                    enc_keys.push(enc_key);
                    enc_key_ptrs.push(enc_key_ptr);
                    pub_key_ptrs.push(key.as_ptr());
                }
                let mut iv = cipher.iv_len().map(|len| vec![0; len]);
                let iv_ptr = iv.as_mut().map_or(ptr::null_mut(), |v| v.as_mut_ptr());
                let mut enc_key_lens = vec![0; enc_keys.len()];

                cvt(ffi::EVP_SealInit(
                    ctx,
                    cipher.as_ptr(),
                    enc_key_ptrs.as_mut_ptr(),
                    enc_key_lens.as_mut_ptr(),
                    iv_ptr,
                    pub_key_ptrs.as_mut_ptr(),
                    pub_key_ptrs.len() as c_int,
                ))?;

                for (buf, len) in enc_keys.iter_mut().zip(&enc_key_lens) {
                    buf.truncate(*len as usize);
                }

                Ok(Seal {
                    ctx,
                    block_size: cipher.block_size(),
                    iv,
                    enc_keys,
                })
            }
        }

        /// Returns the initialization vector, if the cipher uses one.
        #[allow(clippy::option_as_ref_deref)]
        pub fn iv(&self) -> Option<&[u8]> {
            self.iv.as_ref().map(|v| &**v)
        }

        /// Returns the encrypted keys.
        pub fn encrypted_keys(&self) -> &[Vec<u8>] {
            &self.enc_keys
        }

        /// Feeds data from `input` through the cipher, writing encrypted bytes into `output`.
        ///
        /// The number of bytes written to `output` is returned. Note that this may
        /// not be equal to the length of `input`.
        ///
        /// # Panics
        ///
        /// Panics if `output.len() < input.len() + block_size` where `block_size` is
        /// the block size of the cipher (see `Cipher::block_size`), or if
        /// `output.len() > c_int::max_value()`.
        pub fn update(&mut self, input: &[u8], output: &mut [u8]) -> Result<usize, ErrorStack> {
            unsafe {
                assert!(output.len() >= input.len() + self.block_size);
                assert!(output.len() <= c_int::max_value() as usize);
                let mut outl = output.len() as c_int;
                let inl = input.len() as c_int;
                cvt(ffi::EVP_EncryptUpdate(
                    self.ctx,
                    output.as_mut_ptr(),
                    &mut outl,
                    input.as_ptr(),
                    inl,
                ))?;
                Ok(outl as usize)
            }
        }

        /// Finishes the encryption process, writing any remaining data to `output`.
        ///
        /// The number of bytes written to `output` is returned.
        ///
        /// `update` should not be called after this method.
        ///
        /// # Panics
        ///
        /// Panics if `output` is less than the cipher's block size.
        pub fn finalize(&mut self, output: &mut [u8]) -> Result<usize, ErrorStack> {
            unsafe {
                assert!(output.len() >= self.block_size);
                let mut outl = cmp::min(output.len(), c_int::max_value() as usize) as c_int;

                cvt(ffi::EVP_SealFinal(self.ctx, output.as_mut_ptr(), &mut outl))?;

                Ok(outl as usize)
            }
        }
    }

    impl Drop for Seal {
        fn drop(&mut self) {
            unsafe {
                ffi::EVP_CIPHER_CTX_free(self.ctx);
            }
        }
    }

    /// Represents an EVP_Open context.
    pub struct Open {
        ctx: *mut ffi::EVP_CIPHER_CTX,
        block_size: usize,
    }

    impl Open {
        /// Creates a new `Open`.
        pub fn new<T>(
            cipher: Cipher,
            priv_key: &PKeyRef<T>,
            iv: Option<&[u8]>,
            encrypted_key: &[u8],
        ) -> Result<Open, ErrorStack>
        where
            T: HasPrivate,
        {
            unsafe {
                assert!(encrypted_key.len() <= c_int::max_value() as usize);
                match (cipher.iv_len(), iv) {
                    (Some(len), Some(iv)) => assert_eq!(len, iv.len(), "IV length mismatch"),
                    (None, None) => {}
                    (Some(_), None) => panic!("an IV was required but not provided"),
                    (None, Some(_)) => panic!("an IV was provided but not required"),
                }

                let ctx = cvt_p(ffi::EVP_CIPHER_CTX_new())?;
                cvt(ffi::EVP_OpenInit(
                    ctx,
                    cipher.as_ptr(),
                    encrypted_key.as_ptr(),
                    encrypted_key.len() as c_int,
                    iv.map_or(ptr::null(), |v| v.as_ptr()),
                    priv_key.as_ptr(),
                ))?;
                Ok(Open {
                    ctx,
                    block_size: cipher.block_size(),
                })
            }
        }

        /// Feeds data from `input` through the cipher, writing decrypted bytes into `output`.
        ///
        /// The number of bytes written to `output` is returned. Note that this may
        /// not be equal to the length of `input`.
        ///
        /// # Panics
        ///
        /// Panics if `output.len() < input.len() + block_size` where
        /// `block_size` is the block size of the cipher (see `Cipher::block_size`),
        /// or if `output.len() > c_int::max_value()`.
        pub fn update(&mut self, input: &[u8], output: &mut [u8]) -> Result<usize, ErrorStack> {
            unsafe {
                assert!(output.len() >= input.len() + self.block_size);
                assert!(output.len() <= c_int::max_value() as usize);
                let mut outl = output.len() as c_int;
                let inl = input.len() as c_int;
                cvt(ffi::EVP_DecryptUpdate(
                    self.ctx,
                    output.as_mut_ptr(),
                    &mut outl,
                    input.as_ptr(),
                    inl,
                ))?;
                Ok(outl as usize)
            }
        }

        /// Finishes the decryption process, writing any remaining data to `output`.
        ///
        /// The number of bytes written to `output` is returned.
        ///
        /// `update` should not be called after this method.
        ///
        /// # Panics
        ///
        /// Panics if `output` is less than the cipher's block size.
        pub fn finalize(&mut self, output: &mut [u8]) -> Result<usize, ErrorStack> {
            unsafe {
                assert!(output.len() >= self.block_size);
                let mut outl = cmp::min(output.len(), c_int::max_value() as usize) as c_int;

                cvt(ffi::EVP_OpenFinal(self.ctx, output.as_mut_ptr(), &mut outl))?;

                Ok(outl as usize)
            }
        }
    }

    impl Drop for Open {
        fn drop(&mut self) {
            unsafe {
                ffi::EVP_CIPHER_CTX_free(self.ctx);
            }
        }
    }

    #[cfg(test)]
    mod test {
        use super::*;
        use pkey::PKey;
        use symm::Cipher;

        #[test]
        fn public_encrypt_private_decrypt() {
            let private_pem = include_bytes!("../test/rsa.pem");
            let public_pem = include_bytes!("../test/rsa.pem.pub");
            let private_key = PKey::private_key_from_pem(private_pem).unwrap();
            let public_key = PKey::public_key_from_pem(public_pem).unwrap();
            let cipher = Cipher::aes_256_cbc();
            let secret = b"My secret message";

            let mut seal = Seal::new(cipher, &[public_key]).unwrap();
            let mut encrypted = vec![0; secret.len() + cipher.block_size()];
            let mut enc_len = seal.update(secret, &mut encrypted).unwrap();
            enc_len += seal.finalize(&mut encrypted[enc_len..]).unwrap();
            let iv = seal.iv();
            let encrypted_key = &seal.encrypted_keys()[0];

            let mut open = Open::new(cipher, &private_key, iv, &encrypted_key).unwrap();
            let mut decrypted = vec![0; enc_len + cipher.block_size()];
            let mut dec_len = open.update(&encrypted[..enc_len], &mut decrypted).unwrap();
            dec_len += open.finalize(&mut decrypted[dec_len..]).unwrap();

            assert_eq!(&secret[..], &decrypted[..dec_len]);
        }
    }