(feature) Allow opt-out from native_tls crate

Cargo.toml

@@ -21,8 +21,12 @@ maintenance = { status = "actively-developed" }
 is-it-maintained-issue-resolution = { repository = "jonhoo/rust-imap" }
 is-it-maintained-open-issues = { repository = "jonhoo/rust-imap" }
 
+[features]
+tls = ["native-tls"]
+default = ["tls"]
+
 [dependencies]
-native-tls = "0.2.2"
+native-tls = { version = "0.2.2", optional = true }
 regex = "1.0"
 bufstream = "0.1"
 imap-proto = "0.9.0"
@@ -35,3 +39,15 @@ lazy_static = "1.4"
 lettre = "0.9"
 lettre_email = "0.9"
 rustls-connector = "0.8.0"
+
+[[example]]
+name = "basic"
+required-features = ["default"]
+
+[[example]]
+name = "gmail_oauth2"
+required-features = ["default"]
+
+[[test]]
+name = "imap_integration"
+required-features = ["default"]

src/client.rs

@@ -1,5 +1,6 @@
 use base64;
 use bufstream::BufStream;
+#[cfg(feature = "tls")]
 use native_tls::{TlsConnector, TlsStream};
 use nom;
 use std::collections::HashSet;
@@ -109,39 +110,6 @@ impl<T: Read + Write> DerefMut for Session<T> {
     }
 }
 
-/// Connect to a server using an insecure TCP connection.
-///
-/// The returned [`Client`] is unauthenticated; to access session-related methods (through
-/// [`Session`]), use [`Client::login`] or [`Client::authenticate`].
-///
-/// Consider using [`connect`] for a secured connection where possible.
-/// You can upgrade an insecure client to a secure one using [`Client::secure`].
-/// ```rust,no_run
-/// # extern crate native_tls;
-/// # extern crate imap;
-/// # use std::io;
-/// # use native_tls::TlsConnector;
-/// # fn main() {
-/// // a plain, unencrypted TCP connection
-/// let client = imap::connect_insecure(("imap.example.org", 143)).unwrap();
-///
-/// // upgrade to SSL
-/// let tls = TlsConnector::builder().build().unwrap();
-/// let tls_client = client.secure("imap.example.org", &tls);
-/// # }
-/// ```
-pub fn connect_insecure<A: ToSocketAddrs>(addr: A) -> Result<Client<TcpStream>> {
-    match TcpStream::connect(addr) {
-        Ok(stream) => {
-            let mut socket = Client::new(stream);
-
-            socket.read_greeting()?;
-            Ok(socket)
-        }
-        Err(e) => Err(Error::Io(e)),
-    }
-}
-
 /// Connect to a server using a TLS-encrypted connection.
 ///
 /// The returned [`Client`] is unauthenticated; to access session-related methods (through
@@ -162,6 +130,7 @@ pub fn connect_insecure<A: ToSocketAddrs>(addr: A) -> Result<Client<TcpStream>>
 /// let client = imap::connect(("imap.example.org", 993), "imap.example.org", &tls).unwrap();
 /// # }
 /// ```
+#[cfg(feature = "tls")]
 pub fn connect<A: ToSocketAddrs, S: AsRef<str>>(
     addr: A,
     domain: S,
@@ -186,6 +155,7 @@ impl Client<TcpStream> {
     /// This will upgrade an IMAP client from using a regular TCP connection to use TLS.
     ///
     /// The domain parameter is required to perform hostname verification.
+    #[cfg(feature = "tls")]
     pub fn secure<S: AsRef<str>>(
         mut self,
         domain: S,

src/error.rs

@@ -3,14 +3,17 @@
 use std::error::Error as StdError;
 use std::fmt;
 use std::io::Error as IoError;
+#[cfg(feature = "tls")]
 use std::net::TcpStream;
 use std::result;
 use std::str::Utf8Error;
 
 use base64::DecodeError;
 use bufstream::IntoInnerError as BufError;
 use imap_proto::Response;
+#[cfg(feature = "tls")]
 use native_tls::Error as TlsError;
+#[cfg(feature = "tls")]
 use native_tls::HandshakeError as TlsHandshakeError;
 
 /// A convenience wrapper around `Result` for `imap::Error`.
@@ -22,8 +25,10 @@ pub enum Error {
     /// An `io::Error` that occurred while trying to read or write to a network stream.
     Io(IoError),
     /// An error from the `native_tls` library during the TLS handshake.
+    #[cfg(feature = "tls")]
     TlsHandshake(TlsHandshakeError<TcpStream>),
     /// An error from the `native_tls` library while managing the socket.
+    #[cfg(feature = "tls")]
     Tls(TlsError),
     /// A BAD response from the IMAP server.
     Bad(String),
@@ -38,6 +43,8 @@ pub enum Error {
     Validate(ValidateError),
     /// Error appending an e-mail.
     Append,
+    #[doc(hidden)]
+    __Nonexhaustive,
 }
 
 impl From<IoError> for Error {
@@ -58,12 +65,14 @@ impl<T> From<BufError<T>> for Error {
     }
 }
 
+#[cfg(feature = "tls")]
 impl From<TlsHandshakeError<TcpStream>> for Error {
     fn from(err: TlsHandshakeError<TcpStream>) -> Error {
         Error::TlsHandshake(err)
     }
 }
 
+#[cfg(feature = "tls")]
 impl From<TlsError> for Error {
     fn from(err: TlsError) -> Error {
         Error::Tls(err)
@@ -80,7 +89,9 @@ impl fmt::Display for Error {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match *self {
             Error::Io(ref e) => fmt::Display::fmt(e, f),
+            #[cfg(feature = "tls")]
             Error::Tls(ref e) => fmt::Display::fmt(e, f),
+            #[cfg(feature = "tls")]
             Error::TlsHandshake(ref e) => fmt::Display::fmt(e, f),
             Error::Validate(ref e) => fmt::Display::fmt(e, f),
             Error::No(ref data) | Error::Bad(ref data) => {
@@ -95,21 +106,26 @@ impl StdError for Error {
     fn description(&self) -> &str {
         match *self {
             Error::Io(ref e) => e.description(),
+            #[cfg(feature = "tls")]
             Error::Tls(ref e) => e.description(),
+            #[cfg(feature = "tls")]
             Error::TlsHandshake(ref e) => e.description(),
             Error::Parse(ref e) => e.description(),
             Error::Validate(ref e) => e.description(),
             Error::Bad(_) => "Bad Response",
             Error::No(_) => "No Response",
             Error::ConnectionLost => "Connection lost",
             Error::Append => "Could not append mail to mailbox",
+            Error::__Nonexhaustive => "Unknown",
         }
     }
 
     fn cause(&self) -> Option<&dyn StdError> {
         match *self {
             Error::Io(ref e) => Some(e),
+            #[cfg(feature = "tls")]
             Error::Tls(ref e) => Some(e),
+            #[cfg(feature = "tls")]
             Error::TlsHandshake(ref e) => Some(e),
             Error::Parse(ParseError::DataNotUtf8(_, ref e)) => Some(e),
             _ => None,

src/extensions/idle.rs

@@ -3,6 +3,7 @@
 
 use crate::client::Session;
 use crate::error::{Error, Result};
+#[cfg(feature = "tls")]
 use native_tls::TlsStream;
 use std::io::{self, Read, Write};
 use std::net::TcpStream;
@@ -164,6 +165,7 @@ impl<'a> SetReadTimeout for TcpStream {
     }
 }
 
+#[cfg(feature = "tls")]
 impl<'a> SetReadTimeout for TlsStream<TcpStream> {
     fn set_read_timeout(&mut self, timeout: Option<Duration>) -> Result<()> {
         self.get_ref().set_read_timeout(timeout).map_err(Error::Io)

src/lib.rs

@@ -50,13 +50,29 @@
 //!     let body = std::str::from_utf8(body)
 //!         .expect("message was not valid utf-8")
 //!         .to_string();
-//!    
+//!
 //!     // be nice to the server and log out
 //!     imap_session.logout()?;
-//!    
+//!
 //!     Ok(Some(body))
 //! }
 //! ```
+//!
+//! ## Opting out of `native_tls`
+//!
+//! For situations where using openssl becomes problematic, you can disable the
+//! default feature which provides integration with the `native_tls` crate. One major
+//! reason you might want to do this is cross-compiling. To opt out of native_tls, add
+//! this to your Cargo.toml file:
+//!
+//! ```toml
+//! [dependencies.imap]
+//! version = "<some version>"
+//! default-features = false
+//! ```
+//!
+//! Even without `native_tls`, you can still use TLS by leveraging the pure Rust `rustls`
+//! crate. See the example/rustls.rs file for a working example.
 #![deny(missing_docs)]
 #![warn(rust_2018_idioms)]
 

tests/imap_integration.rs

@@ -47,26 +47,16 @@ fn smtp(user: &str) -> lettre::SmtpTransport {
     .transport()
 }
 
-#[test]
-fn connect_insecure() {
-    imap::connect_insecure(&format!(
-        "{}:3143",
-        std::env::var("TEST_HOST").unwrap_or("127.0.0.1".to_string())
-    ))
-    .unwrap();
-}
-
 #[test]
 #[ignore]
 fn connect_insecure_then_secure() {
+    let host = std::env::var("TEST_HOST").unwrap_or("127.0.0.1".to_string());
+    let stream = TcpStream::connect((host.as_ref(), 3143)).unwrap();
+
     // ignored because of https://github.com/greenmail-mail-test/greenmail/issues/135
-    imap::connect_insecure(&format!(
-        "{}:3143",
-        std::env::var("TEST_HOST").unwrap_or("127.0.0.1".to_string())
-    ))
-    .unwrap()
-    .secure("imap.example.com", &tls())
-    .unwrap();
+    imap::Client::new(stream)
+        .secure("imap.example.com", &tls())
+        .unwrap();
 }
 
 #[test]