(feat) default feature for native_tls (aka openssl)

Establishes conditional compilation for all integration with the
native_tls crate in this crate. Since native_tls has been deeply
integrated into this crate for a long time, we want to maintain
backwards compatibility by making this feature part of the default.

For a consumer of this crate to "opt-out", including this in
cargo.toml:

```
[dependencies.imap]
version = 0.16.0        # Replace this with the correct version
default-features = false
```

See the conversation on Github for details on this approach:
https://github.com/jonhoo/rust-imap/issues/123

.cirrus.yml

@@ -17,6 +17,7 @@ task:
   build_script:
     - . $HOME/.cargo/env
     - cargo build --all-targets --verbose
+    - cargo build --all-targets --verbose --no-default-features
   test_script:
     - . $HOME/.cargo/env
     - cargo test --examples

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"]

azure-pipelines.yml

@@ -41,6 +41,8 @@ stages:
        displayName: Run doctests
      - script: cargo test --lib
        displayName: Run unit tests
+     - script: cargo build --all-targets --verbose --no-default-features
+       displayName: Compile without openssl
    - job: integration
      displayName: cargo test
      pool:

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;
@@ -162,6 +163,7 @@ 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 +188,7 @@ 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

@@ -3,6 +3,7 @@
 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;
@@ -10,7 +11,9 @@ 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) => {
@@ -95,7 +106,9 @@ 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(),
@@ -103,13 +116,16 @@ impl StdError for Error {
             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)