(security) Remove connect_insecure

In order to discourage folks from connecting securely, we're removing the
convenience method imap::connect_insecure.

Fear not\! For those who manage security in another way (aka a private network
or similar measures), it is still possible to connect without TLS by using the
imap::Client::new() method. See that method for examples of how to do this.

.cirrus.yml

@@ -17,7 +17,6 @@ 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

azure-pipelines.yml

@@ -41,8 +41,6 @@ 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

@@ -110,39 +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

tests/imap_integration.rs

@@ -47,24 +47,14 @@ 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()
+    imap::Client::new(stream)
     .secure("imap.example.com", &tls())
     .unwrap();
 }