feat(client): add 1.0 compatible client conn API (#3155)

This patch backports client/conn/http1 and http2 modules from 1.0 to
ease transition. It allows code still using 0.14.x to switch to the
per-version Connection types available in 1.0.

Closes #3053 

Co-authored-by: KOVACS Tamas <ktamas@fastmail.fm>

.github/workflows/CI.yml

@@ -62,11 +62,11 @@ jobs:
 
         include:
           - rust: stable
-            features: "--features full"
+            features: "--features full,backports"
           - rust: beta
-            features: "--features full"
+            features: "--features full,backports"
           - rust: nightly
-            features: "--features full,nightly"
+            features: "--features full,nightly,backports"
             benches: true
 
     runs-on: ${{ matrix.os }}

Cargo.toml

@@ -109,6 +109,9 @@ tcp = [
 # C-API support (currently unstable (no semver))
 ffi = ["libc"]
 
+# enable 1.0 backports
+backports = []
+
 # internal features used in CI
 nightly = []
 __internal_happy_eyeballs_tests = []

src/client/conn.rs

@@ -54,6 +54,11 @@
 //! # }
 //! ```
 
+#[cfg(all(feature = "backports", feature = "http1"))]
+pub mod http1;
+#[cfg(all(feature = "backports", feature = "http2"))]
+pub mod http2;
+
 use std::error::Error as StdError;
 use std::fmt;
 #[cfg(not(all(feature = "http1", feature = "http2")))]