Implement async reader

Cargo.toml

@@ -16,13 +16,17 @@ document-features = { version = "0.2", optional = true }
 encoding_rs = { version = "0.8", optional = true }
 serde = { version = "1.0", optional = true }
 memchr = "2.5"
+tokio = { version = "1.19", optional = true, default-features = false, features = ["io-util"] }
+async-recursion = { version = "1.0", optional = true }
 
 [dev-dependencies]
 criterion = "0.3"
 pretty_assertions = "1.2"
 regex = "1"
 serde = { version = "1.0", features = ["derive"] }
 serde-value = "0.7"
+tokio = { version = "1.20", default-features = false, features = ["macros", "rt-multi-thread"] }
+tokio-test = "0.4"
 
 [lib]
 bench = false
@@ -101,6 +105,19 @@ serialize = ["serde"]
 ## Enables support for recognizing all [HTML 5 entities](https://dev.w3.org/html5/html-author/charref)
 escape-html = []
 
+## Enables support for asynchronous reading from `tokio`'s IO-Traits.
+##
+## This can be used for example with `Reader::from_async_reader(read)` where `read`
+## is some type implementing `tokio::io::AsyncBufRead`.
+async = ["tokio", "async-recursion"]
+
+## Enables support for asynchronous reading from files using `tokio`. This feature
+## also automatically enables the `async` feature as well.
+##
+## This can be used for example with `Reader::from_file_async(path)` where `path`
+## is a file path.
+async-fs = ["async", "tokio/fs"]
+
 [package.metadata.docs.rs]
 all-features = true
 

src/lib.rs

@@ -158,5 +158,7 @@ mod writer;
 #[cfg(feature = "serialize")]
 pub use crate::errors::serialize::DeError;
 pub use crate::errors::{Error, Result};
+#[cfg(feature = "async")]
+pub use crate::reader::AsyncReader;
 pub use crate::reader::{Decoder, IoReader, Reader, SliceReader};
 pub use crate::writer::{ElementWriter, Writer};

src/reader.rs

@@ -13,9 +13,13 @@ use crate::name::{LocalName, NamespaceResolver, QName, ResolveResult};
 
 use memchr;
 
+#[cfg(feature = "async")]
+mod async_reader;
 mod io_reader;
 mod slice_reader;
 
+#[cfg(feature = "async")]
+pub use self::async_reader::AsyncReader;
 pub use self::io_reader::IoReader;
 pub use self::slice_reader::SliceReader;