Add sync-to-async and async-to-sync conversion routines

src/reader/async_tokio.rs

@@ -183,6 +183,26 @@ impl<R: AsyncBufRead + Unpin> Reader<TokioAdapter<R>> {
     }
 }
 
+/// Converts any synchronous reader to asynchronous one if inner reader supports that
+impl<R: AsyncBufRead + Unpin> From<Reader<R>> for Reader<TokioAdapter<R>> {
+    fn from(reader: Reader<R>) -> Self {
+        Self {
+            reader: TokioAdapter(reader.reader),
+            parser: reader.parser,
+        }
+    }
+}
+
+/// Converts any asynchronous reader to a synchronous one if inner reader supports that
+impl<R> From<Reader<TokioAdapter<R>>> for Reader<R> {
+    fn from(reader: Reader<TokioAdapter<R>>) -> Self {
+        Self {
+            reader: reader.reader.0,
+            parser: reader.parser,
+        }
+    }
+}
+
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
 impl<R: AsyncBufRead + Unpin> NsReader<TokioAdapter<R>> {
@@ -396,6 +416,30 @@ impl<R: AsyncBufRead + Unpin> NsReader<TokioAdapter<R>> {
     }
 }
 
+/// Converts any synchronous reader to asynchronous one if inner reader supports that
+impl<R: AsyncBufRead + Unpin> From<NsReader<R>> for NsReader<TokioAdapter<R>> {
+    fn from(reader: NsReader<R>) -> Self {
+        Self {
+            reader: reader.reader.into(),
+            buffer: reader.buffer,
+            ns_resolver: reader.ns_resolver,
+            pending_pop: reader.pending_pop,
+        }
+    }
+}
+
+/// Converts any asynchronous reader to a synchronous one if inner reader supports that
+impl<R> From<NsReader<TokioAdapter<R>>> for NsReader<R> {
+    fn from(reader: NsReader<TokioAdapter<R>>) -> Self {
+        Self {
+            reader: reader.reader.into(),
+            buffer: reader.buffer,
+            ns_resolver: reader.ns_resolver,
+            pending_pop: reader.pending_pop,
+        }
+    }
+}
+
 #[cfg(test)]
 mod test {
     use super::TokioAdapter;

src/reader/ns_reader.rs

@@ -22,13 +22,13 @@ pub struct NsReader<R> {
     pub(super) reader: Reader<R>,
     /// Buffer that contains names of namespace prefixes (the part between `xmlns:`
     /// and an `=`) and namespace values.
-    buffer: Vec<u8>,
+    pub(super) buffer: Vec<u8>,
     /// A buffer to manage namespaces
-    ns_resolver: NamespaceResolver,
+    pub(super) ns_resolver: NamespaceResolver,
     /// We cannot pop data from the namespace stack until returned `Empty` or `End`
     /// event will be processed by the user, so we only mark that we should that
     /// in the next [`Self::read_event_impl()`] call.
-    pending_pop: bool,
+    pub(super) pending_pop: bool,
 }
 
 /// Builder methods