Support to set header names of ClientRequest as Camel-Case (#713)

* Support to set header names of `ClientRequest` as Camel-Case

This is the case for supporting to request for servers which don't
perfectly implement the `RFC 7230`. It is important for an app
which uses `ClientRequest` as core part.

* Add field `upper_camel_case_headers` to `ClientRequest`.

* Add function `set_upper_camel_case_headers` to `ClientRequest`
  and `ClientRequestBuilder` to set field `upper_camel_case_headers`.

* Add trait `client::writer::UpperCamelCaseHeader` for
  `http::header::HeaderName`, let it can be converted to Camel-Case
  then writed to buffer.

* Add test `test_client::test_upper_camel_case_headers`.

* Support upper Camel-Case headers

* [actix-http] Add field `upper_camel_case_headers` for `RequestHead`
* [actix-http] Add code for `MessageType` to support upper camel case
* [awc] Add functions for `ClientRequest` to set upper camel case

* Use `Flags::CAMEL_CASE` for upper camel case of headers

actix-http/src/h1/encoder.rs

@@ -43,6 +43,10 @@ pub(crate) trait MessageType: Sized {
 
     fn headers(&self) -> &HeaderMap;
 
+    fn upper_camel_case(&self) -> bool {
+        false
+    }
+
     fn chunked(&self) -> bool;
 
     fn encode_status(&mut self, dst: &mut BytesMut) -> io::Result<()>;
@@ -221,6 +225,10 @@ impl MessageType for RequestHead {
         self.chunked()
     }
 
+    fn upper_camel_case(&self) -> bool {
+        self.upper_camel_case_headers()
+    }
+
     fn headers(&self) -> &HeaderMap {
         &self.headers
     }
@@ -418,6 +426,34 @@ impl<'a> io::Write for Writer<'a> {
     }
 }
 
+fn write_upper_camel_case(value: &[u8], buffer: &mut [u8]) {
+    let mut index = 0;
+    let key = value;
+    let mut key_iter = key.iter();
+
+    if let Some(c) = key_iter.next() {
+        if *c >= b'a' && *c <= b'z' {
+            buffer[index] = *c ^ b' ';
+            index += 1;
+        }
+    } else {
+        return;
+    }
+
+    while let Some(c) = key_iter.next() {
+        buffer[index] = *c;
+        index += 1;
+        if *c == b'-' {
+            if let Some(c) = key_iter.next() {
+                if *c >= b'a' && *c <= b'z' {
+                    buffer[index] = *c ^ b' ';
+                    index += 1;
+                }
+            }
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;