docs(client): add POST request example to client guide

_stable/client/advanced.md

@@ -0,0 +1,77 @@
+---
+title: Advanced Client Usage
+layout: guide
+---
+
+## POST
+Now that we've seen how to make a GET request, let's look at how to make a POST request. This is useful when you need to send data to the server, such as when submitting a form or uploading a file.
+
+To make a POST request, we'll need to change a few things from our GET request:
+
+1. We'll set the method to POST.
+2. We'll need to provide a request body.
+3. We'll need to specify the type of data in our body by adding a `hyper::header::CONTENT_TYPE` header. 
+
+For the body, we have a couple of options. We can use a simple string, a JSON string, or we can use raw bytes. Let's look at all three:
+
+```rust
+# extern crate http_body_util;
+# extern crate hyper;
+# extern crate hyper_util;
+# extern crate tokio;
+# use http_body_util::Empty;
+# use hyper::body::Bytes;
+# use hyper::Request;
+# use hyper_util::rt::TokioIo;
+# use tokio::net::TcpStream;
+# async fn run() -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
+# let url = "http://httpbin.org/ip".parse::<hyper::Uri>()?;
+# let host = url.host().expect("uri has no host");
+# let port = url.port_u16().unwrap_or(80);
+# let addr = format!("{}:{}", host, port);
+# let stream = TcpStream::connect(addr).await?;
+# let io = TokioIo::new(stream);
+# let (mut sender, conn) = hyper::client::conn::http1::handshake(io).await?;
+# tokio::task::spawn(async move {
+# if let Err(err) = conn.await {
+# println!("Connection failed: {:?}", err);
+# }
+# });
+
+// The authority of our URL will be the hostname of the httpbin remote
+let authority = url.authority().unwrap().clone();
+
+// For plain text
+let req_body = Full::<Bytes>::from("Some plain text as a body.");
+let req = Request::builder()
+    .method(hyper::Method::POST)
+    .header(hyper::header::HOST, authority.as_str())
+    .header(hyper::header::CONTENT_TYPE, "text/plain")
+    .body(req_body)?;
+
+// For JSON data
+let json_data = r#"{"key": "value"}"#;
+let req_body = Full::<Bytes>::from(json_data);
+let req = Request::builder()
+    .method(hyper::Method::POST)
+    .header(hyper::header::HOST, authority.as_str())
+    .header(hyper::header::CONTENT_TYPE, "application/json")
+    .body(req_body)?;
+
+// For binary data
+let binary_data = vec![0u8; 128]; // Example binary data
+let req_body = Full::<Bytes>::from(binary_data);
+let req = Request::builder()
+    .method(hyper::Method::POST)
+    .header(hyper::header::HOST, authority.as_str())
+    .header(hyper::header::CONTENT_TYPE, "application/octet-stream")
+    .body(req_body)?;
+
+
+let res = sender.send_request(req).await?;
+
+println!("Response status: {}", res.status());
+# Ok(())
+# }
+# fn main() {}
+```