file-restore: split out internal QMP logic from unrelated fn

Capsule it in a small QMPSock struct impl, make the usage nicer as
the caller should not have to care & keep track of the initial socket
state+details.

A send_raw and send Value method should cover most needs.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

proxmox-file-restore/src/qemu_helper.rs

@@ -7,9 +7,8 @@ use std::time::{Duration, Instant};
 
 use anyhow::{bail, format_err, Error};
 use serde_json::json;
-use tokio::io::AsyncBufRead;
 use tokio::{
-    io::{AsyncBufReadExt, AsyncWrite, AsyncWriteExt},
+    io::{AsyncBufReadExt, AsyncWriteExt},
     time,
 };
 
@@ -124,15 +123,45 @@ async fn create_temp_initramfs(ticket: &str, debug: bool) -> Result<(File, Strin
     Ok((tmp_file, path))
 }
 
-async fn send_qmp_request<T: AsyncBufRead + AsyncWrite + Unpin>(
-    stream: &mut T,
-    request: &str,
-) -> Result<String, Error> {
-    stream.write_all(request.as_bytes()).await?;
-    stream.flush().await?;
+struct QMPSock {
+    sock: tokio::io::BufStream<tokio::net::UnixStream>,
+    initialized: bool,
+}
+
+impl QMPSock {
+    /// Creates a new QMP socket connection. No active initialization is done until actual requests
+    /// are made.
+    pub async fn new(cid: i32) -> Result<Self, Error> {
+        let path = format!("{QMP_SOCKET_PREFIX}{cid}.sock");
+        let sock = tokio::io::BufStream::new(tokio::net::UnixStream::connect(path).await?);
+        Ok(QMPSock {
+            sock,
+            initialized: false,
+        })
+    }
+
+    /// Transparently serializes the QMP request and sends it out with `send_raw`
+    pub async fn send(&mut self, request: serde_json::Value) -> Result<String, Error> {
+        self.send_raw(&serde_json::to_string(&request)?).await
+    }
+
+    /// Send out raw (already serialized) QMP requests, handling initialization transparently
+    pub async fn send_raw(&mut self, request: &str) -> Result<String, Error> {
+        if !self.initialized {
+            let _ = self.sock.read_line(&mut String::new()).await?; // initial qmp message
+            self.do_send("{\"execute\":\"qmp_capabilities\"}\n").await?;
+            self.initialized = true;
+        }
+        self.do_send(request).await
+    }
+
+    async fn do_send(&mut self, request: &str) -> Result<String, Error> {
+        self.sock.write_all(request.as_bytes()).await?;
+        self.sock.flush().await?;
         let mut buf = String::new();
-    let _ = stream.read_line(&mut buf).await?;
+        let _ = self.sock.read_line(&mut buf).await?;
         Ok(buf)
+    }
 }
 
 pub(crate) async fn hotplug_memory(cid: i32, dimm_mb: usize) -> Result<(), Error> {
@@ -140,30 +169,27 @@ pub(crate) async fn hotplug_memory(cid: i32, dimm_mb: usize) -> Result<(), Error
         bail!("cannot set to {dimm_mb}M, maximum is {MAX_MEMORY_DIMM_SIZE}M");
     }
 
-    let path = format!("{QMP_SOCKET_PREFIX}{cid}.sock");
-    let mut stream = tokio::io::BufStream::new(tokio::net::UnixStream::connect(path).await?);
+    let mut qmp = QMPSock::new(cid).await?;
 
-    let _ = stream.read_line(&mut String::new()).await?; // initial qmp message
-    let _ = send_qmp_request(&mut stream, "{\"execute\":\"qmp_capabilities\"}\n").await?;
-
-    let request = json!({
+    qmp.send(json!({
         "execute": "object-add",
         "arguments": {
             "qom-type": "memory-backend-ram",
             "id": "mem0",
             "size": dimm_mb * 1024 * 1024,
         }
-    });
-    let _ = send_qmp_request(&mut stream, &serde_json::to_string(&request)?).await?;
-    let request = json!({
+    }))
+    .await?;
+
+    qmp.send(json!({
         "execute": "device_add",
         "arguments": {
             "driver": "pc-dimm",
             "id": "dimm0",
             "memdev": "mem0",
         }
-    });
-    let _ = send_qmp_request(&mut stream, &serde_json::to_string(&request)?).await?;
+    }))
+    .await?;
 
     Ok(())
 }