Shm mutation example (#1672)

Add SHM buffer mutation functionality to examples
Add payload_mut accessor to ReplyError

Author: yellowhatter

examples/examples/z_sub_shm.rs

@@ -14,6 +14,8 @@
 use std::borrow::Cow;
 
 use clap::Parser;
+#[cfg(all(feature = "shared-memory", feature = "unstable"))]
+use zenoh::shm::{zshm, zshmmut};
 use zenoh::{bytes::ZBytes, config::Config, key_expr::KeyExpr};
 use zenoh_examples::CommonArgs;
 
@@ -31,43 +33,25 @@ async fn main() {
     let subscriber = session.declare_subscriber(&key_expr).await.unwrap();
 
     println!("Press CTRL-C to quit...");
-    while let Ok(sample) = subscriber.recv_async().await {
+    while let Ok(mut sample) = subscriber.recv_async().await {
+        let kind = sample.kind();
+        let key_str = sample.key_expr().as_str().to_owned();
+
         // Print overall payload information
-        let (payload_type, payload) = handle_bytes(sample.payload());
+        let (payload_type, payload) = handle_bytes(sample.payload_mut());
         print!(
             ">> [Subscriber] Received {} ('{}': '{}') [{}] ",
-            sample.kind(),
-            sample.key_expr().as_str(),
-            payload,
-            payload_type,
+            kind, key_str, payload, payload_type,
         );
 
         // Print attachment information
-        if let Some(att) = sample.attachment() {
+        if let Some(att) = sample.attachment_mut() {
             let (attachment_type, attachment) = handle_bytes(att);
             print!(" ({}: {})", attachment_type, attachment);
         }
 
         println!();
     }
-
-    // // Try to get a mutable reference to the SHM buffer. If this subscriber is the only subscriber
-    // // holding a reference to the SHM buffer, then it will be able to get a mutable reference to it.
-    // // With the mutable reference at hand, it's possible to mutate in place the SHM buffer content.
-
-    // while let Ok(mut sample) = subscriber.recv_async().await {
-    //     let kind = sample.kind();
-    //     let key_expr = sample.key_expr().to_string();
-    //     match sample.payload_mut().as_shm_mut() {
-    //         Ok(payload) => println!(
-    //             ">> [Subscriber] Received {} ('{}': '{:02x?}')",
-    //             kind, key_expr, payload
-    //         ),
-    //         Err(e) => {
-    //             println!(">> [Subscriber] Not a ShmBufInner: {:?}", e);
-    //         }
-    //     }
-    // }
 }
 
 #[derive(clap::Parser, Clone, PartialEq, Eq, Hash, Debug)]
@@ -84,7 +68,7 @@ fn parse_args() -> (Config, KeyExpr<'static>) {
     (args.common.into(), args.key)
 }
 
-fn handle_bytes(bytes: &ZBytes) -> (&str, Cow<str>) {
+fn handle_bytes(bytes: &mut ZBytes) -> (&str, Cow<str>) {
     // Determine buffer type for indication purpose
     let bytes_type = {
         // if Zenoh is built without SHM support, the only buffer type it can receive is RAW
@@ -100,10 +84,14 @@ fn handle_bytes(bytes: &ZBytes) -> (&str, Cow<str>) {
             "UNKNOWN"
         }
 
-        // if Zenoh is built with SHM support and with SHM API  we can detect the exact buffer type
+        // if Zenoh is built with SHM support and with SHM API we can detect the exact buffer type
         #[cfg(all(feature = "shared-memory", feature = "unstable"))]
-        match bytes.as_shm() {
-            Some(_) => "SHM",
+        match bytes.as_shm_mut() {
+            // try to mutate SHM buffer to get it's mutability property
+            Some(shm) => match <&mut zshm as TryInto<&mut zshmmut>>::try_into(shm) {
+                Ok(_shm_mut) => "SHM (MUT)",
+                Err(_) => "SHM (IMMUT)",
+            },
             None => "RAW",
         }
     };

zenoh/src/api/query.rs

@@ -86,6 +86,12 @@ impl ReplyError {
         &self.payload
     }
 
+    /// Gets the mutable payload of this ReplyError.
+    #[inline]
+    pub fn payload_mut(&mut self) -> &mut ZBytes {
+        &mut self.payload
+    }
+
     /// Gets the encoding of this ReplyError.
     #[inline]
     pub fn encoding(&self) -> &Encoding {