feat: Add discovery primitives for UDP search and server discovery

- Implemented UDP search and server discovery functions in `discovery.rs`.
- Added Python bindings for auto-broadcast targets, search targets, and PV list retrieval.
- Introduced `Packet` class in `packet.rs` for raw-frame handling with header accessors.
- Created dynamic Python-defined `Source` support in `source.rs` for PVAccess sources.
- Added tests for nested `pvRequest` field selection on MONITOR in `spvirit_monitor_fields.rs`.

Author: MatInGit

Cargo.lock

@@ -1,13 +1,42 @@
 use spvirit_client::PvaClient;
 
+/// Minimal `pvget` example.
+///
+/// Usage:
+///
+/// ```text
+/// cargo run --example pvget -- MY:PV
+/// cargo run --example pvget -- MY:PV --fields value,alarm.severity
+/// ```
 #[tokio::main]
 async fn main() -> Result<(), Box<dyn std::error::Error>> {
-    let pv = std::env::args()
-        .nth(1)
-        .unwrap_or_else(|| "MY:PV:NAME".into());
+    let mut args = std::env::args().skip(1);
+    let mut pv: Option<String> = None;
+    let mut fields: Vec<String> = Vec::new();
 
+    while let Some(a) = args.next() {
+        match a.as_str() {
+            "-F" | "--fields" => {
+                let raw = args.next().ok_or("--fields requires a value")?;
+                fields.extend(
+                    raw.split(',')
+                        .map(|s| s.trim().to_string())
+                        .filter(|s| !s.is_empty()),
+                );
+            }
+            _ if pv.is_none() => pv = Some(a),
+            other => return Err(format!("unexpected argument: {other}").into()),
+        }
+    }
+
+    let pv = pv.unwrap_or_else(|| "MY:PV:NAME".into());
     let client = PvaClient::builder().build();
-    let result = client.pvget(&pv).await?;
+    let result = if fields.is_empty() {
+        client.pvget(&pv).await?
+    } else {
+        let refs: Vec<&str> = fields.iter().map(String::as_str).collect();
+        client.pvget_fields(&pv, &refs).await?
+    };
     println!("{}: {}", result.pv_name, result.value);
     Ok(())
 }

spvirit-client/examples/pvget.rs

@@ -1,18 +1,46 @@
 use spvirit_client::PvaClient;
 use std::ops::ControlFlow;
 
+/// Minimal `pvmonitor` example.
+///
+/// Usage:
+///
+/// ```text
+/// cargo run --example pvmonitor -- MY:PV
+/// cargo run --example pvmonitor -- MY:PV --fields value,alarm.severity
+/// ```
 #[tokio::main]
 async fn main() -> Result<(), Box<dyn std::error::Error>> {
-    let pv = std::env::args()
-        .nth(1)
-        .unwrap_or_else(|| "MY:PV:NAME".into());
+    let mut args = std::env::args().skip(1);
+    let mut pv: Option<String> = None;
+    let mut fields: Vec<String> = Vec::new();
 
+    while let Some(a) = args.next() {
+        match a.as_str() {
+            "-F" | "--fields" => {
+                let raw = args.next().ok_or("--fields requires a value")?;
+                fields.extend(
+                    raw.split(',')
+                        .map(|s| s.trim().to_string())
+                        .filter(|s| !s.is_empty()),
+                );
+            }
+            _ if pv.is_none() => pv = Some(a),
+            other => return Err(format!("unexpected argument: {other}").into()),
+        }
+    }
+
+    let pv = pv.unwrap_or_else(|| "MY:PV:NAME".into());
     let client = PvaClient::builder().build();
-    client
-        .pvmonitor(&pv, |value| {
-            println!("{value}");
-            ControlFlow::Continue(())
-        })
-        .await?;
+    let cb = |value: &spvirit_codec::spvd_decode::DecodedValue| {
+        println!("{value}");
+        ControlFlow::Continue(())
+    };
+    if fields.is_empty() {
+        client.pvmonitor(&pv, cb).await?;
+    } else {
+        let refs: Vec<&str> = fields.iter().map(String::as_str).collect();
+        client.pvmonitor_fields(&pv, &refs, cb).await?;
+    }
     Ok(())
 }

spvirit-client/examples/pvmonitor.rs

@@ -1,17 +1,50 @@
 use spvirit_client::PvaClient;
 
+/// Minimal `pvput` example.
+///
+/// Usage:
+///
+/// ```text
+/// cargo run --example pvput -- MY:PV 42.0
+/// cargo run --example pvput -- MY:PV 42.0 --fields value
+/// ```
 #[tokio::main]
 async fn main() -> Result<(), Box<dyn std::error::Error>> {
-    let pv = std::env::args()
-        .nth(1)
+    let mut args = std::env::args().skip(1);
+    let mut positional: Vec<String> = Vec::new();
+    let mut fields: Vec<String> = Vec::new();
+
+    while let Some(a) = args.next() {
+        match a.as_str() {
+            "-F" | "--fields" => {
+                let raw = args.next().ok_or("--fields requires a value")?;
+                fields.extend(
+                    raw.split(',')
+                        .map(|s| s.trim().to_string())
+                        .filter(|s| !s.is_empty()),
+                );
+            }
+            _ => positional.push(a),
+        }
+    }
+
+    let pv = positional
+        .first()
+        .cloned()
         .unwrap_or_else(|| "MY:PV:NAME".into());
-    let value: f64 = std::env::args()
-        .nth(2)
+    let value: f64 = positional
+        .get(1)
+        .cloned()
         .unwrap_or_else(|| "42.0".into())
         .parse()?;
 
     let client = PvaClient::builder().build();
-    client.pvput(&pv, value).await?;
+    if fields.is_empty() {
+        client.pvput(&pv, value).await?;
+    } else {
+        let refs: Vec<&str> = fields.iter().map(String::as_str).collect();
+        client.pvput_fields(&pv, value, &refs).await?;
+    }
     println!("OK");
     Ok(())
 }

spvirit-client/examples/pvput.rs

@@ -47,7 +47,8 @@ pub mod types;
 
 // --- Re-exports: high-level API ---
 pub use pva_client::{
-    PvaChannel, PvaClient, PvaClientBuilder, client_from_opts, pvinfo, pvmonitor, pvput,
+    PvaChannel, PvaClient, PvaClientBuilder, client_from_opts, pvinfo, pvmonitor,
+    pvmonitor_fields, pvput, pvput_fields,
 };
 pub use pvlist::PvListSource;