Add the subscription message flyweight

aeron-rs/src/command/flyweight.rs

@@ -59,4 +59,14 @@ where
         self.buffer.bounds_check(offset as IndexT, 0)?;
         Ok(&self.buffer[offset..])
     }
+
+    pub(in crate::command) fn string_get(&self, offset: IndexT) -> Result<&str> {
+        self.buffer
+            .get_string((self.base_offset + offset) as IndexT)
+    }
+
+    pub(in crate::command) fn string_put(&mut self, offset: IndexT, value: &str) -> Result<i32> {
+        self.buffer
+            .put_string((self.base_offset + offset) as IndexT, value)
+    }
 }

aeron-rs/src/command/mod.rs

@@ -1,4 +1,5 @@
 //! Message definitions for interactions with the Media Driver
 pub mod correlated_message;
 pub mod flyweight;
+pub mod subscription_message;
 pub mod terminate_driver;

aeron-rs/src/command/subscription_message.rs

@@ -0,0 +1,111 @@
+//! Flyweight implementation for commands to add a subscription
+
+use crate::command::correlated_message::CorrelatedMessageDefn;
+use crate::command::flyweight::Flyweight;
+use crate::concurrent::AtomicBuffer;
+use crate::util::{IndexT, Result};
+use std::mem::size_of;
+
+/// Control message for adding a subscription
+///
+/// ```text
+///  0                   1                   2                   3
+///  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+/// |                         Client ID                             |
+/// |                                                               |
+/// +---------------------------------------------------------------+
+/// |                       Correlation ID                          |
+/// |                                                               |
+/// +---------------------------------------------------------------+
+/// |                 Registration Correlation ID                   |
+/// |                                                               |
+/// +---------------------------------------------------------------+
+/// |                         Stream Id                             |
+/// +---------------------------------------------------------------+
+/// |                      Channel Length                           |
+/// +---------------------------------------------------------------+
+/// |                          Channel                             ...
+/// ...                                                             |
+/// +---------------------------------------------------------------+
+/// ```
+#[repr(C, packed(4))]
+pub struct SubscriptionMessageDefn {
+    correlated_message: CorrelatedMessageDefn,
+    registration_correlation_id: i64,
+    stream_id: i32,
+    channel_length: i32,
+}
+
+// Rust has no `offset_of` macro, so we'll just compute by hand
+const CHANNEL_LENGTH_OFFSET: IndexT =
+    (size_of::<CorrelatedMessageDefn>() + size_of::<i64>() + size_of::<i32>()) as IndexT;
+
+impl<A> Flyweight<A, SubscriptionMessageDefn>
+where
+    A: AtomicBuffer,
+{
+    /// Retrieve the client identifier of this request.
+    pub fn client_id(&self) -> i64 {
+        self.get_struct().correlated_message.client_id
+    }
+
+    /// Set the client identifier of this request.
+    pub fn put_client_id(&mut self, value: i64) -> &mut Self {
+        self.get_struct_mut().correlated_message.client_id = value;
+        self
+    }
+
+    /// Retrieve the correlation identifier associated with this request. Used to
+    /// associate driver responses with a specific request.
+    pub fn correlation_id(&self) -> i64 {
+        self.get_struct().correlated_message.correlation_id
+    }
+
+    /// Set the correlation identifier to be used with this request.
+    pub fn put_correlation_id(&mut self, value: i64) -> &mut Self {
+        self.get_struct_mut().correlated_message.correlation_id = value;
+        self
+    }
+
+    /// Retrieve the registration correlation identifier
+    // QUESTION: What is this ID used for? In the DriverProxy, it's always set to -1
+    pub fn registration_correlation_id(&self) -> i64 {
+        self.get_struct().registration_correlation_id
+    }
+
+    /// Set the registration correlation identifier of this request
+    pub fn put_registration_correlation_id(&mut self, value: i64) -> &mut Self {
+        self.get_struct_mut().registration_correlation_id = value;
+        self
+    }
+
+    /// Get the stream identifier associated with this request.
+    // QUESTION: What is the difference between stream ID and channel?
+    // Both are set in the `BasicSubscriber` example, not sure what they do.
+    pub fn stream_id(&self) -> i32 {
+        self.get_struct().stream_id
+    }
+
+    /// Set the stream identifier of this request
+    pub fn put_stream_id(&mut self, value: i32) -> &mut Self {
+        self.get_struct_mut().stream_id = value;
+        self
+    }
+
+    /// Retrieve the channel name of this request
+    pub fn channel(&self) -> Result<&str> {
+        self.string_get(CHANNEL_LENGTH_OFFSET)
+    }
+
+    /// Set the channel name of this request
+    pub fn put_channel(&mut self, value: &str) -> Result<&mut Self> {
+        self.string_put(CHANNEL_LENGTH_OFFSET, value)?;
+        Ok(self)
+    }
+
+    /// Get the total byte length of this subscription command
+    pub fn length(&self) -> IndexT {
+        size_of::<SubscriptionMessageDefn>() as IndexT + self.get_struct().channel_length
+    }
+}

aeron-rs/src/command/terminate_driver.rs

@@ -5,13 +5,25 @@ use crate::concurrent::AtomicBuffer;
 use crate::util::{IndexT, Result};
 use std::mem::size_of;
 
-/// Raw command to terminate a driver. The `token_length` describes the length
-/// of a buffer immediately trailing this struct definition and part of the
-/// same message.
+/// Command message flyweight to ask the driver process to terminate
+///
+/// ```text
+///  0                   1                   2                   3
+///  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+/// |                       Correlation ID                          |
+/// |                                                               |
+/// +---------------------------------------------------------------+
+/// |                        Token Length                           |
+/// +---------------------------------------------------------------+
+/// |                        Token Buffer                          ...
+///...                                                              |
+/// +---------------------------------------------------------------+
+/// ```
 #[repr(C, packed(4))]
 pub struct TerminateDriverDefn {
-    pub(in crate::command) correlated_message: CorrelatedMessageDefn,
-    pub(in crate::command) token_length: i32,
+    correlated_message: CorrelatedMessageDefn,
+    token_length: i32,
 }
 
 impl<A> Flyweight<A, TerminateDriverDefn>

aeron-rs/src/concurrent/mod.rs

@@ -11,6 +11,7 @@ use std::ptr::{read_volatile, write_volatile};
 
 use memmap::MmapMut;
 use std::ops::{Deref, DerefMut};
+use std::str::from_utf8;
 
 fn bounds_check_slice(slice: &[u8], offset: IndexT, size: IndexT) -> Result<()> {
     if offset < 0 || size < 0 || slice.len() as IndexT - offset < size {
@@ -297,6 +298,50 @@ pub trait AtomicBuffer: Deref<Target = [u8]> + DerefMut<Target = [u8]> {
     fn capacity(&self) -> IndexT {
         self.len() as IndexT
     }
+
+    /// Fetch an ASCII/UTF-8 encoded string from the buffer, prefixed by a 32-bit length value.
+    ///
+    /// ```rust
+    /// # use aeron_rs::concurrent::AtomicBuffer;
+    /// # use std::mem::size_of;
+    /// # use aeron_rs::util::IndexT;
+    /// let mut buffer = vec![0u8; 10];
+    /// let message = [0x48, 0x65, 0x6C, 0x6C, 0x6F, 0x21];
+    /// buffer.put_i32(0, message.len() as IndexT);
+    /// buffer.put_slice(size_of::<i32>() as IndexT, &message[..], 0, message.len() as IndexT);
+    ///
+    /// assert_eq!(buffer.get_string(0), Ok("Hello!"));
+    /// ```
+    fn get_string(&self, offset: IndexT) -> Result<&str> {
+        let length = self.get_i32(offset)?;
+
+        let str_offset = offset + size_of::<i32>() as IndexT;
+        self.bounds_check(str_offset, length)?;
+
+        let start = str_offset as usize;
+        let end = start + length as usize;
+        let string = from_utf8(&self[start..end]).map_err(|_e| AeronError::UnknownEncoding)?;
+        Ok(string)
+    }
+
+    /// Write a string into the buffer, prefixed by a 32-bit length value. Returns the total
+    /// number of bytes written.
+    ///
+    /// ```rust
+    /// # use aeron_rs::concurrent::AtomicBuffer;
+    /// let mut buffer = vec![0u8; 10];
+    /// buffer.put_string(0, "Hello!");
+    /// assert_eq!(buffer.get_string(0), Ok("Hello!"));
+    /// ```
+    fn put_string(&mut self, offset: IndexT, value: &str) -> Result<i32> {
+        let length = value.len() as IndexT;
+        self.put_i32(offset, length)?;
+
+        let str_offset = offset + size_of::<i32>() as IndexT;
+        self.put_slice(str_offset, value.as_bytes(), 0, length)?;
+
+        Ok(size_of::<i32>() as i32 + length)
+    }
 }
 
 impl AtomicBuffer for Vec<u8> {}

aeron-rs/src/util.rs

@@ -18,6 +18,8 @@ pub enum AeronError {
     InsufficientCapacity,
     /// Indication that we have reached an invalid state and can't continue processing
     IllegalState,
+    /// Indication that a string is not encoded in UTF-8/ASCII format
+    UnknownEncoding,
 }
 
 /// Result type for operations in the Aeron client