Create a message queue

The create command creates a new message queue with support of the
typical parameters `mode`, `capacity` and `msgsize`. This command also
supports the global argument `verbose`.

src/cli.rs

@@ -1,3 +1,4 @@
+use crate::create::Create;
 use clap::{crate_authors, crate_version, AppSettings, Clap};
 
 #[derive(Clap, Debug)]
@@ -12,4 +13,11 @@ pub struct Opts {
     /// Produce verbose output
     #[clap(short, long, global = true)]
     pub verbose: bool,
+    #[clap(subcommand)]
+    pub command: Command,
+}
+
+#[derive(Clap, Debug)]
+pub enum Command {
+    Create(Create),
 }

src/create.rs

@@ -0,0 +1,63 @@
+use anyhow::Result;
+use clap::Clap;
+use posixmq::PosixMq;
+use std::fs;
+
+/// Create a POSIX message queue
+#[derive(Clap, Debug)]
+pub struct Create {
+    /// Permissions (octal) to create the queue with
+    #[clap(short = 'p', long)]
+    mode: Option<String>,
+    /// Maximum number of messages in the queue
+    #[clap(short, long)]
+    capacity: Option<usize>,
+    /// Message size in bytes
+    #[clap(short = 's', long)]
+    msgsize: Option<usize>,
+    /// Name of the queue
+    #[clap(value_name = "QNAME")]
+    queue: String,
+}
+
+fn msgsize_default() -> usize {
+    match fs::read_to_string("/proc/sys/fs/mqueue/msgsize_default") {
+        Ok(m) => m.trim().parse::<usize>().unwrap(), // should never fail
+        _ => 8192,
+    }
+}
+
+fn msg_default() -> usize {
+    match fs::read_to_string("/proc/sys/fs/mqueue/msg_default") {
+        Ok(m) => m.trim().parse::<usize>().unwrap(), // should never fail
+        _ => 10,
+    }
+}
+
+impl Create {
+    pub fn run(&self, verbose: bool) -> Result<()> {
+        let mq = &mut posixmq::OpenOptions::readonly();
+
+        if let Some(m) = &self.mode {
+            mq.mode(u32::from_str_radix(&m, 8)?);
+        }
+
+        mq.max_msg_len(self.msgsize.unwrap_or_else(msgsize_default))
+            .capacity(self.capacity.unwrap_or_else(msg_default))
+            .create_new()
+            .open(&self.queue)?;
+
+        if verbose {
+            let mq = PosixMq::open(&self.queue)?;
+            let attributes = mq.attributes()?;
+
+            println!("Created message queue: {} with attributes msgsize: {}, capacity: {}, current_messages: {}",
+                     &self.queue,
+                     &attributes.max_msg_len,
+                     &attributes.capacity,
+                     &attributes.current_messages);
+        }
+
+        Ok(())
+    }
+}

src/main.rs

@@ -1,9 +1,17 @@
+use anyhow::Result;
 use clap::Clap;
 
 mod cli;
+mod create;
 
-use cli::Opts;
+use cli::{Command, Opts};
 
-fn main() {
-    Opts::parse();
+fn main() -> Result<()> {
+    let opts: Opts = Opts::parse();
+
+    match opts.command {
+        Command::Create(c) => c.run(opts.verbose)?,
+    }
+
+    Ok(())
 }