add "show help" command (#505)

This commit adds a new function to handle notify and use it
in the SHOW HELP command, which displays the available options
in the admin console.

Also, adding Fabrízio as a co-author for all the help with the
protocol and the help to structure this PR.

Signed-off-by: Sebastian Webber <sebastian@swebber.me>
Co-authored-by: Fabrízio de Royes Mello <fabriziomello@gmail.com>

Author: sebastianwebber

src/admin.rs

@@ -1,7 +1,7 @@
 use crate::pool::BanReason;
 use crate::stats::pool::PoolStats;
 use bytes::{Buf, BufMut, BytesMut};
-use log::{error, info, trace};
+use log::{debug, error, info, trace};
 use nix::sys::signal::{self, Signal};
 use nix::unistd::Pid;
 use std::collections::HashMap;
@@ -84,6 +84,10 @@ where
             shutdown(stream).await
         }
         "SHOW" => match query_parts[1].to_ascii_uppercase().as_str() {
+            "HELP" => {
+                trace!("SHOW HELP");
+                show_help(stream).await
+            }
             "BANS" => {
                 trace!("SHOW BANS");
                 show_bans(stream).await
@@ -271,6 +275,45 @@ where
     write_all_half(stream, &res).await
 }
 
+/// Show all available options.
+async fn show_help<T>(stream: &mut T) -> Result<(), Error>
+where
+    T: tokio::io::AsyncWrite + std::marker::Unpin,
+{
+    let mut res = BytesMut::new();
+
+    let detail_msg = vec![
+        "",
+        "SHOW HELP|CONFIG|DATABASES|POOLS|CLIENTS|SERVERS|USERS|VERSION",
+        // "SHOW PEERS|PEER_POOLS", // missing PEERS|PEER_POOLS
+        // "SHOW FDS|SOCKETS|ACTIVE_SOCKETS|LISTS|MEM|STATE", // missing FDS|SOCKETS|ACTIVE_SOCKETS|MEM|STATE
+        "SHOW LISTS",
+        // "SHOW DNS_HOSTS|DNS_ZONES", // missing DNS_HOSTS|DNS_ZONES
+        "SHOW STATS", // missing STATS_TOTALS|STATS_AVERAGES|TOTALS
+        "SET key = arg",
+        "RELOAD",
+        "PAUSE [<db>, <user>]",
+        "RESUME [<db>, <user>]",
+        // "DISABLE <db>", // missing
+        // "ENABLE <db>", // missing
+        // "RECONNECT [<db>]", missing
+        // "KILL <db>",
+        // "SUSPEND",
+        "SHUTDOWN",
+        // "WAIT_CLOSE [<db>]", // missing
+    ];
+
+    res.put(notify("Console usage", detail_msg.join("\n\t")));
+    res.put(command_complete("SHOW"));
+
+    // ReadyForQuery
+    res.put_u8(b'Z');
+    res.put_i32(5);
+    res.put_u8(b'I');
+
+    write_all_half(stream, &res).await
+}
+
 /// Show shards and replicas.
 async fn show_databases<T>(stream: &mut T) -> Result<(), Error>
 where

src/messages.rs

@@ -530,6 +530,26 @@ pub fn command_complete(command: &str) -> BytesMut {
     res
 }
 
+/// Create a notify message.
+pub fn notify(message: &str, details: String) -> BytesMut {
+    let mut notify_cmd = BytesMut::new();
+
+    notify_cmd.put_slice("SNOTICE\0".as_bytes());
+    notify_cmd.put_slice("C00000\0".as_bytes());
+    notify_cmd.put_slice(format!("M{}\0", message).as_bytes());
+    notify_cmd.put_slice(format!("D{}\0", details).as_bytes());
+
+    // this extra byte says that is the end of the package
+    notify_cmd.put_u8(0);
+
+    let mut res = BytesMut::new();
+    res.put_u8(b'N');
+    res.put_i32(notify_cmd.len() as i32 + 4);
+    res.put(notify_cmd);
+
+    res
+}
+
 pub fn flush() -> BytesMut {
     let mut bytes = BytesMut::new();
     bytes.put_u8(b'H');