admin: SHOW CONFIG (#50)

* admin: SHOW CONFIG

* test

src/admin.rs

@@ -2,6 +2,8 @@ use bytes::{Buf, BufMut, BytesMut};
 use log::{info, trace};
 use tokio::net::tcp::OwnedWriteHalf;
 
+use std::collections::HashMap;
+
 use crate::config::{get_config, parse};
 use crate::constants::{OID_NUMERIC, OID_TEXT};
 use crate::errors::Error;
@@ -27,6 +29,9 @@ pub async fn handle_admin(stream: &mut OwnedWriteHalf, mut query: BytesMut) -> R
     } else if query.starts_with("RELOAD") {
         trace!("RELOAD");
         reload(stream).await
+    } else if query.starts_with("SHOW CONFIG") {
+        trace!("SHOW CONFIG");
+        show_config(stream).await
     } else {
         Err(Error::ProtocolSyncError)
     }
@@ -61,6 +66,92 @@ pub async fn reload(stream: &mut OwnedWriteHalf) -> Result<(), Error> {
     write_all_half(stream, res).await
 }
 
+pub async fn show_config(stream: &mut OwnedWriteHalf) -> Result<(), Error> {
+    let guard = get_config();
+    let config = &*guard.clone();
+    let config: HashMap<String, String> = config.into();
+    drop(guard);
+
+    // Configs that cannot be changed dynamically.
+    let immutables = ["host", "port", "connect_timeout"];
+
+    // Columns
+    let columns = ["key", "value", "default", "changeable"];
+
+    // RowDescription
+    let mut row_desc = BytesMut::new();
+    row_desc.put_i16(4 as i16); // key, value, default, changeable
+
+    for column in columns {
+        row_desc.put_slice(&format!("{}\0", column).as_bytes());
+
+        // Doesn't belong to any table
+        row_desc.put_i32(0);
+
+        // Doesn't belong to any table
+        row_desc.put_i16(0);
+
+        // Data type
+        row_desc.put_i32(OID_TEXT);
+
+        // text size = variable (-1)
+        row_desc.put_i16(-1);
+
+        // Type modifier: none that I know
+        row_desc.put_i32(-1);
+
+        // Format being used: text (0), binary (1)
+        row_desc.put_i16(0);
+    }
+
+    // Response data
+    let mut res = BytesMut::new();
+    res.put_u8(b'T');
+    res.put_i32(row_desc.len() as i32 + 4);
+    res.put(row_desc);
+
+    // DataRow rows
+    for (key, value) in config {
+        let mut data_row = BytesMut::new();
+
+        data_row.put_i16(4 as i16); // key, value, default, changeable
+
+        let key_bytes = key.as_bytes();
+        let value = value.as_bytes();
+
+        data_row.put_i32(key_bytes.len() as i32);
+        data_row.put_slice(&key_bytes);
+
+        data_row.put_i32(value.len() as i32);
+        data_row.put_slice(&value);
+
+        data_row.put_i32(1 as i32);
+        data_row.put_slice(&"-".as_bytes());
+
+        let changeable = if immutables.iter().filter(|col| *col == &key).count() == 1 {
+            "no".as_bytes()
+        } else {
+            "yes".as_bytes()
+        };
+        data_row.put_i32(changeable.len() as i32);
+        data_row.put_slice(&changeable);
+
+        res.put_u8(b'D');
+        res.put_i32(data_row.len() as i32 + 4);
+        res.put(data_row);
+    }
+
+    res.put_u8(b'C');
+    res.put_i32("SHOW CONFIG\0".as_bytes().len() as i32 + 4);
+    res.put_slice(&"SHOW CONFIG\0".as_bytes());
+
+    res.put_u8(b'Z');
+    res.put_i32(5);
+    res.put_u8(b'I');
+
+    write_all_half(stream, res).await
+}
+
 /// SHOW STATS
 pub async fn show_stats(stream: &mut OwnedWriteHalf) -> Result<(), Error> {
     let columns = [