feat: add dump function for current connections count

lib/Pool.js

@@ -285,6 +285,16 @@ Pool.prototype.escapeId = function escapeId(value) {
   return mysql.escapeId(value, false);
 };
 
+Pool.prototype.dumpConnectionsCount = function () {
+  return {
+    allConnectionsCount       : this._allConnections.length,
+    freeConnectionsCount      : this._freeConnections.length,
+    connectionQueueCount      : this._connectionQueue.length,
+    acquiringConnectionsCount : this._acquiringConnections.length,
+    queryingConnectionsCount  : this._allConnections.length - this._freeConnections.length - this._acquiringConnections.length
+  };
+};
+
 function spliceConnection(array, connection) {
   var index;
   if ((index = array.indexOf(connection)) !== -1) {

test/unit/pool/test-dump-connections-count.js

@@ -0,0 +1,114 @@
+var assert = require('assert');
+var common = require('../../common');
+
+var server = common.createFakeServer();
+
+server.listen(0, function (err) {
+  assert.ifError(err);
+
+  var connectionLimit = 3;
+  var pool = common.createPool({ port: server.port(), connectionLimit: connectionLimit } );
+  assert.deepStrictEqual(connectionLimit, pool.config.connectionLimit);
+  assert.deepStrictEqual(pool.dumpConnectionsCount(), {
+    allConnectionsCount       : 0,
+    freeConnectionsCount      : 0,
+    connectionQueueCount      : 0,
+    acquiringConnectionsCount : 0,
+    queryingConnectionsCount  : 0
+  });
+
+  var conn1, conn2, conn3, conn4, conn5;
+
+  pool.getConnection(function (err, connection) {
+    assert.ifError(err);
+    conn1 = connection;
+  });
+
+  pool.getConnection(function (err, connection) {
+    assert.ifError(err);
+    conn2 = connection;
+  });
+  pool.getConnection(function (err, connection) {
+    assert.ifError(err);
+    conn3 = connection;
+  });
+  pool.getConnection(function (err, connection) {
+    assert.ifError(err);
+    conn4 = connection;
+  });
+  pool.getConnection(function (err, connection) {
+    assert.ifError(err);
+    conn5 = connection;
+  });
+
+  setTimeout(function(){
+    assert.ok(conn1);
+    assert.ok(conn2);
+    assert.ok(conn3);
+    assert.ok(conn4 === undefined);
+    assert.ok(conn5 === undefined);
+    assert.deepStrictEqual(pool.dumpConnectionsCount(), {
+      allConnectionsCount       : 3,
+      freeConnectionsCount      : 0,
+      connectionQueueCount      : 2,
+      acquiringConnectionsCount : 0,
+      queryingConnectionsCount  : 3
+    });
+
+    pool.releaseConnection(conn1);
+    assert.deepStrictEqual(pool.dumpConnectionsCount(), {
+      allConnectionsCount       : 3,
+      freeConnectionsCount      : 0,
+      connectionQueueCount      : 1,
+      acquiringConnectionsCount : 1,
+      queryingConnectionsCount  : 2
+    });
+
+    setTimeout(function() {
+      assert.ok(conn4);
+      assert.ok(conn5 === undefined);
+      assert.deepStrictEqual(pool.dumpConnectionsCount(), {
+        allConnectionsCount       : 3,
+        freeConnectionsCount      : 0,
+        connectionQueueCount      : 1,
+        acquiringConnectionsCount : 0,
+        queryingConnectionsCount  : 3
+      });
+
+      pool.releaseConnection(conn2);
+      pool.releaseConnection(conn3);
+      pool.releaseConnection(conn4);
+      assert.deepStrictEqual(pool.dumpConnectionsCount(), {
+        allConnectionsCount       : 3,
+        freeConnectionsCount      : 2,
+        connectionQueueCount      : 0,
+        acquiringConnectionsCount : 1,
+        queryingConnectionsCount  : 0
+      });
+
+      setTimeout(function() {
+        assert.ok(conn5);
+        pool.releaseConnection(conn5);
+        assert.deepStrictEqual(pool.dumpConnectionsCount(), {
+          allConnectionsCount       : 3,
+          freeConnectionsCount      : 3,
+          connectionQueueCount      : 0,
+          acquiringConnectionsCount : 0,
+          queryingConnectionsCount  : 0
+        });
+        pool.end(function(err){
+          assert.ifError(err);
+          assert.deepStrictEqual(pool.dumpConnectionsCount(), {
+            allConnectionsCount       : 0,
+            freeConnectionsCount      : 0,
+            connectionQueueCount      : 0,
+            acquiringConnectionsCount : 0,
+            queryingConnectionsCount  : 0
+          });
+          server.destroy();
+        });
+      }, 100);
+    }, 100);
+  }, 100);
+
+});