Add MySQLPlugin to plugins (#30)

diff --git a/README.md b/README.md
index 0b1b9f0..94c2d0c 100644
--- a/README.md
+++ b/README.md
@@ -57,6 +57,7 @@
 | `SW_AGENT_LOGGING_LEVEL` | The logging level, could be one of `CRITICAL`, `FATAL`, `ERROR`, `WARN`(`WARNING`), `INFO`, `DEBUG` | `INFO` |
 | `SW_IGNORE_SUFFIX` | The suffices of endpoints that will be ignored (not traced), comma separated | `.jpg,.jpeg,.js,.css,.png,.bmp,.gif,.ico,.mp3,.mp4,.html,.svg` |
 | `SW_TRACE_IGNORE_PATH` | The paths of endpoints that will be ignored (not traced), comma separated | `` |
+| `SW_MYSQL_SQL_PARAMETERS_MAX_LENGTH` | The maximum string length of MySQL parameters to log | `512` |
 | `SW_AGENT_MAX_BUFFER_SIZE` | The maximum buffer size before sending the segment data to backend | `'1000'` |
 
 ## Supported Libraries
@@ -65,9 +66,20 @@
 
 Library | Plugin Name
 | :--- | :--- |
-| built-in `http` and `https` module | `http` |
+| built-in `http` and `https` module | `http` / `https` |
 | [`express`](https://expressjs.com) | `express` |
 | [`axios`](https://github.com/axios/axios) | `axios` |
+| [`mysql`](https://github.com/mysqljs/mysql) | `mysql` |
+
+### Compatible Libraries
+
+The following are packages that have been tested to some extent and are compatible because they work through the instrumentation of an underlying package:
+
+Library | Underlying Plugin Name
+| :--- | :--- |
+| [`request`](https://github.com/request/request) | `http` / `https` |
+| [`request-promise`](https://github.com/request/request-promise) | `http` / `https` |
+| [`koa`](https://github.com/koajs/koa) | `http` / `https` |
 
 ## Contact Us
 * Submit [an issue](https://github.com/apache/skywalking/issues/new) by using [Nodejs] as title prefix.
diff --git a/src/Tag.ts b/src/Tag.ts
index 95e8ab3..305107c 100644
--- a/src/Tag.ts
+++ b/src/Tag.ts
@@ -24,19 +24,25 @@
 }
 
 export default {
+  httpStatusCodeKey: 'http.status.code',  // TODO: maybe find a better place to put these?
+  httpStatusMsgKey: 'http.status.msg',
   httpURLKey: 'http.url',
-  httpMethodKey: 'http.method',  // TODO: maybe find a better place to put these?
+  httpMethodKey: 'http.method',
+  dbTypeKey: 'db.type',
+  dbInstanceKey: 'db.instance',
+  dbStatementKey: 'db.statement',
+  dbSqlParametersKey: 'db.sql.parameters',
 
   httpStatusCode(val: string | number | undefined): Tag {
     return {
-      key: 'http.status.code',
+      key: this.httpStatusCodeKey,
       overridable: true,
       val: `${val}`,
     } as Tag;
   },
   httpStatusMsg(val: string | undefined): Tag {
     return {
-      key: 'http.status.msg',
+      key: this.httpStatusMsgKey,
       overridable: true,
       val: `${val}`,
     } as Tag;
@@ -55,4 +61,32 @@
       val: `${val}`,
     } as Tag;
   },
+  dbType(val: string | undefined): Tag {
+    return {
+      key: this.dbTypeKey,
+      overridable: true,
+      val: `${val}`,
+    } as Tag;
+  },
+  dbInstance(val: string | undefined): Tag {
+    return {
+      key: this.dbInstanceKey,
+      overridable: true,
+      val: `${val}`,
+    } as Tag;
+  },
+  dbStatement(val: string | undefined): Tag {
+    return {
+      key: this.dbStatementKey,
+      overridable: true,
+      val: `${val}`,
+    } as Tag;
+  },
+  dbSqlParameters(val: string | undefined): Tag {
+    return {
+      key: this.dbSqlParametersKey,
+      overridable: false,
+      val: `${val}`,
+    } as Tag;
+  },
 };
diff --git a/src/config/AgentConfig.ts b/src/config/AgentConfig.ts
index 8c9031b..de68ccb 100644
--- a/src/config/AgentConfig.ts
+++ b/src/config/AgentConfig.ts
@@ -27,6 +27,7 @@
   maxBufferSize?: number;
   ignoreSuffix?: string;
   traceIgnorePath?: string;
+  mysql_sql_parameters_max_length?: number;
   // the following is internal state computed from config values
   reIgnoreOperation?: RegExp;
 };
@@ -59,5 +60,6 @@
     Number.parseInt(process.env.SW_AGENT_MAX_BUFFER_SIZE as string, 10) : 1000,
   ignoreSuffix: process.env.SW_IGNORE_SUFFIX ?? '.jpg,.jpeg,.js,.css,.png,.bmp,.gif,.ico,.mp3,.mp4,.html,.svg',
   traceIgnorePath: process.env.SW_TRACE_IGNORE_PATH || '',
+  mysql_sql_parameters_max_length: Math.trunc(Math.max(0, Number(process.env.SW_MYSQL_SQL_PARAMETERS_MAX_LENGTH))) || 512,
   reIgnoreOperation: RegExp(''),  // temporary placeholder so Typescript doesn't throw a fit
 };
diff --git a/src/plugins/MySQLPlugin.ts b/src/plugins/MySQLPlugin.ts
new file mode 100644
index 0000000..6a3e6dd
--- /dev/null
+++ b/src/plugins/MySQLPlugin.ts
@@ -0,0 +1,143 @@
+/*!
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+import SwPlugin from '../core/SwPlugin';
+import ContextManager from '../trace/context/ContextManager';
+import { Component } from '../trace/Component';
+import Tag from '../Tag';
+import { SpanLayer } from '../proto/language-agent/Tracing_pb';
+import { createLogger } from '../logging';
+import PluginInstaller from '../core/PluginInstaller';
+import config from '../config/AgentConfig';
+
+const logger = createLogger(__filename);
+
+class MySQLPlugin implements SwPlugin {
+  readonly module = 'mysql';
+  readonly versions = '*';
+
+  install(installer: PluginInstaller): void {
+    if (logger.isDebugEnabled()) {
+      logger.debug('installing mysql plugin');
+    }
+
+    const Connection = installer.require('mysql/lib/Connection');
+    const _query = Connection.prototype.query;
+
+    Connection.prototype.query = function(sql: any, values: any, cb: any) {
+      const wrapCallback = (_cb: any) => {
+        return function(this: any, error: any, results: any, fields: any) {
+          if (error)
+            span.error(error);
+
+          span.stop();
+
+          return _cb.call(this, error, results, fields);
+        }
+      };
+
+      const host = `${this.config.host}:${this.config.port}`;
+      const span = ContextManager.current.newExitSpan('mysql/query', host).start();
+
+      try {
+        let _sql: any;
+        let _values: any;
+        let streaming: any;
+
+        if (typeof sql === 'function') {
+          sql = wrapCallback(sql);
+
+        } else if (typeof sql === 'object') {
+          _sql = sql.sql;
+
+          if (typeof values === 'function') {
+            values = wrapCallback(values);
+            _values = sql.values;
+
+          } else if (values !== undefined) {
+            _values = values;
+
+            if (typeof cb === 'function') {
+              cb = wrapCallback(cb);
+            } else {
+              streaming = true;
+            }
+
+          } else {
+            streaming = true;
+          }
+
+        } else {
+          _sql = sql;
+
+          if (typeof values === 'function') {
+            values = wrapCallback(values);
+
+          } else if (values !== undefined) {
+            _values = values;
+
+            if (typeof cb === 'function') {
+              cb = wrapCallback(cb);
+            } else {
+              streaming = true;
+            }
+
+          } else {
+            streaming = true;
+          }
+        }
+
+        span.component = Component.MYSQL;
+        span.layer = SpanLayer.DATABASE;
+        span.peer = host;
+
+        span.tag(Tag.dbType('mysql'));
+        span.tag(Tag.dbInstance(this.config.database || ''));
+        span.tag(Tag.dbStatement(_sql || ''));
+
+        if (_values) {
+          let vals = _values.map((v: any) => `${v}`).join(', ');
+
+          if (vals.length > config.mysql_sql_parameters_max_length)
+            vals = vals.splice(0, config.mysql_sql_parameters_max_length);
+
+            span.tag(Tag.dbSqlParameters(`[${vals}]`));
+        }
+
+        const query = _query.call(this, sql, values, cb);
+
+        if (streaming) {
+          query.on('error', (e: any) => span.error(e));
+          query.on('end', () => span.stop());
+        }
+
+        return query;
+
+      } catch (e) {
+        span.error(e);
+        span.stop();
+
+        throw e;
+      }
+    };
+  }
+}
+
+// noinspection JSUnusedGlobalSymbols
+export default new MySQLPlugin();
diff --git a/src/trace/Component.ts b/src/trace/Component.ts
index 1eb9597..6469900 100644
--- a/src/trace/Component.ts
+++ b/src/trace/Component.ts
@@ -20,6 +20,7 @@
 export class Component {
   static readonly UNKNOWN = new Component(0);
   static readonly HTTP = new Component(2);
+  static readonly MYSQL = new Component(5);
   static readonly MONGODB = new Component(9);
   static readonly HTTP_SERVER = new Component(49);
   static readonly EXPRESS = new Component(4002);