chore: copied from log4js core

Author: Gareth Jones

.eslintrc

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+{
+  "root": true,
+	"extends": "airbnb-base",
+	"rules": {
+		"comma-dangle": 0,
+		"indent": 2,
+		"object-shorthand": 0,
+		"func-names": 0,
+		"max-len": [1, 120, 2],
+		"no-use-before-define": ["warn"],
+		"no-param-reassign": 0,
+    "strict": 0,
+    "import/no-extraneous-dependencies": 1,
+    "prefer-spread": 0,
+		"prefer-rest-params": 0,
+		"prefer-destructuring": 0
+	},
+  "parserOptions": {
+    "ecmaVersion": 6
+  }
+}

.travis.yml

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+language: node_js
+dist: trusty
+sudo: false
+node_js:
+  - "10"
+  - "8"
+  - "6"
+after_success:
+  - npm run codecov

README.md

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+# logstash Appender (HTTP) for log4js-node
+
+The logstash appenders for [log4js](https://log4js-node.github.io/log4js-node) send NDJSON formatted log events to [logstash](https://www.elastic.co/products/logstash) receivers. This appender uses HTTP to send the events (there is another logstash appender that uses [UDP](https://github.com/log4js-node/logstashUDP)).
+
+```bash
+npm install log4js @log4js-node/logstashHTTP
+```
+
+## Configuration
+
+* `type` - `@log4js-node/logstashHTTP`
+* `url` - `string` - logFaces receiver servlet URL
+* `application` - `string` (optional) - used to identify your application's logs
+* `logChannel` - `string` (optional) - also used to identify your application's logs [but in a more specific way]
+* `logType` - `string` (optional) - used for the `type` field in the logstash data
+* `timeout` - `integer` (optional, defaults to 5000ms) - the timeout for the HTTP request.
+
+This appender will also pick up Logger context values from the events, and add them as `p_` values in the logFaces event. See the example below for more details.
+
+# Example (default config)
+
+```javascript
+log4js.configure({
+  appenders: {
+    logstash: { type: '@log4js-node/logstashHTTP', url: 'http://localhost:9200/_bulk', application: 'logstash-log4js', logType: 'application', logChannel: 'node' }
+  },
+  categories: {
+    default: { appenders: [ 'logstash' ], level: 'info' }
+  }
+});
+
+const logger = log4js.getLogger();
+logger.addContext('requestId', '123');
+logger.info('some interesting log message');
+logger.error('something has gone wrong');
+```
+This example will result in two log events being sent to your `localhost:9200`. Both events will have a `context.requestId` property with a value of `123`.

lib/index.js

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+'use strict';
+
+/**
+ * logstashHTTP appender sends JSON formatted log events to logstashHTTP receivers.
+ */
+const util = require('util');
+const axios = require('axios');
+
+function wrapErrorsWithInspect(items) {
+  return items.map((item) => {
+    if ((item instanceof Error) && item.stack) {
+      return {
+        inspect: function () {
+          return `${util.format(item)}\n${item.stack}`;
+        }
+      };
+    }
+
+    return item;
+  });
+}
+
+function format(logData) {
+  const data = Array.isArray(logData)
+    ? logData
+    : Array.prototype.slice.call(arguments);
+  return util.format.apply(util, wrapErrorsWithInspect(data));
+}
+
+/**
+ *
+ * For HTTP (browsers or node.js) use the following configuration params:
+ *   {
+ *      "type": "logstashHTTP",       // must be present for instantiation
+ *      "application": "logstash-test",        // name of the application
+ *      "logType": "application",        // type of the application
+ *      "logChannel": "test",        // channel of the application
+ *      "url": "http://lfs-server/_bulk",  // logstash receiver servlet URL
+ *   }
+ */
+function logstashHTTPAppender(config) {
+  const sender = axios.create({
+    baseURL: config.url,
+    timeout: config.timeout || 5000,
+    headers: { 'Content-Type': 'application/x-ndjson' },
+    withCredentials: true,
+  });
+
+  return function log(event) {
+    const logstashEvent = [
+      {
+        index: {
+          _index: config.application,
+          _type: config.logType,
+        },
+      },
+      {
+        message: format(event.data),
+        context: event.context,
+        level: event.level.level / 100,
+        level_name: event.level.levelStr,
+        channel: config.logChannel,
+        datetime: (new Date(event.startTime)).toISOString(),
+        extra: {},
+      },
+    ];
+    const logstashJSON = `${JSON.stringify(logstashEvent[0])}\n${JSON.stringify(logstashEvent[1])}\n`;
+
+    // send to server
+    sender.post('', logstashJSON)
+      .catch((error) => {
+        if (error.response) {
+          console.error(`log4js.logstashHTTP Appender error posting to ${config.url}: ${error.response.status} - ${error.response.data}`);
+          return;
+        }
+        console.error(`log4js.logstashHTTP Appender error: ${error.message}`);
+      });
+  };
+}
+
+function configure(config) {
+  return logstashHTTPAppender(config);
+}
+
+module.exports.configure = configure;