Writing text files

With dart:io, we already read files from the file system, and writing operates in a similar manner, as follows:

import 'dart:io';

void main() {
  File myfile = new File("example.txt");
  myfile.writeAsStringSync("Hello Word!");
}

This demonstrates the synchronous version of the function, with writeAsString being the asynchronous version.

Open the log.dart file in this chapter's project. For this, take a look at the following code snippet:

void log(HttpRequest request) {
  String entry = getLogEntry(request);
  File logstore = new File("accesslog.txt");
  logstore.writeAsStringSync(entry, mode: FileMode.APPEND);
}

To record the web access request to the disk, the log entries will have to be accumulative so that the entries are written with the APPEND mode passed as a named parameter.

Extracting request information

The HttpRequest object and headers property expose metadata from the request to the client. For example, the headers property can give the host and port number. The user-agent identifies which program or web browser was used when making the request, as shown in the following code snippet:

String getLogEntry(HttpRequest request) {

  //USER_AGENT
  HttpHeaders headers = request.headers;
  String reqUri = "${headers.host},${headers.port}${request.uri.toString()}";
  String entry =
      " ${request.connectionInfo.remoteAddress.address}, $reqUri, ${headers[HttpHeaders.USER_AGENT]}\r\n";

  return (new DateTime.now()).toString() + entry;
}

The remoteAddress getter (IP address) can be used to track who was browsing and from which part of the world. Log entries to request the index.html blog would look as follows:

2015-05-17 17:03:48.496 127.0.0.1, 127.0.0.1,8080/index.html, [Mozilla/5.0 (X11; CrOS x86_64 6812.88.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/42.0.2311.153 Safari/537.36]
2015-05-17 17:03:49.177 127.0.0.1, 127.0.0.1,8080/6.png, [Mozilla/5.0 (X11; CrOS x86_64 6812.88.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/42.0.2311.153 Safari/537.36]
2015-05-14 18:52:45.690 127.0.0.1, 127.0.0.1,8080/favicon.ico, [NetSurf/2.9 (Linux; x86_64)]

Browsers will request the page that is browsed to by the user and also other assets such as favicon.ico (the small square graphic that is often shown in the URL bar of a web browser or on a bookmark).