A check for gzip format

index.js

@@ -4,6 +4,7 @@ var assert = require('assert');
 var fs = require('fs');
 var Reader = require('./lib/reader');
 var ip = require('./lib/ip');
+var isGzip = require('./lib/is-gzip');
 var utils = require('./lib/utils');
 
 exports.Reader = Reader;
@@ -15,6 +16,9 @@ exports.open = function(filepath, opts, cb) {
 
   fs.readFile(filepath, function(err, database) {
     if (err) return cb(err);
+    if (isGzip(database)) {
+      return cb(new Error('Looks like you are passing in a file in gzip format, please use mmdb database instead.'));
+    }
     var reader = new Reader(database, opts);
     if (opts && !!opts.watchForUpdates) {
       fs.watch(filepath, function() {

lib/is-gzip.js

@@ -0,0 +1,9 @@
+'use strict';
+
+module.exports = function(buf) {
+  if (!buf || buf.length < 3) {
+    return false;
+  }
+
+  return buf[0] === 0x1f && buf[1] === 0x8b && buf[2] === 0x08;
+};

test/index.js

@@ -84,6 +84,15 @@ describe('index', function() {
       }, /Callback function must be provided/);
     });
 
+    it('should return an error when gzip file attempted', function(done) {
+      var dbPath = path.join(__dirname, 'databases/GeoIP2-City-Test.mmdb.gz');
+      maxmind.open(dbPath, function(err) {
+        assert.equal(err.message,
+          'Looks like you are passing in a file in gzip format, please use mmdb database instead.');
+        done();
+      });
+    });
+
     it('should check for an error when cannot read database on update', function(done) {
       var counter = 0;
       var cb = function(err, reader) {

test/is-gzip.js

@@ -0,0 +1,21 @@
+'use strict';
+
+var assert = require('assert');
+var isGzip = require('../lib/is-gzip');
+
+describe('lib/is-gzip', function() {
+  it('should return false for short buffers', function() {
+    assert.equal(isGzip(new Buffer([1, 2])), false);
+  });
+
+  it('should return false for string buffer', function() {
+    assert.equal(isGzip(new Buffer('kraken')), false);
+  });
+
+  it('should return false for string buffer', function() {
+    // gzipped "kraken" string
+    // shell: `echo "kraken" | gzip | base64`
+    var buffer = new Buffer('H4sIAGBDv1gAA8suSsxOzeMCAKjj9U8HAAAA', 'base64');
+    assert.equal(isGzip(buffer), true);
+  });
+});