negotiate HTTP locales for incoming browser requests

middleware/requestLanguage.js

@@ -0,0 +1,74 @@
+
+/**
+  this middleware is responsible for negotiating HTTP locales for incoming
+  browser requests by reading 'Accept-Language' request headers.
+
+  the preferred language will then be available on the $req object:
+  eg. for 'Accept-Language: fr':
+  ```
+  console.log( req.language );
+
+  {
+    name: 'French',
+    type: 'living',
+    scope: 'individual',
+    iso6393: 'fra',
+    iso6392B: 'fre',
+    iso6392T: 'fra',
+    iso6391: 'fr',
+    defaulted: false
+  }
+  ```
+
+  for configuration options see:
+  https://github.com/florrain/locale
+**/
+
+const locale = require('locale');
+
+/**
+  BCP47 language tags can contain three parts:
+    1. A language subtag (en, zh).
+    2. A script subtag (Hant, Latn).
+    3. A region subtag (US, CN).
+
+  at time of writing we will only be concerned with 1. (the language subtag) with
+  the intention of being compatible with the language standard of whosonfirst data.
+
+  whosonfirst data is in ISO 639-3 format so we will need to configure the library
+  to support all ISO 639-1 (2 char) codes and convert them to 639-1 (3-char) codes.
+
+  see: https://github.com/whosonfirst/whosonfirst-names
+**/
+const iso6393 = require('iso-639-3');
+
+// create a dictionary which maps the ISO 639-1 language subtags to a map
+// of it's represenation in several different standards.
+const language = {};
+iso6393.filter( i => !!i.iso6391 ).forEach( i => language[ i.iso6391 ] = i );
+
+// a pre-processed locale list of language subtags we support (all of them).
+const allLocales = new locale.Locales( Object.keys( language ) );
+
+// return the middleware
+module.exports = function middleware( req, res, next ){
+
+  // parse request & choose best locale
+  var locales = new locale.Locales( req.headers['accept-language'] || '' );
+  var best = locales.best( allLocales );
+
+  // set $req.language property
+  req.language = language[ best.language ] || language.en;
+  req.language.defaulted = best.defaulted;
+
+  // set $req.clean property in order to print language info in response header
+  req.clean = req.clean || {};
+  req.clean.lang = {
+    name: req.language.name,
+    iso6391: req.language.iso6391,
+    iso6393: req.language.iso6393,
+    defaulted: req.language.defaulted
+  };
+
+  next();
+};

package.json

@@ -47,8 +47,10 @@
     "geojson": "^0.4.0",
     "geojson-extent": "^0.3.1",
     "geolib": "^2.0.18",
+    "iso-639-3": "^1.0.0",
     "iso3166-1": "^0.3.0",
     "joi": "^10.1.0",
+    "locale": "^0.1.0",
     "lodash": "^4.5.0",
     "markdown": "0.5.0",
     "morgan": "1.8.1",

routes/v1.js

@@ -18,7 +18,8 @@ var sanitizers = {
 
 /** ----------------------- middleware ------------------------ **/
 var middleware = {
-  calcSize: require('../middleware/sizeCalculator')
+  calcSize: require('../middleware/sizeCalculator'),
+  requestLanguage: require('../middleware/requestLanguage')
 };
 
 /** ----------------------- controllers ----------------------- **/
@@ -108,6 +109,7 @@ function addRoutes(app, peliasConfig) {
     ]),
     search: createRouter([
       sanitizers.search.middleware,
+      middleware.requestLanguage,
       middleware.calcSize(),
       // 3rd parameter is which query module to use, use fallback/geodisambiguation
       //  first, then use original search strategy if first query didn't return anything
@@ -131,6 +133,7 @@ function addRoutes(app, peliasConfig) {
     ]),
     structured: createRouter([
       sanitizers.structured_geocoding.middleware,
+      middleware.requestLanguage,
       middleware.calcSize(),
       controllers.search(peliasConfig.api, esclient, queries.structured_geocoding, not(hasResponseDataOrRequestErrors)),
       postProc.trimByGranularityStructured(),
@@ -150,6 +153,7 @@ function addRoutes(app, peliasConfig) {
     ]),
     autocomplete: createRouter([
       sanitizers.autocomplete.middleware,
+      middleware.requestLanguage,
       controllers.search(peliasConfig.api, esclient, queries.autocomplete, not(hasResponseDataOrRequestErrors)),
       postProc.distances('focus.point.'),
       postProc.confidenceScores(peliasConfig.api),
@@ -165,6 +169,7 @@ function addRoutes(app, peliasConfig) {
     ]),
     reverse: createRouter([
       sanitizers.reverse.middleware,
+      middleware.requestLanguage,
       middleware.calcSize(),
       controllers.coarse_reverse(pipService, coarse_reverse_should_execute),
       controllers.search(peliasConfig.api, esclient, queries.reverse, original_reverse_should_execute),
@@ -184,6 +189,7 @@ function addRoutes(app, peliasConfig) {
     ]),
     nearby: createRouter([
       sanitizers.nearby.middleware,
+      middleware.requestLanguage,
       middleware.calcSize(),
       controllers.search(peliasConfig.api, esclient, queries.reverse, not(hasResponseDataOrRequestErrors)),
       postProc.distances('point.'),
@@ -202,6 +208,7 @@ function addRoutes(app, peliasConfig) {
     ]),
     place: createRouter([
       sanitizers.place.middleware,
+      middleware.requestLanguage,
       controllers.place(peliasConfig.api, esclient),
       postProc.accuracy(),
       postProc.localNamingConventions(),