feat(libpostal): Use libpostal service

BREAKING CHANGE

Use microservice-wrapper to avoid having to load libpostal locally.

Note: this now requires a new configuration section in `pelias.json`, a
top-level `services` key with the usual properties. Here's an example
full `pelias.json`:

```
{
  "api": {
    "textAnalyzer": "libpostal"
  },
  "services": {
    "libpostal": {
      "url": "http://libpostal-service-url:8080",
      "timeout": 4000
    }
  }
}
```

Fixes #106

lib/analyze.js

@@ -1,3 +1,4 @@
+const libpostal_service = require( './libpostal_wrapper' );
 // constants for controlling how we parse ranges, eg: 'α-β'
 // some ranges such as '1-7' are ambiguous; it could mean 'apt 7, no 1'; or
 // it could mean 'apt 1, no 7'; or could even be a valid range 'one to seven'.
@@ -7,32 +8,11 @@ var MIN_RANGE = 1; // the miniumum amount β is higher than α
 var MAX_RANGE = 6; // the maximum amount β is higher than α
 var MIN_RANGE_HOUSENUMBER = 10; // the minimum acceptible value for both α and β
 
-/*
- * Return the appropriate version of node-postal
- */
-
-var _nodepostal_module;
-function get_libpostal() {
-  // lazy load this dependency; since it's large (~2GB RAM) and may be
-  // accidentally required by a process which doesn't use it.
-  if (!_nodepostal_module) {
-    // load the mock library if MOCK_LIBPOSTAL env var is set
-    if (process.env.MOCK_LIBPOSTAL) {
-      _nodepostal_module = require('../test/lib/mock_libpostal');
-    // otherwise load the real thing
-    } else {
-      _nodepostal_module = require('node-postal');
-    }
-  }
-
-  return _nodepostal_module;
-}
-
 /**
   analyze input streetname string and return a list of expansions.
 **/
 function street( streetName ){
-  const postal = get_libpostal();
+  const postal = libpostal_service();
 
   // use libpostal to expand the address
   var expansions = postal.expand.expand_address( streetName );

lib/libpostal_wrapper.js

@@ -0,0 +1,22 @@
+const mock_libpostal = require('../test/lib/mock_libpostal');
+
+// This module is a wrapper around the actual libpostal service library
+// and the mock libpostal library
+// it allows an environment variable to switch which library is used in application code
+
+let libpostal_module;
+function get_libpostal() {
+  // return the mock library if MOCK_LIBPOSTAL env var is set
+  if (process.env.MOCK_LIBPOSTAL) {
+    return mock_libpostal;
+  // otherwise return the actual service
+  } else {
+    // lazy load the libpostal module so that tests can skip configuring the service
+    if (!libpostal_module) {
+      libpostal_module = require( '../libpostal/service' );
+    }
+    return libpostal_module;
+  }
+}
+
+module.exports = get_libpostal;

libpostal/service.js

@@ -0,0 +1,48 @@
+// deasync is used to proved a sync-looking interface
+// to the async call to the libpostal service
+const deasync = require('deasync');
+const microservice_wrapper = require('pelias-microservice-wrapper');
+const pelias_config = require('pelias-config').generate();
+
+if (!pelias_config.services || !pelias_config.services.libpostal || !pelias_config.services.libpostal.url) {
+  throw new Error('The URL to the libpostal service must be set in the services.libpostal.url property of pelias.json');
+}
+
+const LibpostalServiceConfig = class extends microservice_wrapper.ServiceConfiguration {
+  constructor(configBlob) {
+    super('libpostal', configBlob);
+  }
+  getUrl(params) {
+    return this.baseUrl + params.endpoint;
+  }
+  getParameters(params) {
+    return {
+      address: params.address
+    };
+  }
+};
+
+// create an instance of the libpostal service, with a synchronous interface
+const libpostal_service = deasync(microservice_wrapper.service(
+  new LibpostalServiceConfig(pelias_config.services.libpostal)
+));
+
+// create an object that looks like the interface to `node-postal` but uses a remote service
+module.exports = {
+  expand: {
+    expand_address: function(param) {
+      const params = {
+        endpoint: 'expand',
+        address: param
+      };
+
+      // the libpostal service will not handle an empty parameter
+      // so return empty array immediately
+      if (!param) {
+        return [];
+      }
+      const result = libpostal_service(params);
+      return result;
+    }
+  }
+};

package.json

@@ -28,6 +28,7 @@
     "async": "^3.1.0",
     "cli-table3": "^0.5.0",
     "csv-parse": "^4.0.0",
+    "deasync": "^0.1.15",
     "express": "^4.14.0",
     "fs-extra": "^8.0.0",
     "morgan": "^1.9.0",

test/lib/mock_libpostal.js

@@ -22,7 +22,7 @@ module.exports.expand = {
     // is enabled, lazy load real libpostal, and return the real response
     } else if (use_real_libpostal) {
       // lazy load libpostal only when needed
-      if (!real_libpostal) { real_libpostal = require('node-postal'); }
+      if (!real_libpostal) { real_libpostal = require('../../libpostal/service'); }
 
       const real_response = real_libpostal.expand.expand_address(clean_string);
       mock_responses[clean_string] = real_response;