CLDC-3244: Replace postcodes_io gem to improve error handling

Gemfile

@@ -38,7 +38,6 @@ gem "devise_two_factor_authentication"
 # UK postcode parsing and validation
 gem "uk_postcode"
 # Get rich data from postcode lookups. Wraps postcodes.io
-gem "postcodes_io"
 # Use Ruby objects to build reusable markup. A React inspired evolution of the presenter pattern
 gem "view_component", "~> 3.9"
 # Use the AWS S3 SDK as storage mechanism
@@ -111,3 +110,5 @@ end
 # Windows does not include zoneinfo files, so bundle the tzinfo-data gem
 gem "cssbundling-rails"
 gem "tzinfo-data", platforms: %i[mingw mswin x64_mingw jruby]
+
+gem "excon", "~> 0.111.0"

Gemfile.lock

@@ -183,7 +183,7 @@ GEM
     et-orbi (1.2.11)
       tzinfo
     event_stream_parser (1.0.0)
-    excon (0.109.0)
+    excon (0.111.0)
     factory_bot (6.4.6)
       activesupport (>= 5.0.0)
     factory_bot_rails (6.4.3)
@@ -302,8 +302,6 @@ GEM
       racc
     pg (1.5.5)
     possessive (1.0.1)
-    postcodes_io (0.4.0)
-      excon (~> 0.39)
     propshaft (0.8.0)
       actionpack (>= 7.0.0)
       activesupport (>= 7.0.0)
@@ -533,6 +531,7 @@ DEPENDENCIES
   devise_two_factor_authentication
   dotenv-rails
   erb_lint
+  excon (~> 0.111.0)
   factory_bot_rails
   faker
   govuk-components (~> 5.1)
@@ -549,7 +548,6 @@ DEPENDENCIES
   parallel_tests
   pg (~> 1.1)
   possessive
-  postcodes_io
   propshaft
   pry-byebug
   puma (~> 5.6)

app/services/postcode_service.rb

@@ -1,26 +1,23 @@
 class PostcodeService
-  def initialize
-    @pio = Postcodes::IO.new
-  end
 
   def lookup(postcode)
     # Avoid network calls when postcode is invalid
     return unless postcode.match(POSTCODE_REGEXP)
 
-    postcode_lookup = nil
+    result = nil
     begin
       # URI encoding only supports ASCII characters
       ascii_postcode = self.class.clean(postcode)
-      Timeout.timeout(30) { postcode_lookup = @pio.lookup(ascii_postcode) }
-    rescue Timeout::Error
-      Rails.logger.warn("Postcodes.io lookup timed out")
-    end
-    if postcode_lookup && postcode_lookup.info.present?
-      {
-        location_code: postcode_lookup.codes["admin_district"],
-        location_admin_district: postcode_lookup&.admin_district,
+      response = Excon.get("https://api.postcodes.io/postcodes/#{ascii_postcode}", idempotent: true, timeout: 30, expects: [200])
+      parsed_response = JSON.parse(response.body)
+      result = {
+        location_code: parsed_response["result"]["codes"]["admin_district"],
+        location_admin_district: parsed_response["result"]["admin_district"],
       }
+    rescue Excon::Error => e
+      Rails.logger.warn("An error occurred with the postcode lookup request: #{e} #{e.response.body}")
     end
+    result
   end
 
   def self.clean(postcode)

spec/services/postcode_service_spec.rb

@@ -1,9 +1,64 @@
 require "rails_helper"
 
 describe PostcodeService do
-  let(:postcode) { "s r81LS\u00A0" }
+  let(:service) { described_class.new }
 
-  it "returns clean postcode" do
-    expect(described_class.clean(postcode)).to eq "SR81LS"
+  describe "clean" do
+    let(:postcode) { "s r81LS\u00A0" }
+
+    it "returns clean postcode" do
+      expect(described_class.clean(postcode)).to eq "SR81LS"
+    end
+  end
+
+  describe "lookup" do
+    before do
+      Excon.defaults[:mock] = true
+      Excon.defaults[:stubs] = :local
+    end
+
+    context "when the request returns a success response" do
+      before do
+        Excon.stub({}, { body: '{"result": { "admin_district": "District", "codes": { "admin_district": "123" } } }', status: 200 })
+      end
+
+      it "returns the admin district and admin district code" do
+        result = service.lookup("A00 0AA")
+        expect(result[:location_code]).to eq("123")
+        expect(result[:location_admin_district]).to eq("District")
+      end
+    end
+
+    context "when the request returns a not found response" do
+      before do
+        Excon.stub({}, { status: 404 })
+      end
+
+      it "returns nil" do
+        result = service.lookup("A00 0AA")
+        expect(result).to be_nil
+      end
+
+      it "logs the error at warning level" do
+        expect(Rails.logger).to receive(:warn).with(match "404 Not Found")
+        service.lookup("A00 0AA")
+      end
+    end
+
+    context "when the request returns an error response" do
+      before do
+        Excon.stub({}, { body: "This is an error message that is not valid json", status: 500 })
+      end
+
+      it "returns nil" do
+        result = service.lookup("A00 0AA")
+        expect(result).to be_nil
+      end
+
+      it "logs the error at warning level" do
+        expect(Rails.logger).to receive(:warn).with(match "This is an error message that is not valid json")
+        service.lookup("A00 0AA")
+      end
+    end
   end
 end