Handle consecutive path segments containing IDs in collector

Previously, we would fail to strip IDs from paths if they appeared in
consecutive path segments. This is because our regex that looked for IDs
and UUIDs would consume the `/` character that followed them, causing
the next one not to match.

This commit uses a lookahead to match against the `/` without consuming
it.

Signed-off-by: Chris Sinjakli <chris@sinjakli.co.uk>

lib/prometheus/middleware/collector.rb

@@ -137,8 +137,8 @@ def generate_path(env)
 
       def strip_ids_from_path(path)
         path
-          .gsub(%r{/[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}(/|$)}, '/:uuid\\1')
-          .gsub(%r{/\d+(/|$)}, '/:id\\1')
+          .gsub(%r{/[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}(?=/|$)}, '/:uuid\\1')
+          .gsub(%r{/\d+(?=/|$)}, '/:id\\1')
       end
     end
   end

spec/prometheus/middleware/collector_spec.rb

@@ -95,6 +95,34 @@
     expect(registry.get(metric).get(labels: labels)).to include("0.1" => 0, "0.5" => 1)
   end
 
+  it 'handles consecutive path segments containing IDs' do
+    expect(Benchmark).to receive(:realtime).and_yield.and_return(0.3)
+
+    get '/foo/42/24'
+
+    metric = :http_server_requests_total
+    labels = { method: 'get', path: '/foo/:id/:id', code: '200' }
+    expect(registry.get(metric).get(labels: labels)).to eql(1.0)
+
+    metric = :http_server_request_duration_seconds
+    labels = { method: 'get', path: '/foo/:id/:id' }
+    expect(registry.get(metric).get(labels: labels)).to include("0.1" => 0, "0.5" => 1)
+  end
+
+  it 'handles consecutive path segments containing UUIDs' do
+    expect(Benchmark).to receive(:realtime).and_yield.and_return(0.3)
+
+    get '/foo/5180349d-a491-4d73-af30-4194a46bdff3/5180349d-a491-4d73-af30-4194a46bdff2'
+
+    metric = :http_server_requests_total
+    labels = { method: 'get', path: '/foo/:uuid/:uuid', code: '200' }
+    expect(registry.get(metric).get(labels: labels)).to eql(1.0)
+
+    metric = :http_server_request_duration_seconds
+    labels = { method: 'get', path: '/foo/:uuid/:uuid' }
+    expect(registry.get(metric).get(labels: labels)).to include("0.1" => 0, "0.5" => 1)
+  end
+
   it 'prefers sinatra.route to PATH_INFO' do
     metric = :http_server_requests_total