Base64-encode . and .. in Pushgateway job and grouping values

lib/prometheus/client/push.rb

@@ -89,9 +89,9 @@ def parse(url)
       def build_path(job, grouping_key)
         job = job.to_s
 
-        # Job can't be empty, but it can contain `/`, so we need to base64
-        # encode it in that case
-        if job.include?('/')
+        # Job can't be empty, but it can contain `/` or be a dot segment (`.`
+        # or `..`), so we need to base64 encode it in that case
+        if needs_base64?(job)
           encoded_job = Base64.urlsafe_encode64(job)
           path = "#{PATH}/job@base64/#{encoded_job}"
         else
@@ -101,7 +101,7 @@ def build_path(job, grouping_key)
         grouping_key.each do |label, value|
           value = value.to_s
 
-          if value.include?('/')
+          if needs_base64?(value)
             encoded_value = Base64.urlsafe_encode64(value)
             path += "/#{label}@base64/#{encoded_value}"
           # While it's valid for the urlsafe_encode64 function to return an
@@ -126,6 +126,14 @@ def build_path(job, grouping_key)
         path
       end
 
+      # A `/` would split the value into several path segments, and `.` or
+      # `..` are dot segments that HTTP libraries, proxies and the
+      # Pushgateway itself normalise away (so the request would end up at a
+      # different path). The Pushgateway docs ask for base64 in both cases.
+      def needs_base64?(value)
+        value.include?('/') || value == '.' || value == '..'
+      end
+
       def request(req_class, registry = nil)
         validate_no_label_clashes!(registry) if registry
 

spec/prometheus/client/push_spec.rb

@@ -127,6 +127,22 @@
       expect(push.path).to eql('/metrics/job/test-job/foo@base64/YmFyL2Jheg==')
     end
 
+    it 'encodes the job name in url-safe base64 if it is a dot segment' do
+      expect(Prometheus::Client::Push.new(job: '.').path)
+        .to eql('/metrics/job@base64/Lg==')
+      expect(Prometheus::Client::Push.new(job: '..').path)
+        .to eql('/metrics/job@base64/Li4=')
+    end
+
+    it 'encodes grouping key label values that are dot segments in url-safe base64' do
+      push = Prometheus::Client::Push.new(
+        job: 'test-job',
+        grouping_key: { foo: ".", bar: "..", baz: "..." },
+      )
+
+      expect(push.path).to eql('/metrics/job/test-job/foo@base64/Lg==/bar@base64/Li4=/baz/...')
+    end
+
     it 'encodes empty grouping key label values as a single base64 padding character' do
       push = Prometheus::Client::Push.new(
         job: 'test-job',