Add prometheus metric requests_total with headers

Co-authored-by: Julien Salleyron <julien.salleyron@gmail.com>

pkg/metrics/headers.go

@@ -0,0 +1,57 @@
+package metrics
+
+import (
+	"net/http"
+
+	"github.com/go-kit/kit/metrics"
+)
+
+// CounterWithHeaders represents a counter that can use http.Header values as label values.
+type CounterWithHeaders interface {
+	Add(delta float64)
+	With(headers http.Header, labelValues ...string) CounterWithHeaders
+}
+
+// MultiCounterWithHeaders collects multiple individual CounterWithHeaders and treats them as a unit.
+type MultiCounterWithHeaders []CounterWithHeaders
+
+// NewMultiCounterWithHeaders returns a multi-counter, wrapping the passed CounterWithHeaders.
+func NewMultiCounterWithHeaders(c ...CounterWithHeaders) MultiCounterWithHeaders {
+	return c
+}
+
+// Add adds the given delta value to the counter value.
+func (c MultiCounterWithHeaders) Add(delta float64) {
+	for _, counter := range c {
+		counter.Add(delta)
+	}
+}
+
+// With creates a new counter by appending the given label values and http.Header as labels and returns it.
+func (c MultiCounterWithHeaders) With(headers http.Header, labelValues ...string) CounterWithHeaders {
+	next := make(MultiCounterWithHeaders, len(c))
+	for i := range c {
+		next[i] = c[i].With(headers, labelValues...)
+	}
+	return next
+}
+
+// NewCounterWithNoopHeaders returns a CounterWithNoopHeaders.
+func NewCounterWithNoopHeaders(counter metrics.Counter) CounterWithNoopHeaders {
+	return CounterWithNoopHeaders{counter: counter}
+}
+
+// CounterWithNoopHeaders is a counter that satisfies CounterWithHeaders but ignores the given http.Header.
+type CounterWithNoopHeaders struct {
+	counter metrics.Counter
+}
+
+// Add adds the given delta value to the counter value.
+func (c CounterWithNoopHeaders) Add(delta float64) {
+	c.counter.Add(delta)
+}
+
+// With creates a new counter by appending the given label values and returns it.
+func (c CounterWithNoopHeaders) With(_ http.Header, labelValues ...string) CounterWithHeaders {
+	return NewCounterWithNoopHeaders(c.counter.With(labelValues...))
+}