Some conversation-starting progress.

Still tons of work to do, but it's probably far enough along to get some feedback.

pkg/custom-provider/external_provider.go

@@ -0,0 +1,162 @@
+/*
+Copyright 2017 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package provider
+
+import (
+	"fmt"
+	s "strings"
+	"time"
+
+	"github.com/kubernetes-incubator/custom-metrics-apiserver/pkg/provider"
+	apimeta "k8s.io/apimachinery/pkg/api/meta"
+	"k8s.io/apimachinery/pkg/labels"
+	"k8s.io/apimachinery/pkg/selection"
+	"k8s.io/client-go/dynamic"
+	"k8s.io/metrics/pkg/apis/external_metrics"
+
+	prom "github.com/directxman12/k8s-prometheus-adapter/pkg/client"
+)
+
+type externalPrometheusProvider struct {
+	mapper     apimeta.RESTMapper
+	kubeClient dynamic.ClientPool
+	promClient prom.Client
+
+	SeriesRegistry
+
+	rateInterval time.Duration
+}
+
+func NewExternalPrometheusProvider(mapper apimeta.RESTMapper, kubeClient dynamic.ClientPool, promClient prom.Client, labelPrefix string, updateInterval time.Duration, rateInterval time.Duration, stopChan <-chan struct{}) provider.ExternalMetricsProvider {
+	lister := &cachingMetricsLister{
+		updateInterval: updateInterval,
+		promClient:     promClient,
+
+		SeriesRegistry: &basicSeriesRegistry{
+			namer: metricNamer{
+				// TODO: populate the overrides list
+				overrides:   nil,
+				mapper:      mapper,
+				labelPrefix: labelPrefix,
+			},
+		},
+	}
+
+	lister.RunUntil(stopChan)
+
+	return &externalPrometheusProvider{
+		mapper:     mapper,
+		kubeClient: kubeClient,
+		promClient: promClient,
+
+		SeriesRegistry: lister,
+
+		rateInterval: rateInterval,
+	}
+}
+
+func (p *externalPrometheusProvider) GetExternalMetric(namespace string, metricName string, metricSelector labels.Selector) (*external_metrics.ExternalMetricValueList, error) {
+	//TODO: Steps
+	//1. Generate a Prometheus Query.
+	//   Something like my_metric{namespace="namespace" some_label="some_value"}
+	//2. Send that query to Prometheus.
+	//3. Adapt the results.
+	//The query generation for external metrics is much more straightforward
+	//than for custom metrics because no renaming is applied.
+	//So we'll just start with some simple string operations and see how far that gets us.
+	//Then I'll circle back and figure out how much code reuse I can get out of the original implementation.
+	namespaceSelector := p.makeLabelFilter("namespace", "=", namespace)
+	otherSelectors := p.convertSelectors(metricSelector)
+
+	finalTargets := append([]string{namespaceSelector}, otherSelectors...)
+
+	//TODO: Only here to stop compiler issues in this incomplete code.
+	fmt.Printf("len=%d", len(finalTargets))
+
+	//TODO: Construct a real result.
+	return nil, nil
+}
+
+func (p *externalPrometheusProvider) makeLabelFilter(labelName string, operator string, targetValue string) string {
+	return fmt.Sprintf("%s%s\"%s\"", labelName, operator, targetValue)
+}
+
+func (p *externalPrometheusProvider) convertSelectors(metricSelector labels.Selector) []string {
+	requirements, _ := metricSelector.Requirements()
+
+	selectors := []string{}
+	for i := 0; i < len(requirements); i++ {
+		selector := p.convertRequirement(requirements[i])
+
+		selectors = append(selectors, selector)
+	}
+
+	return selectors
+}
+
+func (p *externalPrometheusProvider) convertRequirement(requirement labels.Requirement) string {
+	labelName := requirement.Key()
+	values := requirement.Values().List()
+
+	stringValues := values[0]
+
+	valueCount := len(values)
+	if valueCount > 1 {
+		stringValues = s.Join(values, "|")
+	}
+
+	operator := p.selectOperator(requirement.Operator(), valueCount)
+
+	return p.makeLabelFilter(labelName, operator, stringValues)
+}
+
+func (p *externalPrometheusProvider) selectOperator(operator selection.Operator, valueCount int) string {
+	if valueCount > 1 {
+		return p.selectRegexOperator(operator)
+	}
+
+	return p.selectSingleValueOperator(operator)
+}
+
+func (p *externalPrometheusProvider) selectRegexOperator(operator selection.Operator) string {
+	switch operator {
+	case selection.Equals:
+		return "=~"
+	case selection.NotEquals:
+		return "!~"
+	}
+
+	//TODO: Cover more cases, supply appropriate errors for any unhandled cases.
+	return "="
+}
+
+func (p *externalPrometheusProvider) selectSingleValueOperator(operator selection.Operator) string {
+	switch operator {
+	case selection.Equals:
+		return "="
+	case selection.NotEquals:
+		return "!="
+	}
+
+	//TODO: Cover more cases, supply appropriate errors for any unhandled cases.
+	return "="
+}
+
+func (p *externalPrometheusProvider) ListAllExternalMetrics() []provider.ExternalMetricInfo {
+	//TODO: Provide a real response.
+	return nil
+}