Add partitions func for listing partitions in the local datacenter

dependency/catalog_partitions.go

@@ -0,0 +1,104 @@
+package dependency
+
+import (
+	"context"
+	"log"
+	"net/url"
+	"sort"
+	"time"
+
+	"github.com/pkg/errors"
+)
+
+var (
+	// Ensure implements
+	_ Dependency = (*CatalogPartitionsQuery)(nil)
+
+	// CatalogPartitionsQuerySleepTime is the amount of time to sleep between
+	// queries, since the endpoint does not support blocking queries.
+	CatalogPartitionsQuerySleepTime = 15 * time.Second
+)
+
+// CatalogPartitionsQuery is the representation of a requested catalog partitions
+// dependency from inside a template.
+type CatalogPartitionsQuery struct {
+	stopCh chan struct{}
+}
+
+// NewCatalogPartitionsQuery parses a string of the format @dc.
+func NewCatalogPartitionsQuery() (*CatalogPartitionsQuery, error) {
+	return &CatalogPartitionsQuery{
+		stopCh: make(chan struct{}, 1),
+	}, nil
+}
+
+func (c *CatalogPartitionsQuery) Fetch(clients *ClientSet, opts *QueryOptions) (interface{}, *ResponseMetadata, error) {
+	opts = opts.Merge(&QueryOptions{})
+
+	log.Printf("[TRACE] %s: GET %s", c, &url.URL{
+		Path:     "/v1/partitions",
+		RawQuery: opts.String(),
+	})
+
+	// This is certainly not elegant, but the partitions endpoint does not support
+	// blocking queries, so we are going to "fake it until we make it". When we
+	// first query, the LastIndex will be "0", meaning we should immediately
+	// return data, but future calls will include a LastIndex. If we have a
+	// LastIndex in the query metadata, sleep for 15 seconds before asking Consul
+	// again.
+	//
+	// This is probably okay given the frequency in which partitions actually
+	// change, but is technically not edge-triggering.
+	if opts.WaitIndex != 0 {
+		log.Printf("[TRACE] %s: long polling for %s", c, CatalogDatacentersQuerySleepTime)
+
+		select {
+		case <-c.stopCh:
+			return nil, nil, ErrStopped
+		case <-time.After(CatalogPartitionsQuerySleepTime):
+		}
+	}
+
+	// TODO Consider using a proper context
+	partitions, qm, err := clients.Consul().Partitions().List(context.Background(), opts.ToConsulOpts())
+	if err != nil {
+		return nil, nil, errors.Wrapf(err, c.String())
+	}
+
+	// TODO Consider returning full partition objects instead of just name
+	partitionNames := []string{}
+	for _, partition := range partitions {
+		if partition != nil {
+			partitionNames = append(partitionNames, partition.Name)
+		}
+	}
+
+	log.Printf("[TRACE] %s: returned %d results", c, len(partitionNames))
+
+	sort.Strings(partitionNames)
+
+	rm := &ResponseMetadata{
+		LastIndex:   qm.LastIndex,
+		LastContact: qm.LastContact,
+	}
+
+	return partitionNames, rm, nil
+}
+
+// CanShare returns if this dependency is shareable.
+// TODO What is this?
+func (c *CatalogPartitionsQuery) CanShare() bool {
+	return true
+}
+
+func (c *CatalogPartitionsQuery) String() string {
+	return "catalog.partitions"
+}
+
+func (c *CatalogPartitionsQuery) Stop() {
+	close(c.stopCh)
+}
+
+func (c *CatalogPartitionsQuery) Type() Type {
+	return TypeConsul
+}

docs/templating-language.md

@@ -19,6 +19,7 @@ provides the following functions:
   * [`safeLs`](#safels)
   * [`node`](#node)
   * [`nodes`](#nodes)
+  * [`partitions`](#partitions)
   * [`peerings`](#peerings)
   * [`secret`](#secret)
     + [Format](#format)
@@ -506,6 +507,15 @@ To query a different data center and order by shortest trip time to ourselves:
 To access map data such as `TaggedAddresses` or `Meta`, use
 [Go's text/template][text-template] map indexing.
 
+### `partitions`
+
+Query [Consul][consul] for all partitions.
+
+```golang
+{{ range partitions }}
+{{ . }}{{ end }}
+```
+
 ### `peerings`
 
 Query [Consul][consul] for all peerings.

template/funcs.go

@@ -27,14 +27,15 @@ import (
 
 	"github.com/BurntSushi/toml"
 	spewLib "github.com/davecgh/go-spew/spew"
-	dep "github.com/hashicorp/consul-template/dependency"
 	"github.com/hashicorp/consul/api"
 	socktmpl "github.com/hashicorp/go-sockaddr/template"
 	"github.com/imdario/mergo"
 	"github.com/pkg/errors"
 	"golang.org/x/text/cases"
 	"golang.org/x/text/language"
-	yaml "gopkg.in/yaml.v2"
+	"gopkg.in/yaml.v2"
+
+	dep "github.com/hashicorp/consul-template/dependency"
 )
 
 // now is function that represents the current time in UTC. This is here
@@ -74,6 +75,28 @@ func datacentersFunc(b *Brain, used, missing *dep.Set) func(ignore ...bool) ([]s
 	}
 }
 
+// partitionsFunc returns or accumulates partition dependencies.
+func partitionsFunc(b *Brain, used, missing *dep.Set) func() ([]string, error) {
+	return func() ([]string, error) {
+		result := []string{}
+
+		d, err := dep.NewCatalogPartitionsQuery()
+		if err != nil {
+			return result, err
+		}
+
+		used.Add(d)
+
+		if value, ok := b.Recall(d); ok {
+			return value.([]string), nil
+		}
+
+		missing.Add(d)
+
+		return result, nil
+	}
+}
+
 // envFunc returns a function which checks the value of an environment variable.
 // Invokers can specify their own environment, which takes precedences over any
 // real environment variables

template/template.go

@@ -12,10 +12,11 @@ import (
 	"text/template"
 
 	"github.com/Masterminds/sprig/v3"
-	"github.com/hashicorp/consul-template/config"
-	dep "github.com/hashicorp/consul-template/dependency"
 	"github.com/pkg/errors"
 	"golang.org/x/exp/maps"
+
+	"github.com/hashicorp/consul-template/config"
+	dep "github.com/hashicorp/consul-template/dependency"
 )
 
 var (
@@ -337,6 +338,7 @@ func funcMap(i *funcMapInput) template.FuncMap {
 		"safeLs":       safeLsFunc(i.brain, i.used, i.missing),
 		"node":         nodeFunc(i.brain, i.used, i.missing),
 		"nodes":        nodesFunc(i.brain, i.used, i.missing),
+		"partitions":   partitionsFunc(i.brain, i.used, i.missing),
 		"peerings":     peeringsFunc(i.brain, i.used, i.missing),
 		"secret":       secretFunc(i.brain, i.used, i.missing),
 		"secrets":      secretsFunc(i.brain, i.used, i.missing),