Merge pull request #13309 from influxdata/sgc/feat/13241

Stub implementation of storage schema APIs

storage/engine_schema.go

@@ -0,0 +1,50 @@
+package storage
+
+import (
+	"github.com/influxdata/influxdb"
+	"github.com/influxdata/influxql"
+)
+
+// StringIterator describes the behavior for enumerating a sequence of
+// string values.
+type StringIterator interface {
+	// Next advances the StringIterator to the next value. It returns false
+	// when there are no more values.
+	Next() bool
+
+	// Value returns the current value.
+	Value() string
+}
+
+// TagKeys returns an iterator where the values are tag keys for the bucket
+// matching the predicate within the time range (start, end].
+func (e *Engine) TagKeys(orgID, bucketID influxdb.ID, start, end int64, predicate influxql.Expr) StringIterator {
+	// This method would be invoked when the consumer wants to get the following schema information for an arbitrary
+	// time range in a single bucket:
+	//
+	// * All tag keys;
+	// * All tag keys filtered by an arbitrary predicate, e.g., tag keys for a measurement or tag keys appearing alongside another tag key pair.
+	//
+	return nullStringIterator
+}
+
+// TagValues returns an iterator which enumerates the values for the specific
+// tagKey in the given bucket matching the predicate within the
+// time range (start, end].
+func (e *Engine) TagValues(orgID, bucketID influxdb.ID, tagKey string, start, end int64, predicate influxql.Expr) StringIterator {
+	// This method would be invoked when the consumer wants to get the following schema information for an arbitrary
+	// time range in a single bucket:
+	//
+	// * All measurement names, i.e. tagKey == _measurement);
+	// * All field names for a specific measurement using a predicate
+	//     * i.e. tagKey is "_field", predicate _measurement == "<measurement>"
+	//
+	return nullStringIterator
+}
+
+var nullStringIterator StringIterator = &emptyStringIterator{}
+
+type emptyStringIterator struct{}
+
+func (*emptyStringIterator) Next() bool    { return false }
+func (*emptyStringIterator) Value() string { return "" }