Add query describe endpoint

This commit adds the query describe endpoint- a service endpoint the
returns information about a posted query. This endpoint is meant for
internal use from within ZUI and is not meant for public consumption.

compiler/describe.go

@@ -0,0 +1,26 @@
+package compiler
+
+import (
+	"context"
+
+	"github.com/brimdata/zed/compiler/data"
+	"github.com/brimdata/zed/compiler/describe"
+	"github.com/brimdata/zed/compiler/parser"
+	"github.com/brimdata/zed/compiler/semantic"
+	"github.com/brimdata/zed/lakeparse"
+)
+
+func Describe(ctx context.Context, query string, src *data.Source, head *lakeparse.Commitish) (*describe.Info, error) {
+	seq, sset, err := Parse(query)
+	if err != nil {
+		return nil, err
+	}
+	entry, err := semantic.AnalyzeAddSource(ctx, seq, src, head)
+	if err != nil {
+		if list, ok := err.(parser.ErrorList); ok {
+			list.SetSourceSet(sset)
+		}
+		return nil, err
+	}
+	return describe.Analyze(ctx, src, entry)
+}

compiler/describe/analyze.go

@@ -0,0 +1,156 @@
+package describe
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/brimdata/zed/compiler/ast/dag"
+	"github.com/brimdata/zed/compiler/data"
+	"github.com/brimdata/zed/compiler/optimizer"
+	"github.com/brimdata/zed/lake"
+	"github.com/brimdata/zed/order"
+	"github.com/brimdata/zed/pkg/field"
+	"github.com/segmentio/ksuid"
+)
+
+type Info struct {
+	Sources  []Source  `json:"sources"`
+	Channels []Channel `json:"channels"`
+}
+
+type Source interface {
+	Source()
+}
+
+type (
+	LakeMeta struct {
+		Kind string `json:"kind"`
+		Meta string `json:"meta"`
+	}
+	Pool struct {
+		Kind string      `json:"kind"`
+		Name string      `json:"name"`
+		ID   ksuid.KSUID `json:"id"`
+	}
+	Path struct {
+		Kind string `json:"kind"`
+		URI  string `json:"uri"`
+	}
+)
+
+func (*LakeMeta) Source() {}
+func (*Pool) Source()     {}
+func (*Path) Source()     {}
+
+type Channel struct {
+	AggregationKeys field.List     `json:"aggregation_keys"`
+	Sort            *order.SortKey `json:"sort"`
+}
+
+func Analyze(ctx context.Context, source *data.Source, seq dag.Seq) (*Info, error) {
+	var info Info
+	var err error
+	if info.Sources, err = describeSources(ctx, source.Lake(), seq[0]); err != nil {
+		return nil, err
+	}
+	sortKeys, err := optimizer.New(ctx, source).SortKeys(seq)
+	if err != nil {
+		return nil, err
+	}
+	aggKeys := describeAggs(seq, []field.List{nil})
+	for i := range sortKeys {
+		// Convert SortKey to a pointer so a nil sort is encoded as null for
+		// JSON/ZSON.
+		var s *order.SortKey
+		if !sortKeys[i].IsNil() {
+			s = &sortKeys[i]
+		}
+		info.Channels = append(info.Channels, Channel{
+			Sort:            s,
+			AggregationKeys: aggKeys[i],
+		})
+	}
+	return &info, nil
+}
+
+func describeSources(ctx context.Context, lk *lake.Root, o dag.Op) ([]Source, error) {
+	switch o := o.(type) {
+	case *dag.Fork:
+		var s []Source
+		for _, p := range o.Paths {
+			out, err := describeSources(ctx, lk, p[0])
+			if err != nil {
+				return nil, err
+			}
+			s = append(s, out...)
+		}
+		return s, nil
+	case *dag.DefaultScan:
+		return []Source{&Path{Kind: "Path", URI: "stdio://stdin"}}, nil
+	case *dag.FileScan:
+		return []Source{&Path{Kind: "Path", URI: o.Path}}, nil
+	case *dag.HTTPScan:
+		return []Source{&Path{Kind: "Path", URI: o.URL}}, nil
+	case *dag.PoolScan:
+		return sourceOfPool(ctx, lk, o.ID)
+	case *dag.Lister:
+		return sourceOfPool(ctx, lk, o.Pool)
+	case *dag.SeqScan:
+		return sourceOfPool(ctx, lk, o.Pool)
+	case *dag.CommitMetaScan:
+		return sourceOfPool(ctx, lk, o.Pool)
+	case *dag.LakeMetaScan:
+		return []Source{&LakeMeta{Kind: "LakeMeta", Meta: o.Meta}}, nil
+	default:
+		return nil, fmt.Errorf("unsupported source type %T", o)
+	}
+}
+
+func sourceOfPool(ctx context.Context, lk *lake.Root, id ksuid.KSUID) ([]Source, error) {
+	p, err := lk.OpenPool(ctx, id)
+	if err != nil {
+		return nil, err
+	}
+	return []Source{&Pool{
+		Kind: "Pool",
+		ID:   id,
+		Name: p.Name,
+	}}, nil
+}
+
+func describeAggs(seq dag.Seq, parents []field.List) []field.List {
+	for _, op := range seq {
+		parents = describeOpAggs(op, parents)
+	}
+	return parents
+}
+
+func describeOpAggs(op dag.Op, parents []field.List) []field.List {
+	switch op := op.(type) {
+	case *dag.Fork:
+		var aggs []field.List
+		for _, p := range op.Paths {
+			aggs = append(aggs, describeAggs(p, []field.List{nil})...)
+		}
+		return aggs
+	case *dag.Scatter:
+		var aggs []field.List
+		for _, p := range op.Paths {
+			aggs = append(aggs, describeAggs(p, []field.List{nil})...)
+		}
+		return aggs
+	case *dag.Summarize:
+		// The field list for aggregation with no keys is an empty slice and
+		// not nil.
+		keys := field.List{}
+		for _, k := range op.Keys {
+			keys = append(keys, k.LHS.(*dag.This).Path)
+		}
+		return []field.List{keys}
+	}
+	// If more than one parent reset to nil aggregation.
+	if len(parents) > 1 {
+		return []field.List{nil}
+	}
+	return parents
+}

compiler/optimizer/optimizer.go

@@ -257,6 +257,10 @@ func (o *Optimizer) optimizeSourcePaths(seq dag.Seq) (dag.Seq, error) {
 	})
 }
 
+func (o *Optimizer) SortKeys(seq dag.Seq) ([]order.SortKey, error) {
+	return o.propagateSortKey(copyOps(seq), []order.SortKey{order.Nil})
+}
+
 // propagateSortKey analyzes a Seq and attempts to push the scan order of the data source
 // into the first downstream aggregation.  (We could continue the analysis past that
 // point but don't bother yet because we do not yet support any optimization
@@ -330,7 +334,7 @@ func (o *Optimizer) propagateSortKeyOp(op dag.Op, parents []order.SortKey) ([]or
 		// We'll live this as unknown for now even though the groupby
 		// and not try to optimize downstream of the first groupby
 		// unless there is an excplicit sort encountered.
-		return nil, nil
+		return []order.SortKey{order.Nil}, nil
 	case *dag.Fork:
 		var keys []order.SortKey
 		for _, seq := range op.Paths {

service/core.go

@@ -188,6 +188,7 @@ func (c *Core) addAPIServerRoutes() {
 	c.authhandle("/pool/{pool}/revision/{revision}/vector", handleVectorDelete).Methods("DELETE")
 	c.authhandle("/pool/{pool}/stats", handlePoolStats).Methods("GET")
 	c.authhandle("/query", handleQuery).Methods("OPTIONS", "POST")
+	c.authhandle("/query/describe", handleQueryDescribe).Methods("OPTIONS", "POST")
 	c.authhandle("/query/status/{requestID}", handleQueryStatus).Methods("GET")
 }
 

service/handlers.go

@@ -11,13 +11,15 @@ import (
 	"github.com/brimdata/zed/api"
 	"github.com/brimdata/zed/api/queryio"
 	"github.com/brimdata/zed/compiler"
+	"github.com/brimdata/zed/compiler/data"
 	"github.com/brimdata/zed/compiler/optimizer/demand"
 	"github.com/brimdata/zed/compiler/parser"
 	"github.com/brimdata/zed/lake"
 	lakeapi "github.com/brimdata/zed/lake/api"
 	"github.com/brimdata/zed/lake/commits"
 	"github.com/brimdata/zed/lake/journal"
 	"github.com/brimdata/zed/lakeparse"
+	"github.com/brimdata/zed/pkg/storage"
 	"github.com/brimdata/zed/runtime"
 	"github.com/brimdata/zed/runtime/exec"
 	"github.com/brimdata/zed/runtime/sam/op"
@@ -170,6 +172,20 @@ func handleCompile(c *Core, w *ResponseWriter, r *Request) {
 	w.Respond(http.StatusOK, ast)
 }
 
+func handleQueryDescribe(c *Core, w *ResponseWriter, r *Request) {
+	var req api.QueryRequest
+	if !r.Unmarshal(w, &req) {
+		return
+	}
+	src := data.NewSource(storage.NewRemoteEngine(), c.root)
+	info, err := compiler.Describe(r.Context(), req.Query, src, &req.Head)
+	if err != nil {
+		w.Error(srverr.ErrInvalid(err))
+		return
+	}
+	w.Respond(http.StatusOK, info)
+}
+
 func handleBranchGet(c *Core, w *ResponseWriter, r *Request) {
 	branchName, ok := r.StringFromPath(w, "branch")
 	if !ok {