Propagate not found as GQL errors (#3200)

go/datas/remote_database_handlers.go

@@ -6,6 +6,7 @@ package datas
 
 import (
 	"compress/gzip"
+	"errors"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -431,21 +432,32 @@ func handleGraphQL(w http.ResponseWriter, req *http.Request, ps URLParams, cs ch
 	db := NewDatabase(cs)
 
 	var rootValue types.Value
+	var err error
 	if len(dsTokens) == 1 {
 		ds := dsTokens[0]
 		dataset := db.GetDataset(ds)
-		rootValue = dataset.Head()
+		var ok bool
+		rootValue, ok = dataset.MaybeHead()
+		if !ok {
+			err = fmt.Errorf("Dataset %s not found", ds)
+		}
 	} else {
 		h := hash.Parse(hTokens[0])
 		rootValue = db.ReadValue(h)
+		if rootValue == nil {
+			err = errors.New("Root value not found")
+		}
 	}
-	d.PanicIfTrue(rootValue == nil)
 
 	w.Header().Add("Content-Type", "application/json")
 	writer := respWriter(req, w)
 	defer writer.Close()
 
-	ngql.Query(rootValue, qTokens[0], db, writer)
+	if err != nil {
+		ngql.Error(err, writer)
+	} else {
+		ngql.Query(rootValue, qTokens[0], db, writer)
+	}
 }
 
 func handleBaseGet(w http.ResponseWriter, req *http.Request, ps URLParams, rt chunks.ChunkStore) {

go/ngql/query.go

@@ -5,7 +5,6 @@
 package ngql
 
 import (
-	"bytes"
 	"context"
 	"encoding/json"
 	"io"
@@ -13,6 +12,7 @@ import (
 	"github.com/attic-labs/noms/go/d"
 	"github.com/attic-labs/noms/go/types"
 	"github.com/graphql-go/graphql"
+	"github.com/graphql-go/graphql/gqlerrors"
 )
 
 const (
@@ -49,7 +49,7 @@ func constructQueryType(rootValue types.Value, tm *typeMap) *graphql.Object {
 
 // Query takes |rootValue|, builds a GraphQL scheme from rootValue.Type() and
 // executes |query| against it, encoding the result to |w|.
-func Query(rootValue types.Value, query string, vr types.ValueReader, w io.Writer) error {
+func Query(rootValue types.Value, query string, vr types.ValueReader, w io.Writer) {
 	tm := newTypeMap()
 
 	queryObj := constructQueryType(rootValue, tm)
@@ -63,8 +63,18 @@ func Query(rootValue types.Value, query string, vr types.ValueReader, w io.Write
 		Context:       ctx,
 	})
 
-	rJSON, err := json.Marshal(r)
-	d.Chk.NoError(err)
-	io.Copy(w, bytes.NewBuffer([]byte(rJSON)))
-	return nil
+	err := json.NewEncoder(w).Encode(r)
+	d.PanicIfError(err)
+}
+
+// Error writes an error as a GraphQL error to a writer.
+func Error(err error, w io.Writer) {
+	r := graphql.Result{
+		Errors: []gqlerrors.FormattedError{
+			{Message: err.Error()},
+		},
+	}
+
+	jsonErr := json.NewEncoder(w).Encode(r)
+	d.PanicIfError(jsonErr)
 }

go/ngql/query_test.go

@@ -6,6 +6,7 @@ package ngql
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 	"testing"
 
@@ -31,7 +32,7 @@ func (suite *QueryGraphQLSuite) SetupTest() {
 func (suite *QueryGraphQLSuite) assertQueryResult(v types.Value, q, expect string) {
 	buff := &bytes.Buffer{}
 	Query(v, q, suite.vs, buff)
-	suite.Equal(expect, string(buff.Bytes()))
+	suite.Equal(expect+"\n", string(buff.Bytes()))
 }
 
 func (suite *QueryGraphQLSuite) TestScalars() {
@@ -327,3 +328,10 @@ func (suite *QueryGraphQLSuite) TestLoFi() {
 	t := types.StringType
 	suite.assertQueryResult(t, "{root}", `{"data":{"root":"pej65tf21rubhu9cb0oi5gqrkgf26aql"}}`)
 }
+
+func (suite *QueryGraphQLSuite) TestError() {
+	buff := &bytes.Buffer{}
+	Error(errors.New("Some error string"), buff)
+	suite.Equal(buff.String(), `{"data":null,"errors":[{"message":"Some error string","locations":null}]}
+`)
+}