graphql: add Graphql-TouchedUids header in HTTP response (#5572)

This PR adds the Graphql-TouchedUids header in the HTTP response sent by GraphQL.

Fixes #GRAPHQL-489.

graphql/e2e/common/common.go

@@ -221,6 +221,9 @@ func RunAll(t *testing.T) {
 	// schema tests
 	t.Run("graphql descriptions", graphQLDescriptions)
 
+	// header tests
+	t.Run("touched uids header", touchedUidsHeader)
+
 	// encoding
 	t.Run("gzip compression", gzipCompression)
 	t.Run("gzip compression header", gzipCompressionHeader)

graphql/e2e/common/query.go

@@ -19,8 +19,11 @@ package common
 import (
 	"encoding/json"
 	"fmt"
+	"io/ioutil"
 	"math/rand"
+	"net/http"
 	"sort"
+	"strconv"
 	"strings"
 	"testing"
 	"time"
@@ -61,6 +64,33 @@ func queryCountryByRegExp(t *testing.T, regexp string, expectedCountries []*coun
 	}
 }
 
+func touchedUidsHeader(t *testing.T) {
+	query := &GraphQLParams{
+		Query: `query {
+			queryCountry {
+				name
+			}
+		}`,
+	}
+	req, err := query.createGQLPost(graphqlURL)
+	require.NoError(t, err)
+
+	client := http.Client{Timeout: 10 * time.Second}
+	resp, err := client.Do(req)
+	require.NoError(t, err)
+
+	// confirm that the header value is a non-negative integer
+	touchedUidsInHeader, err := strconv.ParseUint(resp.Header.Get("Graphql-TouchedUids"), 10, 64)
+	require.NoError(t, err)
+
+	// confirm that the value in header is same as the value in body
+	var gqlResp GraphQLResponse
+	b, err := ioutil.ReadAll(resp.Body)
+	require.NoError(t, err)
+	require.NoError(t, json.Unmarshal(b, &gqlResp))
+	require.Equal(t, touchedUidsInHeader, uint64(gqlResp.Extensions["touched_uids"].(float64)))
+}
+
 // This test checks that all the different combinations of
 // request sending compressed / uncompressed query and receiving
 // compressed / uncompressed result.

graphql/schema/response.go

@@ -32,6 +32,14 @@ type Extensions struct {
 	TouchedUids uint64 `json:"touched_uids,omitempty"`
 }
 
+// GetTouchedUids returns TouchedUids
+func (e *Extensions) GetTouchedUids() uint64 {
+	if e == nil {
+		return 0
+	}
+	return e.TouchedUids
+}
+
 // Merge merges ext with e
 func (e *Extensions) Merge(ext *Extensions) {
 	if e == nil || ext == nil {
@@ -69,6 +77,14 @@ func ErrorResponse(err error) *Response {
 	}
 }
 
+// GetExtensions returns a *Extensions
+func (r *Response) GetExtensions() *Extensions {
+	if r == nil {
+		return nil
+	}
+	return r.Extensions
+}
+
 // WithError generates GraphQL errors from err and records those in r.
 func (r *Response) WithError(err error) {
 	r.Errors = append(r.Errors, AsGQLErrors(err)...)

graphql/web/http.go

@@ -20,6 +20,7 @@ import (
 	"compress/gzip"
 	"context"
 	"encoding/json"
+	"strconv"
 
 	"io"
 	"io/ioutil"
@@ -39,6 +40,8 @@ import (
 	"go.opencensus.io/trace"
 )
 
+const touchedUidsHeader = "Graphql-TouchedUids"
+
 // An IServeGraphQL can serve a GraphQL endpoint (currently only ons http)
 type IServeGraphQL interface {
 
@@ -86,6 +89,9 @@ func (gh *graphqlHandler) Resolve(ctx context.Context, gqlReq *schema.Request) *
 func write(w http.ResponseWriter, rr *schema.Response, acceptGzip bool) {
 	var out io.Writer = w
 
+	// set TouchedUids header
+	w.Header().Set(touchedUidsHeader, strconv.FormatUint(rr.GetExtensions().GetTouchedUids(), 10))
+
 	// If the receiver accepts gzip, then we would update the writer
 	// and send gzipped content instead.
 	if acceptGzip {