[query] Fix Content-Type for OpenAPI handler

src/query/api/v1/handler/graphite/find.go

@@ -110,7 +110,7 @@ func (h *grahiteFindHandler) ServeHTTP(
 ) {
 	ctx := context.WithValue(r.Context(), handler.HeaderKey, r.Header)
 	logger := logging.WithContext(ctx, h.instrumentOpts)
-	w.Header().Set("Content-Type", "application/json")
+	w.Header().Set(xhttp.HeaderContentType, xhttp.ContentTypeJSON)
 
 	// NB: need to run two separate queries, one of which will match only the
 	// provided matchers, and one which will match the provided matchers with at

src/query/api/v1/handler/graphite/render_parser.go

@@ -33,6 +33,7 @@ import (
 	"github.com/m3db/m3/src/query/graphite/graphite"
 	"github.com/m3db/m3/src/query/graphite/ts"
 	"github.com/m3db/m3/src/query/util/json"
+	xhttp "github.com/m3db/m3/src/x/net/http"
 )
 
 const (
@@ -54,12 +55,12 @@ func WriteRenderResponse(
 	format string,
 ) error {
 	if format == pickleFormat {
-		w.Header().Set("Content-Type", "application/octet-stream")
+		w.Header().Set(xhttp.HeaderContentType, xhttp.ContentTypeOctetStream)
 		return renderResultsPickle(w, series.Values)
 	}
 
 	// NB: return json unless requesting specifically `pickleFormat`
-	w.Header().Set("Content-Type", "application/json")
+	w.Header().Set(xhttp.HeaderContentType, xhttp.ContentTypeJSON)
 	return renderResultsJSON(w, series.Values)
 }
 

src/query/api/v1/handler/openapi/openapi.go

@@ -74,6 +74,7 @@ func (h *DocHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	w.Header().Set(xhttp.HeaderContentType, xhttp.ContentTypeHTMLUTF8)
 	w.Write(doc)
 }
 

src/query/api/v1/handler/prom/common.go

@@ -25,6 +25,8 @@ import (
 	"net/http"
 	"time"
 
+	xhttp "github.com/m3db/m3/src/x/net/http"
+
 	jsoniter "github.com/json-iterator/go"
 	promql "github.com/prometheus/prometheus/promql/parser"
 	promstorage "github.com/prometheus/prometheus/storage"
@@ -100,7 +102,7 @@ func respond(w http.ResponseWriter, data interface{}, warnings promstorage.Warni
 		return
 	}
 
-	w.Header().Set("Content-Type", "application/json")
+	w.Header().Set(xhttp.HeaderContentType, xhttp.ContentTypeJSON)
 	w.WriteHeader(http.StatusOK)
 	w.Write(b)
 }
@@ -117,7 +119,7 @@ func respondError(w http.ResponseWriter, err error, code int) {
 		return
 	}
 
-	w.Header().Set("Content-Type", "application/json")
+	w.Header().Set(xhttp.HeaderContentType, xhttp.ContentTypeJSON)
 	w.WriteHeader(code)
 	w.Write(b)
 }

src/query/api/v1/handler/prometheus/common_test.go

@@ -33,6 +33,7 @@ import (
 
 	"github.com/m3db/m3/src/query/models"
 	"github.com/m3db/m3/src/query/test"
+	xhttp "github.com/m3db/m3/src/x/net/http"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -93,7 +94,7 @@ func TestTimeoutParseWithPostRequestParam(t *testing.T) {
 	require.NoError(t, form.Close())
 
 	req := httptest.NewRequest("POST", "/dummy", buff)
-	req.Header.Set("Content-Type", form.FormDataContentType())
+	req.Header.Set(xhttp.HeaderContentType, form.FormDataContentType())
 
 	timeout, err := ParseRequestTimeout(req, time.Second)
 	assert.NoError(t, err)

src/query/api/v1/handler/prometheus/native/common_test.go

@@ -92,7 +92,7 @@ func TestParamParsing(t *testing.T) {
 func TestParamParsing_POST(t *testing.T) {
 	params := defaultParams().Encode()
 	req := httptest.NewRequest("POST", PromReadURL, strings.NewReader(params))
-	req.Header.Add("Content-Type", "application/x-www-form-urlencoded")
+	req.Header.Add(xhttp.HeaderContentType, xhttp.ContentTypeFormURLEncoded)
 
 	r, err := testParseParams(req)
 	require.NoError(t, err, "unable to parse request")

src/query/api/v1/handler/prometheus/native/complete_tags.go

@@ -66,7 +66,7 @@ func NewCompleteTagsHandler(opts options.HandlerOptions) http.Handler {
 func (h *CompleteTagsHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	ctx := context.WithValue(r.Context(), handler.HeaderKey, r.Header)
 	logger := logging.WithContext(ctx, h.instrumentOpts)
-	w.Header().Set("Content-Type", "application/json")
+	w.Header().Set(xhttp.HeaderContentType, xhttp.ContentTypeJSON)
 
 	tagCompletionQueries, rErr := prometheus.ParseTagCompletionParamsToQueries(r)
 	if rErr != nil {

src/query/api/v1/handler/prometheus/native/list_tags.go

@@ -70,7 +70,7 @@ func NewListTagsHandler(opts options.HandlerOptions) http.Handler {
 func (h *ListTagsHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	ctx := context.WithValue(r.Context(), handler.HeaderKey, r.Header)
 	logger := logging.WithContext(ctx, h.instrumentOpts)
-	w.Header().Set("Content-Type", "application/json")
+	w.Header().Set(xhttp.HeaderContentType, xhttp.ContentTypeJSON)
 
 	query := &storage.CompleteTagsQuery{
 		CompleteNameOnly: true,

src/query/api/v1/handler/prometheus/native/read.go

@@ -131,7 +131,7 @@ func (h *promReadHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	w.Header().Set("Content-Type", "application/json")
+	w.Header().Set(xhttp.HeaderContentType, xhttp.ContentTypeJSON)
 	handleroptions.AddWarningHeaders(w, result.Meta)
 	h.promReadMetrics.fetchSuccess.Inc(1)
 

src/query/api/v1/handler/prometheus/remote/match.go

@@ -70,7 +70,7 @@ func NewPromSeriesMatchHandler(opts options.HandlerOptions) http.Handler {
 func (h *PromSeriesMatchHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	ctx := context.WithValue(r.Context(), handler.HeaderKey, r.Header)
 	logger := logging.WithContext(ctx, h.instrumentOpts)
-	w.Header().Set("Content-Type", "application/json")
+	w.Header().Set(xhttp.HeaderContentType, xhttp.ContentTypeJSON)
 	w.Header().Set("Access-Control-Allow-Origin", "*")
 
 	queries, err := prometheus.ParseSeriesMatchQuery(r, h.tagOptions)

src/query/api/v1/handler/prometheus/remote/read.go

@@ -173,7 +173,7 @@ func (h *promReadHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 			})
 		}
 
-		w.Header().Set("Content-Type", "application/json")
+		w.Header().Set(xhttp.HeaderContentType, xhttp.ContentTypeJSON)
 		handleroptions.AddWarningHeaders(w, readResult.Meta)
 
 		err = json.NewEncoder(w).Encode(result)
@@ -226,7 +226,7 @@ func WriteSnappyCompressed(
 		return err
 	}
 
-	w.Header().Set("Content-Type", "application/x-protobuf")
+	w.Header().Set(xhttp.HeaderContentType, xhttp.ContentTypeProtobuf)
 	w.Header().Set("Content-Encoding", "snappy")
 	handleroptions.AddWarningHeaders(w, readResult.Meta)
 

src/query/api/v1/handler/prometheus/remote/read_test.go

@@ -50,6 +50,7 @@ import (
 	"github.com/m3db/m3/src/query/test/m3"
 	xclock "github.com/m3db/m3/src/x/clock"
 	"github.com/m3db/m3/src/x/instrument"
+	xhttp "github.com/m3db/m3/src/x/net/http"
 	xtest "github.com/m3db/m3/src/x/test"
 
 	"github.com/golang/mock/gomock"
@@ -89,7 +90,7 @@ func TestParseExpr(t *testing.T) {
 
 	start := time.Now().Truncate(time.Hour)
 	req := httptest.NewRequest(http.MethodPost, "/", buildBody(query, start))
-	req.Header.Add("Content-Type", "application/x-www-form-urlencoded")
+	req.Header.Add(xhttp.HeaderContentType, xhttp.ContentTypeFormURLEncoded)
 	readReq, err := ParseExpr(req)
 	require.NoError(t, err)
 
@@ -248,7 +249,7 @@ func TestQueryKillOnClientDisconnect(t *testing.T) {
 		Timeout: 1 * time.Millisecond,
 	}
 
-	_, err := c.Post(server.URL, "application/x-protobuf", test.GeneratePromReadBody(t))
+	_, err := c.Post(server.URL, xhttp.ContentTypeProtobuf, test.GeneratePromReadBody(t))
 	assert.Error(t, err)
 }
 
@@ -257,7 +258,7 @@ func TestQueryKillOnTimeout(t *testing.T) {
 	defer server.Close()
 
 	req, _ := http.NewRequest("POST", server.URL, test.GeneratePromReadBody(t))
-	req.Header.Add("Content-Type", "application/x-protobuf")
+	req.Header.Add(xhttp.HeaderContentType, xhttp.ContentTypeProtobuf)
 	req.Header.Add("timeout", "1ms")
 	resp, err := http.DefaultClient.Do(req)
 	require.NoError(t, err)

src/query/api/v1/handler/prometheus/remote/tag_values.go

@@ -79,7 +79,7 @@ func NewTagValuesHandler(options options.HandlerOptions) http.Handler {
 func (h *TagValuesHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	ctx := context.WithValue(r.Context(), handler.HeaderKey, r.Header)
 	logger := logging.WithContext(ctx, h.instrumentOpts)
-	w.Header().Set("Content-Type", "application/json")
+	w.Header().Set(xhttp.HeaderContentType, xhttp.ContentTypeJSON)
 
 	query, err := h.parseTagValuesToQuery(r)
 	if err != nil {

src/query/api/v1/handler/search_test.go

@@ -40,6 +40,7 @@ import (
 	"github.com/m3db/m3/src/query/test/m3"
 	"github.com/m3db/m3/src/query/test/seriesiter"
 	"github.com/m3db/m3/src/x/ident"
+	xhttp "github.com/m3db/m3/src/x/net/http"
 
 	"github.com/golang/mock/gomock"
 	"github.com/stretchr/testify/assert"
@@ -129,7 +130,7 @@ func TestSearchEndpoint(t *testing.T) {
 
 	urlWithLimit := fmt.Sprintf("%s%s", server.URL, "?limit=90")
 	req, _ := http.NewRequest("POST", urlWithLimit, generateSearchBody(t))
-	req.Header.Add("Content-Type", "application/json")
+	req.Header.Add(xhttp.HeaderContentType, xhttp.ContentTypeJSON)
 	resp, err := http.DefaultClient.Do(req)
 	require.NoError(t, err)
 	defer resp.Body.Close()

src/x/net/http/response.go

@@ -30,6 +30,26 @@ import (
 	"go.uber.org/zap"
 )
 
+const (
+	// HeaderContentType is the HTTP Content Type header.
+	HeaderContentType = "Content-Type"
+
+	// ContentTypeJSON is the Content-Type value for a JSON response.
+	ContentTypeJSON = "application/json"
+
+	// ContentTypeFormURLEncoded is the Content-Type value for a URL-encoded form.
+	ContentTypeFormURLEncoded = "application/x-www-form-urlencoded"
+
+	// ContentTypeHTMLUTF8 is the Content-Type value for UTF8-encoded HTML.
+	ContentTypeHTMLUTF8 = "text/html; charset=utf-8"
+
+	// ContentTypeProtobuf is the Content-Type value for a Protobuf message.
+	ContentTypeProtobuf = "application/x-protobuf"
+
+	// ContentTypeOctetStream is the Content-Type value for binary data.
+	ContentTypeOctetStream = "application/octet-stream"
+)
+
 // WriteJSONResponse writes generic data to the ResponseWriter
 func WriteJSONResponse(w http.ResponseWriter, data interface{}, logger *zap.Logger) {
 	jsonData, err := json.Marshal(data)
@@ -39,7 +59,7 @@ func WriteJSONResponse(w http.ResponseWriter, data interface{}, logger *zap.Logg
 		return
 	}
 
-	w.Header().Set("Content-Type", "application/json")
+	w.Header().Set(HeaderContentType, ContentTypeJSON)
 	w.Write(jsonData)
 }
 
@@ -48,7 +68,7 @@ func WriteJSONResponse(w http.ResponseWriter, data interface{}, logger *zap.Logg
 func WriteProtoMsgJSONResponse(w http.ResponseWriter, data proto.Message, logger *zap.Logger) {
 	marshaler := jsonpb.Marshaler{EmitDefaults: true}
 
-	w.Header().Set("Content-Type", "application/json")
+	w.Header().Set(HeaderContentType, ContentTypeJSON)
 	err := marshaler.Marshal(w, data)
 	if err != nil {
 		logger.Error("unable to marshal json", zap.Error(err))