roachtest: make follower-reads test use protobuf encoded requests

Previously, the roachtest for
`follower-reads/mixed-version/single-region` used JSON encoding for the
`ts/query` endpoint. This caused the client to send the newly updated
`timerseries` proto to an older cluster in JSON format. Although this
was defined as an `optional` field in the proto, since it was encoded in
JSON, that information was lost over the wire.

In other places, such as DBConsole, we expect the client to be sending
protobuf encoded messages and not JSON. In the same way, roachtests
(another client) should do the same. When this message is sent as a
protobuf, the `optional` tag of the field is encoded in the message and
the server is able to process is it as such.

There are related links in the issue:
#99117.

Fixes #99117.

Release note: None

pkg/cmd/roachtest/tests/follower_reads.go

@@ -730,7 +730,7 @@ func verifyHighFollowerReadRatios(
 	}
 
 	var response tspb.TimeSeriesQueryResponse
-	if err := httputil.PostJSON(http.Client{}, url, &request, &response); err != nil {
+	if err := httputil.PostProtobuf(ctx, http.Client{}, url, &request, &response); err != nil {
 		t.Fatal(err)
 	}
 

pkg/util/httputil/http.go

@@ -12,6 +12,7 @@ package httputil
 
 import (
 	"bytes"
+	"context"
 	"io"
 	"net/http"
 	"strconv"
@@ -110,6 +111,42 @@ func PostJSONWithRequest(
 	return doJSONRequest(httpClient, req, response)
 }
 
+// PostProtobuf uses the supplied client to POST request to the URL specified by
+// the parameters and unmarshal the result into response, using a
+// protobuf-encoded request body.
+func PostProtobuf(
+	ctx context.Context, httpClient http.Client, path string, request, response protoutil.Message,
+) error {
+	buf, err := protoutil.Marshal(request)
+	if err != nil {
+		return err
+	}
+	reader := bytes.NewReader(buf)
+	req, err := http.NewRequestWithContext(ctx, "POST", path, reader)
+	if err != nil {
+		return err
+	}
+	if timeout := httpClient.Timeout; timeout > 0 {
+		req.Header.Set("Grpc-Timeout", strconv.FormatInt(timeout.Nanoseconds(), 10)+"n")
+	}
+	req.Header.Set(AcceptHeader, ProtoContentType)
+	req.Header.Set(ContentTypeHeader, ProtoContentType)
+	resp, err := httpClient.Do(req)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+	b, err := io.ReadAll(resp.Body)
+	if contentType := resp.Header.Get(ContentTypeHeader); !(resp.StatusCode == http.StatusOK && contentType == ProtoContentType) {
+		// NB: errors.Wrapf(nil, ...) returns nil.
+		// nolint:errwrap
+		return errors.Errorf(
+			"status: %s, content-type: %s, body: %s, error: %v", resp.Status, contentType, b, err,
+		)
+	}
+	return protoutil.Unmarshal(b, response)
+}
+
 func doJSONRequest(
 	httpClient http.Client, req *http.Request, response protoutil.Message,
 ) (*http.Response, error) {