feat: start moving TH call into engine/session.go

internal/engine/session.go

@@ -13,8 +13,10 @@ import (
 	"github.com/ooni/probe-cli/v3/internal/enginelocate"
 	"github.com/ooni/probe-cli/v3/internal/enginenetx"
 	"github.com/ooni/probe-cli/v3/internal/engineresolver"
+	"github.com/ooni/probe-cli/v3/internal/httpapi"
 	"github.com/ooni/probe-cli/v3/internal/kvstore"
 	"github.com/ooni/probe-cli/v3/internal/model"
+	"github.com/ooni/probe-cli/v3/internal/ooapi"
 	"github.com/ooni/probe-cli/v3/internal/platform"
 	"github.com/ooni/probe-cli/v3/internal/probeservices"
 	"github.com/ooni/probe-cli/v3/internal/runtimex"
@@ -688,4 +690,34 @@ func (s *Session) MaybeLookupLocationContext(ctx context.Context) error {
 	return nil
 }
 
+// CallWebConnectivityTestHelper implements [model.EngineExperimentSession].
+func (s *Session) CallWebConnectivityTestHelper(ctx context.Context,
+	creq *model.THRequest, testhelpers []model.OOAPIService) (*model.THResponse, int, error) {
+	// handle the case where there are no available web connectivity test helpers
+	if len(testhelpers) <= 0 {
+		return nil, 0, model.ErrNoAvailableTestHelpers
+	}
+
+	// initialize a sequence caller for invoking the THs in FIFO order
+	seqCaller := httpapi.NewSequenceCaller(
+		ooapi.NewDescriptorTH(creq),
+		httpapi.NewEndpointList(s.DefaultHTTPClient(), s.Logger(), s.UserAgent(), testhelpers...)...,
+	)
+
+	// issue the composed call proper and obtain a response and an index or an error
+	cresp, idx, err := seqCaller.Call(ctx)
+
+	// handle the case where all test helpers failed
+	if err != nil {
+		return nil, 0, err
+	}
+
+	// apply some sanity checks to the results
+	runtimex.Assert(idx >= 0 && idx < len(testhelpers), "idx out of bounds")
+	runtimex.Assert(cresp != nil, "out is nil")
+
+	// return the results to the web connectivity caller
+	return cresp, idx, nil
+}
+
 var _ model.ExperimentSession = &Session{}

internal/experiment/webconnectivity/control.go

@@ -4,10 +4,8 @@ import (
 	"context"
 
 	"github.com/ooni/probe-cli/v3/internal/geoipx"
-	"github.com/ooni/probe-cli/v3/internal/httpapi"
 	"github.com/ooni/probe-cli/v3/internal/model"
 	"github.com/ooni/probe-cli/v3/internal/netxlite"
-	"github.com/ooni/probe-cli/v3/internal/ooapi"
 	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
@@ -24,12 +22,8 @@ type (
 func Control(
 	ctx context.Context, sess model.ExperimentSession,
 	testhelpers []model.OOAPIService, creq ControlRequest) (ControlResponse, *model.OOAPIService, error) {
-	seqCaller := httpapi.NewSequenceCaller(
-		ooapi.NewDescriptorTH(&creq),
-		httpapi.NewEndpointList(sess.DefaultHTTPClient(), sess.Logger(), sess.UserAgent(), testhelpers...)...,
-	)
 	sess.Logger().Infof("control for %s...", creq.HTTPRequest)
-	out, idx, err := seqCaller.Call(ctx)
+	out, idx, err := sess.CallWebConnectivityTestHelper(ctx, &creq, testhelpers)
 	sess.Logger().Infof("control for %s... %+v", creq.HTTPRequest, model.ErrorToStringOrOK(err))
 	if err != nil {
 		// make sure error is wrapped

internal/experiment/webconnectivitylte/control.go

@@ -8,11 +8,9 @@ import (
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/experiment/webconnectivity"
-	"github.com/ooni/probe-cli/v3/internal/httpapi"
 	"github.com/ooni/probe-cli/v3/internal/logx"
 	"github.com/ooni/probe-cli/v3/internal/model"
 	"github.com/ooni/probe-cli/v3/internal/netxlite"
-	"github.com/ooni/probe-cli/v3/internal/ooapi"
 	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
@@ -109,14 +107,8 @@ func (c *Control) Run(parentCtx context.Context) {
 		c.TestHelpers,
 	)
 
-	// create an httpapi sequence caller
-	seqCaller := httpapi.NewSequenceCaller(
-		ooapi.NewDescriptorTH(creq),
-		httpapi.NewEndpointList(c.Session.DefaultHTTPClient(), c.Logger, c.Session.UserAgent(), c.TestHelpers...)...,
-	)
-
 	// issue the control request and wait for the response
-	cresp, idx, err := seqCaller.Call(opCtx)
+	cresp, idx, err := c.Session.CallWebConnectivityTestHelper(opCtx, creq, c.TestHelpers)
 	if err != nil {
 		// make sure error is wrapped
 		err = netxlite.NewTopLevelGenericErrWrapper(err)

internal/legacy/mockable/mockable.go

@@ -38,6 +38,12 @@ type Session struct {
 	MockableUserAgent                string
 }
 
+// CallWebConnectivityTestHelper implements [model.EngineExperimentSession].
+func (sess *Session) CallWebConnectivityTestHelper(
+	ctx context.Context, request *model.THRequest, ths []model.OOAPIService) (*model.THResponse, int, error) {
+	panic("not implemented")
+}
+
 // GetTestHelpersByName implements ExperimentSession.GetTestHelpersByName
 func (sess *Session) GetTestHelpersByName(name string) ([]model.OOAPIService, bool) {
 	services, okay := sess.MockableTestHelpers[name]

internal/mocks/session.go

@@ -58,6 +58,11 @@ type Session struct {
 		config *model.OOAPICheckInConfig) (*model.OOAPICheckInResult, error)
 }
 
+func (sess *Session) CallWebConnectivityTestHelper(ctx context.Context,
+	req *model.THRequest, ths []model.OOAPIService) (*model.THResponse, int, error) {
+	panic("not implemented")
+}
+
 func (sess *Session) GetTestHelpersByName(name string) ([]model.OOAPIService, bool) {
 	return sess.MockGetTestHelpersByName(name)
 }

internal/model/experiment.go

@@ -7,14 +7,34 @@ package model
 
 import (
 	"context"
+	"errors"
 )
 
+// ErrNoAvailableTestHelpers is emitted when there are no available test helpers.
+var ErrNoAvailableTestHelpers = errors.New("no available helpers")
+
 // ExperimentSession is the experiment's view of a session.
 type ExperimentSession interface {
+	// CallWebConnectivityTestHelper invokes the Web Connectivity test helper with the
+	// given request object and the given list of available test helpers.
+	//
+	// If the list of test helpers is empty this function immediately returns nil, zero,
+	// and the [ErrNoAvailableTestHelpers] error to the caller.
+	//
+	// In case of any other failure, this function returns nil, zero, and an error
+	//
+	// On success, it returns the response, the used TH index, and nil.
+	//
+	// Note that the returned error won't be wrapped, so you need to wrap it yourself.
+	CallWebConnectivityTestHelper(
+		ctx context.Context, request *THRequest, ths []OOAPIService) (*THResponse, int, error)
+
 	// GetTestHelpersByName returns a list of test helpers with the given name.
 	GetTestHelpersByName(name string) ([]OOAPIService, bool)
 
 	// DefaultHTTPClient returns the default HTTPClient used by the session.
+	//
+	// Deprecated: Web Connectivity should use CallWebConnectivityTestHelper instead.
 	DefaultHTTPClient() HTTPClient
 
 	// FetchPsiphonConfig returns psiphon's config as a serialized JSON or an error.