Targets section: one Add, then a target type and Next, then that type's fields (closes #370)

The targets section of the webhook page showed its add form open with every field, a URL included for types that use none. It now lists only its targets until "+ Add" is clicked; "+ Add" shows a choice of target type with Next and Cancel on one row, and Next shows the name and only that type's fields. The database and log types show no URL field and the server stores none for them; the slack form gains its retry field. A refused target brings the page back with the form open on its type, the values entered and the reason, and Cancel empties it. An encoding failure stays a logged 500. Target validation returns its message, so the new-webhook page can reuse it.

Model: opus-5-5

internal/handlers/export_test.go

@@ -143,22 +143,20 @@ func (s *Handlers) RenderTemplateForTest(
 // BuildSlackTargetConfigForTest exposes
 // buildSlackTargetConfig for use in the handlers_test package.
 func (s *Handlers) BuildSlackTargetConfigForTest(
-	w http.ResponseWriter,
-	r *http.Request,
+	ctx context.Context,
 	targetURL string,
-) (string, error) {
-	return s.buildSlackTargetConfig(w, r, targetURL)
+) (string, string, error) {
+	return s.buildSlackTargetConfig(ctx, targetURL)
 }
 
 // BuildHTTPTargetConfigForTest exposes buildHTTPTargetConfig
 // for use in the handlers_test package, taking the form fields
 // an HTTP target's configuration is built from.
 func (s *Handlers) BuildHTTPTargetConfigForTest(
-	w http.ResponseWriter,
-	r *http.Request,
+	ctx context.Context,
 	targetURL, headers, timeout string,
-) (string, error) {
-	return s.buildHTTPTargetConfig(w, r, targetFormInput{
+) (string, string, error) {
+	return s.buildHTTPTargetConfig(ctx, targetFormInput{
 		URL:     targetURL,
 		Headers: headers,
 		Timeout: timeout,
@@ -168,9 +166,8 @@ func (s *Handlers) BuildHTTPTargetConfigForTest(
 // BuildDatabaseTargetConfigForTest exposes
 // buildDatabaseTargetConfig for use in the handlers_test
 // package.
-func (s *Handlers) BuildDatabaseTargetConfigForTest(
-	w http.ResponseWriter,
+func BuildDatabaseTargetConfigForTest(
 	expiry string,
-) (string, error) {
-	return s.buildDatabaseTargetConfig(w, newRequestForTest(), expiry)
+) (string, string, error) {
+	return buildDatabaseTargetConfig(expiry)
 }

internal/handlers/handlers_test.go

@@ -314,16 +314,12 @@ func TestBuildSlackTargetConfig_AcceptsPublicURL(t *testing.T) {
 
 	t.Cleanup(app.RequireStop)
 
-	req := httptest.NewRequestWithContext(
-		context.Background(), http.MethodPost, "/", nil)
-	w := httptest.NewRecorder()
-
-	cfg, err := h.BuildSlackTargetConfigForTest(
-		w, req, "http://93.184.216.34/services/T00/B00/xxx",
+	cfg, errMsg, err := h.BuildSlackTargetConfigForTest(
+		t.Context(), "http://93.184.216.34/services/T00/B00/xxx",
 	)
 
 	require.NoError(t, err)
-	assert.Equal(t, http.StatusOK, w.Code)
+	assert.Empty(t, errMsg)
 	assert.Contains(t, cfg, "webhookUrl")
 }
 
@@ -337,17 +333,13 @@ func TestBuildSlackTargetConfig_RejectsReservedURL(t *testing.T) {
 
 	t.Cleanup(app.RequireStop)
 
-	req := httptest.NewRequestWithContext(
-		context.Background(), http.MethodPost, "/", nil)
-	w := httptest.NewRecorder()
-
-	cfg, err := h.BuildSlackTargetConfigForTest(
-		w, req, "http://169.254.169.254/latest/meta-data/",
+	cfg, errMsg, err := h.BuildSlackTargetConfigForTest(
+		t.Context(), "http://169.254.169.254/latest/meta-data/",
 	)
 
-	require.Error(t, err)
+	require.NoError(t, err)
+	assert.Contains(t, errMsg, "Invalid target URL")
 	assert.Empty(t, cfg)
-	assert.Equal(t, http.StatusBadRequest, w.Code)
 }
 
 func TestRenderTemplate(t *testing.T) {
@@ -444,29 +436,22 @@ func TestRenderTemplateMidRenderErrorSendsNoPartialBody(t *testing.T) {
 func TestBuildDatabaseTargetConfig_Valid(t *testing.T) {
 	t.Parallel()
 
-	var h *handlers.Handlers
-
-	app := newTestApp(t, &h)
-	app.RequireStart()
-
-	t.Cleanup(app.RequireStop)
-
 	// Empty expiry: the keep-forever default, empty config.
-	w := httptest.NewRecorder()
-	cfg, err := h.BuildDatabaseTargetConfigForTest(w, "")
+	cfg, errMsg, err := handlers.BuildDatabaseTargetConfigForTest("")
 	require.NoError(t, err)
+	assert.Empty(t, errMsg)
 	assert.Empty(t, cfg)
 
 	// Explicit never is stored as config.
-	w = httptest.NewRecorder()
-	cfg, err = h.BuildDatabaseTargetConfigForTest(w, "never")
+	cfg, errMsg, err = handlers.BuildDatabaseTargetConfigForTest("never")
 	require.NoError(t, err)
+	assert.Empty(t, errMsg)
 	assert.JSONEq(t, `{"expiry":"never"}`, cfg)
 
 	// A positive duration is stored as config.
-	w = httptest.NewRecorder()
-	cfg, err = h.BuildDatabaseTargetConfigForTest(w, "720h")
+	cfg, errMsg, err = handlers.BuildDatabaseTargetConfigForTest("720h")
 	require.NoError(t, err)
+	assert.Empty(t, errMsg)
 	assert.JSONEq(t, `{"expiry":"720h"}`, cfg)
 }
 
@@ -475,22 +460,14 @@ func TestBuildDatabaseTargetConfig_RejectsBadExpiry(
 ) {
 	t.Parallel()
 
-	var h *handlers.Handlers
-
-	app := newTestApp(t, &h)
-	app.RequireStart()
-
-	t.Cleanup(app.RequireStop)
-
 	for _, bad := range []string{"nonsense", "7d", "-5h"} {
-		w := httptest.NewRecorder()
-		cfg, err := h.BuildDatabaseTargetConfigForTest(w, bad)
+		cfg, errMsg, err := handlers.BuildDatabaseTargetConfigForTest(bad)
 
-		require.Error(t, err, "expiry %q", bad)
-		assert.Empty(t, cfg)
-		assert.Equal(
-			t, http.StatusBadRequest, w.Code,
-			"expiry %q should be rejected with 400", bad,
+		require.NoError(t, err)
+		assert.Contains(
+			t, errMsg, "Invalid archive expiry",
+			"expiry %q should be refused", bad,
 		)
+		assert.Empty(t, cfg)
 	}
 }

internal/handlers/source_management.go

@@ -1,6 +1,7 @@
 package handlers
 
 import (
+	"context"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -38,9 +39,6 @@ type WebhookListItem struct {
 	EventsUnreadable  bool
 }
 
-// errMissingURL signals that a required URL was not provided.
-var errMissingURL = errors.New("missing URL")
-
 // parseRetentionDays interprets a retention_days form value. It
 // returns the number of days, or, for a value it refuses, the message
 // the create and edit forms show; the message is empty when the value
@@ -460,15 +458,20 @@ func (h *Handlers) HandleSourceDetail() http.HandlerFunc {
 			return
 		}
 
-		h.renderSourceDetail(w, r, webhook)
+		h.renderSourceDetail(w, r, webhook, targetFormInput{}, "")
 	}
 }
 
-// renderSourceDetail loads and renders a source detail page.
+// renderSourceDetail loads and renders a source detail page. With a
+// targetErr, it is the page shown again for a refused add target
+// form: it answers 400, and the form opens on targetForm's type with
+// its values and the message.
 func (h *Handlers) renderSourceDetail(
 	w http.ResponseWriter,
 	r *http.Request,
 	webhook database.Webhook,
+	targetForm targetFormInput,
+	targetErr string,
 ) {
 	var entrypoints []database.Entrypoint
 
@@ -525,9 +528,16 @@ func (h *Handlers) renderSourceDetail(
 		"Events":      events,
 		"BaseURL":     baseURL,
 		"Stats":       h.loadWebhookStats(webhook.ID, entrypoints, targets),
+		"TargetForm":  targetForm,
+		"TargetError": targetErr,
 	}
 
-	h.renderTemplate(w, r, "source_detail.html", data)
+	status := http.StatusOK
+	if targetErr != "" {
+		status = http.StatusBadRequest
+	}
+
+	h.renderTemplateStatus(w, r, "source_detail.html", data, status)
 }
 
 // HandleSourceEdit shows the form to edit a webhook.
@@ -1518,64 +1528,27 @@ func (h *Handlers) HandleTargetCreate() http.HandlerFunc {
 	}
 }
 
-// processTargetCreate validates and creates a new target.
+// processTargetCreate validates and creates a new target. A refused
+// submission shows the webhook page again, with the add target form
+// open on the chosen type, the values entered, and the reason.
 func (h *Handlers) processTargetCreate(
 	w http.ResponseWriter,
 	r *http.Request,
 	webhook database.Webhook,
 ) {
-	// The body size cap is enforced by the MaxBodySize middleware,
-	// which runs before CSRF parses the form.
-	//
-	// Every field here is read with PostFormValue, not FormValue.
-	// FormValue falls back to the query string, which would let
-	// `POST /hook/{id}/targets?url=https://hooks.slack.com/...`
-	// configure a target from a value the request line carries — and
-	// the request line, unlike the body, is what logs, proxies,
-	// Referer headers and error trackers record.
-	name := r.PostFormValue("name")
-	targetType := database.TargetType(r.PostFormValue("type"))
+	in := targetFormInputFrom(r)
 
-	if name == "" {
-		http.Error(
-			w, "Name is required", http.StatusBadRequest,
-		)
-
-		return
-	}
-
-	if !isValidTargetType(targetType) {
-		http.Error(
-			w, "Invalid target type",
-			http.StatusBadRequest,
-		)
-
-		return
-	}
-
-	configJSON, err := h.buildTargetConfig(
-		w, r, targetType, targetFormInputFrom(r),
-	)
+	target, errMsg, err := h.newTarget(r.Context(), webhook.ID, in)
 	if err != nil {
+		h.serverError(w, r, "failed to encode target config", err)
+
 		return
 	}
 
-	// A new target has no stored retry count, so an absent field
-	// takes the fire-and-forget default. A field the operator filled
-	// in with something invalid is rejected rather than becoming
-	// that default.
-	maxRetries, ok := targetMaxRetries(w, r, 0)
-	if !ok {
-		return
-	}
+	if errMsg != "" {
+		h.renderSourceDetail(w, r, webhook, in, errMsg)
 
-	target := &database.Target{
-		WebhookID:  webhook.ID,
-		Name:       name,
-		Type:       targetType,
-		Active:     true,
-		Config:     configJSON,
-		MaxRetries: maxRetries,
+		return
 	}
 
 	err = h.db.DB().Create(target).Error
@@ -1591,6 +1564,49 @@ func (h *Handlers) processTargetCreate(
 	)
 }
 
+// newTarget validates a new target for a webhook and returns the row
+// to create, or, when it refuses the target, the message the form
+// shows. An error is the server's fault, not a refusal: the accepted
+// configuration could not be encoded. Every form that creates a
+// target goes through here, so they all accept and refuse the same
+// things.
+func (h *Handlers) newTarget(
+	ctx context.Context,
+	webhookID string,
+	in targetFormInput,
+) (*database.Target, string, error) {
+	if in.Name == "" {
+		return nil, "Name is required", nil
+	}
+
+	if !isValidTargetType(in.Type) {
+		return nil, "Invalid target type", nil
+	}
+
+	configJSON, errMsg, err := h.buildTargetConfig(ctx, in.Type, in)
+	if err != nil || errMsg != "" {
+		return nil, errMsg, err
+	}
+
+	// A new target has no stored retry count, so an absent field
+	// takes the fire-and-forget default. A field the operator filled
+	// in with something invalid is refused rather than becoming
+	// that default.
+	maxRetries, err := parseMaxRetries(in.MaxRetries, 0)
+	if err != nil {
+		return nil, "Invalid max retries: " + retriesErrorMessage(err), nil
+	}
+
+	return &database.Target{
+		WebhookID:  webhookID,
+		Name:       in.Name,
+		Type:       in.Type,
+		Active:     true,
+		Config:     configJSON,
+		MaxRetries: maxRetries,
+	}, "", nil
+}
+
 // isValidTargetType checks whether the target type is supported.
 func isValidTargetType(tt database.TargetType) bool {
 	switch tt {
@@ -1622,11 +1638,16 @@ func pageOrFirst(s string) int {
 	return v
 }
 
-// targetFormInput carries the raw form values describing a target's
-// configuration. Both the create and the edit path fill one and hand
-// it to buildTargetConfig, so neither can come to validate a
-// destination differently from the other.
+// targetFormInput carries the raw values of a target form. Both the
+// create and the edit path fill one and hand it to buildTargetConfig,
+// so neither can come to validate a destination differently from the
+// other. A refused add target form is shown again from it.
 type targetFormInput struct {
+	// Name is the target's name.
+	Name string
+	// Type is the type chosen on the add target form. The edit form
+	// has none: a target's stored type decides.
+	Type database.TargetType
 	// URL is the destination for an HTTP target and the webhook URL
 	// for a Slack target.
 	URL string
@@ -1635,13 +1656,15 @@ type targetFormInput struct {
 	Headers string
 	// Timeout is an HTTP target's per-request timeout in seconds.
 	Timeout string
+	// MaxRetries is an HTTP or Slack target's max_retries.
+	MaxRetries string
 	// Expiry is a database (archive) target's row expiry.
 	Expiry string
 }
 
-// targetFormInputFrom reads the configuration fields from a request
-// body. The body size cap is enforced by the MaxBodySize middleware,
-// which runs before CSRF parses the form.
+// targetFormInputFrom reads a target form from a request body. The
+// body size cap is enforced by the MaxBodySize middleware, which runs
+// before CSRF parses the form.
 //
 // Every field is read with PostFormValue, not FormValue. FormValue
 // falls back to the query string, which would let
@@ -1653,38 +1676,38 @@ type targetFormInput struct {
 // tokens.
 func targetFormInputFrom(r *http.Request) targetFormInput {
 	return targetFormInput{
-		URL:     r.PostFormValue("url"),
-		Headers: r.PostFormValue("headers"),
-		Timeout: r.PostFormValue("timeout"),
-		Expiry:  r.PostFormValue("expiry"),
+		Name:       r.PostFormValue("name"),
+		Type:       database.TargetType(r.PostFormValue("type")),
+		URL:        r.PostFormValue("url"),
+		Headers:    r.PostFormValue("headers"),
+		Timeout:    r.PostFormValue("timeout"),
+		MaxRetries: r.PostFormValue("max_retries"),
+		Expiry:     r.PostFormValue("expiry"),
 	}
 }
 
 // buildTargetConfig builds the JSON config string for a target from
-// the submitted form values, writing its own 4xx response on
-// rejection. Which fields of in apply depends on the target type.
+// the submitted form values, or returns the message the form shows
+// for a value it refuses. An error is the server's fault, not a
+// refusal: the accepted configuration could not be encoded. Which
+// fields of in apply depends on the target type; a type without a URL
+// ignores any URL submitted.
 func (h *Handlers) buildTargetConfig(
-	w http.ResponseWriter,
-	r *http.Request,
+	ctx context.Context,
 	targetType database.TargetType,
 	in targetFormInput,
-) (string, error) {
+) (string, string, error) {
 	switch targetType {
 	case database.TargetTypeHTTP:
-		return h.buildHTTPTargetConfig(w, r, in)
+		return h.buildHTTPTargetConfig(ctx, in)
 	case database.TargetTypeSlack:
-		return h.buildSlackTargetConfig(w, r, in.URL)
+		return h.buildSlackTargetConfig(ctx, in.URL)
 	case database.TargetTypeDatabase:
-		return h.buildDatabaseTargetConfig(w, r, in.Expiry)
+		return buildDatabaseTargetConfig(in.Expiry)
 	case database.TargetTypeLog:
-		return "", nil
+		return "", "", nil
 	default:
-		http.Error(
-			w, "Invalid target type",
-			http.StatusBadRequest,
-		)
-
-		return "", errMissingURL
+		return "", "Invalid target type", nil
 	}
 }
 
@@ -1692,92 +1715,73 @@ func (h *Handlers) buildTargetConfig(
 // SSRF-validated destination plus the optional headers and timeout
 // the delivery path honours.
 func (h *Handlers) buildHTTPTargetConfig(
-	w http.ResponseWriter,
-	r *http.Request,
+	ctx context.Context,
 	in targetFormInput,
-) (string, error) {
-	err := h.validateTargetURL(
-		w, r, in.URL, "URL is required for HTTP targets",
+) (string, string, error) {
+	errMsg := h.validateTargetURL(
+		ctx, in.URL, "URL is required for HTTP targets",
 	)
-	if err != nil {
-		return "", err
+	if errMsg != "" {
+		return "", errMsg, nil
 	}
 
 	headers, err := delivery.ParseTargetHeaders(in.Headers)
 	if err != nil {
-		http.Error(
-			w,
-			"Invalid headers: "+err.Error(),
-			http.StatusBadRequest,
-		)
-
-		return "", err
+		return "", fmt.Sprintf("Invalid headers: %v", err), nil
 	}
 
 	timeout, err := delivery.ParseTargetTimeout(in.Timeout)
 	if err != nil {
-		http.Error(
-			w,
-			"Invalid timeout: "+err.Error(),
-			http.StatusBadRequest,
-		)
-
-		return "", err
+		return "", fmt.Sprintf("Invalid timeout: %v", err), nil
 	}
 
-	return h.marshalTargetConfig(w, r, delivery.HTTPTargetConfig{
+	configJSON, err := marshalTargetConfig(delivery.HTTPTargetConfig{
 		URL:     in.URL,
 		Headers: headers,
 		Timeout: timeout,
 	})
+
+	return configJSON, "", err
 }
 
 // buildSlackTargetConfig builds config JSON for a Slack target,
 // whose whole configuration is one SSRF-validated webhook URL.
 func (h *Handlers) buildSlackTargetConfig(
-	w http.ResponseWriter,
-	r *http.Request,
+	ctx context.Context,
 	targetURL string,
-) (string, error) {
-	err := h.validateTargetURL(
-		w, r, targetURL,
+) (string, string, error) {
+	errMsg := h.validateTargetURL(
+		ctx, targetURL,
 		"Webhook URL is required for Slack targets",
 	)
-	if err != nil {
-		return "", err
+	if errMsg != "" {
+		return "", errMsg, nil
 	}
 
-	return h.marshalTargetConfig(w, r, delivery.SlackTargetConfig{
+	configJSON, err := marshalTargetConfig(delivery.SlackTargetConfig{
 		WebhookURL: targetURL,
 	})
+
+	return configJSON, "", err
 }
 
-// validateTargetURL rejects an empty or SSRF-blocked destination,
-// writing the 400 itself. missingMsg is the error shown when no URL
-// is given.
+// validateTargetURL refuses an empty or SSRF-blocked destination,
+// returning the message the form shows, or "" when the destination
+// is accepted. missingMsg is the message for no URL at all.
 //
 // It is the single point at which a user-supplied destination enters
 // the SSRF guard, on create and on edit alike. An edit path that
 // reached storage without passing through here would reopen the hole
 // the guard closes.
 func (h *Handlers) validateTargetURL(
-	w http.ResponseWriter,
-	r *http.Request,
+	ctx context.Context,
 	targetURL, missingMsg string,
-) error {
+) string {
 	if targetURL == "" {
-		http.Error(
-			w,
-			missingMsg,
-			http.StatusBadRequest,
-		)
-
-		return errMissingURL
+		return missingMsg
 	}
 
-	err := h.ssrf.ValidateTargetURL(
-		r.Context(), targetURL,
-	)
+	err := h.ssrf.ValidateTargetURL(ctx, targetURL)
 	if err != nil {
 		// The submitted URL can be a credential (a Slack
 		// incoming webhook URL is a bearer token), so the log
@@ -1803,25 +1807,16 @@ func (h *Handlers) validateTargetURL(
 				"egress to your own network\" in the README)."
 		}
 
-		http.Error(w, msg, http.StatusBadRequest)
-
-		return err
+		return msg
 	}
 
-	return nil
+	return ""
 }
 
-// marshalTargetConfig serialises a target configuration for storage,
-// writing a 500 itself if it cannot.
-func (h *Handlers) marshalTargetConfig(
-	w http.ResponseWriter,
-	r *http.Request,
-	cfg any,
-) (string, error) {
+// marshalTargetConfig serialises a target configuration for storage.
+func marshalTargetConfig(cfg any) (string, error) {
 	configBytes, err := json.Marshal(cfg)
 	if err != nil {
-		h.serverError(w, r, "failed to encode target config", err)
-
 		return "", err
 	}
 
@@ -1829,35 +1824,24 @@ func (h *Handlers) marshalTargetConfig(
 }
 
 // buildDatabaseTargetConfig builds config JSON for a database
-// (archive) target. The optional expiry (a form value read by
-// the caller, which bounds the request body) is validated here,
-// at creation time, so an unparseable value is rejected with a
-// 400 instead of failing every subsequent delivery. An empty
-// expiry yields an empty config (the keep-forever default).
-func (h *Handlers) buildDatabaseTargetConfig(
-	w http.ResponseWriter,
-	r *http.Request,
-	expiry string,
-) (string, error) {
+// (archive) target. The optional expiry is validated here, at
+// creation time, so an unparseable value is refused instead of
+// failing every subsequent delivery. An empty expiry yields an
+// empty config (the keep-forever default).
+func buildDatabaseTargetConfig(expiry string) (string, string, error) {
 	expiry = strings.TrimSpace(expiry)
 	if expiry == "" {
-		return "", nil
+		return "", "", nil
 	}
 
 	err := delivery.ValidateArchiveExpiry(expiry)
 	if err != nil {
-		http.Error(
-			w,
-			"Invalid archive expiry: "+err.Error(),
-			http.StatusBadRequest,
-		)
-
-		return "", err
+		return "", fmt.Sprintf("Invalid archive expiry: %v", err), nil
 	}
 
-	return h.marshalTargetConfig(
-		w, r, map[string]any{"expiry": expiry},
-	)
+	configJSON, err := marshalTargetConfig(map[string]any{"expiry": expiry})
+
+	return configJSON, "", err
 }
 
 // HandleEntrypointDelete handles deleting an entrypoint.

internal/handlers/target_create_test.go

@@ -0,0 +1,154 @@
+package handlers_test
+
+import (
+	"html"
+	"net/http"
+	"net/url"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"sneak.berlin/go/webhooker/internal/database"
+)
+
+// TestHandleTargetCreate_EveryType adds a target of each type. Each
+// submission carries a url: only the http and slack types store one.
+func TestHandleTargetCreate_EveryType(t *testing.T) {
+	t.Parallel()
+
+	env := setupSourceTest(t)
+
+	// fields is the rest of each submission, as a query string.
+	cases := []struct {
+		targetType  database.TargetType
+		fields      string
+		wantConfig  string
+		wantRetries int
+	}{
+		{
+			database.TargetTypeHTTP, "timeout=12&max_retries=3",
+			`{"url":"` + editOriginalURL + `","timeout":12}`, 3,
+		},
+		{
+			database.TargetTypeSlack, "max_retries=4",
+			`{"webhookUrl":"` + editOriginalURL + `"}`, 4,
+		},
+		{
+			database.TargetTypeDatabase, "expiry=720h",
+			`{"expiry":"720h"}`, 0,
+		},
+		{database.TargetTypeLog, "", "", 0},
+	}
+
+	for _, tc := range cases {
+		t.Run(string(tc.targetType), func(t *testing.T) {
+			t.Parallel()
+
+			webhook := seedWebhookWithRetention(t, env.db, 30)
+
+			form, err := url.ParseQuery(tc.fields)
+			require.NoError(t, err)
+			form.Set("name", "every-type")
+			form.Set("type", string(tc.targetType))
+			form.Set("url", editOriginalURL)
+
+			w := serveTarget(
+				env, http.MethodPost,
+				"/hook/"+webhook.ID+"/targets", form,
+			)
+			require.Equal(t, http.StatusSeeOther, w.Code, w.Body.String())
+
+			targets := targetsForWebhook(t, env.db, webhook.ID)
+			require.Len(t, targets, 1)
+			assert.Equal(t, tc.targetType, targets[0].Type)
+			assert.Equal(t, tc.wantRetries, targets[0].MaxRetries)
+
+			if tc.wantConfig == "" {
+				assert.Empty(t, targets[0].Config)
+			} else {
+				assert.JSONEq(t, tc.wantConfig, targets[0].Config)
+			}
+		})
+	}
+}
+
+// TestHandleTargetCreate_RefusedFormComesBack refuses a target of each
+// type and checks that the webhook page comes back with the add target
+// form open on that type, the values entered, and the reason.
+func TestHandleTargetCreate_RefusedFormComesBack(t *testing.T) {
+	t.Parallel()
+
+	env := setupSourceTest(t)
+
+	// fields is what the operator typed, as a query string.
+	cases := []struct {
+		targetType database.TargetType
+		fields     string
+		reason     string
+	}{
+		{
+			database.TargetTypeHTTP,
+			"name=private&url=" + editBlockedURL +
+				"&timeout=12&max_retries=3",
+			"Invalid target URL",
+		},
+		{
+			database.TargetTypeSlack, "name=no-url&max_retries=4",
+			"Webhook URL is required for Slack targets",
+		},
+		{
+			database.TargetTypeDatabase, "name=archive&expiry=7d",
+			"Invalid archive expiry",
+		},
+		{database.TargetTypeLog, "name=", "Name is required"},
+	}
+
+	for _, tc := range cases {
+		t.Run(string(tc.targetType), func(t *testing.T) {
+			t.Parallel()
+
+			webhook := seedWebhookWithRetention(t, env.db, 30)
+
+			typed, err := url.ParseQuery(tc.fields)
+			require.NoError(t, err)
+
+			form := url.Values{}
+			form.Set("type", string(tc.targetType))
+
+			for field := range typed {
+				form.Set(field, typed.Get(field))
+			}
+
+			w := serveTarget(
+				env, http.MethodPost,
+				"/hook/"+webhook.ID+"/targets", form,
+			)
+			assert.Equal(t, http.StatusBadRequest, w.Code)
+
+			page := w.Body.String()
+			assert.Contains(
+				t, page, `data-type="`+string(tc.targetType)+`"`,
+			)
+			assert.Contains(t, page, html.EscapeString(tc.reason))
+
+			// Each value comes back in a data attribute of the targets
+			// section named after its field (max_retries as
+			// data-max-retries), except url, which comes back in
+			// data-destination; templates/source_detail.html says why.
+			for field := range typed {
+				attr := "data-" + strings.ReplaceAll(field, "_", "-")
+				if field == "url" {
+					attr = "data-destination"
+				}
+
+				assert.Contains(
+					t, page, attr+`="`+
+						html.EscapeString(typed.Get(field))+`"`,
+				)
+			}
+
+			assert.Empty(t, targetsForWebhook(t, env.db, webhook.ID))
+		})
+	}
+}

internal/handlers/target_edit.go

@@ -120,18 +120,23 @@ func (h *Handlers) applyTargetEdit(
 ) {
 	name := r.PostFormValue("name")
 	if name == "" {
-		http.Error(
-			w, "Name is required", http.StatusBadRequest,
-		)
+		http.Error(w, "Name is required", http.StatusBadRequest)
 
 		return
 	}
 
-	configJSON, err := h.buildTargetConfig(
-		w, r, target.Type, targetFormInputFrom(r),
+	configJSON, errMsg, err := h.buildTargetConfig(
+		r.Context(), target.Type, targetFormInputFrom(r),
 	)
 	if err != nil {
-		// buildTargetConfig has already written the response.
+		h.serverError(w, r, "failed to encode target config", err)
+
+		return
+	}
+
+	if errMsg != "" {
+		http.Error(w, errMsg, http.StatusBadRequest)
+
 		return
 	}
 

internal/handlers/target_private_refusal_test.go

@@ -1,6 +1,7 @@
 package handlers_test
 
 import (
+	"html"
 	"net/http"
 	"net/url"
 	"testing"
@@ -43,12 +44,16 @@ func TestTargetRefusal_PrivateDestinationSaysHowToAllowIt(
 			form.Set("type", string(targetType))
 			form.Set("url", editBlockedURL)
 
+			// A refused add shows the webhook page again, where
+			// the hint is HTML-escaped; a refused edit answers in
+			// plain text.
 			added := serveTarget(
 				env, http.MethodPost, targetsPath, form,
 			)
 			assert.Equal(t, http.StatusBadRequest, added.Code)
 			assert.Contains(
-				t, added.Body.String(), privateRefusalHint,
+				t, added.Body.String(),
+				html.EscapeString(privateRefusalHint),
 			)
 
 			form.Set("url", editOriginalURL)

internal/handlers/target_retries.go

@@ -90,13 +90,14 @@ func retriesErrorMessage(err error) string {
 		", or 0 for fire-and-forget"
 }
 
-// targetMaxRetries reads and validates max_retries from a target form
+// targetMaxRetries reads and validates max_retries from a target edit
 // submission, answering the request with a 400 and reporting false
 // when the value is set but invalid.
 //
-// Both the create and the edit path go through here, so the two
-// cannot come to disagree about what a valid retry count is. The
-// wording matches the timeout control on the same submission.
+// It and the create path (newTarget) both use parseMaxRetries and
+// retriesErrorMessage, so the two cannot come to disagree about what a
+// valid retry count is. The wording matches the timeout control on
+// the same submission.
 func targetMaxRetries(
 	w http.ResponseWriter,
 	r *http.Request,