Mask the target URL in delivery errors, SSRF logs and log page data (closes #118)

A delivery target URL is itself a credential: a Slack incoming
webhook URL is a bearer token. Three paths still reproduced it
in full.

Transport failures were the worst of them. net/http embeds the
request URL in every *url.Error it returns, so any DNS, TLS,
timeout or dial failure wrote the whole webhook URL into
DeliveryResult.Error — on disk, in the per-webhook database,
behind a json tag that a REST API would serialize.

maskURL moves to url_mask.go and is exported as MaskURL, and
maskURLError joins it: it rebuilds the *url.Error with the URL
masked, keeping the operation and the wrapped cause, so a
refused connection still reads differently from a DNS failure
or a timeout and errors.Is/As/Timeout still work. It is applied
where the errors are raised — executeHTTPRequest, shared by the
Slack and HTTP targets, and the request-construction paths — so
downstream wrapping is safe by construction. url.Parse embeds
the URL too, so ValidateTargetURL's parse branch gets the same
treatment; its error is logged and shown.

The SSRF rejection log now records only the masked URL, and
loadTargetMap hands the event log page TargetViews and a
delivery projection instead of raw target rows, so the stored
config blob has no path to that template either.

internal/delivery/ssrf.go

@@ -92,7 +92,12 @@ func ValidateTargetURL(
 ) error {
 	parsed, err := url.Parse(targetURL)
 	if err != nil {
-		return fmt.Errorf("invalid URL: %w", err)
+		// url.Parse embeds the whole URL in its error, and
+		// this one is logged and shown; mask it. Every other
+		// branch below reports only the hostname.
+		return fmt.Errorf(
+			"invalid URL: %w", maskURLError(err),
+		)
 	}
 
 	err = validateScheme(parsed.Scheme)

internal/delivery/target_config_view.go

@@ -3,7 +3,6 @@ package delivery
 import (
 	"encoding/json"
 	"fmt"
-	"net/url"
 	"strconv"
 
 	"sneak.berlin/go/webhooker/internal/database"
@@ -17,9 +16,6 @@ import (
 // browser history, screenshots and screen shares.
 const configUnavailable = "(unavailable)"
 
-// urlPathElision stands in for a URL's elided path.
-const urlPathElision = "/..."
-
 // ConfigField is one labelled, display-safe value derived
 // from a target's stored configuration.
 type ConfigField struct {
@@ -202,23 +198,5 @@ func databaseConfigFields(configJSON string) []ConfigField {
 // parse into a scheme and host yields the neutral
 // placeholder, never the raw string.
 func (c *SlackTargetConfig) MaskedWebhookURL() string {
-	return maskURL(c.WebhookURL)
-}
-
-// maskURL renders a URL as scheme plus host with everything
-// that can carry a secret removed.
-func maskURL(raw string) string {
-	parsed, err := url.Parse(raw)
-	if err != nil || parsed.Scheme == "" ||
-		parsed.Host == "" {
-		return configUnavailable
-	}
-
-	masked := parsed.Scheme + "://" + parsed.Host
-
-	if parsed.Path != "" && parsed.Path != "/" {
-		masked += urlPathElision
-	}
-
-	return masked
+	return MaskURL(c.WebhookURL)
 }

internal/delivery/target_http.go

@@ -363,7 +363,8 @@ func (t *httpTarget) doHTTPRequest(
 	)
 	if reqErr != nil {
 		return 0, "", 0, fmt.Errorf(
-			"creating request: %w", reqErr,
+			"creating request: %w",
+			maskURLError(reqErr),
 		)
 	}
 
@@ -492,8 +493,19 @@ func applyRequestHeaders(
 // executeHTTPRequest sends an HTTP request using the provided
 // client. URLs are validated by the config parsers and the
 // SSRF-safe transport before reaching here.
+//
+// Transport failures are masked here, at the single point
+// where every target's request errors are born, because the
+// caller stores them in DeliveryResult.Error: an unmasked
+// *url.Error would write the target URL — the credential for
+// a Slack incoming webhook — into the per-webhook database.
 func executeHTTPRequest(
 	client *http.Client, req *http.Request,
 ) (*http.Response, error) {
-	return client.Do(req) //#nosec G704 -- validated URL, SSRF-safe transport
+	resp, err := client.Do(req) //#nosec G704 -- validated URL, SSRF-safe transport
+	if err != nil {
+		return nil, maskURLError(err)
+	}
+
+	return resp, nil
 }

internal/delivery/target_slack.go

@@ -125,7 +125,7 @@ func (t *slackTarget) attempt(
 	if err != nil {
 		return attemptResult{
 			success: false,
-			errMsg:  err.Error(),
+			errMsg:  maskURLError(err).Error(),
 		}
 	}
 

internal/delivery/url_mask.go

@@ -0,0 +1,61 @@
+package delivery
+
+import (
+	"errors"
+	"net/url"
+)
+
+// urlPathElision stands in for a URL's elided path.
+const urlPathElision = "/..."
+
+// MaskURL renders a URL as scheme plus host with everything
+// that can carry a secret removed. A delivery target URL is
+// itself a credential — a Slack incoming webhook URL is a
+// bearer token — so the path, query and userinfo are never
+// reproduced, in a page, a log line or a stored error. A URL
+// that does not parse into a scheme and host yields the
+// neutral placeholder, never the raw string.
+func MaskURL(raw string) string {
+	parsed, err := url.Parse(raw)
+	if err != nil || parsed.Scheme == "" ||
+		parsed.Host == "" {
+		return configUnavailable
+	}
+
+	masked := parsed.Scheme + "://" + parsed.Host
+
+	if parsed.Path != "" && parsed.Path != "/" {
+		masked += urlPathElision
+	}
+
+	return masked
+}
+
+// maskURLError strips the credential from an error raised
+// against a request URL. The net/http and net/url packages
+// embed the full request URL in every *url.Error they return,
+// so an unmodified transport error persisted into
+// DeliveryResult.Error writes the credential to disk.
+//
+// The masked error keeps the operation and the wrapped cause,
+// so a DNS failure still reads differently from a refused
+// connection, a TLS handshake failure or a timeout, and Is,
+// As, Timeout and Temporary keep working on it. Only the
+// path, query and userinfo of the URL are dropped. Errors
+// that carry no URL are returned unchanged.
+//
+// Call it where the error is raised, before any wrapping: it
+// replaces the *url.Error itself, so any context wrapped
+// around it first would be discarded.
+func maskURLError(err error) error {
+	var urlErr *url.Error
+	if !errors.As(err, &urlErr) {
+		return err
+	}
+
+	return &url.Error{
+		Op:  urlErr.Op,
+		URL: MaskURL(urlErr.URL),
+		Err: urlErr.Err,
+	}
+}

internal/delivery/url_mask_test.go

@@ -0,0 +1,196 @@
+package delivery_test
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/google/uuid"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"gorm.io/gorm"
+	"sneak.berlin/go/webhooker/internal/database"
+	"sneak.berlin/go/webhooker/internal/delivery"
+)
+
+// The path of a Slack incoming webhook URL is the credential:
+// whoever holds these segments can post to the channel
+// forever. None of them may reach a stored delivery error,
+// which lives on disk in the per-webhook database and is
+// serialized by the JSON tag on DeliveryResult.Error.
+const (
+	maskSecretPath = "/services/T00000000/B00000000/" +
+		"XXXXXXXXXXXXXXXXXXXXXXXX"
+)
+
+// assertNoCredential fails if the whole path or any single
+// segment of it survived into the message, so a partial leak
+// fails the test too.
+func assertNoCredential(t *testing.T, msg string) {
+	t.Helper()
+
+	segments := []string{
+		maskSecretPath,
+		"services",
+		"T00000000",
+		"B00000000",
+		"XXXXXXXXXXXXXXXXXXXXXXXX",
+	}
+
+	for _, segment := range segments {
+		assert.NotContains(t, msg, segment)
+	}
+}
+
+// storedDeliveryError returns the error string persisted for a
+// delivery, which is what an operator and any future API read.
+func storedDeliveryError(
+	t *testing.T, db *gorm.DB, deliveryID string,
+) string {
+	t.Helper()
+
+	var result database.DeliveryResult
+
+	require.NoError(t, db.Where(
+		"delivery_id = ?", deliveryID,
+	).First(&result).Error)
+
+	return result.Error
+}
+
+// deliverSlackTo runs a Slack delivery against webhookURL and
+// returns the error string it persisted.
+func deliverSlackTo(
+	t *testing.T, webhookURL string,
+) string {
+	t.Helper()
+
+	db := testWebhookDB(t)
+	e := testEngine(t, 1)
+	targetID := uuid.New().String()
+
+	slackCfg, err := json.Marshal(
+		delivery.SlackTargetConfig{
+			WebhookURL: webhookURL,
+		},
+	)
+	require.NoError(t, err)
+
+	event := seedEvent(t, db, `{"test":true}`)
+
+	dlv := seedDelivery(
+		t, db, event.ID, targetID,
+		database.DeliveryStatusPending,
+	)
+
+	d := buildSlackDelivery(
+		dlv, event, targetID,
+		"test-slack-mask", string(slackCfg),
+	)
+
+	e.ExportDeliverSlack(context.TODO(), db, d)
+
+	assertDeliveryStatus(t, db, dlv.ID,
+		database.DeliveryStatusFailed,
+	)
+
+	return storedDeliveryError(t, db, dlv.ID)
+}
+
+// TestDeliverSlack_TransportErrorMasksWebhookURL is the
+// load-bearing regression test: a transport failure must not
+// persist the webhook URL's credential into the database, and
+// must still say what went wrong and where.
+func TestDeliverSlack_TransportErrorMasksWebhookURL(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	// A server closed before use gives a deterministic
+	// transport failure against a known host.
+	ts := httptest.NewServer(http.NewServeMux())
+	host := ts.URL
+
+	ts.Close()
+
+	errMsg := deliverSlackTo(t, host+maskSecretPath)
+
+	require.NotEmpty(t, errMsg)
+	assertNoCredential(t, errMsg)
+
+	// The diagnostic value survives: the operation, the host
+	// and the transport failure are all still reported, and
+	// only the path is elided.
+	assert.Contains(t, errMsg, "sending request")
+	assert.Contains(t, errMsg, "Post")
+	assert.Contains(t, errMsg, host+"/...")
+	assert.Contains(t, errMsg, "connection refused")
+}
+
+// TestDeliverSlack_UnparsableURLMasksWebhookURL covers the
+// other error path out of a Slack attempt: url.Parse also
+// embeds the whole URL in the error it returns.
+func TestDeliverSlack_UnparsableURLMasksWebhookURL(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	errMsg := deliverSlackTo(
+		t,
+		"https://hooks.slack.com"+maskSecretPath+"\n",
+	)
+
+	require.NotEmpty(t, errMsg)
+	assertNoCredential(t, errMsg)
+	assert.Contains(t, errMsg, "invalid control character")
+}
+
+// TestDoHTTPRequest_TransportErrorMasksURL proves the HTTP
+// target's transport errors are masked too; its destination
+// URL can carry a token in a query string.
+func TestDoHTTPRequest_TransportErrorMasksURL(t *testing.T) {
+	t.Parallel()
+
+	ts := httptest.NewServer(http.NewServeMux())
+	host := ts.URL
+
+	ts.Close()
+
+	e := testEngine(t, 1)
+
+	cfg, err := e.ExportParseHTTPConfig(
+		newHTTPTargetConfig(host + maskSecretPath),
+	)
+	require.NoError(t, err)
+
+	statusCode, _, _, reqErr := e.ExportDoHTTPRequest(
+		context.TODO(), cfg,
+		&database.Event{Body: `{"test":true}`},
+	)
+	require.Error(t, reqErr)
+	assert.Zero(t, statusCode)
+
+	assertNoCredential(t, reqErr.Error())
+	assert.Contains(t, reqErr.Error(), host+"/...")
+	assert.Contains(
+		t, reqErr.Error(), "connection refused",
+	)
+}
+
+// TestValidateTargetURL_UnparsableURLIsMasked proves the SSRF
+// validator's error does not carry the submitted URL, which
+// the handler both logs and shows.
+func TestValidateTargetURL_UnparsableURLIsMasked(t *testing.T) {
+	t.Parallel()
+
+	err := delivery.ValidateTargetURL(
+		context.TODO(),
+		"https://hooks.slack.com"+maskSecretPath+"\n",
+	)
+	require.Error(t, err)
+
+	assertNoCredential(t, err.Error())
+	assert.Contains(t, err.Error(), "invalid URL")
+}