Extract out `db.QuestionMarks` function (#6568)

We use this pattern in several places: there is a query that needs to
have a variable number of placeholders (question marks) in it, depending
on how many items we are inserting or querying for. For instance, when
issuing a precertificate we add that precertificate's names to the
"issuedNames" table. To make things more efficient, we do that in a
single query, whether there is one name on the certificate or a hundred.
That means interpolating into the query string with series of question
marks that matches the number of names.

We have a helper type MultiInserter that solves this problem for simple
inserts, but it does not solve the problem for selects or more complex
inserts, and we still have a number of places that generate their
sequence of question marks manually.

This change updates addIssuedNames to use MultiInserter. To enable that,
it also narrows the interface required by MultiInserter.Insert, so it's
easier to mock in tests.

This change adds the new function db.QuestionMarks, which generates e.g.
`?,?,?` depending on the input N.

In a few places I had to rename a function parameter named `db` to avoid
shadowing the `db` package.

cmd/expiration-mailer/main.go

@@ -212,16 +212,14 @@ func (m *mailer) updateLastNagTimestamps(ctx context.Context, certs []*x509.Cert
 
 // updateLastNagTimestampsChunk processes a single chunk (up to 65k) of certificates.
 func (m *mailer) updateLastNagTimestampsChunk(ctx context.Context, certs []*x509.Certificate) {
-	qmarks := make([]string, len(certs))
 	params := make([]interface{}, len(certs)+1)
 	for i, cert := range certs {
-		qmarks[i] = "?"
 		params[i+1] = core.SerialToString(cert.SerialNumber)
 	}
 
 	query := fmt.Sprintf(
 		"UPDATE certificateStatus SET lastExpirationNagSent = ? WHERE serial IN (%s)",
-		strings.Join(qmarks, ","),
+		db.QuestionMarks(len(certs)),
 	)
 	params[0] = m.clk.Now()
 

db/interfaces.go

@@ -64,6 +64,14 @@ type Executor interface {
 	Query(string, ...interface{}) (*sql.Rows, error)
 }
 
+// Queryer offers the Query method. Note that this is not read-only (i.e. not
+// Selector), since a Query can be `INSERT`, `UPDATE`, etc. The difference
+// between Query and Exec is that Query can return rows. So for instance it is
+// suitable for inserting rows and getting back ids.
+type Queryer interface {
+	Query(string, ...interface{}) (*sql.Rows, error)
+}
+
 // Transaction extends an Executor and adds Rollback, Commit, and WithContext.
 type Transaction interface {
 	Executor

db/multi.go

@@ -18,20 +18,23 @@ type MultiInserter struct {
 }
 
 // NewMultiInserter creates a new MultiInserter, checking for reasonable table
-// name and list of fields.
-func NewMultiInserter(table string, fields string, retCol string) (*MultiInserter, error) {
+// name and list of fields. returningColumn is the name of a column to be used
+// in a `RETURNING xyz` clause at the end. If it is empty, no `RETURNING xyz`
+// clause is used. If returningColumn is present, it must refer to a column
+// that can be parsed into an int64.
+func NewMultiInserter(table string, fields string, returningColumn string) (*MultiInserter, error) {
 	numFields := len(strings.Split(fields, ","))
 	if len(table) == 0 || len(fields) == 0 || numFields == 0 {
 		return nil, fmt.Errorf("empty table name or fields list")
 	}
-	if strings.Contains(retCol, ",") {
-		return nil, fmt.Errorf("return column must be singular, but got %q", retCol)
+	if strings.Contains(returningColumn, ",") {
+		return nil, fmt.Errorf("return column must be singular, but got %q", returningColumn)
 	}
 
 	return &MultiInserter{
 		table:     table,
 		fields:    fields,
-		retCol:    retCol,
+		retCol:    returningColumn,
 		numFields: numFields,
 		values:    make([][]interface{}, 0),
 	}, nil
@@ -50,12 +53,10 @@ func (mi *MultiInserter) Add(row []interface{}) error {
 // for gorp to use in place of the query's question marks. Currently only
 // used by .Insert(), below.
 func (mi *MultiInserter) query() (string, []interface{}) {
-	questionsRow := strings.TrimRight(strings.Repeat("?,", mi.numFields), ",")
-
 	var questionsBuf strings.Builder
 	var queryArgs []interface{}
 	for _, row := range mi.values {
-		fmt.Fprintf(&questionsBuf, "(%s),", questionsRow)
+		fmt.Fprintf(&questionsBuf, "(%s),", QuestionMarks(mi.numFields))
 		queryArgs = append(queryArgs, row...)
 	}
 
@@ -71,12 +72,12 @@ func (mi *MultiInserter) query() (string, []interface{}) {
 }
 
 // Insert performs the action represented by .query() on the provided database,
-// which is assumed to already have a context attached. If a non-empty retCol
-// was provided, then it returns the list of values from that column returned
-// by the query.
-func (mi *MultiInserter) Insert(exec Executor) ([]int64, error) {
+// which is assumed to already have a context attached. If a non-empty
+// returningColumn was provided, then it returns the list of values from that
+// column returned by the query.
+func (mi *MultiInserter) Insert(queryer Queryer) ([]int64, error) {
 	query, queryArgs := mi.query()
-	rows, err := exec.Query(query, queryArgs...)
+	rows, err := queryer.Query(query, queryArgs...)
 	if err != nil {
 		return nil, err
 	}
@@ -94,9 +95,15 @@ func (mi *MultiInserter) Insert(exec Executor) ([]int64, error) {
 		}
 	}
 
-	err = rows.Close()
-	if err != nil {
-		return nil, err
+	// Hack: sometimes in unittests we make a mock Queryer that returns a nil
+	// `*sql.Rows`. A nil `*sql.Rows` is not actually valid— calling `Close()`
+	// on it will panic— but here we choose to treat it like an empty list,
+	// and skip calling `Close()` to avoid the panic.
+	if rows != nil {
+		err = rows.Close()
+		if err != nil {
+			return nil, err
+		}
 	}
 
 	return ids, nil

db/qmarks.go

@@ -0,0 +1,21 @@
+package db
+
+import "strings"
+
+// QuestionMarks returns a string consisting of N question marks, joined by
+// commas. If n is <= 0, panics.
+func QuestionMarks(n int) string {
+	if n <= 0 {
+		panic("db.QuestionMarks called with n <=0")
+	}
+	var qmarks strings.Builder
+	qmarks.Grow(2 * n)
+	for i := 0; i < n; i++ {
+		if i == 0 {
+			qmarks.WriteString("?")
+		} else {
+			qmarks.WriteString(",?")
+		}
+	}
+	return qmarks.String()
+}

db/qmarks_test.go

@@ -0,0 +1,19 @@
+package db
+
+import (
+	"testing"
+
+	"github.com/letsencrypt/boulder/test"
+)
+
+func TestQuestionMarks(t *testing.T) {
+	test.AssertEquals(t, QuestionMarks(1), "?")
+	test.AssertEquals(t, QuestionMarks(2), "?,?")
+	test.AssertEquals(t, QuestionMarks(3), "?,?,?")
+}
+
+func TestQuestionMarksPanic(t *testing.T) {
+	defer func() { recover() }()
+	QuestionMarks(0)
+	t.Errorf("calling QuestionMarks(0) did not panic as expected")
+}

sa/model.go

@@ -765,22 +765,27 @@ func deleteOrderFQDNSet(
 	return nil
 }
 
-func addIssuedNames(db db.Execer, cert *x509.Certificate, isRenewal bool) error {
+func addIssuedNames(queryer db.Queryer, cert *x509.Certificate, isRenewal bool) error {
 	if len(cert.DNSNames) == 0 {
 		return berrors.InternalServerError("certificate has no DNSNames")
 	}
-	var qmarks []string
-	var values []interface{}
+
+	multiInserter, err := db.NewMultiInserter("issuedNames", "reversedName, serial, notBefore, renewal", "")
+	if err != nil {
+		return err
+	}
 	for _, name := range cert.DNSNames {
-		values = append(values,
+		err = multiInserter.Add([]interface{}{
 			ReverseName(name),
 			core.SerialToString(cert.SerialNumber),
 			cert.NotBefore,
-			isRenewal)
-		qmarks = append(qmarks, "(?, ?, ?, ?)")
+			isRenewal,
+		})
+		if err != nil {
+			return err
+		}
 	}
-	query := `INSERT INTO issuedNames (reversedName, serial, notBefore, renewal) VALUES ` + strings.Join(qmarks, ", ") + `;`
-	_, err := db.Exec(query, values...)
+	_, err = multiInserter.Insert(queryer)
 	return err
 }
 
@@ -932,10 +937,8 @@ type authzValidity struct {
 // status and expiration date of each of them. It assumes that the provided
 // database selector already has a context associated with it.
 func getAuthorizationStatuses(s db.Selector, ids []int64) ([]authzValidity, error) {
-	var qmarks []string
 	var params []interface{}
 	for _, id := range ids {
-		qmarks = append(qmarks, "?")
 		params = append(params, id)
 	}
 	var validityInfo []struct {
@@ -944,7 +947,8 @@ func getAuthorizationStatuses(s db.Selector, ids []int64) ([]authzValidity, erro
 	}
 	_, err := s.Select(
 		&validityInfo,
-		fmt.Sprintf("SELECT status, expires FROM authz2 WHERE id IN (%s)", strings.Join(qmarks, ",")),
+		fmt.Sprintf("SELECT status, expires FROM authz2 WHERE id IN (%s)",
+			db.QuestionMarks(len(ids))),
 		params...,
 	)
 	if err != nil {

sa/sa_test.go

@@ -122,7 +122,6 @@ func createPendingAuthorization(t *testing.T, sa *SQLStorageAuthority, domain st
 	err = sa.dbMap.Insert(&am)
 	test.AssertNotError(t, err, "creating test authorization")
 
-	t.Log(am.ID)
 	return am.ID
 }
 
@@ -717,12 +716,12 @@ func TestFQDNSetsExists(t *testing.T) {
 	test.Assert(t, exists.Exists, "FQDN set does exist")
 }
 
-type execRecorder struct {
+type queryRecorder struct {
 	query string
 	args  []interface{}
 }
 
-func (e *execRecorder) Exec(query string, args ...interface{}) (sql.Result, error) {
+func (e *queryRecorder) Query(query string, args ...interface{}) (*sql.Rows, error) {
 	e.query = query
 	e.args = args
 	return nil, nil
@@ -732,7 +731,7 @@ func TestAddIssuedNames(t *testing.T) {
 	serial := big.NewInt(1)
 	expectedSerial := "000000000000000000000000000000000001"
 	notBefore := time.Date(2018, 2, 14, 12, 0, 0, 0, time.UTC)
-	placeholdersPerName := "(?, ?, ?, ?)"
+	placeholdersPerName := "(?,?,?,?)"
 	baseQuery := "INSERT INTO issuedNames (reversedName, serial, notBefore, renewal) VALUES"
 
 	testCases := []struct {
@@ -807,7 +806,7 @@ func TestAddIssuedNames(t *testing.T) {
 
 	for _, tc := range testCases {
 		t.Run(tc.Name, func(t *testing.T) {
-			var e execRecorder
+			var e queryRecorder
 			err := addIssuedNames(
 				&e,
 				&x509.Certificate{
@@ -819,7 +818,7 @@ func TestAddIssuedNames(t *testing.T) {
 			test.AssertNotError(t, err, "addIssuedNames failed")
 			expectedPlaceholders := placeholdersPerName
 			for i := 0; i < len(tc.IssuedNames)-1; i++ {
-				expectedPlaceholders = fmt.Sprintf("%s, %s", expectedPlaceholders, placeholdersPerName)
+				expectedPlaceholders = fmt.Sprintf("%s,%s", expectedPlaceholders, placeholdersPerName)
 			}
 			expectedQuery := fmt.Sprintf("%s %s;", baseQuery, expectedPlaceholders)
 			test.AssertEquals(t, e.query, expectedQuery)

sa/saro.go

@@ -760,10 +760,8 @@ func (ssa *SQLStorageAuthorityRO) GetAuthorizations2(ctx context.Context, req *s
 		identifierTypeToUint[string(identifier.DNS)],
 	}
 
-	qmarks := make([]string, len(req.Domains))
-	for i, n := range req.Domains {
-		qmarks[i] = "?"
-		params = append(params, n)
+	for _, name := range req.Domains {
+		params = append(params, name)
 	}
 
 	query := fmt.Sprintf(
@@ -775,7 +773,7 @@ func (ssa *SQLStorageAuthorityRO) GetAuthorizations2(ctx context.Context, req *s
 			identifierType = ? AND
 			identifierValue IN (%s)`,
 		authzFields,
-		strings.Join(qmarks, ","),
+		db.QuestionMarks(len(req.Domains)),
 	)
 
 	_, err := ssa.dbReadOnlyMap.Select(
@@ -965,30 +963,31 @@ func (ssa *SQLStorageAuthorityRO) GetValidAuthorizations2(ctx context.Context, r
 		return nil, errIncompleteRequest
 	}
 
-	var authzModels []authzModel
+	query := fmt.Sprintf(
+		`SELECT %s FROM authz2 WHERE
+			registrationID = ? AND
+			status = ? AND
+			expires > ? AND
+			identifierType = ? AND
+			identifierValue IN (%s)`,
+		authzFields,
+		db.QuestionMarks(len(req.Domains)),
+	)
+
 	params := []interface{}{
 		req.RegistrationID,
 		statusUint(core.StatusValid),
 		time.Unix(0, req.Now),
 		identifierTypeToUint[string(identifier.DNS)],
 	}
-	qmarks := make([]string, len(req.Domains))
-	for i, n := range req.Domains {
-		qmarks[i] = "?"
-		params = append(params, n)
+	for _, domain := range req.Domains {
+		params = append(params, domain)
 	}
+
+	var authzModels []authzModel
 	_, err := ssa.dbReadOnlyMap.Select(
 		&authzModels,
-		fmt.Sprintf(
-			`SELECT %s FROM authz2 WHERE
-			registrationID = ? AND
-			status = ? AND
-			expires > ? AND
-			identifierType = ? AND
-			identifierValue IN (%s)`,
-			authzFields,
-			strings.Join(qmarks, ","),
-		),
+		query,
 		params...,
 	)
 	if err != nil {