Don't use more than 999 variables in SQLite querys. (#1425)

* Don't use more than 999 variables in SQLite querys.

Solve this problem in a more general and reusable way.
Also fix #1369
Add some unit tests.

Signed-off-by: Henrik Sölver <henrik.solver@gmail.com>

* Don't rely on testify for basic assertions

* Readability improvements and linting

Co-authored-by: Henrik Sölver <henrik.solver@gmail.com>

internal/sqlutil/sql.go

@@ -15,10 +15,14 @@
 package sqlutil
 
 import (
+	"context"
 	"database/sql"
 	"errors"
 	"fmt"
 	"runtime"
+	"strings"
+
+	"github.com/matrix-org/util"
 )
 
 // ErrUserExists is returned if a username already exists in the database.
@@ -107,3 +111,44 @@ func SQLiteDriverName() string {
 	}
 	return "sqlite3"
 }
+
+func minOfInts(a, b int) int {
+	if a <= b {
+		return a
+	}
+	return b
+}
+
+// QueryProvider defines the interface for querys used by RunLimitedVariablesQuery.
+type QueryProvider interface {
+	QueryContext(ctx context.Context, query string, args ...interface{}) (*sql.Rows, error)
+}
+
+// SQLite3MaxVariables is the default maximum number of host parameters in a single SQL statement
+// SQLlite can handle. See https://www.sqlite.org/limits.html for more information.
+const SQLite3MaxVariables = 999
+
+// RunLimitedVariablesQuery split up a query with more variables than the used database can handle in multiple queries.
+func RunLimitedVariablesQuery(ctx context.Context, query string, qp QueryProvider, variables []interface{}, limit uint, rowHandler func(*sql.Rows) error) error {
+	var start int
+	for start < len(variables) {
+		n := minOfInts(len(variables)-start, int(limit))
+		nextQuery := strings.Replace(query, "($1)", QueryVariadic(n), 1)
+		rows, err := qp.QueryContext(ctx, nextQuery, variables[start:start+n]...)
+		if err != nil {
+			util.GetLogger(ctx).WithError(err).Error("QueryContext returned an error")
+			return err
+		}
+		err = rowHandler(rows)
+		if closeErr := rows.Close(); closeErr != nil {
+			util.GetLogger(ctx).WithError(closeErr).Error("RunLimitedVariablesQuery: failed to close rows")
+			return err
+		}
+		if err != nil {
+			util.GetLogger(ctx).WithError(err).Error("RunLimitedVariablesQuery: rowHandler returned error")
+			return err
+		}
+		start = start + n
+	}
+	return nil
+}