database/sql: allow drivers to support custom arg types

Previously all arguments were passed through driver.IsValid.
This checked arguments against a few fundamental go types and
prevented others from being passed in as arguments.

The new interface driver.NamedValueChecker may be implemented
by both driver.Stmt and driver.Conn. This allows
this new interface to completely supersede the
driver.ColumnConverter interface as it can be used for
checking arguments known to a prepared statement and
arbitrary query arguments. The NamedValueChecker may be
skipped with driver.ErrSkip after all special cases are
exhausted to use the default argument converter.

In addition if driver.ErrRemoveArgument is returned
the argument will not be passed to the query at all,
useful for passing in driver specific per-query options.

Add a canonical Out argument wrapper to be passed
to OUTPUT parameters. This will unify checks that need to
be written in the NameValueChecker.

The statement number check is also moved to the argument
converter so the NamedValueChecker may remove arguments
passed to the query.

Fixes #13567
Fixes #18079
Updates #18417
Updates #17834
Updates #16235
Updates #13067
Updates #19797

Change-Id: I89088bd9cca4596a48bba37bfd20d987453ef237
Reviewed-on: https://go-review.googlesource.com/38533
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

1 files changed, 30 insertions, 0 deletions

diff --git a/src/database/sql/driver/driver.go b/src/database/sql/driver/driver.go
index d66196fd48..0262ca24ba 100644
--- a/src/database/sql/driver/driver.go
+++ b/src/database/sql/driver/driver.go
@@ -262,9 +262,39 @@ type StmtQueryContext interface {
 	QueryContext(ctx context.Context, args []NamedValue) (Rows, error)
 }
 
+// ErrRemoveArgument may be returned from NamedValueChecker to instruct the
+// sql package to not pass the argument to the driver query interface.
+// Return when accepting query specific options or structures that aren't
+// SQL query arguments.
+var ErrRemoveArgument = errors.New("driver: remove argument from query")
+
+// NamedValueChecker may be optionally implemented by Conn or Stmt. It provides
+// the driver more control to handle Go and database types beyond the default
+// Values types allowed.
+//
+// The sql package checks for value checkers in the following order,
+// stopping at the first found match: Stmt.NamedValueChecker, Conn.NamedValueChecker,
+// Stmt.ColumnConverter, DefaultParameterConverter.
+//
+// If CheckNamedValue returns ErrRemoveArgument, the NamedValue will not be included in
+// the final query arguments. This may be used to pass special options to
+// the query itself.
+//
+// If ErrSkip is returned the column converter error checking
+// path is used for the argument. Drivers may wish to return ErrSkip after
+// they have exhausted their own special cases.
+type NamedValueChecker interface {
+	// CheckNamedValue is called before passing arguments to the driver
+	// and is called in place of any ColumnConverter. CheckNamedValue must do type
+	// validation and conversion as appropriate for the driver.
+	CheckNamedValue(*NamedValue) error
+}
+
 // ColumnConverter may be optionally implemented by Stmt if the
 // statement is aware of its own columns' types and can convert from
 // any type to a driver Value.
+//
+// Deprecated: Drivers should implement NamedValueChecker.
 type ColumnConverter interface {
 	// ColumnConverter returns a ValueConverter for the provided
 	// column index. If the type of a specific column isn't known