From b037a616903746de8e647f53503d4edca29192ec Mon Sep 17 00:00:00 2001
From: David Anderson <dave@natulte.net>
Date: Fri, 21 Aug 2015 17:12:18 -0700
Subject: [PATCH] Add support for interface{} arguments in Go SQLite functions.

This enabled support for functions like Foo(a interface{}) and
Bar(a ...interface{}).
---
 callback.go     | 24 ++++++++++++++++++++++++
 sqlite3.go      | 13 ++++++++-----
 sqlite3_test.go | 28 ++++++++++++++++++++++++++++
 3 files changed, 60 insertions(+), 5 deletions(-)

diff --git a/callback.go b/callback.go
index 1692106..b1704fe 100644
--- a/callback.go
+++ b/callback.go
@@ -108,8 +108,32 @@ func callbackArgString(v *C.sqlite3_value) (reflect.Value, error) {
 	}
 }
 
+func callbackArgGeneric(v *C.sqlite3_value) (reflect.Value, error) {
+	switch C.sqlite3_value_type(v) {
+	case C.SQLITE_INTEGER:
+		return callbackArgInt64(v)
+	case C.SQLITE_FLOAT:
+		return callbackArgFloat64(v)
+	case C.SQLITE_TEXT:
+		return callbackArgString(v)
+	case C.SQLITE_BLOB:
+		return callbackArgBytes(v)
+	case C.SQLITE_NULL:
+		// Interpret NULL as a nil byte slice.
+		var ret []byte
+		return reflect.ValueOf(ret), nil
+	default:
+		panic("unreachable")
+	}
+}
+
 func callbackArg(typ reflect.Type) (callbackArgConverter, error) {
 	switch typ.Kind() {
+	case reflect.Interface:
+		if typ.NumMethod() != 0 {
+			return nil, errors.New("the only supported interface type is interface{}")
+		}
+		return callbackArgGeneric, nil
 	case reflect.Slice:
 		if typ.Elem().Kind() != reflect.Uint8 {
 			return nil, errors.New("the only supported slice type is []byte")
diff --git a/sqlite3.go b/sqlite3.go
index 8bb9826..73e67e3 100644
--- a/sqlite3.go
+++ b/sqlite3.go
@@ -232,11 +232,14 @@ func (tx *SQLiteTx) Rollback() error {
 
 // RegisterFunc makes a Go function available as a SQLite function.
 //
-// The function can accept arguments of any real numeric type
-// (i.e. not complex), as well as []byte and string. It must return a
-// value of one of those types, and optionally an error as a second
-// value. Variadic functions are allowed, if the variadic argument is
-// one of the allowed types.
+// The Go function can have arguments of the following types: any
+// numeric type except complex, bool, []byte, string and
+// interface{}. interface{} arguments are given the direct translation
+// of the SQLite data type: int64 for INTEGER, float64 for FLOAT,
+// []byte for BLOB, string for TEXT.
+//
+// The function can additionally be variadic, as long as the type of
+// the variadic argument is one of the above.
 //
 // If pure is true. SQLite will assume that the function's return
 // value depends only on its inputs, and make more aggressive
diff --git a/sqlite3_test.go b/sqlite3_test.go
index a563c08..62db05b 100644
--- a/sqlite3_test.go
+++ b/sqlite3_test.go
@@ -1071,6 +1071,20 @@ func TestFunctionRegistration(t *testing.T) {
 	regex := func(re, s string) (bool, error) {
 		return regexp.MatchString(re, s)
 	}
+	generic := func(a interface{}) int64 {
+		switch a.(type) {
+		case int64:
+			return 1
+		case float64:
+			return 2
+		case []byte:
+			return 3
+		case string:
+			return 4
+		default:
+			panic("unreachable")
+		}
+	}
 	variadic := func(a, b int64, c ...int64) int64 {
 		ret := a + b
 		for _, d := range c {
@@ -1078,6 +1092,9 @@ func TestFunctionRegistration(t *testing.T) {
 		}
 		return ret
 	}
+	variadicGeneric := func(a ...interface{}) int64 {
+		return int64(len(a))
+	}
 
 	sql.Register("sqlite3_FunctionRegistration", &SQLiteDriver{
 		ConnectHook: func(conn *SQLiteConn) error {
@@ -1105,9 +1122,15 @@ func TestFunctionRegistration(t *testing.T) {
 			if err := conn.RegisterFunc("regex", regex, true); err != nil {
 				return err
 			}
+			if err := conn.RegisterFunc("generic", generic, true); err != nil {
+				return err
+			}
 			if err := conn.RegisterFunc("variadic", variadic, true); err != nil {
 				return err
 			}
+			if err := conn.RegisterFunc("variadicGeneric", variadicGeneric, true); err != nil {
+				return err
+			}
 			return nil
 		},
 	})
@@ -1131,9 +1154,14 @@ func TestFunctionRegistration(t *testing.T) {
 		{"SELECT not(0)", true},
 		{`SELECT regex("^foo.*", "foobar")`, true},
 		{`SELECT regex("^foo.*", "barfoobar")`, false},
+		{"SELECT generic(1)", int64(1)},
+		{"SELECT generic(1.1)", int64(2)},
+		{`SELECT generic(NULL)`, int64(3)},
+		{`SELECT generic("foo")`, int64(4)},
 		{"SELECT variadic(1,2)", int64(3)},
 		{"SELECT variadic(1,2,3,4)", int64(10)},
 		{"SELECT variadic(1,1,1,1,1,1,1,1,1,1)", int64(10)},
+		{`SELECT variadicGeneric(1,"foo",2.3, NULL)`, int64(4)},
 	}
 
 	for _, op := range ops {