Fix empty objects (#5)

A top level empty object returns a TRUE condition as you're not
filtering on anything. Nested empty objects will return an error as they
most likely indicate an error.

---------

Co-authored-by: Koen Bollen <213502+koenbollen@users.noreply.github.com>

Author: erikdubbelboer

examples/basic_test.go

@@ -29,6 +29,20 @@ func ExampleNewConverter() {
 	// []interface {}{"2020-01-01T00:00:00Z", "John"}
 }
 
+func ExampleNewConverter_emptyfilter() {
+	converter := filter.NewConverter(filter.WithEmptyCondition("TRUE")) // The default is FALSE if you don't change it.
+
+	mongoFilterQuery := `{}`
+	conditions, _, err := converter.Convert([]byte(mongoFilterQuery), 1)
+	if err != nil {
+		// handle error
+	}
+
+	fmt.Println(conditions)
+	// Output:
+	// TRUE
+}
+
 func ExampleNewConverter_nonIsolatedConditions() {
 	converter := filter.NewConverter()
 

filter/converter.go

@@ -26,13 +26,16 @@ type Converter struct {
 		driver.Valuer
 		sql.Scanner
 	}
+	emptyCondition string
 }
 
 // NewConverter creates a new Converter with optional nested JSONB field mapping.
 //
 // Note: When using github.com/lib/pq, the filter.WithArrayDriver should be set to pq.Array.
 func NewConverter(options ...Option) *Converter {
-	converter := &Converter{}
+	converter := &Converter{
+		emptyCondition: "FALSE",
+	}
 	for _, option := range options {
 		if option != nil {
 			option(converter)
@@ -56,6 +59,10 @@ func (c *Converter) Convert(query []byte, startAtParameterIndex int) (conditions
 		return "", nil, err
 	}
 
+	if len(mongoFilter) == 0 {
+		return c.emptyCondition, []any{}, nil
+	}
+
 	conditions, values, err = c.convertFilter(mongoFilter, startAtParameterIndex)
 	if err != nil {
 		return "", nil, err
@@ -68,6 +75,10 @@ func (c *Converter) convertFilter(filter map[string]any, paramIndex int) (string
 	var conditions []string
 	var values []any
 
+	if len(filter) == 0 {
+		return "", nil, fmt.Errorf("empty objects not allowed")
+	}
+
 	keys := []string{}
 	for key := range filter {
 		keys = append(keys, key)

filter/converter_test.go

@@ -193,6 +193,21 @@ func TestConverter_Convert(t *testing.T) {
 			[]any{[]any{}},
 			nil,
 		},
+		{
+			"empty filter",
+			nil,
+			`{}`,
+			`FALSE`,
+			[]any{},
+			nil,
+		}, {
+			"empty or conditions",
+			nil,
+			`{"$or": [{}, {}]}`,
+			``,
+			nil,
+			fmt.Errorf("empty objects not allowed"),
+		},
 	}
 
 	for _, tt := range tests {
@@ -245,3 +260,17 @@ func TestConverter_Convert_startAtParameterIndex(t *testing.T) {
 		t.Errorf("Converter.Convert(..., 1234551231231231231) error = %v, want nil", err)
 	}
 }
+
+func TestConverter_WithEmptyCondition(t *testing.T) {
+	c := filter.NewConverter(filter.WithEmptyCondition("TRUE"))
+	conditions, values, err := c.Convert([]byte(`{}`), 1)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if want := "TRUE"; conditions != want {
+		t.Errorf("Converter.Convert() conditions = %v, want %v", conditions, want)
+	}
+	if len(values) != 0 {
+		t.Errorf("Converter.Convert() values = %v, want nil", values)
+	}
+}

filter/options.go

@@ -39,3 +39,13 @@ func WithArrayDriver(f func(a any) interface {
 		c.arrayDriver = f
 	}
 }
+
+// WithEmptyCondition is an option to specify the condition to be used when the
+// input query filter is empty. (e.g. you have a query with no conditions)
+//
+// The default value is `FALSE`, because it's the safer choice in most cases.
+func WithEmptyCondition(condition string) Option {
+	return func(c *Converter) {
+		c.emptyCondition = condition
+	}
+}

fuzz/testdata/fuzz/FuzzConverter/439ca8de24f74c60

@@ -0,0 +1,2 @@
+go test fuzz v1
+string("{\"$or\":[{},{}]}")

integration/postgres_test.go

@@ -291,6 +291,12 @@ func TestIntegration_BasicOperators(t *testing.T) {
 			nil,
 			errors.New("pq: invalid input syntax for type integer: \"town1\""),
 		},
+		{
+			`empty object`,
+			`{}`, // Should return FALSE as the condition.
+			[]int{},
+			nil,
+		},
 	}
 
 	for _, tt := range tests {