fix: handle nested objects when skipping unused fields

Signed-off-by: Kyle McCullough <kylemcc@gmail.com>

flatten_json.go

@@ -168,7 +168,7 @@ func (fj *flattenJSON) readObject(pathNode SegmentsTreeTracker) error {
 			if pathNode.IsRoot() {
 				return errEarlyStop
 			} else {
-				return fj.skipUntil('}')
+				return fj.leaveObject()
 			}
 		}
 
@@ -532,7 +532,7 @@ func (fj *flattenJSON) readLiteral(literal []byte) ([]byte, error) {
 	return literal, nil
 }
 
-func (fj *flattenJSON) skipUntil(symbol byte) error {
+func (fj *flattenJSON) leaveObject() error {
 	for fj.eventIndex < len(fj.event) {
 		ch := fj.event[fj.eventIndex]
 
@@ -542,7 +542,14 @@ func (fj *flattenJSON) skipUntil(symbol byte) error {
 			if err != nil {
 				return err
 			}
-		case symbol:
+		case '{', '[':
+			// ch+2 is the matching closing brace, since both '}' and ']' are 2 characters away
+			// from '{' and ']', respectively
+			err := fj.skipBlock(ch, ch+2)
+			if err != nil {
+				return err
+			}
+		case '}':
 			return nil
 		}
 

flatten_json_test.go

@@ -2,6 +2,7 @@ package quamina
 
 import (
 	"bytes"
+	"fmt"
 	"os"
 	"testing"
 )
@@ -315,6 +316,76 @@ func TestFJErrorCases(t *testing.T) {
 	}
 }
 
+func TestSkipUnusedPaths(t *testing.T) {
+	// Each of theses cases has a nested object with additional values that should
+	// be skipped after the specified paths have been checked
+	//
+	// e.g., take the following object and paths:
+	//
+	//     object: { "a": { "b": 1, "c": 2} }
+	//     paths:  ["a\nb", "d"]
+	//
+	// After the flattener evaluates a.b, it should skip a.c before looking
+	// for d in the outer object.
+	//
+	// These tests make sure that the flattener correctly skips remaining
+	// values including nested objects and arrays.
+	//
+	// The tests below contain an additional path to look for after the
+	// paths in the nested object to make sure the flattener correctly
+	// exits the nested object and begings parsing the rest of the event
+	// at the correct location.
+	cases := []struct {
+		event        string
+		matcherPaths []string
+	}{
+		{
+			event:        `{"nested":{"thing":"whatever","extra":{}}}`,
+			matcherPaths: []string{"nested\nthing", "another"},
+		},
+		{
+			event:        `{"nested":{"thing":"whatever","extra":{"empty": false}}}`,
+			matcherPaths: []string{"nested\nthing", "another"},
+		},
+		{
+			event:        `{"nested":{"thing":"whatever","extra":[{}]}}`,
+			matcherPaths: []string{"nested\nthing", "another"},
+		},
+		{
+			event:        `{"nested":{"thing":"whatever","extra":[{"empty": false}]}}`,
+			matcherPaths: []string{"nested\nthing", "another"},
+		},
+		{
+			event:        `{"nested":{"thing":"whatever","extra":[]}}`,
+			matcherPaths: []string{"nested\nthing", "another"},
+		},
+		{
+			event:        `{"nested":{"thing":"whatever","extra":[1,"two",true,null]}}`,
+			matcherPaths: []string{"nested\nthing", "another"},
+		},
+		{
+			event:        `{"nested":{"thing":"whatever","extra":[],"andAnother":{}}}`,
+			matcherPaths: []string{"nested\nthing", "another"},
+		},
+	}
+
+	for i, c := range cases {
+		t.Run(fmt.Sprintf("case_%d", i), func(t *testing.T) {
+			matcher := fakeMatcher(c.matcherPaths...)
+
+			fj := newJSONFlattener().(*flattenJSON)
+
+			// ignore the fields - this test isn't concerned with the flattening result
+			_, err := fj.Flatten([]byte(c.event), matcher.getSegmentsTreeTracker())
+
+			// make sure the flattener didn't return an error
+			if err != nil {
+				t.Fatalf("failed to flatten json: %v", err)
+			}
+		})
+	}
+}
+
 func fakeMatcher(paths ...string) *coreMatcher {
 	m := newCoreMatcher()
 	for _, path := range paths {