FlexBuffers: JSON output supports indentation

include/flatbuffers/flexbuffers.h

@@ -360,16 +360,40 @@ class Map : public Vector {
   bool IsTheEmptyMap() const { return data_ == EmptyMap().data_; }
 };
 
+inline void IndentString(std::string &s, int indent,
+                         const char *indent_string) {
+  for (int i = 0; i < indent; i++) s += indent_string;
+}
+
+template<typename T>
+void AppendToString(std::string &s, T &&v, bool keys_quoted, bool indented,
+                    int cur_indent, const char *indent_string) {
+  s += "[";
+  s += indented ? "\n" : " ";
+  for (size_t i = 0; i < v.size(); i++) {
+    if (i) {
+      s += ",";
+      s += indented ? "\n" : " ";
+    }
+    if (indented) IndentString(s, cur_indent, indent_string);
+    v[i].ToString(true, keys_quoted, s, indented, cur_indent,
+                  indent_string);
+  }
+  if (indented) {
+    s += "\n";
+    IndentString(s, cur_indent - 1, indent_string);
+  } else {
+    s += " ";
+  }
+  s += "]";
+}
+
 template<typename T>
 void AppendToString(std::string &s, T &&v, bool keys_quoted) {
-  s += "[ ";
-  for (size_t i = 0; i < v.size(); i++) {
-    if (i) s += ", ";
-    v[i].ToString(true, keys_quoted, s);
-  }
-  s += " ]";
+  AppendToString(s, v, keys_quoted);
 }
 
+
 class Reference {
  public:
   Reference()
@@ -542,8 +566,13 @@ class Reference {
   // Convert any type to a JSON-like string. strings_quoted determines if
   // string values at the top level receive "" quotes (inside other values
   // they always do). keys_quoted determines if keys are quoted, at any level.
-  // TODO(wvo): add further options to have indentation/newlines.
   void ToString(bool strings_quoted, bool keys_quoted, std::string &s) const {
+    ToString(strings_quoted, keys_quoted, s, false, 0, "");
+  }
+
+  // This version additionally allow you to specify if you want indentation.
+  void ToString(bool strings_quoted, bool keys_quoted, std::string &s,
+                bool indented, int cur_indent, const char *indent_string) const {
     if (type_ == FBT_STRING) {
       String str(Indirect(), byte_width_);
       if (strings_quoted) {
@@ -569,7 +598,8 @@ class Reference {
     } else if (IsBool()) {
       s += AsBool() ? "true" : "false";
     } else if (IsMap()) {
-      s += "{ ";
+      s += "{";
+      s += indented ? "\n" : " ";
       auto m = AsMap();
       auto keys = m.Keys();
       auto vals = m.Values();
@@ -590,18 +620,28 @@ class Reference {
             }
           }
         }
+        if (indented) IndentString(s, cur_indent + 1, indent_string);
         keys[i].ToString(true, kq, s);
         s += ": ";
-        vals[i].ToString(true, keys_quoted, s);
-        if (i < keys.size() - 1) s += ", ";
+        vals[i].ToString(true, keys_quoted, s, indented, cur_indent + 1, indent_string);
+        if (i < keys.size() - 1) {
+          s += ",";
+          if (!indented) s += " ";
+        }
+        if (indented) s += "\n";
       }
-      s += " }";
+      if (!indented) s += " ";
+      if (indented) IndentString(s, cur_indent, indent_string);
+      s += "}";
     } else if (IsVector()) {
-      AppendToString<Vector>(s, AsVector(), keys_quoted);
+      AppendToString<Vector>(s, AsVector(), keys_quoted, indented,
+                             cur_indent + 1, indent_string);
     } else if (IsTypedVector()) {
-      AppendToString<TypedVector>(s, AsTypedVector(), keys_quoted);
+      AppendToString<TypedVector>(s, AsTypedVector(), keys_quoted, indented,
+                                  cur_indent + 1, indent_string);
     } else if (IsFixedTypedVector()) {
-      AppendToString<FixedTypedVector>(s, AsFixedTypedVector(), keys_quoted);
+      AppendToString<FixedTypedVector>(s, AsFixedTypedVector(), keys_quoted,
+                                       indented, cur_indent + 1, indent_string);
     } else if (IsBlob()) {
       auto blob = AsBlob();
       flatbuffers::EscapeString(reinterpret_cast<const char *>(blob.data()),

tests/flexbuffers_test.cpp

@@ -132,6 +132,12 @@ void FlexBuffersTest() {
   // And from FlexBuffer back to JSON:
   auto jsonback = jroot.ToString();
   TEST_EQ_STR(jsontest, jsonback.c_str());
+  // With indentation:
+  std::string jsonback_indented;
+  jroot.ToString(true, false, jsonback_indented, true, 0, "  ");
+  auto jsontest_indented =
+    "{\n  a: [\n    123,\n    456.0\n  ],\n  b: \"hello\",\n  c: true,\n  d: false\n}";
+  TEST_EQ_STR(jsontest_indented, jsonback_indented.c_str());
 
   slb.Clear();
   slb.Vector([&]() {