Add method GenerateTextFromTable issue #5249 (#5266)

* Create a function GenerateGenerateTextFromTable in order to create a json from any Table

Signed-off-by: Anthony Liot <anthony.liot@gmail.com>

* Update the test to failed if loadfile or parser return false

Signed-off-by: Anthony Liot <anthony.liot@gmail.com>

* Fix snake_case name typo + space before &/*

Signed-off-by: Anthony Liot <anthony.liot@gmail.com>

* use auto

Signed-off-by: Anthony Liot <anthony.liot@gmail.com>

* Use clang-format on the added code

Signed-off-by: Anthony Liot <anthony.liot@gmail.com>

3 files changed, 69 insertions, 0 deletions

diff --git a/include/flatbuffers/idl.h b/include/flatbuffers/idl.h
index 05d666cb..40dfba40 100644
--- a/include/flatbuffers/idl.h
+++ b/include/flatbuffers/idl.h
@@ -834,6 +834,10 @@ extern std::string MakeCamel(const std::string &in, bool first = true);
 // strict_json adds "quotes" around field names if true.
 // If the flatbuffer cannot be encoded in JSON (e.g., it contains non-UTF-8
 // byte arrays in String values), returns false.
+extern bool GenerateTextFromTable(const Parser &parser,
+                                  const void *table,
+                                  const std::string &tablename,
+                                  std::string *text);
 extern bool GenerateText(const Parser &parser,
                          const void *flatbuffer,
                          std::string *text);
diff --git a/src/idl_gen_text.cpp b/src/idl_gen_text.cpp
index fb75a795..4c61ff99 100644
--- a/src/idl_gen_text.cpp
+++ b/src/idl_gen_text.cpp
@@ -263,6 +263,23 @@ static bool GenStruct(const StructDef &struct_def, const Table *table,
 }
 
 // Generate a text representation of a flatbuffer in JSON format.
+bool GenerateTextFromTable(const Parser &parser, const void *table,
+                           const std::string &table_name, std::string *_text) {
+  auto struct_def = parser.LookupStruct(table_name);
+  if (struct_def == nullptr) {
+    return false;
+  }
+  auto text = *_text;
+  text.reserve(1024);  // Reduce amount of inevitable reallocs.
+  auto root = static_cast<const Table *>(table);
+  if (!GenStruct(*struct_def, root, 0, parser.opts, _text)) {
+    return false;
+  }
+  text += NewLine(parser.opts);
+  return true;
+}
+
+// Generate a text representation of a flatbuffer in JSON format.
 bool GenerateText(const Parser &parser, const void *flatbuffer,
                   std::string *_text) {
   std::string &text = *_text;
diff --git a/tests/test.cpp b/tests/test.cpp
index 6da1dff9..04c014d8 100644
--- a/tests/test.cpp
+++ b/tests/test.cpp
@@ -1702,6 +1702,53 @@ void InvalidFloatTest() {
   TestError("table T { F:float; } root_type T; { F:null }", invalid_msg);
 }
 
+void GenerateTableTextTest() {
+  std::string schemafile;
+  std::string jsonfile;
+  bool ok =
+      flatbuffers::LoadFile((test_data_path + "monster_test.fbs").c_str(),
+                            false, &schemafile) &&
+      flatbuffers::LoadFile((test_data_path + "monsterdata_test.json").c_str(),
+                            false, &jsonfile);
+  TEST_EQ(ok, true);
+  auto include_test_path =
+      flatbuffers::ConCatPathFileName(test_data_path, "include_test");
+  const char *include_directories[] = {test_data_path.c_str(),
+                                       include_test_path.c_str(), nullptr};
+  flatbuffers::IDLOptions opt;
+  opt.indent_step = -1;
+  flatbuffers::Parser parser(opt);
+  ok = parser.Parse(schemafile.c_str(), include_directories) &&
+       parser.Parse(jsonfile.c_str(), include_directories);
+  TEST_EQ(ok, true);
+  // Test root table
+  const Monster *monster = GetMonster(parser.builder_.GetBufferPointer());
+  std::string jsongen;
+  auto result = GenerateTextFromTable(parser, monster, "MyGame.Example.Monster",
+                                      &jsongen);
+  TEST_EQ(result, true);
+  // Test sub table
+  const Vec3 *pos = monster->pos();
+  jsongen.clear();
+  result = GenerateTextFromTable(parser, pos, "MyGame.Example.Vec3", &jsongen);
+  TEST_EQ(result, true);
+  TEST_EQ_STR(
+      jsongen.c_str(),
+      "{x: 1.0,y: 2.0,z: 3.0,test1: 3.0,test2: \"Green\",test3: {a: 5,b: 6}}");
+  const Test &test3 = pos->test3();
+  jsongen.clear();
+  result =
+      GenerateTextFromTable(parser, &test3, "MyGame.Example.Test", &jsongen);
+  TEST_EQ(result, true);
+  TEST_EQ_STR(jsongen.c_str(), "{a: 5,b: 6}");
+  const Test *test4 = monster->test4()->Get(0);
+  jsongen.clear();
+  result =
+      GenerateTextFromTable(parser, test4, "MyGame.Example.Test", &jsongen);
+  TEST_EQ(result, true);
+  TEST_EQ_STR(jsongen.c_str(), "{a: 10,b: 20}");
+}
+
 template<typename T>
 void NumericUtilsTestInteger(const char *lower, const char *upper) {
   T x;
@@ -2602,6 +2649,7 @@ int FlatBufferTests() {
   IsAsciiUtilsTest();
   ValidFloatTest();
   InvalidFloatTest();
+  GenerateTableTextTest();
   return 0;
 }