Handle default-constructed JSON objects

libqpdf/JSON.cc

@@ -191,7 +191,7 @@ JSON::JSON_blob::write(Pipeline* p, size_t) const
 void
 JSON::write(Pipeline* p, size_t depth) const
 {
-    if (nullptr == m->value) {
+    if (!m) {
         *p << "null";
     } else {
         m->value->write(p, depth);
@@ -201,6 +201,9 @@ JSON::write(Pipeline* p, size_t depth) const
 std::string
 JSON::unparse() const
 {
+    if (!m) {
+        return "null";
+    }
     std::string s;
     Pl_String p("unparse", nullptr, s);
     write(&p, 0);
@@ -275,8 +278,8 @@ JSON::makeDictionary()
 JSON
 JSON::addDictionaryMember(std::string const& key, JSON const& val)
 {
-    if (auto* obj = dynamic_cast<JSON_dictionary*>(m->value.get())) {
+    if (auto* obj = m ? dynamic_cast<JSON_dictionary*>(m->value.get()) : nullptr) {
-        return obj->members[encode_string(key)] = val.m->value ? val : makeNull();
+        return obj->members[encode_string(key)] = val.m ? val : makeNull();
     } else {
         throw std::runtime_error("JSON::addDictionaryMember called on non-dictionary");
     }
@@ -285,15 +288,11 @@ JSON::addDictionaryMember(std::string const& key, JSON const& val)
 bool
 JSON::checkDictionaryKeySeen(std::string const& key)
 {
-    auto* obj = dynamic_cast<JSON_dictionary*>(m->value.get());
+    if (auto* obj = m ? dynamic_cast<JSON_dictionary*>(m->value.get()) : nullptr) {
-    if (nullptr == obj) {
+        return !obj->parsed_keys.insert(key).second;
+    }
     throw std::logic_error("JSON::checkDictionaryKey called on non-dictionary");
-    }
+    return false; // unreachable
-    if (obj->parsed_keys.count(key)) {
-        return true;
-    }
-    obj->parsed_keys.insert(key);
-    return false;
 }
 
 JSON
@@ -305,17 +304,17 @@ JSON::makeArray()
 JSON
 JSON::addArrayElement(JSON const& val)
 {
-    auto* arr = dynamic_cast<JSON_array*>(m->value.get());
+    if (auto* arr = m ? dynamic_cast<JSON_array*>(m->value.get()) : nullptr) {
-    if (nullptr == arr) {
+        if (val.m) {
-        throw std::runtime_error("JSON::addArrayElement called on non-array");
-    }
-    if (val.m->value.get()) {
             arr->elements.push_back(val);
         } else {
             arr->elements.push_back(makeNull());
         }
         return arr->elements.back();
     }
+    throw std::runtime_error("JSON::addArrayElement called on non-array");
+    return {}; // unreachable
+}
 
 JSON
 JSON::makeString(std::string const& utf8)
@@ -362,19 +361,19 @@ JSON::makeBlob(std::function<void(Pipeline*)> fn)
 bool
 JSON::isArray() const
 {
-    return m->value->type_code == vt_array;
+    return m ? m->value->type_code == vt_array : false;
 }
 
 bool
 JSON::isDictionary() const
 {
-    return m->value->type_code == vt_dictionary;
+    return m && m->value->type_code == vt_dictionary;
 }
 
 bool
 JSON::getString(std::string& utf8) const
 {
-    if (m->value->type_code == vt_string) {
+    if (m && m->value->type_code == vt_string) {
         auto v = dynamic_cast<JSON_string const*>(m->value.get());
         utf8 = v->utf8;
         return true;
@@ -385,7 +384,7 @@ JSON::getString(std::string& utf8) const
 bool
 JSON::getNumber(std::string& value) const
 {
-    if (m->value->type_code == vt_number) {
+    if (m && m->value->type_code == vt_number) {
         auto v = dynamic_cast<JSON_number const*>(m->value.get());
         value = v->encoded;
         return true;
@@ -396,7 +395,7 @@ JSON::getNumber(std::string& value) const
 bool
 JSON::getBool(bool& value) const
 {
-    if (m->value->type_code == vt_bool) {
+    if (m && m->value->type_code == vt_bool) {
         auto v = dynamic_cast<JSON_bool const*>(m->value.get());
         value = v->value;
         return true;
@@ -407,13 +406,13 @@ JSON::getBool(bool& value) const
 bool
 JSON::isNull() const
 {
-    return m->value->type_code == vt_null;
+    return m && m->value->type_code == vt_null;
 }
 
 JSON
 JSON::getDictItem(std::string const& key) const
 {
-    if (auto v = dynamic_cast<JSON_dictionary const*>(m->value.get())) {
+    if (auto v = m ? dynamic_cast<JSON_dictionary const*>(m->value.get()) : nullptr) {
         if (auto it = v->members.find(key); it != v->members.end()) {
             return it->second;
         }
@@ -424,39 +423,37 @@ JSON::getDictItem(std::string const& key) const
 bool
 JSON::forEachDictItem(std::function<void(std::string const& key, JSON value)> fn) const
 {
-    auto v = dynamic_cast<JSON_dictionary const*>(m->value.get());
+    if (auto v = m ? dynamic_cast<JSON_dictionary const*>(m->value.get()) : nullptr) {
-    if (v == nullptr) {
+        for (auto const& [key, value]: v->members) {
-        return false;
+            fn(key, value);
-    }
-    for (auto const& k: v->members) {
-        fn(k.first, JSON(k.second));
         }
         return true;
     }
+    return false;
+}
 
 bool
 JSON::forEachArrayItem(std::function<void(JSON value)> fn) const
 {
-    auto v = dynamic_cast<JSON_array const*>(m->value.get());
+    if (auto v = m ? dynamic_cast<JSON_array const*>(m->value.get()) : nullptr) {
-    if (v == nullptr) {
-        return false;
-    }
         for (auto const& i: v->elements) {
             fn(JSON(i));
         }
         return true;
     }
+    return false;
+}
 
 bool
 JSON::checkSchema(JSON schema, std::list<std::string>& errors)
 {
-    return checkSchemaInternal(m->value.get(), schema.m->value.get(), 0, errors, "");
+    return m && checkSchemaInternal(m->value.get(), schema.m->value.get(), 0, errors, "");
 }
 
 bool
 JSON::checkSchema(JSON schema, unsigned long flags, std::list<std::string>& errors)
 {
-    return checkSchemaInternal(m->value.get(), schema.m->value.get(), flags, errors, "");
+    return m && checkSchemaInternal(m->value.get(), schema.m->value.get(), flags, errors, "");
 }
 
 bool
@@ -1374,23 +1371,27 @@ JSON::parse(std::string const& s)
 void
 JSON::setStart(qpdf_offset_t start)
 {
+    if (m) {
         m->start = start;
     }
+}
 
 void
 JSON::setEnd(qpdf_offset_t end)
 {
+    if (m) {
         m->end = end;
     }
+}
 
 qpdf_offset_t
 JSON::getStart() const
 {
-    return m->start;
+    return m ? m->start : 0;
 }
 
 qpdf_offset_t
 JSON::getEnd() const
 {
-    return m->end;
+    return m ? m->end : 0;
 }

libtests/json.cc

@@ -2,8 +2,10 @@
 
 #include <qpdf/JSON.hh>
 #include <qpdf/Pipeline.hh>
+#include <qpdf/Pl_String.hh>
 #include <qpdf/QPDF.hh>
 #include <qpdf/QPDFObjectHandle.hh>
+
 #include <iostream>
 
 static void
@@ -131,6 +133,51 @@ test_main()
         "  \"blob\": \"AQIDBAX//v38+w==\",\n"
         "  \"normal\": \"string\"\n"
         "}");
+
+    // Check default constructed JSON object (order as per JSON.hh).
+    JSON uninitialized;
+    std::string ws;
+    auto pl = Pl_String ("", nullptr, ws);
+    uninitialized.write(&pl);
+    assert(ws == "null");
+    assert(uninitialized.unparse() == "null");
+    try {
+        uninitialized.addDictionaryMember("key", jarr);
+        assert(false);
+    } catch (std::runtime_error&) {
+    }
+    assert(jmap.addDictionaryMember("42", uninitialized).isNull());
+    try {
+        uninitialized.addArrayElement(jarr);
+        assert(false);
+    } catch (std::runtime_error&) {
+    }
+    assert(jarr.addArrayElement(uninitialized).isNull());
+    assert(!uninitialized.isArray());
+    assert(!uninitialized.isDictionary());
+    try {
+        uninitialized.checkDictionaryKeySeen("key");
+        assert(false);
+    } catch (std::logic_error&) {
+    }
+    std::string st_out = "unchanged";
+    assert(!uninitialized.getString(st_out));
+    assert(!uninitialized.getNumber(st_out));
+    bool b_out = true;
+    assert(!uninitialized.getBool(b_out));
+    assert(b_out && st_out == "unchanged");
+    assert(!uninitialized.isNull());
+    assert(uninitialized.getDictItem("42").isNull());
+    assert(!uninitialized.forEachDictItem([](auto k, auto v) {}));
+    assert(!uninitialized.forEachArrayItem([](auto v) {}));
+    std::list<std::string> e;
+    assert(!uninitialized.checkSchema(JSON(), 0, e));
+    assert(!uninitialized.checkSchema(JSON(), e));
+    assert(e.empty());
+    uninitialized.setStart(0);
+    uninitialized.setEnd(0);
+    assert(uninitialized.getStart() == 0);
+    assert(uninitialized.getEnd() == 0);
 }
 
 static void