Store::JsonParser: validate input before parsing

Avoid leaving Store half-filled.

Author: Evgenii Zhemchugov

src/Store/Json.cpp

@@ -206,6 +206,12 @@ const char* json_scan(const char* input) {
   };
 }
 
+bool json_valid(const char* input) {
+  input = json_scan(input);
+  input = json_scan_whitespace(input);
+  return input && !*input;
+};
+
 bool json_decode_r(const char*& input, bool& value, adl_tag) {
   const char* i = json_scan_whitespace(input);
   if (!i) return false;

src/Store/Json.h

@@ -100,6 +100,8 @@ const char* json_scan_object(const char* input);
 const char* json_scan_array(const char* input);
 const char* json_scan(const char* input); // generic
 
+bool json_valid(const char* input);
+
 
 // json_encode_r implements encoding of specific objects. Add overloads to this
 // function to support custom classes.

src/Store/Store.cpp

@@ -124,6 +124,10 @@ namespace ToolFramework {
   }
 
   bool Store::JsonParser(const char* input) {
+    if (!json_valid(input)) return false; // invalid JSON string
+
+    // We have validated input, so in the following `return false` should never
+    // happen. We keep it, however, just in case.
     bool result = json_decode_object(
         input,
         [this](const char*& input_, std::string key) -> bool {
@@ -165,8 +169,6 @@ namespace ToolFramework {
     );
     if (!result) return false;
 
-    input = json_scan_whitespace(input);
-    if (!input || *input) return false; // junk at the end
     return true;
   };