messagereader.cpp

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// Reading a message JSON with Reader (SAX-style API).
// The JSON should be an object with key-string pairs.
 
#include "rapidjson/reader.h"
#include "rapidjson/error/en.h"
#include <iostream>
#include <string>
#include <map>
 
using namespace std;
using namespace rapidjson;
 
typedef map<string, string> MessageMap;
 
#if defined(__GNUC__)
RAPIDJSON_DIAG_PUSH
RAPIDJSON_DIAG_OFF(effc++)
#endif
 
#ifdef __clang__
RAPIDJSON_DIAG_PUSH
RAPIDJSON_DIAG_OFF(switch-enum)
#endif
 
struct MessageHandler
    : public BaseReaderHandler<UTF8<>, MessageHandler> {
    MessageHandler() : messages_(), state_(kExpectObjectStart), name_() {}
 
    bool StartObject() {
        switch (state_) {
        case kExpectObjectStart:
            state_ = kExpectNameOrObjectEnd;
            return true;
        default:
            return false;
        }
    }
 
    bool String(const char* str, SizeType length, bool) {
        switch (state_) {
        case kExpectNameOrObjectEnd:
            name_ = string(str, length);
            state_ = kExpectValue;
            return true;
        case kExpectValue:
            messages_.insert(MessageMap::value_type(name_, string(str, length)));
            state_ = kExpectNameOrObjectEnd;
            return true;
        default:
            return false;
        }
    }
 
    bool EndObject(SizeType) { return state_ == kExpectNameOrObjectEnd; }
 
    bool Default() { return false; } // All other events are invalid.
 
    MessageMap messages_;
    enum State {
        kExpectObjectStart,
        kExpectNameOrObjectEnd,
        kExpectValue
    }state_;
    std::string name_;
};
 
#if defined(__GNUC__)
RAPIDJSON_DIAG_POP
#endif
 
#ifdef __clang__
RAPIDJSON_DIAG_POP
#endif
 
static void ParseMessages(const char* json, MessageMap& messages) {
    Reader reader;
    MessageHandler handler;
    StringStream ss(json);
    if (reader.Parse(ss, handler))
        messages.swap(handler.messages_);   // Only change it if success.
    else {
        ParseErrorCode e = reader.GetParseErrorCode();
        size_t o = reader.GetErrorOffset();
        cout << "Error: " << GetParseError_En(e) << endl;;
        cout << " at offset " << o << " near '" << string(json).substr(o, 10) << "...'" << endl;
    }
}
 
int main() {
    MessageMap messages;
 
    const char* json1 = "{ \"greeting\" : \"Hello!\", \"farewell\" : \"bye-bye!\" }";
    cout << json1 << endl;
    ParseMessages(json1, messages);
 
    for (MessageMap::const_iterator itr = messages.begin(); itr != messages.end(); ++itr)
        cout << itr->first << ": " << itr->second << endl;
 
    cout << endl << "Parse a JSON with invalid schema." << endl;
    const char* json2 = "{ \"greeting\" : \"Hello!\", \"farewell\" : \"bye-bye!\", \"foo\" : {} }";
    cout << json2 << endl;
    ParseMessages(json2, messages);
 
    return 0;
}