Performance improvements in json parsing

cppcms/json.h

@@ -486,6 +486,19 @@ namespace json {
 		bool load(std::istream &in,bool full,int *line_number=0);
 
 		///
+		/// Read a value from character range
+		///
+		/// Note: only JSON object and JSON array are considered valid values
+		///
+		/// \param begin - begin of the text range, at the end points to the end of parsed range
+		/// \param end - end of the text range
+		/// \param full  require EOF once the object is read, otherwise consider it as syntax error
+		/// \param line_number  return a number of the line where syntax error occurred
+		/// \result returns true if the value was read successfully, otherwise returns false to indicate a syntax error.
+		///
+		bool load(char const *&begin,char const *end,bool full,int *line_number=0);
+
+		///
 		/// Compare two values objects, return true if they are same
 		///
 		bool operator==(value const &other) const;

src/json.cpp

@@ -840,11 +840,11 @@ namespace json {
 
 			int next()
 			{
+				std::streambuf *buf = is_.rdbuf();
 				for(;;) {
-					char c;
-					if(!is_.get(c))
+					int c;
+					if((c=buf->sbumpc())==-1)
 						return tock_eof;
-					
 					switch(c) {
 					case '[':
 					case '{':
@@ -861,7 +861,7 @@ namespace json {
 						line++;
 						break;
 					case '"':
-						is_.unget();
+						buf->sungetc();
 						if(parse_string())
 							return tock_str;
 						return tock_err;
@@ -888,13 +888,13 @@ namespace json {
 					case '7':
 					case '8':
 					case '9':
-						is_.unget();
+						buf->sungetc();
 						if(parse_number())
 							return tock_number;
 						return tock_err;
 					case '/':
 						if(check("/")) {
-							while(is_.get(c) && c!='\n')
+							while((c=buf->sbumpc())!=-1 && c!='\n')
 								;
 							if(c=='\n')
 								break;
@@ -912,21 +912,22 @@ namespace json {
 
 			bool check(char const *s)
 			{
-				char c;
-				while(*s && is_.get(c) && c==*s)
+				std::streambuf *buf = is_.rdbuf();
+				while(*s && buf->sbumpc()==std::char_traits<char>::to_int_type(*s))
 					s++;
 				return *s==0;
 			}
 			bool parse_string()
 			{
-				char c;
+				int c;
+				std::streambuf *buf=is_.rdbuf();
 				str.clear();
-				if(!is_.get(c) || c!='"')
+				if((c=buf->sbumpc())==-1 || c!='"')
 					return false;
 				bool second_surragate_expected=false;
 				uint16_t first_surragate = 0;
 				for(;;) {
-					if(!is_.get(c))
+					if((c=buf->sbumpc())==-1)
 						return false;
 					if(second_surragate_expected && c!='\\')
 						return false;
@@ -935,7 +936,7 @@ namespace json {
 					if(c=='"')
 						break;
 					if(c=='\\') {
-						if(!is_.get(c))
+						if((c=buf->sbumpc())==-1)
 							return false;
 						if(second_surragate_expected && c!='u')
 							return false;
@@ -1056,6 +1057,28 @@ namespace json {
 		}
 #endif
 
+		class charbuf : public std::streambuf {
+		public:
+			charbuf(char const *begin,char const *end)
+			{
+				setg(const_cast<char *>(begin),const_cast<char *>(begin),const_cast<char *>(end));
+			}
+			char const *position()
+			{
+				return gptr();
+			}
+		};
+		
+		bool parse_stream(std::istream &in,value &out,bool force_eof,int &error_at_line);
+		bool parse_stream(char const *&begin,char const *end,value &out,bool force_eof,int &error_at_line)
+		{
+			charbuf b(begin,end);
+			std::istream is(&b);
+			bool r=parse_stream(is,out,force_eof,error_at_line);
+			begin = b.position();
+			return r;
+		}
+
 		bool parse_stream(std::istream &in,value &out,bool force_eof,int &error_at_line)
 		{
 			tockenizer tock(in);
@@ -1270,7 +1293,6 @@ namespace json {
 	bool value::load(std::istream &in,bool full,int *line_number)
 	{
 		int err_line;
-		value v;
 		if(!parse_stream(in,*this,full,err_line)) {
 			if(line_number)
 				*line_number=err_line;
@@ -1279,6 +1301,17 @@ namespace json {
 		return true;
 
 	}
+	bool value::load(char const *&begin,char const *end,bool full,int *line_number)
+	{
+		int err_line;
+		if(!parse_stream(begin,end,*this,full,err_line)) {
+			if(line_number)
+				*line_number=err_line;
+			return false;
+		}
+		return true;
+
+	}
 	
 	std::istream &operator>>(std::istream &in,value &v)
 	{

tests/json_test.cpp

@@ -34,12 +34,21 @@ public:
 json::value Parse(std::string s,int line)
 {
 	std::istringstream ss(s);
+	json::value v2;
+	char const *begin,*end;
+	begin = s.c_str();
+	end = begin + s.size();
+	bool r=v2.load(begin,end,true);
 	json::value v;
 	if(!v.load(ss,true)) {
+		TEST(!r);
 		std::ostringstream tmp;
 		tmp << "Parsing error of " << s << " in line " << line;
 		throw parsing_error(tmp.str());
 	}
+	TEST(ss.get()==-1);
+	TEST(begin == end);
+	TEST(v==v2);
 	return v;
 }
 
@@ -212,6 +221,11 @@ int main()
 			long double val = std::numeric_limits<long double>::max() / 100;
 			THROWS(v["x"]=val);
 		}
+		char const *part="{}[]";
+		TEST(v.load(part,part+4,false));
+		TEST(*part=='[');
+		TEST(v.type() == cppcms::json::is_object);
+		TEST(!v.load(part,part+4,true));
 
 	}
 	catch(std::exception const &e)