pgLab/pgsql/ArrayParser.cpp

#include "ArrayParser.h"
#include <stdexcept>

using namespace Pgsql;

namespace {

	constexpr char ArrayStart = '{';
	constexpr char ArrayEnd = '}';
	constexpr char Quote = '"';
	constexpr char Seperator = ',';

}

ArrayParser::ArrayParser(const char *array_string, int length)
	: data(array_string)
	, end(length >= 0 ? array_string + length : array_string + strlen(array_string))
	, pos(array_string)
{
	initializeParse();
}


ArrayParser::NextElemResult ArrayParser::GetNextElem()
{
	// We should be at the start of an element or at the end of the array
	NextElemResult result = { false, std::nullopt };
	if (pos < end && *pos != ArrayEnd) {
		if (*pos == Quote) {
			// parse quoted value, slow path removing escapes
			parseQuotedValue();
			result.ok = true;
			result.value = std::string_view(temp);
		}
		else {
			// parse unquoted value, fast path no escapes
			const char *start = pos;
			while (pos < end && *pos != Seperator && *pos != ArrayEnd) ++pos;
			if (pos == end) // reached end of data shouldn't happen
				throw std::runtime_error("Invalid input");

			result.ok = true;
			if ((pos - start) != 4 || std::strncmp(start, "NULL", 4) != 0)
				result.value = std::string_view(start, pos-start);

		}
		// move to start of next element
		++pos; // skip seperator
		skipWhitespace();

	}
	return result;
}


void ArrayParser::parseQuotedValue()
{
	std::string s;
	// internal function thus we can safely assumed the caller already verified
	// the opening quote
	++pos;
	if (pos == end)
		throw std::runtime_error("Invalid input");

	while (pos < end) {
		if (*pos == Quote) {
			++pos;
			break;
		}
		if (*pos == '\\') {
			++pos;
			if (pos == end)
				throw std::runtime_error("Invalid input");
		}
		s += *pos;
		++pos;
	}
	temp = std::move(s);
}


void ArrayParser::initializeParse()
{
	// Test if non empty string (empty string is an empty array)
	//
	skipWhitespace();
	if (pos < end) {
		// first character should be opening brace
		if (*pos != ArrayStart) {
			throw std::runtime_error("Unexpected input");
		}
		++pos;
		skipWhitespace();
		// Position is now first element or end of array when the array is empty
		// GetNextElem can take it from here
	}
}

inline void ArrayParser::skipWhitespace()
{
	while (pos < end && (*pos == ' ' || *pos == '\t')) ++pos;
}