Implemented ArrayParser and unit tests to verify its working.

pgsql/ArrayParser.cpp

@@ -0,0 +1,102 @@
+#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)
+	: data(array_string)
+	, end(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 == 0) // 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;
+}