3 files changed, 79 insertions, 13 deletions

diff --git a/main.cpp b/main.cpp
index 2d3f828..a4b47ed 100644
--- a/main.cpp
+++ b/main.cpp
@@ -296,11 +296,17 @@ static void playMatch(Player &p1, Player &p2, int index, const Params &params) {
 				throw StopCompetitionError();
 			}
 
+			for (const auto &p : referee.playerWriteLines()) {
+				assert(0 <= p.first && p.first < 2);
+				procs[p.first].writeLine(p.second);
+			}
+
 			if (referee.gameEnded()) {
 				mres.status = MatchResult::Status::ok;
 
 				optional<vector<int>> oscores = referee.getScores();
 				assert(oscores);
+				assert(oscores->size() == 2);
 				mres.sc1 = oscores->at(0);
 				mres.sc2 = oscores->at(1);
 
diff --git a/referee.cpp b/referee.cpp
index 7bf3a93..15f49c3 100644
--- a/referee.cpp
+++ b/referee.cpp
@@ -39,21 +39,45 @@ bool Referee::moveValid(int player, const string_view line) {
 
 	proc.writeLine(s);
 
-	optional<string> response = proc.readLine();
+	optional<string> response = readLine();
 	if (response) {
-		if (referee_verbose) {
-			cout << "REF(" << proc.getPid() << ") read <" << *response << ">" << endl;
-		}
-
+		bool result;
 		if (*response == "valid end") {
 			isEnd = true;
 			readScores();
-			return true;
+			result = true;
 		} else if (*response == "valid") {
-			return true;
+			result = true;
 		} else {
-			return false;
+			result = false;
+		}
+
+		if (featureWriteLines) {
+			writeLinesList.clear();
+
+			while (true) {
+				optional<string> line = readLine();
+				if (!line) {
+					if (referee_verbose) {
+						cout << "REF(" << proc.getPid() << ") EOF!" << endl;
+					}
+					return false;
+				}
+
+				if (line == "write_end") break;
+
+				size_t idx = line->find(' ');
+				if (idx == string::npos) {
+					cerr << "Referee feature_write_lines protocol violation!" << endl;
+					exit(1);
+				}
+
+				int player = stoi(line->substr(0, idx));
+				writeLinesList.emplace_back(player, line->substr(idx + 1));
+			}
 		}
+
+		return result;
 	} else {
 		if (referee_verbose) {
 			cout << "REF(" << proc.getPid() << ") EOF!" << endl;
@@ -62,21 +86,41 @@ bool Referee::moveValid(int player, const string_view line) {
 	}
 }
 
+vector<pair<int, string>> Referee::playerWriteLines() {
+	return writeLinesList;
+}
+
 bool Referee::gameEnded() {
 	return isEnd;
 }
 
+optional<string> Referee::readLine() {
+	while (true) {
+		optional<string> line = proc.readLine();
+		if (!line) return line;
+
+		if (referee_verbose) {
+			cout << "REF(" << proc.getPid() << ") read <" << *line << ">" << endl;
+		}
+
+		if (line->substr(0, 8) != "feature ") return line;
+
+		string featname = line->substr(8);
+		if (featname == "write_lines") featureWriteLines = true;
+		else {
+			cerr << "Referee requested unsupported feature '" << featname << "'" << endl;
+			exit(1);
+		}
+	}
+}
+
 void Referee::readScores() {
-	optional<string> line = proc.readLine();
+	optional<string> line = readLine();
 	if (!line) {
 		cerr << "Referee stopped before providing scores" << endl;
 		exit(1);
 	}
 
-	if (referee_verbose) {
-		cout << "REF(" << proc.getPid() << ") readScores <" << *line << ">" << endl;
-	}
-
 	size_t cursor = 0;
 	while (cursor < line->size()) {
 		size_t idx = line->find(' ', cursor);
diff --git a/referee.h b/referee.h
index 0121196..891021d 100644
--- a/referee.h
+++ b/referee.h
@@ -4,6 +4,7 @@
 #include <string>
 #include <string_view>
 #include <optional>
+#include <utility>
 #include "process.h"
 
 using namespace std;
@@ -14,6 +15,10 @@ class Referee {
 	bool isEnd = false;
 	vector<int> scores;
 
+	bool featureWriteLines = false;
+	vector<pair<int, string>> writeLinesList;
+
+	optional<string> readLine();
 	void readScores();
 
 public:
@@ -22,6 +27,7 @@ public:
 
 	// player: 0 = first player, 1 = second player
 	bool moveValid(int player, const string_view line);
+	vector<pair<int, string>> playerWriteLines();
 
 	bool gameEnded();
 	optional<vector<int>> getScores();
@@ -45,4 +51,14 @@ then write a line to stdout that is equal to either 'valid', 'invalid', or
 'valid end', the referee should write a line containing as many integers
 (separated by spaces) as there are players, giving their scores at the end of
 the game.
+
+FEATURES
+At any time the referee may write 'feature <name>' to stdout, which enables the
+protocol feature with the given name. The following features are supported:
+- 'write_lines': After a move validity judgement, the referee should write lines
+  of the form '<player> <line>' to stdout, where <player> is the index of the
+  player on whose stdin to write <line>. The referee should signal the end of
+  this list by writing a line 'write_end' to stdout.
+  This allows the referee to write additional data to players' inputs after they
+  have written their moves.
 */