Make logging respect stream flushes

also add override keyword and fix overflow() behavior

src/util/stream.h

@@ -23,48 +23,55 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include <string_view>
 #include <functional>
 
-template<int BufferLength, typename Emitter = std::function<void(std::string_view)> >
+template<unsigned int BufferLength, typename Emitter = std::function<void(std::string_view)> >
 class StringStreamBuffer : public std::streambuf {
 public:
 	StringStreamBuffer(Emitter emitter) : m_emitter(emitter) {
 		buffer_index = 0;
 	}
 
-	int overflow(int c) {
-		push_back(c);
-		return c;
+	int overflow(int c) override {
+		if (c != traits_type::eof())
+			push_back(c);
+		return 0;
 	}
 
 	void push_back(char c) {
-		if (c == '\n' || c == '\r') {
-			if (buffer_index)
-				m_emitter(std::string_view(buffer, buffer_index));
-			buffer_index = 0;
+		// emit only complete lines, or if the buffer is full
+		if (c == '\n') {
+			sync();
 		} else {
 			buffer[buffer_index++] = c;
 			if (buffer_index >= BufferLength) {
-				m_emitter(std::string_view(buffer, buffer_index));
-				buffer_index = 0;
+				sync();
 			}
 		}
 	}
 
-	std::streamsize xsputn(const char *s, std::streamsize n) {
+	std::streamsize xsputn(const char *s, std::streamsize n) override {
 		for (std::streamsize i = 0; i < n; ++i)
 			push_back(s[i]);
 		return n;
 	}
+
+	int sync() override {
+		if (buffer_index)
+			m_emitter(std::string_view(buffer, buffer_index));
+		buffer_index = 0;
+		return 0;
+	}
+
 private:
 	Emitter m_emitter;
+	unsigned int buffer_index;
 	char buffer[BufferLength];
-	int buffer_index;
 };
 
 class DummyStreamBuffer : public std::streambuf {
-	int overflow(int c) {
-		return c;
+	int overflow(int c) override {
+		return 0;
 	}
-	std::streamsize xsputn(const char *s, std::streamsize n) {
+	std::streamsize xsputn(const char *s, std::streamsize n) override {
 		return n;
 	}
 };