socket ring buffer and readline

uttt.c

@@ -29,7 +29,15 @@ const struct ut_state ut_initial = {
 		.playBoard = -1,
 		.player = 'X',
 		.host_player = '\0',
-	};
+};
+
+struct ut_socket_buffer {
+	int fd;
+	char *buf;
+	size_t len;
+	size_t start;
+	size_t stop;
+};
 
 const char *HELP_TEXT = "\
 Usage: uttt (--local | --host | --join)\n\
@@ -295,6 +303,60 @@ int ut_writefill(int fd, const char *x, size_t l)
 	return 0;
 }
 
+int ut_socket_buffer_size(struct ut_socket_buffer *sockbuf) {
+	int size = sockbuf->stop - sockbuf->start;
+	if (size < 0) {size += sockbuf->len;}
+	return size;
+}
+
+/* Copies up to (and including) first '\n' in socket buffer, otherwise whole buffer */
+int ut_readline_buffer(struct ut_socket_buffer *sockbuf, char *line, size_t len) {
+	int size = ut_socket_buffer_size(sockbuf);
+	for (int i = sockbuf->start; i < sockbuf->start + size; i++) {
+		if (i > len) {return -1;}
+		line[i] = sockbuf->buf[i % sockbuf->len];
+		if (sockbuf->buf[i] == '\n') {
+			sockbuf->start = (sockbuf->start + i + 1) % sockbuf->len;
+			return i + 1;
+		}
+	}
+	sockbuf->start = (sockbuf->start + size) % sockbuf->len;
+	return size;
+}
+
+int ut_readline_socket(struct ut_socket_buffer *sockbuf, char *line, size_t len) {
+	while (len > 0) {
+		int r = read(sockbuf->fd, line, len);
+		if (r < 0) {
+			if (errno == EAGAIN || errno == EWOULDBLOCK || errno == EINTR) {continue;}
+			else {return -2;}
+		}
+		else if (r == 0) {return -2;}
+		for (int i = 0; i < r; i++) {
+			if (line[i] == '\n') {
+				int size = ut_socket_buffer_size(sockbuf);
+				if (r - i >= sockbuf->len - size) {return -1;}
+				for (int j = 0; j < r - i; j++) {
+					sockbuf->buf[(sockbuf->stop + j) % sockbuf->len] = line[i + j];
+				}
+				sockbuf->stop = (sockbuf->stop + r - i) % sockbuf->len;
+				return i;
+			}
+		}
+		line += r;
+		len -= r;
+	}
+}
+
+int ut_readline(struct ut_socket_buffer *sockbuf, char *line, size_t len) {
+	int nb = ut_readline_buffer(sockbuf, line, len);
+	if (nb < 0) {return nb;}
+	if (line[nb - 1] == '\n') {return nb - 1;}
+	int ns = ut_readline_socket(sockbuf, line + nb, len - nb);
+	if (ns < 0) {return ns;}
+	return nb + ns;
+}
+
 #define MAX_LINE 128
 
 int ut_dprintf(int fd, const char *restrict format, ...)