fn retry when overflow input buffer

const std = @import("std");

fn flush(reader: anytype) @TypeOf(reader).Error!void {
    var scratch: [64]u8 = undefined;
    while (try reader.read(&scratch) != 0) {}
}

fn nextLine(reader: anytype, buffer: []u8) !?[]const u8 {
    var line = (try reader.readUntilDelimiterOrEof(
        buffer,
        '\n',
    )) orelse return null;
    // trim annoying windows-only carriage return character
    if (@import("builtin").os.tag == .windows) {
        return std.mem.trimRight(u8, line, "\r");
    } else {
        return line;
    }
}

pub fn main() anyerror!void {
    const stdout = std.io.getStdOut();
    const stdin = std.io.getStdIn();

    try stdout.writeAll(
        \\ Enter ten bytes or less:
    );

    var buffer: [10]u8 = undefined;

    const input = while (true) {
        const x = nextLine(stdin.reader(), &buffer) catch {
            flush(stdin.reader());
            continue;
        };
        break x;
    } else unreachable; // (see comment) fallback value could be an empty string maybe?

    try stdout.writer().print("You entered: \"{s}\"\n", .{input});
}