Fix stream size

[takei-yuya]

ssize_t recv(int sockfd, void *buf, size_t len, int flags);
ssize_t send(int sockfd, const void *buf, size_t len, int flags);
ssize_t write(int fd, const void *buf, size_t count);
ssize_t read(int fd, void *buf, size_t count);

buffer length should be size_t.
This prevents error when the CGI server from returning a body larger than 2GiB.