To read and write bytes via Socket

[Yoshinori Kohyama]

Hello all.

Please help me to read and write bytes via Socket.

For example, assumed that I want to send 5 bytes [0x00, 0x01, 0x7f, 0x80, 0xff] to a TCP server.

I did:

(require '[clojure.java.io :refer :all])

(with-open [s (java.net.Socket. "ip.of.test.server" port_of_test_server)]

  (let [^java.io.BufferedWriter wtr (writer s)

        ^chars obuf (char-array (map char [0 1 127 128 255]))]

    (.write wtr obuf 0 5)

    (.flush wtr))))

Then, my test server received bytes: [0x00, 0x01, 0x7f, 0xc2, 0x80, 0xc3, 0xbf].

* I think I should use a char array so that read() requires 'char[]'.

* What is the valid char value to send a byte 0x80?

* How can I make the char value from 0x80 int?

* How are things about read.

* Does character encoding environment affect? (I use -Dfile.encoding=UTF-8)

Thank you in advance.

Yoshinori Kohyama

[Armando Blancas]

With UTF-8 characters are encoded in a variable number of bytes according to various ranges, as you can see here in section "Description":

http://en.wikipedia.org/wiki/UTF-8

 

Since you're sending your bytes as chars but read back as bytes, your last two bytes create chars that later produce two bytes each, and thus you see seven bytes at the other end. You may want to get an output stream from the socket and write single bytes directly.

[Yoshinori Kohyama]

Armando, thank you for your reply.

Writing single value with

  void write(int c)

sends same 2 bytes for values larger than 127 as using

  void write(char[] cbuf, int off, int len)

of BufferedReader http://docs.oracle.com/javase/jp/6/api/java/io/BufferedWriter.html

Code:

  (require '[clojure.java.io :refer :all])

  (with-open [s (java.net.Socket. "ip.of.test.server" port_of_test_server)]

    (let [^java.io.BufferedWriter wtr (writer s)]

      (doseq [i [0 1 127 128 255]]

        (.write wtr i))

      (.flush wtr)))

sends same bytes as code in my previous post.

I can't find other appropriate methods of BuffererdReader, Reader and OutputStreamReader

  http://docs.oracle.com/javase/jp/6/api/java/io/Writer.html

  http://docs.oracle.com/javase/jp/6/api/java/io/OutputStreamWriter.html

than

  void write(int c)

  void write(char[] cbuf)

  void write(char[] cbuf, int off, int len)

.

Does anyone have any information?

Thanks in advance.

Yoshinori Kohyama

[Yoshinori Kohyama]

Resolved.

I overlooked that OutputStream has

  void write(byte[] b, int off, int len)

.

With write(byte[] ...) of OutputStream instead of write(char[] ...) of BufferedWritersends I can send the bytes that I want to send.

Code:

  (require '[clojure.java.io :refer :all])

  (with-open [s (java.net.Socket. "ip.of.test.server" port_of_test_server)]

    (let [^java.io.OutputStream os (.getOutputStream s)

          ^bytes obuf (byte-array (map #(byte (if (< % 128) % (- % 256)))

                                       [0 1 127 128 255]))]

      (.write os obuf 0 5)

      (.flush os)))

sent [0x00, 0x01, 0x7f, 0x80, 0xff] to my test server.

Thank you, Armando and all.

Regards,

Yoshinori Kohyama