Develop Reference

JAVA :I'm not able to send response(json) back to the client from server

I have a client application which send POST request(json) to a custom server. The server must send a response(json) to the incoming message, but i haven't detected any response on the client side.
The problem is not on the client's side, because if it sends a request to another server, then after a few seconds it receives a response and I see it in the logs.
SERVER CODE
try{
server = new ServerSocket(4321);
client = server.accept();
PrintWriter out = new PrintWriter(client.getOutputStream(), true);
System.out.println("Connection received from " + client.getInetAddress());
BufferedReader in = new BufferedReader(new InputStreamReader(client.getInputStream()));
String s = "SERVER: Started.";
Gson gson = new Gson();
String json = gson.toJson(jsonObject.toString());
while ((s = in.readLine()) != null) {
System.out.println("RECV: "+s);
ss = s.split("PUSH\\s");
out.println("HTTP/1.1 200 OK");
out.println("application/json;charset=UTF-8");
out.println("application/json;charset=UTF-8");
out.println("Jersey/2.27 (HttpUrlConnection 1.8.0_291)");
out.println("no-cache");
out.println("no-cache");
out.println("hostname:4321");
out.println("keep-alive");
out.println("392");
out.println("\n");
out.println(json);
} catch(Exception e) {e.printStackTrace();}
I think the root of my issue is out.println(). I don't know exactly what the server should send back to client.
Response must contain json!
Also, i don't have the client code.
Could you help?

While I definitively wouldn't recommend writing an HTTP server this way there are at least two problems in your code:
You are missing header names, e.g. application/json;charset=UTF-8 should read Content-Type: application/json;charset=UTF-8
out.println() uses the line separator string as defined by the system property line.separator (e.g. \n for Linux). HTTP on the other hand needs \r\n, so better write it like this: out.print("HTTP/1.1 200 OK\r\n");
Try this:
out.print("HTTP/1.1 200 OK" + "\r\n");
out.print("Content-Type: application/json" + "\r\n");
// you shouldn't need the other headers…
out.print("\r\n");
out.print(json);

BufferedReader is not reading body of request

I am trying to read the data from an HttpPost, but when I read the data from BufferedReader I only get the header info. Please see the code below.
Here is the server
try {
ServerSocket server = new ServerSocket(8332);
System.out.println("Listening for connection on port 8332 ....");
while (true) {
try (Socket socket = server.accept()) {
BufferedReader buffer = new BufferedReader(new InputStreamReader(socket.getInputStream()));
String request = "";
String line;
while ((line = buffer.readLine()) != null) {
System.out.println(line);
request += line;
}
System.out.print("port 8332 reading: " + request);
} catch (IOException e) {
System.out.print(e.getMessage());
}
}
} catch (IOException e){
System.out.print(e.getMessage());
}
Here is the Client
HttpClient client = HttpClientBuilder.create().build();
HttpPost post = new HttpPost("http://localhost:8332");
try {
StringEntity params =new StringEntity("details={\"name\":\"myname\",\"age\":\"20\"} ");
post.addHeader("content-type", "application/x-www-form-urlencoded");
post.setEntity(params);
client.execute(post);
} catch (IOException e){
System.out.println(e);
}
When I run this program I just get the following output
Listening for connection on port 8332 ....
POST / HTTP/1.1
content-type: application/x-www-form-urlencoded
Content-Length: 37
Host: localhost:8332
Connection: Keep-Alive
User-Agent: Apache-HttpClient/4.5.6 (Java/1.8.0_131)
Accept-Encoding: gzip,deflate
Upon debugging it seems like the program is not exiting this while loop
while ((line = buffer.readLine()) != null) {
System.out.println(line);
request += line;
}
But I can't figure out why. Please help I have been stuck all day.
Thanks in advance

But I can't figure out why.
The only way that your server will get a null from buffer.readLine() is if the client closes its socket output stream.
The problem is that the client side is trying to keep the connection alive ... which means that it won't close its socket output stream. That means that the server needs to respect the "content-length" header; i.e. count the number of bytes read rather than looking for an end-of-stream.
Fundamentally, your server side is not implementing the HTTP 1.1 specification correctly.
What to do?
Well my advice is to not try to implement HTTP starting from sockets. Use and existing framework ... or the Apache HttpComponents library.
But if you insist on doing it this way1, read the HTTP specification thoroughly before you start trying to implement it. And consult the spec whenever you run into problems with your implementation to check that you are doing the right thing.
1 - Definition: Masochism - the enjoyment of an activity that appears to be painful or tedious.

Use !=0 instead of !=null in your while loop:
while((line = buffer.readLine()).length() !=0) {
output:
port 8332 reading: POST / HTTP/1.1content-type:
application/x-www-form-urlencodedContent-Length: 18Host:
localhost:8332Connection: Keep-AliveUser-Agent:
Apache-HttpClient/4.5.3 (Java/1.8.0_171)Accept-Encoding:
gzip,deflateorg.apache.http.NoHttpResponseException: localhost:8332
failed to respond

Why InputStreamReader cannot read the content of a websocket package?

To understand the behaviour of the websocket, I created a simple SocketServer in java to exchange the messages. The server is expected to follow the operations as:
1) Listening at port 8080
2) A websocket handshake message generated manually on the browser client and received by the server.
3) Construct a response to the handshake message and reply to the client
4) Read out actually websocket info bytes with the same connection.
The problem has happened at step 4. when the server has responded with the handshake message, the InputStreamReader can no longer receive any new message. It blocked at the readline() method even though the client has sent the message already. From wireshark, I can see the client sent message and server respond ack. Any help would be appreciated, thanks.
Update: I just noted this question has been asked before. I will study the suggestions on the other posts first.
Update: The behavior is as same as this post:
Weird websocket behavior: only send data when close the tab
When the webtab closes, the read stream received the data package.
wireshark screen captures:
The tcp stream trace
The packages sequence
The log:
inputline: GET / HTTP/1.1
inputline: Host: localhost:8080
inputline: Connection: Upgrade
inputline: Pragma: no-cache
inputline: Cache-Control: no-cache
inputline: Upgrade: websocket
inputline: Origin: file://
inputline: Sec-WebSocket-Version: 13
inputline: User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_5)AppleWebKit/537.36 (KHTML, like Gecko) Chrome/59.0.3071.115 Safari/537.36
inputline: Accept-Encoding: gzip, deflate, br
inputline: Accept-Language: en,zh-TW;q=0.8,zh;q=0.6,zh-CN;q=0.4
inputline: Sec-WebSocket-Key: Yin4xn04vr9iBH1b2dU15A==
inputline: Sec-WebSocket-Extensions: permessage-deflate; client_max_window_bits
inputline:
response: HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept: +Y9whLTzCdyN1INpAxjkO6yD2Nw=
The server socket code:
public class EchoServer {
public static String HTTP_VERSION_HEADER = "HTTP/1.1";
public static void main(String[] args) throws IOException {
int portNumber = 8080;
try (
ServerSocket serverSocket =
new ServerSocket(Integer.parseInt("8080"));
Socket clientSocket = serverSocket.accept();
PrintWriter out =
new PrintWriter(clientSocket.getOutputStream(), true);
BufferedReader in = new BufferedReader(
new InputStreamReader(clientSocket.getInputStream()));
) {
String inputLine;
StringBuilder sb = new StringBuilder();
while ( true) {
inputLine = in.readLine();
if(inputLine == null) {
System.out.println("input is null");
continue;
}
System.out.println("inputline: " + inputLine);
sb.append(inputLine).append(System.lineSeparator());
if(inputLine.equals("")) {
Message msg = new Message(sb.toString(), new Date());
HttpMessage tmpMessage = new HttpMessage(msg.getText(), new Date());
String response = generateHandshakeResponse(tmpMessage);
System.out.println("response: " + response);
out.println(response);
out.flush();
}
}
} catch (IOException e) {
System.out.println("Exception caught when trying to listen on port "
+ portNumber + " or listening for a connection");
System.out.println(e.getMessage());
}
}
private static String generateHandshakeResponse(HttpMessage message) {
String webSocketKey = message.getVal(HttpMessage.SEC_WEBSOCKET_KEY);
String webSocketAccept = webSocketKey + "258EAFA5-E914-47DA-95CA-C5AB0DC85B11";
byte[] bytes = DigestUtils.sha1(webSocketAccept);
String secWebSocketAcceptVal = Base64.encodeBase64String(bytes);
StringBuilder sb = new StringBuilder();
sb.append(HTTP_VERSION_HEADER).append(" 101 ").append("Switching Protocols\r\n");
sb.append("Upgrade: websocket\r\n");
sb.append("Connection: Upgrade\r\n");
sb.append("Sec-WebSocket-Accept: ").append(secWebSocketAcceptVal).append("\r\n");
sb.append("\n\n") //<--- this line fixed the problem
//log.debug(sb.toString());
return sb.toString();
}
}
The client code:
<!doctype html>
<html lang="en">
<head>
<title>Websocket Client</title>
</head>
<body>
<script>
var exampleSocket = new WebSocket("ws://localhost:8080");
exampleSocket.onopen = function (event) {
console.log("connection opened..");
exampleSocket.send("Can you hear me?");
};
exampleSocket.onmessage = function (event) {
console.log(event.data);
}
function sendMsg(){
console.log("send message..");
exampleSocket.send("hello hello");
}
</script>
<button onclick="sendMsg()" title="send">send</button>
</body>
</html>

Thanks a lot to EJP, the problem is a missing blank line at the response handshake to indicate the end of the message.

Reading from a socket using buffered reader blocks [duplicate]

This question already has answers here:
Buffered Reader HTTP POST
(4 answers)
Closed 7 years ago.
I am trying to create a http server in java.
The following is a fragment of my code.
ServerSocket s = new ServerSocket(80);
while(true){
Socket client = s.accept();
BufferedReader in = new BufferedReader(
new InputStreamReader(client.getInputStream()));
String input = in.readLine(), ff;
System.out.println(input);
while((ff = in.readLine()) != null){
System.out.println(ff);
}
System.out.println("asd");
in.close();
client.close();
}
Asd is never printed. When I try to do a POST on the local host, it sends me all the headers but doesn't send any content data. It just waits there doing nothing.
I am doing a post using Jquery
$.post("http://127.0.0.1/",
{
name: "Donald Duck",
city: "Duckburg"
},
function(data,status){
alert("Data: " + data + "\nStatus: " + status);
});
This is what is being printed on the screen:
POST / HTTP/1.1
Host: 127.0.0.1
Connection: keep-alive
Content-Length: 5
Accept: */*
Origin: http://www.w3schools.com
User-Agent: Mozilla/5.0 (X11; Linux i686) AppleWebKit/537.36 (KHTML, like Gecko) Ubuntu Chromium/47.0.2526.73 Chrome/47.0.2526.73 Safari/537.36
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
That's it, nothing after this. It waits indefinitely at this point.

My guess would be that your actual content/payload is not terminated by the expected line delimiters as described in BufferedReader#readLine().
This blocks your in.readLine() invocation.
I would try to use the read() method instead and see if that helps. As in
while((value = in.read()) != -1) {
char c = (char)value;
System.out.println(c);
}
Edit: In fact, your question most likely duplicates this question: Buffered Reader HTTP POST

Java HTTP Server response incomplete

I am trying to build my own embedded HTTP Server for Java with very specific usage for an internal closed system. Using embedded solution that already exists meant that I need to strip them down to refit them for my internal system's specific use cases.
I have managed to get my Java HTTPD receive HTTP Requests from web browsers but the Requests that the HTTPD receives are incomplete.
Below is the server thread codes (pretending the ServerSocket works perfectly fine):
public class HttpThread implements Runnable {
private Socket socket;
private DataInputStream in;
private PrintStream out;
private BufferedReader br;
private String EOF = "\n";
private String STATUS_200 = "HTTP/1.1 200 OK" + EOF;
public HttpThread(Socket socket) throws IOException {
this.socket = socket;
this.in = new DataInputStream(this.socket.getInputStream());
this.out = new PrintStream(new BufferedOutputStream(this.socket.getOutputStream()));
}
#Override
public void run() {
System.out.println("New thread...");
try {
processInput();
//socket.close();
} catch (IOException ex) {
Logger.getLogger(HttpThread.class.getName()).log(Level.SEVERE, null, ex);
} finally {
if (br != null) {
try {
br.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
//System.out.println("Thread END...");
}
private String processInput() throws IOException {
String line;
StringBuilder buff = new StringBuilder();
br = new BufferedReader(new InputStreamReader(in));
while ((line = br.readLine()) != null) {
buff.append(line);
System.out.println(">>> " + line);
if (line.trim().isEmpty()) {
break;
}
}
out.print(STATUS_200);
out.print("Server: Test Server\n" +
"Content-Type: text/html; charset=UTF-8\n" +
"Connection: close");
out.print(EOF);
out.print("<html><body>yello</body></html>");
out.print(EOF);
out.flush();
System.out.println(STATUS_200);
return buff.toString();
}
}
I am using this HTML Script to test the server thread to simulate a POST request:
<html>
<body onLoad="document.test.submit();">
<form action="http://localhost:9999/" method="POST" name="test">
<input type=hidden name="userid" value="1443"/>
<input type=hidden name="password" value="1443"/>
</form>
</body>
</html>
When I use the browser to call the HTML codes the Java HTTPD receives an incomplete response:
New thread...
>>> POST / HTTP/1.1
>>> Host: localhost:9999
>>> Connection: keep-alive
>>> Content-Length: 25
>>> Cache-Control: max-age=0
>>> Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
>>> Origin: null
>>> User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/28.0.1500.72 Safari/537.36
>>> Content-Type: application/x-www-form-urlencoded
>>> Accept-Encoding: gzip,deflate,sdch
>>> Accept-Language: en-GB,en-US;q=0.8,en;q=0.6
>>>
HTTP/1.1 200 OK
New thread...
>>> GET /favicon.ico HTTP/1.1
>>> Host: localhost:9999
>>> Connection: keep-alive
>>> Accept: */*
>>> User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/28.0.1500.72 Safari/537.36
>>> Accept-Encoding: gzip,deflate,sdch
>>> Accept-Language: en-GB,en-US;q=0.8,en;q=0.6
>>>
HTTP/1.1 200 OK
It seems that the HTTPD only received the HTTP headers and stopped receiving the POST body.
May I know of some solutions to solve the above problem ?
Thanks.

The HTTP headers and body are separated by an empty line (also see the HTTP RFC, especially the chapter "5 Request"). Your server reads the socket Inputstream but breaks on an empty line :
if (line.trim().isEmpty()) {
break;
}
Therefore obviously you will not receive the body. You should fully consume the Inputstream instead.
Besides that, I would advise you to use already existing solutions. There is an abundance of HTTP server implementations, that are well tested and proven in real world usage. Save yourself alot of headache and use an existing lightweight server like e.g. Jetty, Netty or similar ones.

I switched out the while loop that does the readline() with the following code:
int i;
byte[] buffer = new byte[2048];
i = in.read(buffer);
for (int j = 0; j < i; j++) {
buff.append((char) buffer[j]);
}
System.out.println(buff.toString());
and the problem is solved.
Pyranja, thanks for the help.
Thanks to http://kcd.sytes.net/articles/simple_web_server.php IF you follow concisely. Somehow the br.readline() is not fully reading the lines properly after the empty line.
The code fragment should now look like:
private String processInput() throws IOException {
String line;
StringBuilder buff = new StringBuilder();
int i;
byte[] buffer = new byte[2048];
i = in.read(buffer);
for (int j = 0; j < i; j++) {
buff.append((char) buffer[j]);
}
System.out.println(buff.toString());
out.print(STATUS_200);
out.print("Server: Test Server\n" +
"Content-Type: text/html; charset=UTF-8\n" +
"Connection: close");
out.print(EOF);
out.print("<html><body>yello</body></html>");
out.print(EOF);
out.flush();
System.out.println(STATUS_200);
return buff.toString();
}
I guess it's a good experience learning how to build a simple HTTP Server :D .