I'm trying to build a "full-duplex" HTTP streaming request using Apache HTTPClient.
In my first attempt, I tried using the following request code:
URL url=new URL(/* code goes here */);
HttpPost request=new HttpPost(url.toString());
request.addHeader("Connection", "close");
PipedOutputStream requestOutput=new PipedOutputStream();
PipedInputStream requestInput=new PipedInputStream(requestOutput, DEFAULT_PIPE_SIZE);
ContentType requestContentType=getContentType();
InputStreamEntity requestEntity=new InputStreamEntity(requestInput, -1, requestContentType);
request.setEntity(requestEntity);
HttpEntity responseEntity=null;
HttpResponse response=getHttpClient().execute(request); // <-- Hanging here
try {
if(response.getStatusLine().getStatusCode() != 200)
throw new IOException("Unexpected status code: "+response.getStatusLine().getStatusCode());
responseEntity = response.getEntity();
}
finally {
if(responseEntity == null)
request.abort();
}
InputStream responseInput=responseEntity.getContent();
ContentType responseContentType;
if(responseEntity.getContentType() != null)
responseContentType = ContentType.parse(responseEntity.getContentType().getValue());
else
responseContentType = DEFAULT_CONTENT_TYPE;
Reader responseStream=decode(responseInput, responseContentType);
Writer requestStream=encode(requestOutput, getContentType());
The request hangs at the line indicated above. It seems that the code is trying to send the entire request before it gets the response. In retrospect, this makes sense. However, it's not what I was hoping for. :)
Instead, I was hoping to send the request headers with Transfer-Encoding: chunked, receive a response header of HTTP/1.1 200 OK with a Transfer-Encoding: chunked header of its own, and then I'd have a full-duplex streaming HTTP connection to work with.
Happily, my HTTPClient has another NIO-based asynchronous client with good usage examples (like this one). My questions are:
Is my interpretation of the synchronous HTTPClient behavior correct? Or is there something I can do to continue using the (simpler) synchronous HTTPClient in the manner I described?
Does the NIO-based client wait to send the whole request before seeking a response? Or will I be able to send the request incrementally and receive the response incrementally at the same time?
If HTTPClient will not support this modality, is there another HTTP client library that will? Or should I be planning to write a (minimal) HTTP client to support this modality?
Here is my view on skim reading the code:
I cannot completely agree with the fact that a non-200 response means failure. All 2XX responses are mostly valid. Check wiki for more details
For any TCP request, I would recommend to receive the entire response to confirm that it is valid. I say this because, a partial response may mostly be treated as bad response as most of the client implementations cannot make use of it. (Imagine a case where server is responding with 2MB of data and it goes down during this time)
A separate thread must be writing to the OutputStream for your code to
work.
The code above provides the HTTPClient with a PipedInputStream.
PipedInputStream makes bytes available as they are written to the corresponding OutputStream.
The code above does not write to the OutputStream (which must be done by a separate thread.
Therefore the code is hanging exactly where your comment is.
Under the hood, the Apache client says "inputStream.read()" which in the case of piped streams requires that outputStream.write(bytes) was called previously (by a separate thread).
Since you aren't pumping bytes into the associated OutputStream from a separate thread the InputStream just sits and waits for the OutputStream to be written to by "some other thread."
From the JavaDocs:
A piped input stream should be connected to a piped output stream;
the piped input stream then provides whatever data bytes are written
to the piped output stream.
Typically, data is read from a PipedInputStream object by one thread
and data is written to the corresponding PipedOutputStream by some
other thread.
Attempting to use both objects from a single thread is not
recommended, as it may deadlock the thread.
The piped input stream contains a buffer, decoupling read operations
from write operations, within limits. A pipe is said to be "broken"
if a thread that was providing data bytes to the connected piped
output stream is no longer alive.
Note: Seems to me, since piped streams and concurrency were not mentioned in your problem statement, that it's not necessary. Try wrapping a ByteArrayInputStream() with the Entity object instead first for a sanity check... that should help you narrow down the issue.
Update
Incidentally, I wrote an inversion of Apache's HTTP Client API [PipedApacheClientOutputStream] which provides an OutputStream interface for HTTP POST using Apache Commons HTTP Client 4.3.4. This may be close to what you are looking for...
Calling-code looks like this:
// Calling-code manages thread-pool
ExecutorService es = Executors.newCachedThreadPool(
new ThreadFactoryBuilder()
.setNameFormat("apache-client-executor-thread-%d")
.build());
// Build configuration
PipedApacheClientOutputStreamConfig config = new
PipedApacheClientOutputStreamConfig();
config.setUrl("http://localhost:3000");
config.setPipeBufferSizeBytes(1024);
config.setThreadPool(es);
config.setHttpClient(HttpClientBuilder.create().build());
// Instantiate OutputStream
PipedApacheClientOutputStream os = new
PipedApacheClientOutputStream(config);
// Write to OutputStream
os.write(...);
try {
os.close();
} catch (IOException e) {
logger.error(e.getLocalizedMessage(), e);
}
// Do stuff with HTTP response
...
// Close the HTTP response
os.getResponse().close();
// Finally, shut down thread pool
// This must occur after retrieving response (after is) if interested
// in POST result
es.shutdown();
Note - In practice the same client, executor service, and config will likely be reused throughout the life of the application, so the outer prep and close code in the above example will likely live in bootstrap/init and finalization code rather than directly inline with the OutputStream instantiation.
Related
I'm trying to build a HTTP server in Java out of curiosity.
I know that HTTP uses sockets underneath(correct me if i'm wrong). So started programming initially using ServerSocket class.
public class Server
{
public static void main(String[] args) throws IOException
{
System.out.println("Listening.....");
ServerSocket ss = new ServerSocket(80);
while(true)
{
Socket s = ss.accept();
Scanner sc = new Scanner(s.getInputStream());
while(sc.hasNextLine())
{
String line = sc.nextLine();
if(line.equals(""))
break;
else
System.out.println(line);
}
System.out.println("-------------------------------");
PrintStream ps = new PrintStream(s.getOutputStream());
ps.println("Hello from Server");
s.close();
ps.close();
sc.close();
}
}
}
(I'm using Thread in my actual code to serve multiple users. I've just provided the basic code.)
I'm getting all the headers from the web browser. But how can I send the files and images?
For, simple HTML I can read the file and use PrintStream to print it on the web browser.
But how can I send JavaScript, Images etc to the browser?
HTTP has a protocol to it, you need to follow that protocol. The HTTP 1.1 protocol spec still in wide use is RFC 2616 (though it has officially been replaced with newer RFCs 7230, 7231, 7232, 7233, 7234, and 7235).
In my answer to another question, I show the correct way to read an inbound HTTP request from a Java Socket directly.
When sending a reply back, you can use a PrintStream or PrintWriter to send the response HTTP headers. However, the body content is sent as raw bytes, based on the format specified by the Content-Type and Transfer-Encoding response headers. Typically, you would just send the raw bytes directly to the socket's OutputStream, or at least to a BufferedOutputStream attached to it. If you are sending a pre-existing file from disk, regardless of its type, you could just open an InputStream for the file and then copy its data directly to the socket's OutputStream. If you are generating data dynamically, then you would send the data to the socket's OutputStream using whatever intermediate classes are appropriate. Print... classes are only appropriate for textual data, not binary data, like images.
That being said, Java has its own HttpServer and HttpsServer classes. You should consider using them.
Basically the same way. You should "print" the raw bytes to the socket's OutputStream.
However, for the browser to be able to understand it, you need to shape your response according to the HTTP/1.1 protocol. Specifying a Content-Type header will tell the browser what it is receiving from you. Specifying a Content-Length header will tell the browser how many bytes it is receiving from you. Etc.
I have a task to download & upload a file using HTTP protocol in Android (Java platform).
I am using following code for uploading a file:
HttpURLConnection httpURLConnection = (HttpURLConnection) serverUrl.openConnection();
....
httpURLConnection.connect();
OutputStream os = httpURLConnection.getOutputStream();
And Using following code for downloading a file:
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
...
urlConnection.connect();
DataInputStream stream = new DataInputStream(urlConnection.getInputStream());
As per my observation connect() for both the case takes time because it is communicating with network at this point. And for file upload, getOutputStream() gets execute very fast so does it means it is not communicating to network?
Whereas getInputStream() (in file download) takes some time (around 200 to 2500 mili sec) to execute. Does it mean it is communicating with network at this point? If yes then why so?
Experts, Please provide your comments on this & correct me if I am wrong anywhere.
HTTP is a request/response protocol. You need a TCP connection. The connect() method creates that. Then you need to send a request. You call getOutputStream() for that, and you write it.
At this point nothing has been written to the network (in normal transfer mode), because the content-length header has to be set, and Java doesn't know when you've finished writing. So when you call getInputStream() (or getResponseCode()), Java sets the content-length header, writes the request, waits for the server to start generating a response, reads all the response headers, and then gives you an input stream positioned at the beginning of the body of the response. All those steps take time.
You must limit buffering by specifying the streaming mode either by giving the final length of the uploaded information via setFixedLengthStreamingMode method, or setting mode to streaming if final length is not known via setChunkedStreamingMode method:
// For best performance, you should call either setFixedLengthStreamingMode(int) when the body length is known in advance,
// or setChunkedStreamingMode(int) when it is not. Otherwise HttpURLConnection will be forced to buffer the complete request body in memory
// before it is transmitted, wasting (and possibly exhausting) heap and increasing latency.
//
// see: https://developer.android.com/reference/java/net/HttpURLConnection.html
_connection.setChunkedStreamingMode(1024);
If you don't, the real transfer will occur when you call getInputStream().
See https://developer.android.com/reference/java/net/HttpURLConnection.html
I am using Apache HttpClient (from Apache HTTP Components 4.3) in order to execute a GET against a ShoutCast stream:
CloseableHttpClient client = HttpClients.createDefault();
HttpGet request = new HttpGet("http://relay3.181.fm:8062/");
CloseableHttpResponse response = client.execute(request);
The call to client.execute() never returns, and according to the debugger it is a nested invocation to java.net.SocketInputStream#socketRead0() which is the last node in the call stack. From profiling the code, my only conclusion (based on a steadily rising number of char[] allocations) is that it simply "latches on" to the stream and keeps pulling bytes from the socket indefinitely.
What I would like is for the client to simply work normally and give me a HTTPResponse which I can use to pull what I want from the stream. As a matter of fact, I have been able to do so with other ShoutCast streams, but not this one.
Is there any way to work around this? Could I for example tell the client to break off after a certain number of bytes?
That site is very particular. If you don't specify a supported User-Agent (like Mozilla), the server keep streaming bytes. I don't know what these bytes are meant to represent, audio perhaps.
If you print out the bytes that you receive, you will see
ICY 200 OK
icy-notice1:<BR>This stream requires Winamp<BR>
icy-notice2:SHOUTcast Distributed Network Audio Server/Linux v1.9.8<BR>
icy-name:181.FM - The Beatles Channel
icy-genre:Oldies
icy-url:http://www.181.fm
content-type:audio/mpeg
icy-pub:1
icy-br:128
which indicates that the response is not a valid HTTP response. It is an ICY response from the ICY protocol.
Now the default HttpClient you are using uses a DefaultHttpResponseParser which is a
Lenient HTTP response parser implementation that can skip malformed
data until a valid HTTP response message head is encountered.
In other words, it keeps reading the bytes the server is sending until it finds a valid HTTP response header, which will never happen, thus the infinite read.
I don't think you will be able to accomplish what you want with the Http Components library. Either look for an ICY client implementation in Java or spin your own.
i'm developing an android application that fetches data from a restful web service.
i was thinking about the best way to implement this, my code is working but i'm sure it can be optimized.
here's my current code state:
i'm calling the restResource from a service using a scheduler.
the bad part is opening and closing connection on every request.
(the rest resource keeps realtime data( i have to fetch it every second), when it's empty it returns an empty array)
httpResponse = client.execute(request);
responseCode = httpResponse.getStatusLine().getStatusCode();
message = httpResponse.getStatusLine().getReasonPhrase();
HttpEntity entity = httpResponse.getEntity();
if (entity != null) {
InputStream instream = entity.getContent();
response = convertStreamToString(instream);
instream.close();
}
how to make use of the keepalive header returned with the response?
I have done this before using long-polling, in which my RESTful call blocks until either there is a timeout or it has something to reply with. Either way, the calling client would re-call the RESTful service again on either response (timeout or valid).
I am not sure how to you could use the keepalive header, but it seems like what you would do is send it, and then simply keep the connection open. In your server-side java code, you would get the output buffer for the response and start sending stuff down. On the client side, get the input buffer (not sure how this happens in Android, but I am under the impression its Java code, so there are loads of ways you can do any of this) and start reading. At some point I would think you would need to force the connection close, just because you don't want to keep it open indefinately.
Again, I have never tried it this way, so I don't know. Also, I am not sure if this breaks some unspoken laws of RESTful services. I have never read anything to contradict this approach.
Let's say I have a java program that makes an HTTP request on a server using HTTP 1.1 and doesn't close the connection. I make one request, and read all data returned from the input stream I have bound to the socket. However, upon making a second request, I get no response from the server (or there's a problem with the stream - it doesn't provide any more input). If I make the requests in order (Request, request, read) it works fine, but (request, read, request, read) doesn't.
Could someone shed some insight onto why this might be happening? (Code snippets follow). No matter what I do, the second read loop's isr_reader.read() only ever returns -1.
try{
connection = new Socket("SomeServer", port);
con_out = connection.getOutputStream();
con_in = connection.getInputStream();
PrintWriter out_writer = new PrintWriter(con_out, false);
out_writer.print("GET http://somesite HTTP/1.1\r\n");
out_writer.print("Host: thehost\r\n");
//out_writer.print("Content-Length: 0\r\n");
out_writer.print("\r\n");
out_writer.flush();
// If we were not interpreting this data as a character stream, we might need to adjust byte ordering here.
InputStreamReader isr_reader = new InputStreamReader(con_in);
char[] streamBuf = new char[8192];
int amountRead;
StringBuilder receivedData = new StringBuilder();
while((amountRead = isr_reader.read(streamBuf)) > 0){
receivedData.append(streamBuf, 0, amountRead);
}
// Response is processed here.
if(connection != null && !connection.isClosed()){
//System.out.println("Connection Still Open...");
out_writer.print("GET http://someSite2\r\n");
out_writer.print("Host: somehost\r\n");
out_writer.print("Connection: close\r\n");
out_writer.print("\r\n");
out_writer.flush();
streamBuf = new char[8192];
amountRead = 0;
receivedData.setLength(0);
while((amountRead = isr_reader.read(streamBuf)) > 0 || amountRead < 1){
if (amountRead > 0)
receivedData.append(streamBuf, 0, amountRead);
}
}
// Process response here
}
Responses to questions:
Yes, I'm receiving chunked responses from the server.
I'm using raw sockets because of an outside restriction.
Apologies for the mess of code - I was rewriting it from memory and seem to have introduced a few bugs.
So the consensus is I have to either do (request, request, read) and let the server close the stream once I hit the end, or, if I do (request, read, request, read) stop before I hit the end of the stream so that the stream isn't closed.
According to your code, the only time you'll even reach the statements dealing with sending the second request is when the server closes the output stream (your input stream) after receiving/responding to the first request.
The reason for that is that your code that is supposed to read only the first response
while((amountRead = isr_reader.read(streamBuf)) > 0) {
receivedData.append(streamBuf, 0, amountRead);
}
will block until the server closes the output stream (i.e., when read returns -1) or until the read timeout on the socket elapses. In the case of the read timeout, an exception will be thrown and you won't even get to sending the second request.
The problem with HTTP responses is that they don't tell you how many bytes to read from the stream until the end of the response. This is not a big deal for HTTP 1.0 responses, because the server simply closes the connection after the response thus enabling you to obtain the response (status line + headers + body) by simply reading everything until the end of the stream.
With HTTP 1.1 persistent connections you can no longer simply read everything until the end of the stream. You first need to read the status line and the headers, line by line, and then, based on the status code and the headers (such as Content-Length) decide how many bytes to read to obtain the response body (if it's present at all). If you do the above properly, your read operations will complete before the connection is closed or a timeout happens, and you will have read exactly the response the server sent. This will enable you to send the next request and then read the second response in exactly the same manner as the first one.
P.S. Request, request, read might be "working" in the sense that your server supports request pipelining and thus, receives and processes both request, and you, as a result, read both responses into one buffer as your "first" response.
P.P.S Make sure your PrintWriter is using the US-ASCII encoding. Otherwise, depending on your system encoding, the request line and headers of your HTTP requests might be malformed (wrong encoding).
Writing a simple http/1.1 client respecting the RFC is not such a difficult task.
To solve the problem of the blocking i/o access where reading a socket in java, you must use java.nio classes.
SocketChannels give the possibility to perform a non-blocking i/o access.
This is necessary to send HTTP request on a persistent connection.
Furthermore, nio classes will give better performances.
My stress test give to following results :
HTTP/1.0 (java.io) -> HTTP/1.0 (java.nio) = +20% faster
HTTP/1.0 (java.io) -> HTTP/1.1 (java.nio with persistent connection) = +110% faster
Make sure you have a Connection: keep-alive in your request. This may be a moot point though.
What kind of response is the server returning? Are you using chunked transfer? If the server doesn't know the size of the response body, it can't provide a Content-Length header and has to close the connection at the end of the response body to indicate to the client that the content has ended. In this case, the keep-alive won't work. If you're generating content on-the-fly with PHP, JSP etc., you can enable output buffering, check the size of the accumulated body, push the Content-Length header and flush the output buffer.
Is there a particular reason you're using raw sockets and not Java's URL Connection or Commons HTTPClient?
HTTP isn't easy to get right. I know Commons HTTP Client can re-use connections like you're trying to do.
If there isn't a specific reason for you using Sockets this is what I would recommend :)
Writing your own correct client HTTP/1.1 implementation is nontrivial; historically most people who I've seen attempt it have got it wrong. Their implementation usually ignores the spec and just does what appears to work with one particular test server - in particular, they usually ignore the requirement to be able to handle chunked responses.
Writing your own HTTP client is probably a bad idea, unless you have some VERY strange requirements.