SIP & SDP – Session Description Protocol

byTouK
August 5, 2008
2 minute read

Protokołu SIP jest protokołem sygnalizacyjnym używanym do inicjowania sesji multimedialnych. SIP umożliwiają realizacje negocjacji charakterystyki sesji oraz jej aktualizacje ale sam w sobie nie zawiera mechanizmów do opisu kształtu sesji, przenoszonej za pomocą protkołu RTP. W tym celu SIP wykorzystuje protokół SDP (Session Descriptions Protocol)
wchodzący bezpośrednio w skład komunikatu. SDP zawiera informacje o rodzaju
mediów, kodekach i ich parametrach, adresach IP, kierunku strumieniów, dostępnym pasmie itp.

Opis sesji:

v= (protocol version) – wersja protokołu -> “0”
o= (originator and session identifier) – zrodlo i identyfikator sesji -> “dowolna_nazwa id_sesji wersja_sesji IN (IP4|IP6) adresIP_zródła_sesji”
s= (session subject) – temat sesjii -> “-“
i=* (session information) – opis sesji -> nie używany
u=* (URI of description) – uri dodatkowe opisu sesji -> nie używany
e=* (email address) – adres email osoby odpowiedzialnej za sesje -> nie używany
p=* (phone number) – numer telefoniczny osoby odpowiedzialnej za sesje -> nie używany
c=* (connection information) – opis połaczenia, nie wymagany jeśli obecny dla każdego strumienia mediów -> “IN (IP4|IP6) adresIP”
b=* (zero or more bandwidth information lines) – sugerowane pasmo -> nie używany
One or more time descriptions
z=* (time zone adjustments)- definicja strefy czasu -> nie używany
k=* (encryption key) – klucz szyfrujący -> nie używane
a=* (zero or more session attribute lines) – atrybuty: sendonly – jeśli strona tylko chce wysyłać media, recvonly – jeśli strona chce tylko odbierać media, inactive – bez mediów, sendrecv – jeśli strona chce wysyłać i odbierać media
Zero or more media descriptions

Opis Czasu:

t= (time the session is active) – czas sesji -> “0 0”
r=* (zero or more repeat times) – cykliczność sesji -> nie używany

Opis Mediów:

m= (media name and transport address) – opis mediów -> “(audio|video|text) RTP/AVP opis danych medialnych”
i=* (media title) – opis mediów -> nie używany
c=* (connection information) – opis połaczenia, nie wymagany jeśli obecny w opisie sesji, nadpisuje wartość z opisu sesji -> “IN (IP4|IP6) AdresIP”
b=* (zero or more bandwidth information lines) – sugerowane pasmo -> nie używany
k=* (encryption key) – klucz szyfrujący -> nie używane
a=* (zero or more media attribute lines) – atrybuty strumienia, nadpisują atrybuty zdefiniowane w opisie sesji: sendonly – jeśli strona tylko chce wysyłać media, recvonly
– jeśli strona chce tylko odbierać media, inactive – bez mediów,
sendrecv – jeśli strona chce wysyłać i odbierać media, rtcp – port dla rtcp jesli nie, ptime – dlugosc mediów w sekunadach w przesylanym pakiecie, rtpmap – mapuje numer typu zawartosci do konkretnego kodeka i jego czestotliwosci, fmtp – umożliwia mapowanie parametrow tak aby sdp nie musialo tego rozumiec

TouK

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Read emails from imap with Spring Intergration

byJakub Nabrdalik
April 1, 2011

What's the easiest way to read emails from IMAP account in Java? Depends what your background is. If you have any experience in Apache Camel, ServiceMix, Mule, you already know the answer. If you don't, and your application is using Spring alr...What's the easiest way to read emails from IMAP account in Java? Depends what your background is. If you have any experience in Apache Camel, ServiceMix, Mule, you already know the answer. If you don't, and your application is using Spring alr...

DDevelopment & Design

Using WsLite in practice

byPiotr Jagielski
January 3, 2013

TL;DR

There is a example working GitHub project which covers unit testing and request/response logging when using WsLite.

Why Groovy WsLite ?

I’m a huge fan of Groovy WsLite project for calling SOAP web services. Yes, in a real world you have to deal with those - big companies have huge amount of “legacy” code and are crazy about homogeneous architecture - only SOAP, Java, Oracle, AIX…

But I also never been comfortable with XFire/CXF approach of web service client code generation. I wrote a bit about other posibilites in this post. With JAXB you can also experience some freaky classloading errors - as Tomek described on his blog. In a large commercial project the “the less code the better” principle is significant. And the code generated from XSD could look kinda ugly - especially more complicated structures like sequences, choices, anys etc.

Using WsLite with native Groovy concepts like XmlSlurper could be a great choice. But since it’s a dynamic approach you have to be really careful - write good unit tests and log requests. Below are my few hints for using WsLite in practice.

Unit testing

Suppose you have some invocation of WsLite SOAPClient (original WsLite example):

def getMothersDay(long _year) {
    def response = client.send(SOAPAction: action) {
       body {
           GetMothersDay('xmlns':'http://www.27seconds.com/Holidays/US/Dates/') {
              year(_year)
           }
       }
    }
    response.GetMothersDayResponse.GetMothersDayResult.text()
}

How can the unit test like? My suggestion is to mock SOAPClient and write a simple helper to test that builded XML is correct. Example using great SpockFramework:

void setup() {
   client = Mock(SOAPClient)
   service.client = client
}

def "should pass year to GetMothersDay and return date"() {
  given:
      def year = 2013
  when:
      def date = service.getMothersDay(year)
  then:
      1 * client.send(_, _) >> { Map params, Closure requestBuilder ->
            Document doc = buildAndParseXml(requestBuilder)
            assertXpathEvaluatesTo("$year", '//ns:GetMothersDay/ns:year', doc)
            return mockResponse(Responses.mothersDay)
      }
      date == "2013-05-12T00:00:00"
}

This uses a real cool feature of Spock - even when you mock the invocation with “any mark” (_), you are able to get actual arguments. So we can build XML that would be passed to SOAPClient's send method and check that specific XPaths are correct:

void setup() {
    engine = XMLUnit.newXpathEngine()
    engine.setNamespaceContext(new SimpleNamespaceContext(namespaces()))
}

protected Document buildAndParseXml(Closure xmlBuilder) {
    def writer = new StringWriter()
    def builder = new MarkupBuilder(writer)
    builder.xml(xmlBuilder)
    return XMLUnit.buildControlDocument(writer.toString())
}

protected void assertXpathEvaluatesTo(String expectedValue,
                                      String xpathExpression, Document doc) throws XpathException {
    Assert.assertEquals(expectedValue,
            engine.evaluate(xpathExpression, doc))
}

protected Map namespaces() {
    return [ns: 'http://www.27seconds.com/Holidays/US/Dates/']
}

The XMLUnit library is used just for XpathEngine, but it is much more powerful for comparing XML documents. The NamespaceContext is needed to use correct prefixes (e.g. ns:GetMothersDay) in your Xpath expressions.

Finally - the mock returns SOAPResponse instance filled with envelope parsed from some constant XML:

protected SOAPResponse mockResponse(String resp) {
    def envelope = new XmlSlurper().parseText(resp)
    new SOAPResponse(envelope: envelope)
}

Request and response logging

The WsLite itself doesn’t use any logging framework. We usually handle it by adding own sendWithLogging method:

private SOAPResponse sendWithLogging(String action, Closure cl) {
    SOAPResponse response = client.send(SOAPAction: action, cl)
    log(response?.httpRequest, response?.httpResponse)
    return response
}

private void log(HTTPRequest request, HTTPResponse response) {
    log.debug("HTTPRequest $request with content:\n${request?.contentAsString}")
    log.debug("HTTPResponse $response with content:\n${response?.contentAsString}")
}

This logs the actual request and response send through SOAPClient. But it logs only when invocation is successful and errors are much more interesting… So here goes withExceptionHandler method:

private SOAPResponse withExceptionHandler(Closure cl) {
    try {
        cl.call()
    } catch (SOAPFaultException soapEx) {
        log(soapEx.httpRequest, soapEx.httpResponse)
        def message = soapEx.hasFault() ? soapEx.fault.text() : soapEx.message
        throw new InfrastructureException(message)
    } catch (HTTPClientException httpEx) {
        log(httpEx.request, httpEx.response)
        throw new InfrastructureException(httpEx.message)
    }
}
def send(String action, Closure cl) {
    withExceptionHandler {
        sendWithLogging(action, cl)
    }
}

XmlSlurper gotchas

Working with XML document with XmlSlurper is generally great fun, but is some cases could introduce some problems. A trivial example is parsing an id with a number to Long value:

def id = Long.valueOf(edit.'@id' as String)

The Attribute class (which edit.'@id' evaluates to) can be converted to String using as operator, but converting to Long requires using valueOf.

The second example is a bit more complicated. Consider following XML fragment:

<edit id="3">
   <params>
      <param value="label1" name="label"/>
      <param value="2" name="param2"/>
   </params>
   <value>123</value>
</edit>
<edit id="6">
   <params>
      <param value="label2" name="label"/>
      <param value="2" name="param2"/>
   </params>
   <value>456</value>
</edit>

We want to find id of edit whose label is label1. The simplest solution seems to be:

def param = doc.edit.params.param.find { it['@value'] == 'label1' }
def edit = params.parent().parent()

But it doesn’t work! The parent method returns multiple edits, not only the one that is parent of given param…

Here’s the correct solution:

doc.edit.find { edit ->
    edit.params.param.find { it['@value'] == 'label1' }
}

Example

The example working project covering those hints could be found on GitHub.