facebook - WSO2 ESB: error de carácter inesperado al enviar JSON al servicio proxy

wso2esb

Question

Estoy intentando recuperar datos de Facebook usando el Conector de Facebook WSO2 en WSO2 ESB 4.9.0. He proporcionado la configuración del proxy a continuación.

<?xml version="1.0" encoding="UTF-8"?>
<proxy xmlns="http://ws.apache.org/ns/synapse"
       name="facebook_getFeed"
       transports="https,http"
       statistics="disable"
       trace="disable"
       startOnLoad="true">
   <target>
      <inSequence onError="fault">
         <property name="messageType" value="application/json" scope="axis2"/>
         <log level="full"/>
         <property name="apiUrl" expression="json-eval($.apiUrl)"/>
         <property name="apiVersion" expression="json-eval($.apiVersion)"/>
         <property name="accessToken" expression="json-eval($.accessToken)"/>
         <property name="userId" expression="json-eval($.userId)"/>
         <property name="numOfFeeds" expression="json-eval($.numOfFeeds)"/>
         <property name="fields" expression="json-eval($.fields)"/>
         <facebook.init>
            <apiUrl>{$ctx:apiUrl}</apiUrl>
            <accessToken>{$ctx:accessToken}</accessToken>
            <apiVersion>{$ctx:apiVersion}</apiVersion>
         </facebook.init>
         <facebook.getFeeds>
            <userId>{$ctx:userId}</userId>
            <numOfFeeds>{$ctx:numOfFeeds}</numOfFeeds>
            <fields>{$ctx:fields}</fields>
         </facebook.getFeeds>
         <respond/>
      </inSequence>
      <outSequence>
         <property name="messageType" value="application/json" scope="axis2"/>
         <send/>
      </outSequence>
   </target>
   <description/>
</proxy> 

El problema que estoy teniendo es que cada vez que hago una solicitud POST al servicio agota el tiempo. Al verificar los registros de errores de ESB, parece que hubo un "Error al compilar una secuencia de paso".

[2015-12-15 15:16:54,284] ERROR - RelayUtils Error while building Passthrough stream
org.apache.axiom.om.OMException: com.ctc.wstx.exc.WstxUnexpectedCharException: Unexpected character ''{'' (code 123) in prolog; expected ''<''
 at [row,col {unknown-source}]: [1,1]
        at org.apache.axiom.om.impl.builder.StAXOMBuilder.next(StAXOMBuilder.java:296)
        at org.apache.axiom.om.impl.llom.OMDocumentImpl.getOMDocumentElement(OMDocumentImpl.java:109)
        at org.apache.axiom.om.impl.builder.StAXOMBuilder.getDocumentElement(StAXOMBuilder.java:570)
        at org.apache.axiom.om.impl.builder.StAXOMBuilder.getDocumentElement(StAXOMBuilder.java:566)
        at org.apache.synapse.transport.passthru.util.DeferredMessageBuilder.getDocument(DeferredMessageBuilder.java:149)
        at org.apache.synapse.transport.passthru.util.RelayUtils.builldMessage(RelayUtils.java:133)
        at org.apache.synapse.transport.passthru.util.RelayUtils.buildMessage(RelayUtils.java:98)
        at org.apache.synapse.mediators.AbstractListMediator.mediate(AbstractListMediator.java:72)
        at org.apache.synapse.mediators.AbstractListMediator.mediate(AbstractListMediator.java:48)
        at org.apache.synapse.mediators.base.SequenceMediator.mediate(SequenceMediator.java:149)
        at org.apache.synapse.core.axis2.ProxyServiceMessageReceiver.receive(ProxyServiceMessageReceiver.java:185)
        at org.apache.axis2.engine.AxisEngine.receive(AxisEngine.java:180)
        at org.apache.synapse.transport.passthru.ServerWorker.processNonEntityEnclosingRESTHandler(ServerWorker.java:317)
        at org.apache.synapse.transport.passthru.ServerWorker.processEntityEnclosingRequest(ServerWorker.java:363)
        at org.apache.synapse.transport.passthru.ServerWorker.run(ServerWorker.java:142)
        at org.apache.axis2.transport.base.threads.NativeWorkerPool$1.run(NativeWorkerPool.java:172)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
        at java.lang.Thread.run(Thread.java:745)
Caused by: com.ctc.wstx.exc.WstxUnexpectedCharException: Unexpected character ''{'' (code 123) in prolog; expected ''<''
 at [row,col {unknown-source}]: [1,1]
        at com.ctc.wstx.sr.StreamScanner.throwUnexpectedChar(StreamScanner.java:639)
        at com.ctc.wstx.sr.BasicStreamReader.nextFromProlog(BasicStreamReader.java:2052)
        at com.ctc.wstx.sr.BasicStreamReader.next(BasicStreamReader.java:1134)
        at org.apache.axiom.util.stax.wrapper.XMLStreamReaderWrapper.next(XMLStreamReaderWrapper.java:225)
        at org.apache.axiom.util.stax.dialect.DisallowDoctypeDeclStreamReaderWrapper.next(DisallowDoctypeDeclStreamReaderWrapper.java:34)
        at org.apache.axiom.om.impl.builder.StAXOMBuilder.parserNext(StAXOMBuilder.java:681)
        at org.apache.axiom.om.impl.builder.StAXOMBuilder.next(StAXOMBuilder.java:214)
        ... 18 more
[2015-12-15 15:16:54,377] ERROR - SequenceMediator Error while building message
org.apache.axis2.AxisFault: Error while building Passthrough stream
        at org.apache.synapse.transport.passthru.util.RelayUtils.handleException(RelayUtils.java:283)
        at org.apache.synapse.transport.passthru.util.RelayUtils.builldMessage(RelayUtils.java:142)
        at org.apache.synapse.transport.passthru.util.RelayUtils.buildMessage(RelayUtils.java:98)
        at org.apache.synapse.mediators.AbstractListMediator.mediate(AbstractListMediator.java:72)
        at org.apache.synapse.mediators.AbstractListMediator.mediate(AbstractListMediator.java:48)
        at org.apache.synapse.mediators.base.SequenceMediator.mediate(SequenceMediator.java:149)
        at org.apache.synapse.core.axis2.ProxyServiceMessageReceiver.receive(ProxyServiceMessageReceiver.java:185)
        at org.apache.axis2.engine.AxisEngine.receive(AxisEngine.java:180)
        at org.apache.synapse.transport.passthru.ServerWorker.processNonEntityEnclosingRESTHandler(ServerWorker.java:317)
        at org.apache.synapse.transport.passthru.ServerWorker.processEntityEnclosingRequest(ServerWorker.java:363)
        at org.apache.synapse.transport.passthru.ServerWorker.run(ServerWorker.java:142)
        at org.apache.axis2.transport.base.threads.NativeWorkerPool$1.run(NativeWorkerPool.java:172)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
        at java.lang.Thread.run(Thread.java:745)
Caused by: org.apache.axiom.om.OMException: com.ctc.wstx.exc.WstxUnexpectedCharException: Unexpected character ''{'' (code 123) in prolog; expected ''<''
 at [row,col {unknown-source}]: [1,1]
        at org.apache.axiom.om.impl.builder.StAXOMBuilder.next(StAXOMBuilder.java:296)
        at org.apache.axiom.om.impl.llom.OMDocumentImpl.getOMDocumentElement(OMDocumentImpl.java:109)
        at org.apache.axiom.om.impl.builder.StAXOMBuilder.getDocumentElement(StAXOMBuilder.java:570)
        at org.apache.axiom.om.impl.builder.StAXOMBuilder.getDocumentElement(StAXOMBuilder.java:566)
        at org.apache.synapse.transport.passthru.util.DeferredMessageBuilder.getDocument(DeferredMessageBuilder.java:149)
        at org.apache.synapse.transport.passthru.util.RelayUtils.builldMessage(RelayUtils.java:133)
        ... 13 more

En cuanto a la configuración de proxy anterior, tengo un mediador de registro que realmente imprime con éxito la carga JSON, ¿así que eso me llevaría a pensar que tiene algo que ver con el formateador de mensajes?

La configuración de mi formateador / creador de mensajes dentro del archivo Axis2.xml es la siguiente:

<!--JSON Message Formatters-->
<messageFormatter contentType="application/json" class="org.apache.synapse.commons.json.JsonStreamFormatter"/>

<!--JSON Message Builders-->
<messageBuilder contentType="application/json" class="org.apache.synapse.commons.json.JsonStreamBuilder"/>

Todo lo demás en este archivo es según la configuración predeterminada.

¿Qué podría estar yendo mal aquí?

Solicitud de muestra

Utilizando la UI de Soap (identificador oculto de IP y acceso en la carga útil):

POST http://[SERVER_IP]:8280/services/facebook_getFeed <br>
HTTP/1.1 <br>
Accept-Encoding: gzip,deflate <br>
Content-Type: application/json <br>
Content-Length: 207 <br>
Host: [SERVER_IP]:8280 <br>
Connection: Keep-Alive <br>
User-Agent: Apache-HttpClient/4.1.1 (java 1.5) <br>

Datos de carga útil:

{
"apiUrl":"https://graph.facebook.com",
"apiVersion":"v2.4",
"accessToken":"[TOKEN HERE]",
"userId":"409521282507981",
"numOfFeeds":"10",
"fields":"message,id,created_time"
}

Registros de alambre

Según lo solicitado por @RavindraRanwala:

[2015-12-15 17:29:38,650] DEBUG - wire >> "POST /services/facebook_getFeed HTTP/1.1[/r][/n]"
[2015-12-15 17:29:38,652] DEBUG - wire >> "Accept-Encoding: gzip,deflate[/r][/n]"
[2015-12-15 17:29:38,653] DEBUG - wire >> "Content-Type: application/json[/r][/n]"
[2015-12-15 17:29:38,653] DEBUG - wire >> "Content-Length: 207[/r][/n]"
[2015-12-15 17:29:38,663] DEBUG - wire >> "Host: [SERVER_IP]:8280[/r][/n]"
[2015-12-15 17:29:38,663] DEBUG - wire >> "Connection: Keep-Alive[/r][/n]"
[2015-12-15 17:29:38,664] DEBUG - wire >> "User-Agent: Apache-HttpClient/4.1.1 (java 1.5)[/r][/n]"
[2015-12-15 17:29:38,665] DEBUG - wire >> "[/r][/n]"
[2015-12-15 17:29:38,666] DEBUG - wire >> "{[/n]"
[2015-12-15 17:29:38,666] DEBUG - wire >> ""apiUrl":"https://graph.facebook.com",[/n]"
[2015-12-15 17:29:38,667] DEBUG - wire >> ""apiVersion":"v2.4",[/n]"
[2015-12-15 17:29:38,668] DEBUG - wire >> ""accessToken":"[ACCESS_TOKEN]",[/n]"
[2015-12-15 17:29:38,669] DEBUG - wire >> ""userId":"409521282507981",[/n]"
[2015-12-15 17:29:38,669] DEBUG - wire >> ""numOfFeeds":"10",[/n]"
[2015-12-15 17:29:38,679] DEBUG - wire >> ""fields":"message,id,created_time"[/n]"
[2015-12-15 17:29:38,679] DEBUG - wire >> "}"
[2015-12-15 17:29:38,812]  INFO - LogMediator To: /services/facebook_getFeed, MessageID: urn:uuid:27814841-6067-466c-b55f-b7fdd67c8d3b, Direction: request, Payload: {
"apiUrl":"https://graph.facebook.com",
"apiVersion":"v2.4",
"accessToken":"[ACCESS_TOKEN]",
"userId":"409521282507981",
"numOfFeeds":"10",
"fields":"message,id,created_time"
}
[2015-12-15 17:29:38,909]  INFO - TimeoutHandler This engine will expire all callbacks after : 120 seconds, irrespective of the timeout action, after the specified or optional timeout
[2015-12-15 17:29:40,267] DEBUG - wire << "GET /409521282507981/feed?limit=10&access_token=[ACCESS_TOKEN]&fields= HTTP/1.1[/r][/n]"
[2015-12-15 17:29:40,269] DEBUG - wire << "Accept-Encoding: gzip,deflate[/r][/n]"
[2015-12-15 17:29:40,278] DEBUG - wire << "Content-Type: application/json[/r][/n]"
[2015-12-15 17:29:40,279] DEBUG - wire << "Host: graph.facebook.com:443[/r][/n]"
[2015-12-15 17:29:40,280] DEBUG - wire << "Connection: Keep-Alive[/r][/n]"
[2015-12-15 17:29:40,281] DEBUG - wire << "User-Agent: Synapse-PT-HttpComponents-NIO[/r][/n]"
[2015-12-15 17:29:40,281] DEBUG - wire << "[/r][/n]"
[2015-12-15 17:29:40,554] DEBUG - wire >> "HTTP/1.1 200 OK[/r][/n]"
[2015-12-15 17:29:40,557] DEBUG - wire >> "Access-Control-Allow-Origin: *[/r][/n]"
[2015-12-15 17:29:40,558] DEBUG - wire >> "Content-Type: text/javascript; charset=UTF-8[/r][/n]"
[2015-12-15 17:29:40,559] DEBUG - wire >> "X-FB-Trace-ID: E5Iewv3ixeR[/r][/n]"
[2015-12-15 17:29:40,560] DEBUG - wire >> "X-FB-Rev: 2091546[/r][/n]"
[2015-12-15 17:29:40,561] DEBUG - wire >> "ETag: "ca13846784e4a3383090ca79b7a295fd23aa5641"[/r][/n]"
[2015-12-15 17:29:40,561] DEBUG - wire >> "Pragma: no-cache[/r][/n]"
[2015-12-15 17:29:40,562] DEBUG - wire >> "Cache-Control: private, no-cache, no-store, must-revalidate[/r][/n]"
[2015-12-15 17:29:40,563] DEBUG - wire >> "Facebook-API-Version: v2.5[/r][/n]"
[2015-12-15 17:29:40,563] DEBUG - wire >> "Expires: Sat, 01 Jan 2000 00:00:00 GMT[/r][/n]"
[2015-12-15 17:29:40,564] DEBUG - wire >> "Vary: Accept-Encoding[/r][/n]"
[2015-12-15 17:29:40,565] DEBUG - wire >> "Content-Encoding: gzip[/r][/n]"
[2015-12-15 17:29:40,565] DEBUG - wire >> "X-FB-Debug: G+b1bsKrSFxPDc4u1RDGIpHACsTbiJV6n1nGgNfMYwc0IqGO2fif1pnr9/o/dhQ1DLSpl7pXheknjzMwvH948w==[/r][/n]"
[2015-12-15 17:29:40,575] DEBUG - wire >> "Date: Tue, 15 Dec 2015 06:29:46 GMT[/r][/n]"
[2015-12-15 17:29:40,576] DEBUG - wire >> "Connection: keep-alive[/r][/n]"
[2015-12-15 17:29:40,578] DEBUG - wire >> "Content-Length: 814[/r][/n]"
[2015-12-15 17:29:40,579] DEBUG - wire >> "[/r][/n]"
[2015-12-15 17:29:40,580] DEBUG - wire >> "[0x1f][0x8b][0x8][0x0][0x0][0x0][0x0][0x0][0x0][0x3][0xad][0x93][0xef]o[0xa3]6[0x18][0xc7][0xff][0x15][0xc4][0x8b]J[0xd3]z[0x89]⌂[0x3][0x96][0xaa][0x89]$M[0xbb][0xb4][0xd7]6[0x97]/[0xda][0xb0]L[0x91]K[0x1c]B![0x98][0x82][0x9][0xcd]z[0xfd][0xdf]g[0xba]{Q[0xe5][0xa6]p[0x9a][0x6][0xbc][0xb0][0x85][0xad][0xcf][0xd7][0x1f]?[0xcf][0xab][0xbd][0x12]Z[0xd8][0xfc][0x8f]W{+[0xcb]RD[0xd2][0xe6][0xf6
3][0x97][0x96][0xf9][0x84]u[0xa5]D*,[0xfe][0x8b]}j[0x87][0x85][0x14]Z[0xae][0x96]:[0xde]6k[0x10][0x80][0xf8][0x13][0x84][0x9f][0x90];[0x5][0x88][0x3][0xc8][0xb1][0xfb]+0[0x8f]Y[0x19][0xaf][0xcc]⌂[0x2]<[0x8a] r[0x11][0x5][0x8e][0xe7][0xc2]%[0xc4].t[0x10]c[0x18][0x1][0x87]B[0x97][0xd8]o[0xa7][0x1f][0x91][0x13][0xb5][0x95]z[0x13]gQ[0xc3][0xad][0xb]e[0x6][0x1b]Y[0xc8][0xce]q0[0xe0][0x80]q[0xe0][0x1d][0x5][0x13][0x88] c[0x84][0xb9][0x1
][0x10]y[0x7][0xdc]QUjK[0xcb]R7[0xe8]T[0x85]B[0xc7]*[0xb3]D$[0xe2][0xac][0xd3]9Fw[0xa6][0x8]sJ8[0xa6][0xed]t[0xc]IC''[0xc][0x1e][0xd0][0xef][/n]"
[2015-12-15 17:29:40,592] DEBUG - wire >> "[0xa9][0xf5][0xde]*k)[0xb5][0x95][0xa7]"[0x94][0x96]V[0xd6]F[0xec][0xa4][0x95]VY[0xb8]i[/r][0x80][0x10][0x87][0xc7][0xbd]7[0x1](1/u[0xcc][0xdc]=[0x8][0xf0][0xbb]U[0x8b][0xd2]j[0xc4]''[0x8d][0x0][0xf1][0xa8]*[0xdd]L[0xcb][0xf].B][0x89]4[0xdd][0xb7]E[0x81][0x88]#[0xa7]5[/n]"
[2015-12-15 17:29:40,595] DEBUG - wire >> "![0xd8]3Q<[0x0][0xf0]A[0x94][0xdb][0x8d]%[0xb2][0x95][0xb5][0x15][0xfb]Gy[0x18][0xc1][0x94][0x84]L[0xd3][0x9f][0xb8][0x10]@9[0x81][0xad]!0[0x81][0xc]![0xc2][0x98]w[0x18][0xc2]7[0x9][0xc2][0x8d][0xc][0x13][0xeb][0x7][0x11][0xc7][0xd1][0x88]c[0xc2]I{-[0x98]6[0xf0]L-P[0xec][0xb2][0x1f][0xce]⌂[0xfa].@[0xa4][0xa5]2[0x3][0xa5]M[0xfd][[0xb9]2[0xe5][0xb9].[0xd4][0xd6]d[0x91]VU[0xca][0xa2]E[0x81][
0x4][0x8f][0xa3]v[0x5]f[/n]"
[2015-12-15 17:29:40,596] DEBUG - wire >> ")uMq[0x1e][0xd6][0xa4][0xff][0x1]*[0xde][0x91]mD[0xe0]p[0xc4]Z[0x89][0xc0][0x81][0xa0]!:[0x18][0x1d][0x12][0x9b]S[0xff]T[0xc7]AN[0xcd][0xd7][0xde][0xef][0x0]3dX[0x18][0xb8][0xc0]~[0xfb][0xf3][0xd4][0xce]Ed[0xca][0xdb][0xe6][0xaf]v^[0xc8]][0xac][0xaa][0xd2]l[0xdc]h[0x9d][0x97]|[0xd1]]t[0xa3]B[0xe4][0x9b][0xce][0xda][0xb4][0xdf][0xa3]RI''T[n[0xea]t[0xd1][0xdd][0xa1][0xe]]t[0xf][0x0][0x8b][0x
xca][0xd5]oi[0xbc][0x8d][0xf5][0x19][0x4]''e[0x9c][0x85][0xf2][0xcc][0xdc]+e[0xc0],uOD[0x18][0x9a][0xa3]-[0xb5]Jdv[0x6][0x1d][0xe8]0[0x8][0x8c]l[0x88][0x18]`[0xee][0xb7]Y[0xaa][0xcb][0xde]6z[0xca][0xa6][0x18][0xe6]j[0xb6][0xbf][0xf4][0x96]U[0x8][0x7][0xe]B[0xf5][0xc9]r[0xf9]O[0xd0][0xef]{e[0x16].[0xfd][0x95]?N@[0x8][0x8a]z[0x94][0x8c][0xb0]?q[0x82][0xde][0xa4][0x1e]^[0x87][0xec]9[0xae]f~[0x92]D[0x14][0xf5]/[0x15][0xf4][0xcb]"[0xbc]
]d=[0xbc]x[0x92][0xee]/&[0xdb][0xfb]r[0xf0][0xbc]&[0x81]/[0xf4]|[0x15][0x5][0xfe][0xe7]/[0x8f][0xf1][0x1d]<⌂[0xa9][0xf7]+_EW[0x15]c[0x13]W[0xcb]$y[0xbe][0x9a]{[0xeb][0x9b][0x88][0xc2]r[0x1a][0xf4][0xf2][0xcf][0xf7][0xa3]][0x1d][0xc][0x82]A[0x13][0xe5][0xbb][0xa9]3hLg[0xf2]E[0xff]⌂[0xca][0xfe][0xbb][0xa1]*[0xd3]q[0xfa].[0x9b][0x9a].[0x82][0xde][0xbf]+[0x1b][0xf4][0xc7][0xf2][0xe6]|>[0xc3]t|[[0x8f]]q3[0x8c][0xf1][0xae][0x9f][0x93][0
xe8]k[0x8c]/[0xef][0xee]f[0xe7][0xc9][0xa4][0xbe][0x8c][0x3]?[0xbd][0xdf][0xe5]_[0xfb]/[0xfb][0xb1][0x1f][0xf4][0xc9]5[0xb9][0x9e][0x5]f0[0xdd][0x8f]Y[0xe0][0xc3][0xc9][0xee]<{[0xc8].[0xd4]z>[0xa4]^[0xc8]*⌂=[0x99][0xc6][0xf][0x4][0xdc]#:q[0x9d][0xa2][0xff][0xc4]n[0x91][0xfc][0xcb][0x1b]^[0xd4][0xf]Q[0xa3][0xcc]~{[0xfb][0x1b][0x92][0x12][0xdf])M[0x7][0x0][0x0]"
[2015-12-15 17:29:40,674] ERROR - RelayUtils Error while building Passthrough stream
org.apache.axiom.om.OMException: com.ctc.wstx.exc.WstxUnexpectedCharException: Unexpected character ''{'' (code 123) in prolog; expected ''<''
 at [row,col {unknown-source}]: [1,1]
        at org.apache.axiom.om.impl.builder.StAXOMBuilder.next(StAXOMBuilder.java:296)
        at org.apache.axiom.om.impl.llom.OMDocumentImpl.getOMDocumentElement(OMDocumentImpl.java:109)
        at org.apache.axiom.om.impl.builder.StAXOMBuilder.getDocumentElement(StAXOMBuilder.java:570)
        at org.apache.axiom.om.impl.builder.StAXOMBuilder.getDocumentElement(StAXOMBuilder.java:566)
        at org.apache.synapse.transport.passthru.util.DeferredMessageBuilder.getDocument(DeferredMessageBuilder.java:149)
        at org.apache.synapse.transport.passthru.util.RelayUtils.builldMessage(RelayUtils.java:133)
        at org.apache.synapse.transport.passthru.util.RelayUtils.buildMessage(RelayUtils.java:98)
        at org.apache.synapse.mediators.AbstractListMediator.mediate(AbstractListMediator.java:72)
        at org.apache.synapse.mediators.template.InvokeMediator.mediate(InvokeMediator.java:154)
        at org.apache.synapse.mediators.base.SequenceMediator.mediate(SequenceMediator.java:267)
        at org.apache.synapse.core.axis2.Axis2SynapseEnvironment.mediateFromContinuationStateStack(Axis2SynapseEnvironment.java:679)
        at org.apache.synapse.core.axis2.Axis2SynapseEnvironment.injectMessage(Axis2SynapseEnvironment.java:244)
        at org.apache.synapse.core.axis2.SynapseCallbackReceiver.handleMessage(SynapseCallbackReceiver.java:529)
        at org.apache.synapse.core.axis2.SynapseCallbackReceiver.receive(SynapseCallbackReceiver.java:172)
        at org.apache.axis2.engine.AxisEngine.receive(AxisEngine.java:180)
        at org.apache.synapse.transport.passthru.ClientWorker.run(ClientWorker.java:247)
        at org.apache.axis2.transport.base.threads.NativeWorkerPool$1.run(NativeWorkerPool.java:172)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
        at java.lang.Thread.run(Thread.java:745)
Caused by: com.ctc.wstx.exc.WstxUnexpectedCharException: Unexpected character ''{'' (code 123) in prolog; expected ''<''
 at [row,col {unknown-source}]: [1,1]
        at com.ctc.wstx.sr.StreamScanner.throwUnexpectedChar(StreamScanner.java:639)
        at com.ctc.wstx.sr.BasicStreamReader.nextFromProlog(BasicStreamReader.java:2052)
        at com.ctc.wstx.sr.BasicStreamReader.next(BasicStreamReader.java:1134)
        at org.apache.axiom.util.stax.wrapper.XMLStreamReaderWrapper.next(XMLStreamReaderWrapper.java:225)
        at org.apache.axiom.util.stax.dialect.DisallowDoctypeDeclStreamReaderWrapper.next(DisallowDoctypeDeclStreamReaderWrapper.java:34)
        at org.apache.axiom.om.impl.builder.StAXOMBuilder.parserNext(StAXOMBuilder.java:681)
        at org.apache.axiom.om.impl.builder.StAXOMBuilder.next(StAXOMBuilder.java:214)
        ... 19 more
[2015-12-15 17:29:40,902] ERROR - TemplateMediator Error while building message
org.apache.axis2.AxisFault: Error while building Passthrough stream
        at org.apache.synapse.transport.passthru.util.RelayUtils.handleException(RelayUtils.java:283)
        at org.apache.synapse.transport.passthru.util.RelayUtils.builldMessage(RelayUtils.java:142)
        at org.apache.synapse.transport.passthru.util.RelayUtils.buildMessage(RelayUtils.java:98)
        at org.apache.synapse.mediators.AbstractListMediator.mediate(AbstractListMediator.java:72)
        at org.apache.synapse.mediators.template.InvokeMediator.mediate(InvokeMediator.java:154)
        at org.apache.synapse.mediators.base.SequenceMediator.mediate(SequenceMediator.java:267)
        at org.apache.synapse.core.axis2.Axis2SynapseEnvironment.mediateFromContinuationStateStack(Axis2SynapseEnvironment.java:679)
        at org.apache.synapse.core.axis2.Axis2SynapseEnvironment.injectMessage(Axis2SynapseEnvironment.java:244)
        at org.apache.synapse.core.axis2.SynapseCallbackReceiver.handleMessage(SynapseCallbackReceiver.java:529)
        at org.apache.synapse.core.axis2.SynapseCallbackReceiver.receive(SynapseCallbackReceiver.java:172)
        at org.apache.axis2.engine.AxisEngine.receive(AxisEngine.java:180)
        at org.apache.synapse.transport.passthru.ClientWorker.run(ClientWorker.java:247)
        at org.apache.axis2.transport.base.threads.NativeWorkerPool$1.run(NativeWorkerPool.java:172)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
        at java.lang.Thread.run(Thread.java:745)
Caused by: org.apache.axiom.om.OMException: com.ctc.wstx.exc.WstxUnexpectedCharException: Unexpected character ''{'' (code 123) in prolog; expected ''<''
 at [row,col {unknown-source}]: [1,1]
        at org.apache.axiom.om.impl.builder.StAXOMBuilder.next(StAXOMBuilder.java:296)
        at org.apache.axiom.om.impl.llom.OMDocumentImpl.getOMDocumentElement(OMDocumentImpl.java:109)
        at org.apache.axiom.om.impl.builder.StAXOMBuilder.getDocumentElement(StAXOMBuilder.java:570)
        at org.apache.axiom.om.impl.builder.StAXOMBuilder.getDocumentElement(StAXOMBuilder.java:566)
        at org.apache.synapse.transport.passthru.util.DeferredMessageBuilder.getDocument(DeferredMessageBuilder.java:149)
        at org.apache.synapse.transport.passthru.util.RelayUtils.builldMessage(RelayUtils.java:133)
        ... 14 more
Caused by: com.ctc.wstx.exc.WstxUnexpectedCharException: Unexpected character ''{'' (code 123) in prolog; expected ''<''
 at [row,col {unknown-source}]: [1,1]
        at com.ctc.wstx.sr.StreamScanner.throwUnexpectedChar(StreamScanner.java:639)
        at com.ctc.wstx.sr.BasicStreamReader.nextFromProlog(BasicStreamReader.java:2052)
        at com.ctc.wstx.sr.BasicStreamReader.next(BasicStreamReader.java:1134)
        at org.apache.axiom.util.stax.wrapper.XMLStreamReaderWrapper.next(XMLStreamReaderWrapper.java:225)
        at org.apache.axiom.util.stax.dialect.DisallowDoctypeDeclStreamReaderWrapper.next(DisallowDoctypeDeclStreamReaderWrapper.java:34)
        at org.apache.axiom.om.impl.builder.StAXOMBuilder.parserNext(StAXOMBuilder.java:681)
        at org.apache.axiom.om.impl.builder.StAXOMBuilder.next(StAXOMBuilder.java:214)
        ... 19 more
[2015-12-15 17:29:40,991] ERROR - LogMediator To: http://www.w3.org/2005/08/addressing/anonymous, WSAction: , SOAPAction: , MessageID: urn:uuid:85e6d771-e7c6-4764-8431-01e0fb4782e6, Direction: request, MESSAGE = Executing default ''fault'' sequence, ERROR_CODE = 0, ERROR_MESSAGE = Error while building message, Envelope: <?xml version=''1.0'' encoding=''utf-8''?><soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
nv:Body/></soapenv:Envelope>

Answer 1

Muchas gracias @RavindraRanwala y @ThusithaThilinaDayaratne por llevarme a la resolución de este problema.

Después de consultar los registros de conexión, parece que la API de Facebook responde con texto / tipo de contenido de JavaScript. No tenía ningún generador de mensajes / formateador habilitado dentro del ESB para manejar este tipo de contenido, por lo que el proceso terminó fallando. Todo lo que tenía que hacer era abrir el archivo de configuración axis2.xml y anexar los siguientes creadores de mensajes:

<!--JSON Message Builders-->
<messageBuilder contentType="application/json" class="org.apache.synapse.commons.json.JsonStreamBuilder"/>
<messageBuilder contentType="text/javascript" class="org.apache.synapse.commons.json.JsonStreamBuilder"/>

... y formateadores:

<!--JSON Message Formatters-->
<messageFormatter contentType="application/json" class="org.apache.synapse.commons.json.JsonStreamFormatter"/>
<messageFormatter contentType="text/javascript" class="org.apache.synapse.commons.json.JsonStreamFormatter"/>

La documentación más actualizada en el conector de Facebook parece estar en la página de GitHub, donde se aclara toda la información necesaria del constructor / formateador:

https://github.com/wso2/esb-connectors/tree/master/facebook/facebook-connector/facebook-connector-1.0.0