REST POST /api/channels accepts a structurally-invalid channel; it deploys "healthy" but sends corrupt (undefined) content

[MichaelLeeHobbs]

OIE bug: POST /api/channels accepts a structurally-invalid channel; it deploys "healthy" but sends corrupt content

Component: REST API — ChannelServlet POST /api/channels
Version observed: Open Integration Engine 4.5.2 (openintegrationengine/engine:4.5.2-alpine)
Severity: data-integrity — a channel that reports deployed and healthy silently sends corrupt messages.
Scope: reproduces on a stock OIE with no extensions installed, using the built-in TCP Sender.

The issue

POST /api/channels accepts a channel whose XML is structurally incomplete/invalid — it neither
validates/rejects it nor normalizes it. The server then deploys it (channel and destination both STARTED,
no warnings), but the destination sends the message content as the literal string undefined on the
wire — a corrupt message — with no error anywhere.

Opening the same channel in the Administrator and saving it (which normalizes the config) fixes it. That
confirms the POSTed config was genuinely invalid and that the REST endpoint should have caught it — the
Administrator's create/save path validates/normalizes; the REST create path does neither.

What "invalid" means here

Compared with the Administrator-normalized version of the same channel, the accepted XML has:

Field	Accepted by REST	Administrator-normalized
transmissionModeProperties class	com.mirth.connect.model.transmission.framemode.FrameModeProperties (base)	com.mirth.connect.plugins.mllpmode.MLLPModeProperties (+ useMLLPv2/ackBytes/nackBytes/maxRetries)
<pluginProperties/> on each connector	absent	present (empty)
queueBufferSize	0	1000

Correcting the transmission mode and queueBufferSize alone does not resolve the undefined output;
the Administrator's full normalization (which also adds <pluginProperties/>) does.

Reproduce

Stock OIE 4.5.2, no extensions, plus any MLLP listener at the destination's host:port:

1. POST /api/channels with the attached stock-channel-incomplete.xml (Channel Reader source →
   built-in TCP Sender destination, template ${message.encodedData}). → HTTP 200 (accepted).
2. POST /api/channels/stock-hl7v2-test/_deploy. → 204, channel + destination STARTED, no warnings.
3. Send any message — REST POST /channels/{id}/messages?destinationMetaDataId=1 or the Administrator's
   Send Message. → the listener receives the literal bytes undefined, not the message. Status SENT,
   no error.
4. Open the channel in the Administrator, make a trivial edit, save, redeploy. Repeat step 3 → the listener
   now receives the correct message.

Observed here (stock OIE 4.5.2, no extensions): step 1 → HTTP 200; step 2 → 204, STARTED; step 3 →
listener received undefined.

Expected

POST /api/channels should reject a structurally-invalid channel with a clear error (or normalize it the
way the Administrator's save does) — not accept it, report it healthy, and silently emit corrupt content.

Attachment

• stock-channel-incomplete.xml — the exact XML that was accepted.

stock-channel-incomplete.xml — the exact XML that was accepted

<channel version="4.5.2">
  <id>stock-hl7v2-test</id>
  <nextMetaDataId>1</nextMetaDataId>
  <name>stock-hl7v2-test</name>
  <revision>1</revision>
  <sourceConnector version="4.5.2">
    <metaDataId>0</metaDataId>
    <name>sourceConnector</name>
    <properties class="com.mirth.connect.connectors.vm.VmReceiverProperties" version="4.5.2">
      <sourceConnectorProperties version="4.5.2">
        <responseVariable>None</responseVariable>
        <respondAfterProcessing>true</respondAfterProcessing>
        <processBatch>false</processBatch>
        <firstResponse>false</firstResponse>
        <processingThreads>1</processingThreads>
        <resourceIds class="linked-hash-map">
          <entry>
            <string>Default Resource</string>
            <string>[Default Resource]</string>
          </entry>
        </resourceIds>
        <queueBufferSize>0</queueBufferSize>
      </sourceConnectorProperties>
    </properties>
    <transformer version="4.5.2">
      <elements/>
      <inboundDataType>HL7V2</inboundDataType>
      <outboundDataType>HL7V2</outboundDataType>
      <inboundProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2DataTypeProperties" version="4.5.2">
        <serializationProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2SerializationProperties" version="4.5.2">
          <handleRepetitions>true</handleRepetitions>
          <handleSubcomponents>true</handleSubcomponents>
          <useStrictParser>false</useStrictParser>
          <useStrictValidation>false</useStrictValidation>
          <stripNamespaces>false</stripNamespaces>
          <segmentDelimiter>\r</segmentDelimiter>
          <convertLineBreaks>true</convertLineBreaks>
        </serializationProperties>
        <deserializationProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2DeserializationProperties" version="4.5.2">
          <useStrictParser>false</useStrictParser>
          <useStrictValidation>false</useStrictValidation>
          <segmentDelimiter>\r</segmentDelimiter>
        </deserializationProperties>
        <batchProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2BatchProperties" version="4.5.2">
          <splitType>MSH_Segment</splitType>
          <batchScript></batchScript>
        </batchProperties>
        <responseGenerationProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2ResponseGenerationProperties" version="4.5.2">
          <segmentDelimiter>\r</segmentDelimiter>
          <successfulACKCode>AA</successfulACKCode>
          <successfulACKMessage></successfulACKMessage>
          <errorACKCode>AE</errorACKCode>
          <errorACKMessage>An Error Occurred Processing Message.</errorACKMessage>
          <rejectedACKCode>AR</rejectedACKCode>
          <rejectedACKMessage>Message Rejected.</rejectedACKMessage>
          <msh15ACKAccept>false</msh15ACKAccept>
          <dateFormat>yyyyMMddHHmmss.SSS</dateFormat>
        </responseGenerationProperties>
        <responseValidationProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2ResponseValidationProperties" version="4.5.2">
          <successfulACKCode>AA,CA</successfulACKCode>
          <errorACKCode>AE,CE</errorACKCode>
          <rejectedACKCode>AR,CR</rejectedACKCode>
          <validateMessageControlId>true</validateMessageControlId>
          <originalMessageControlId>Destination_Encoded</originalMessageControlId>
          <originalIdMapVariable></originalIdMapVariable>
        </responseValidationProperties>
      </inboundProperties>
      <outboundProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2DataTypeProperties" version="4.5.2">
        <serializationProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2SerializationProperties" version="4.5.2">
          <handleRepetitions>true</handleRepetitions>
          <handleSubcomponents>true</handleSubcomponents>
          <useStrictParser>false</useStrictParser>
          <useStrictValidation>false</useStrictValidation>
          <stripNamespaces>false</stripNamespaces>
          <segmentDelimiter>\r</segmentDelimiter>
          <convertLineBreaks>true</convertLineBreaks>
        </serializationProperties>
        <deserializationProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2DeserializationProperties" version="4.5.2">
          <useStrictParser>false</useStrictParser>
          <useStrictValidation>false</useStrictValidation>
          <segmentDelimiter>\r</segmentDelimiter>
        </deserializationProperties>
        <batchProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2BatchProperties" version="4.5.2">
          <splitType>MSH_Segment</splitType>
          <batchScript></batchScript>
        </batchProperties>
        <responseGenerationProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2ResponseGenerationProperties" version="4.5.2">
          <segmentDelimiter>\r</segmentDelimiter>
          <successfulACKCode>AA</successfulACKCode>
          <successfulACKMessage></successfulACKMessage>
          <errorACKCode>AE</errorACKCode>
          <errorACKMessage>An Error Occurred Processing Message.</errorACKMessage>
          <rejectedACKCode>AR</rejectedACKCode>
          <rejectedACKMessage>Message Rejected.</rejectedACKMessage>
          <msh15ACKAccept>false</msh15ACKAccept>
          <dateFormat>yyyyMMddHHmmss.SSS</dateFormat>
        </responseGenerationProperties>
        <responseValidationProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2ResponseValidationProperties" version="4.5.2">
          <successfulACKCode>AA,CA</successfulACKCode>
          <errorACKCode>AE,CE</errorACKCode>
          <rejectedACKCode>AR,CR</rejectedACKCode>
          <validateMessageControlId>true</validateMessageControlId>
          <originalMessageControlId>Destination_Encoded</originalMessageControlId>
          <originalIdMapVariable></originalIdMapVariable>
        </responseValidationProperties>
      </outboundProperties>
    </transformer>
    <filter version="4.5.2">
      <elements/>
    </filter>
    <transportName>Channel Reader</transportName>
    <mode>SOURCE</mode>
    <enabled>true</enabled>
    <waitForPrevious>true</waitForPrevious>
  </sourceConnector>
  <destinationConnectors>
    <connector version="4.5.2">
      <metaDataId>1</metaDataId>
      <name>Destination 1</name>
      <properties class="com.mirth.connect.connectors.tcp.TcpDispatcherProperties" version="4.5.2">
        <destinationConnectorProperties version="4.5.2">
          <queueEnabled>true</queueEnabled>
          <sendFirst>false</sendFirst>
          <retryIntervalMillis>10000</retryIntervalMillis>
          <regenerateTemplate>false</regenerateTemplate>
          <retryCount>0</retryCount>
          <rotate>false</rotate>
          <includeFilterTransformer>false</includeFilterTransformer>
          <threadCount>1</threadCount>
          <threadAssignmentVariable></threadAssignmentVariable>
          <validateResponse>true</validateResponse>
          <resourceIds class="linked-hash-map">
            <entry>
              <string>Default Resource</string>
              <string>[Default Resource]</string>
            </entry>
          </resourceIds>
          <queueBufferSize>0</queueBufferSize>
          <reattachAttachments>true</reattachAttachments>
        </destinationConnectorProperties>
        <transmissionModeProperties class="com.mirth.connect.model.transmission.framemode.FrameModeProperties">
          <pluginPointName>MLLP</pluginPointName>
          <startOfMessageBytes>0B</startOfMessageBytes>
          <endOfMessageBytes>1C0D</endOfMessageBytes>
        </transmissionModeProperties>
        <serverMode>false</serverMode>
        <remoteAddress>sink</remoteAddress>
        <remotePort>6661</remotePort>
        <overrideLocalBinding>false</overrideLocalBinding>
        <localAddress>0.0.0.0</localAddress>
        <localPort>0</localPort>
        <sendTimeout>5000</sendTimeout>
        <bufferSize>65536</bufferSize>
        <maxConnections>10</maxConnections>
        <keepConnectionOpen>false</keepConnectionOpen>
        <checkRemoteHost>false</checkRemoteHost>
        <responseTimeout>2000</responseTimeout>
        <ignoreResponse>false</ignoreResponse>
        <queueOnResponseTimeout>true</queueOnResponseTimeout>
        <dataTypeBinary>false</dataTypeBinary>
        <charsetEncoding>DEFAULT_ENCODING</charsetEncoding>
        <template>${message.encodedData}</template>
      </properties>
      <transformer version="4.5.2">
        <elements/>
        <inboundDataType>HL7V2</inboundDataType>
        <outboundDataType>HL7V2</outboundDataType>
        <inboundProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2DataTypeProperties" version="4.5.2">
          <serializationProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2SerializationProperties" version="4.5.2">
            <handleRepetitions>true</handleRepetitions>
            <handleSubcomponents>true</handleSubcomponents>
            <useStrictParser>false</useStrictParser>
            <useStrictValidation>false</useStrictValidation>
            <stripNamespaces>false</stripNamespaces>
            <segmentDelimiter>\r</segmentDelimiter>
            <convertLineBreaks>true</convertLineBreaks>
          </serializationProperties>
          <deserializationProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2DeserializationProperties" version="4.5.2">
            <useStrictParser>false</useStrictParser>
            <useStrictValidation>false</useStrictValidation>
            <segmentDelimiter>\r</segmentDelimiter>
          </deserializationProperties>
          <batchProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2BatchProperties" version="4.5.2">
            <splitType>MSH_Segment</splitType>
            <batchScript></batchScript>
          </batchProperties>
          <responseGenerationProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2ResponseGenerationProperties" version="4.5.2">
            <segmentDelimiter>\r</segmentDelimiter>
            <successfulACKCode>AA</successfulACKCode>
            <successfulACKMessage></successfulACKMessage>
            <errorACKCode>AE</errorACKCode>
            <errorACKMessage>An Error Occurred Processing Message.</errorACKMessage>
            <rejectedACKCode>AR</rejectedACKCode>
            <rejectedACKMessage>Message Rejected.</rejectedACKMessage>
            <msh15ACKAccept>false</msh15ACKAccept>
            <dateFormat>yyyyMMddHHmmss.SSS</dateFormat>
          </responseGenerationProperties>
          <responseValidationProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2ResponseValidationProperties" version="4.5.2">
            <successfulACKCode>AA,CA</successfulACKCode>
            <errorACKCode>AE,CE</errorACKCode>
            <rejectedACKCode>AR,CR</rejectedACKCode>
            <validateMessageControlId>true</validateMessageControlId>
            <originalMessageControlId>Destination_Encoded</originalMessageControlId>
            <originalIdMapVariable></originalIdMapVariable>
          </responseValidationProperties>
        </inboundProperties>
        <outboundProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2DataTypeProperties" version="4.5.2">
          <serializationProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2SerializationProperties" version="4.5.2">
            <handleRepetitions>true</handleRepetitions>
            <handleSubcomponents>true</handleSubcomponents>
            <useStrictParser>false</useStrictParser>
            <useStrictValidation>false</useStrictValidation>
            <stripNamespaces>false</stripNamespaces>
            <segmentDelimiter>\r</segmentDelimiter>
            <convertLineBreaks>true</convertLineBreaks>
          </serializationProperties>
          <deserializationProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2DeserializationProperties" version="4.5.2">
            <useStrictParser>false</useStrictParser>
            <useStrictValidation>false</useStrictValidation>
            <segmentDelimiter>\r</segmentDelimiter>
          </deserializationProperties>
          <batchProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2BatchProperties" version="4.5.2">
            <splitType>MSH_Segment</splitType>
            <batchScript></batchScript>
          </batchProperties>
          <responseGenerationProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2ResponseGenerationProperties" version="4.5.2">
            <segmentDelimiter>\r</segmentDelimiter>
            <successfulACKCode>AA</successfulACKCode>
            <successfulACKMessage></successfulACKMessage>
            <errorACKCode>AE</errorACKCode>
            <errorACKMessage>An Error Occurred Processing Message.</errorACKMessage>
            <rejectedACKCode>AR</rejectedACKCode>
            <rejectedACKMessage>Message Rejected.</rejectedACKMessage>
            <msh15ACKAccept>false</msh15ACKAccept>
            <dateFormat>yyyyMMddHHmmss.SSS</dateFormat>
          </responseGenerationProperties>
          <responseValidationProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2ResponseValidationProperties" version="4.5.2">
            <successfulACKCode>AA,CA</successfulACKCode>
            <errorACKCode>AE,CE</errorACKCode>
            <rejectedACKCode>AR,CR</rejectedACKCode>
            <validateMessageControlId>true</validateMessageControlId>
            <originalMessageControlId>Destination_Encoded</originalMessageControlId>
            <originalIdMapVariable></originalIdMapVariable>
          </responseValidationProperties>
        </outboundProperties>
      </transformer>
      <responseTransformer version="4.5.2">
        <elements/>
        <inboundDataType>HL7V2</inboundDataType>
        <outboundDataType>HL7V2</outboundDataType>
        <inboundProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2DataTypeProperties" version="4.5.2">
          <serializationProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2SerializationProperties" version="4.5.2">
            <handleRepetitions>true</handleRepetitions>
            <handleSubcomponents>true</handleSubcomponents>
            <useStrictParser>false</useStrictParser>
            <useStrictValidation>false</useStrictValidation>
            <stripNamespaces>false</stripNamespaces>
            <segmentDelimiter>\r</segmentDelimiter>
            <convertLineBreaks>true</convertLineBreaks>
          </serializationProperties>
          <deserializationProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2DeserializationProperties" version="4.5.2">
            <useStrictParser>false</useStrictParser>
            <useStrictValidation>false</useStrictValidation>
            <segmentDelimiter>\r</segmentDelimiter>
          </deserializationProperties>
          <batchProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2BatchProperties" version="4.5.2">
            <splitType>MSH_Segment</splitType>
            <batchScript></batchScript>
          </batchProperties>
          <responseGenerationProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2ResponseGenerationProperties" version="4.5.2">
            <segmentDelimiter>\r</segmentDelimiter>
            <successfulACKCode>AA</successfulACKCode>
            <successfulACKMessage></successfulACKMessage>
            <errorACKCode>AE</errorACKCode>
            <errorACKMessage>An Error Occurred Processing Message.</errorACKMessage>
            <rejectedACKCode>AR</rejectedACKCode>
            <rejectedACKMessage>Message Rejected.</rejectedACKMessage>
            <msh15ACKAccept>false</msh15ACKAccept>
            <dateFormat>yyyyMMddHHmmss.SSS</dateFormat>
          </responseGenerationProperties>
          <responseValidationProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2ResponseValidationProperties" version="4.5.2">
            <successfulACKCode>AA,CA</successfulACKCode>
            <errorACKCode>AE,CE</errorACKCode>
            <rejectedACKCode>AR,CR</rejectedACKCode>
            <validateMessageControlId>true</validateMessageControlId>
            <originalMessageControlId>Destination_Encoded</originalMessageControlId>
            <originalIdMapVariable></originalIdMapVariable>
          </responseValidationProperties>
        </inboundProperties>
        <outboundProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2DataTypeProperties" version="4.5.2">
          <serializationProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2SerializationProperties" version="4.5.2">
            <handleRepetitions>true</handleRepetitions>
            <handleSubcomponents>true</handleSubcomponents>
            <useStrictParser>false</useStrictParser>
            <useStrictValidation>false</useStrictValidation>
            <stripNamespaces>false</stripNamespaces>
            <segmentDelimiter>\r</segmentDelimiter>
            <convertLineBreaks>true</convertLineBreaks>
          </serializationProperties>
          <deserializationProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2DeserializationProperties" version="4.5.2">
            <useStrictParser>false</useStrictParser>
            <useStrictValidation>false</useStrictValidation>
            <segmentDelimiter>\r</segmentDelimiter>
          </deserializationProperties>
          <batchProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2BatchProperties" version="4.5.2">
            <splitType>MSH_Segment</splitType>
            <batchScript></batchScript>
          </batchProperties>
          <responseGenerationProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2ResponseGenerationProperties" version="4.5.2">
            <segmentDelimiter>\r</segmentDelimiter>
            <successfulACKCode>AA</successfulACKCode>
            <successfulACKMessage></successfulACKMessage>
            <errorACKCode>AE</errorACKCode>
            <errorACKMessage>An Error Occurred Processing Message.</errorACKMessage>
            <rejectedACKCode>AR</rejectedACKCode>
            <rejectedACKMessage>Message Rejected.</rejectedACKMessage>
            <msh15ACKAccept>false</msh15ACKAccept>
            <dateFormat>yyyyMMddHHmmss.SSS</dateFormat>
          </responseGenerationProperties>
          <responseValidationProperties class="com.mirth.connect.plugins.datatypes.hl7v2.HL7v2ResponseValidationProperties" version="4.5.2">
            <successfulACKCode>AA,CA</successfulACKCode>
            <errorACKCode>AE,CE</errorACKCode>
            <rejectedACKCode>AR,CR</rejectedACKCode>
            <validateMessageControlId>true</validateMessageControlId>
            <originalMessageControlId>Destination_Encoded</originalMessageControlId>
            <originalIdMapVariable></originalIdMapVariable>
          </responseValidationProperties>
        </outboundProperties>
      </responseTransformer>
      <filter version="4.5.2">
        <elements/>
      </filter>
      <transportName>TCP Sender</transportName>
      <mode>DESTINATION</mode>
      <enabled>true</enabled>
      <waitForPrevious>true</waitForPrevious>
    </connector>
  </destinationConnectors>
  <properties version="4.5.2">
    <clearGlobalChannelMap>true</clearGlobalChannelMap>
    <messageStorageMode>DEVELOPMENT</messageStorageMode>
    <encryptData>false</encryptData>
    <encryptAttachments>false</encryptAttachments>
    <encryptCustomMetaData>false</encryptCustomMetaData>
    <removeContentOnCompletion>false</removeContentOnCompletion>
    <removeOnlyFilteredOnCompletion>false</removeOnlyFilteredOnCompletion>
    <removeAttachmentsOnCompletion>false</removeAttachmentsOnCompletion>
    <initialState>STARTED</initialState>
    <storeAttachments>true</storeAttachments>
    <metaDataColumns/>
    <attachmentProperties version="4.5.2">
      <type>None</type>
      <properties/>
    </attachmentProperties>
    <resourceIds class="linked-hash-map">
      <entry>
        <string>Default Resource</string>
        <string>[Default Resource]</string>
      </entry>
    </resourceIds>
  </properties>
</channel>

[e210]

Great report, and the attached XML made it super easy to reproduce — thanks! I was curious to understand what was really going on here, so I spent some time digging into it (with a good deal of help from Claude 😉) and I think I found the actual root cause. Spoiler: it's not pluginProperties.

TL;DR: the field whose absence produces the undefined output is <preprocessingScript>. pluginProperties, transmissionModeProperties and queueBufferSize are innocent bystanders.

What's actually happening

1. You're right that POST /api/channels does zero validation/normalization — DefaultChannelController.updateChannel only checks name uniqueness. Everything missing from the XML is just null on the model, including preprocessingScript.

2. At deploy time the null script gets string-concatenated into the generated JS wrapper in JavaScriptBuilder.generateScript:

   builder.append("function doScript() {\n" + script + " \n}\n");

   With script == null, Java happily produces a function whose body is the literal expression null. 😅

3. compileAndAddScript only keeps a channel preprocessor if it differs from the default (return message;). A body of null does differ... so this garbage script gets compiled and cached as a "custom" preprocessor. (A channel saved from the Administrator carries the default script explicitly → equal to default → dropped from the cache → preprocessor skipped. That's exactly why open-and-save in the Administrator fixes it.)

4. Here's where undefined is born: doScript() returns JS undefined, and the guard in executePreprocessorScripts is if (result != null) — but Rhino's Undefined is not Java null, so it sails through and Context.jsToJava(result, String.class) turns it into the literal string "undefined". That becomes the processed raw.

5. From there it's all downhill: the lenient HL7v2 parser swallows "undefined" without blinking, it becomes the encoded data, and ${message.encodedData} puts it on the wire. SENT, no errors, corrupt message.

How I verified it (e2e, not just code reading)

Stock 4.5.2 container + a little MLLP sink logging raw bytes:

Channel variant	Bytes on the wire
Attached XML as-is	\x0b undefined \x1c\r
+ only the default <preprocessingScript> (still no pluginProperties, base FrameModeProperties, queueBufferSize 0)	correct HL7 message 🎉
+ only <pluginProperties/> (no preprocessingScript)	\x0b undefined \x1c\r

Rows 2–3 pretty much settle it. The reason the full Administrator normalization fixed it in your test is that it also adds the default channel scripts, not just pluginProperties. Also worth noting: the corruption happens at the source connector (the destination's raw input is already undefined), so this bites every connector type, not just TCP Sender.

Bonus finding from the same session: I accidentally PUT an XML with <pluginProperties/> in a structurally wrong spot (directly under <connector>) and the API happily returned 200 {"boolean":true}... while silently storing a gutted, disabled channel. So the missing-validation surface is even broader than the issue describes.

Suggested fixes (in order of bang-for-buck)

1. Guard against Undefined in executePreprocessorScripts (and the postprocessor twin) — treat it as "no result". This alone kills the data corruption, including for user scripts that just don't return anything.
2. Treat null/blank scripts as absent in compileAndAddScript/generateScript, instead of compiling a literal null body.
3. Validate/normalize in POST /api/channels (what this issue asks for) — apply server-side defaults to missing structural fields before persisting.

[MichaelLeeHobbs]

@e210 Amazing work. Made my head hurt, lol.