Concatenate long strings from multiple records into one string - string

Question

I have a situation where I need to concatenate long strings from multiple records in an Oracle database into a single string. These long strings are portions of a larger XML string, and my ultimate goal is to be able to convert this XML into something resembling query results and pull out specific values.
The data would look something like this, with the MSG_LINE_TEXT field being VARCHAR2(4000). So if the total message is less than 4000 characters, then there'd only be one record. In theory, there could be an infinite number of records for each message, although the highest I've seen so far is 14 records, which means I need to be able to handle strings that are at least 56000 characters long.
MESSAGE_ID MSG_LINE_NUMBER MSG_LINE_TEXT
---------- --------------- --------------------------------
17415414 1 Some XML snippet here
17415414 2 Some XML snippet here
17415414 3 Some XML snippet here
17415414 4 Some XML snippet here
The total XML for one MESSAGE_ID might look something like this. There could be many App_Advice_Error tags, although this specific example only contains one.
<tXML>
<Header>
<Source>MANH_prod_wmsweb</Source>
<Action_Type />
<Sequence_Number />
<Company_ID>1</Company_ID>
<Msg_Locale />
<Version />
<Internal_Reference_ID>17415414</Internal_Reference_ID>
<Internal_Date_Time_Stamp>2021-02-09 13:45:22</Internal_Date_Time_Stamp>
<External_Reference_ID />
<External_Date_Time_Stamp />
<User_ID>ESBUSER</User_ID>
<Message_Type>RESPONSE</Message_Type>
</Header>
<Response>
<Persistent_State>0</Persistent_State>
<Error_Type>2</Error_Type>
<Resp_Code>501</Resp_Code>
<Response_Details>
<Application_Advice>
<Shipper_ID />
<Imported_Object_Type>ASN</Imported_Object_Type>
<Response_Type>Error</Response_Type>
<Transaction_Date>2/9/21 13:45</Transaction_Date>
<Application_Ackg_Code>TE</Application_Ackg_Code>
<Business_Unit></Business_Unit>
<Tran_Set_Identifier_Code></Tran_Set_Identifier_Code>
<Transaction_Purpose_Code>11</Transaction_Purpose_Code>
<Imported_Message_Id></Imported_Message_Id>
<Imported_Object_Id>Reference Number Here</Imported_Object_Id>
<Additional_References>
<Additional_Reference_Info>
<Reference_Type>BusinessPartner</Reference_Type>
<Reference_ID></Reference_ID>
</Additional_Reference_Info>
</Additional_References>
<App_Advice_Errors>
<App_Advice_Error>
<App_Error_Text>Some error text here</App_Error_Text>
<Error_Message_Tokens>
<Error_Message_Token>Object that errored out</Error_Message_Token>
</Error_Message_Tokens>
<App_Err_Cond_Code>6100234</App_Err_Cond_Code>
</App_Advice_Error>
</App_Advice_Errors>
<Imported_Data></Imported_Data>
</Application_Advice>
</Response_Details>
</Response>
</tXML>
The values that I'm most interested in pulling out are the App_Err_Cond_Code, Error_Message_Token, and App_Error_Text tags. I had tried using something like this:
extractvalue(xmltype(msg_line_text), '//XPath of Tag')
This works beautifully for stuff where the entire XML is less than 4000 characters, i.e. the entire XML is stored in a single record. The problem comes when there are multiple records, because each individual snippet of XML isn't a valid XML string on its own, and so XMLTYPE throws an error, hence the reason I'm trying to concatenate them all into a single string, which I can then use with the above method.
I've tried a variety of ways to do this - LISTAGG, XMLAGG, SYS_CONNECT_BY_PATH, as well as writing a custom function something like this:
with
function get_messages(pTranLogID number) return string
is
xml varchar2;
begin
xml := '';
for msg in (
select r.msg_line_text
from tran_log_response_message r, tran_log t
where
t.message_id = r.message_id
and t.tran_log_id = pTranLogID
order by r.msg_line_number
)
loop
xml := xml || msg.msg_line_text;
end loop;
return 'test';
end;
select
tran_log_id, get_messages(tran_log_id)
from
tran_log
where
tran_log_id = '20633610';
/
The problem is that every one of these methods complained that the string was too long. Does anyone have any other ideas? Or maybe a better approach to this problem?
Thanks.