HPCC-30353 Export SDS data using PTree content streaming

[wangkx]

Before this change, the data read from Dali stores into a temporary file before streaming to an ESP client. With this change, the data is directly streamed to the client.

Type of change:

• This change is a bug fix (non-breaking change which fixes an issue).
• This change is a new feature (non-breaking change which adds functionality).
• This change improves the code (refactor or other change that does not change the functionality)
• This change fixes warnings (the fix does not alter the functionality or the generated code)
• This change is a breaking change (fix or feature that will cause existing behavior to change).
• This change alters the query API (existing queries will have to be recompiled)

Checklist:

• My code follows the code style of this project.
  • My code does not create any new warnings from compiler, build system, or lint.
• The commit message is properly formatted and free of typos.
  • The commit message title makes sense in a changelog, by itself.
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• My change requires a change to the documentation.
  • I have updated the documentation accordingly, or...
  • I have created a JIRA ticket to update the documentation.
  • Any new interfaces or exported functions are appropriately commented.
• I have read the CONTRIBUTORS document.
• The change has been fully tested:
  • I have added tests to cover my changes.
  • All new and existing tests passed.
  • I have checked that this change does not introduce memory leaks.
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• I have given due consideration to all of the following potential concerns:
  • Scalability
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  • Security
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  • Existing deployed queries will not be broken
  • This change fixes the problem, not just the symptom
  • The target branch of this pull request is appropriate for such a change.
• There are no similar instances of the same problem that should be addressed
  • I have addressed them here
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• This is a user interface / front-end modification
  • I have tested my changes in multiple modern browsers
  • The component(s) render as expected

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Testing:

[github-actions]

https://track.hpccsystems.com/browse/HPCC-30353
Jira updated

[wangkx]

The 2 failing checks look like unrelated to the changes in this PR:
Docker smoketest build / build-images (pull_request) Failing after 45m:
#16 2478.2 CMake Error at scripts/cmake/vcpkg_execute_build_process.cmake:134 (message): ...
Test Build / Build Docker (centos-7, pull_request) (pull_request) Failing after 47m:
gmake[2]: *** [tools/vkey/CMakeFiles/vkey.dir/build.make:198: RelWithDebInfo/bin/vkey] Error 1

[wangkx]

@ghalliday please merge

[ghalliday]

@afishbeck looks like a good improvement. How often is this used (is 9.4 or master the best target?)

[afishbeck]

@ghalliday think of this service as a replacement backend for daliadmin type functionality. Although it actually makes it easier to access. Someone like you or myself might go to the ESP form for this, or use curl on the command line, and get some info out of DALI.

As this is more just an underlying improvement rather than bug fix you could certainly target master.