Wait for http request completion with condition variable

[pifopi]

Hello !

It's related to the memory issue I reported on discord. The root cause is that a http_request ptr is stored in several lambda but the lifecycle of the lambda is bigger than the life of http_request

This one is fine [processor, rv, hci, this, owner, start, _url](https_client* client) {
This one isn't owner->queue_work(0, [owner, this, result, hci, _url]() {

In the second lambda and depending on when you shutdown dpp (if you do it very early, before shards are started), you will delete this http_request before the lambda finish and then it's undefined behaviour as you kept a this ptr. I tried to make a shared_ptr implementation to fix that but it's leaking memory like crazy (like before the fix that created this crash 0d5e932). I then tested this wait for completion and it works. I added custom logs to confirm that the wait saved me from crashing

http_request::outer lambda start :dpp::http_request@0x19770c20af0: completed=false
http_request::outer lambda stop :dpp::http_request@0x19770c20af0: completed=false
http_request::inner lambda start :dpp::http_request@0x19770c20af0: completed=false
http_request::inner lambda stop :dpp::http_request@0x19770c20af0: completed=true
http_request::outer lambda start :dpp::http_request@0x19770bde310: completed=false
http_request::outer lambda stop :dpp::http_request@0x19770bde310: completed=false`
http_request::inner lambda start :dpp::http_request@0x19770bde310: completed=false
[Sun Dec 14 16:04:05 2025] DEBUG: Cluster: 998 of 1000 session starts remaining
[Sun Dec 14 16:04:05 2025] INFO: Auto Shard: Bot requires 1 shard
[Sun Dec 14 16:04:05 2025] DEBUG: Starting with 1 shards...
[Sun Dec 14 16:04:05 2025] DEBUG: Connecting new session...
[Sun Dec 14 16:04:05 2025] INFO: Shard id 0 (1/1) ready!
[Sun Dec 14 16:04:05 2025] DEBUG: Resume URL for session cccfaf4f25ad5336dfdbbc1c9c8ad29d is wss://gateway-us-east1-d.discord.gg (host: gateway-us-east1-d.discord.gg)
http_request::~http_request begin this:dpp::http_request@0x19770c20af0: completed=true
http_request::~http_request end this:dpp::http_request@0x19770c20af0: completed=true
http_request::~http_request begin this:dpp::http_request@0x19770bde310: completed=false
[Sun Dec 14 16:04:10 2025] DEBUG: Shards started.
http_request::inner lambda stop :dpp::http_request@0x19770bde310: completed=true
http_request::~http_request end this:dpp::http_request@0x19770bde310: completed=true

Code change checklist

• I have ensured that all methods and functions are fully documented using doxygen style comments.
• My code follows the coding style guide.
• I tested that my change works before raising the PR.
• I have ensured that I did not break any existing API calls.
• I have not built my pull request using AI, a static analysis tool or similar without any human oversight.

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[pifopi]

It is better than #1522 but I'm keeping both PR to be able to compare

[pifopi]

Putting this as a draft while I figure out issues with unit tests