upload: adaptive payload buffer and packet chunk size for fast connections

[got3nks]

Summary

Two minimal changes to UploadClient.cpp that significantly improve upload throughput on fast connections by scaling two previously hardcoded constants with the actual slot data rate.

Adaptive payload buffer

Replaces the hardcoded 100 KiB per-client payload buffer with a rate-adaptive value:

const uint32 payloadBufferLimit = std::min(std::max(GetUploadDatarate() * 10u, 180u*1024u), 16u*1024u*1024u);

• Floor: 180 KiB — matches eMule's slow-connection baseline (EMBLOCKSIZE × 1)
• Scales to ~10 seconds worth of data at the current slot rate
• Ceiling: 16 MiB — prevents unbounded memory use

The 100 KiB stock buffer drains in ~10ms at 10 MB/s, leaving the socket queue empty while CreateNextBlockPackage() refills synchronously from disk. A larger buffer gives the main thread more headroom between disk reads.

Adaptive packet chunk size

Replaces the hardcoded 10 KiB packet split threshold with a rate-adaptive value:

const uint32 chunkSize = std::min(std::max(GetUploadDatarate() / 8u, 10240u), 131072u);

Applied in both CreateStandardPackets() and CreatePackedPackets().

• Floor: 10 KiB — preserves stock behaviour on slow connections
• Ceiling: 128 KiB — well within MAX_PACKET_SIZE (2 MB), compatible with all peers
• Larger packets reduce per-packet header overhead and throttler loop iterations at high speed

Backward compatibility

• Connections below ~80 KiB/s use exactly the same constants as stock aMule
• No wire protocol changes — compatible with all eMule/aMule clients
• Both changes are in UploadClient.cpp only, no throttler or socket layer touched

Test results

Tested on a 1 Gbps dedicated server running aMule in Docker:

• Before (stock aMule): ~450 KB/s per upload slot
• After: 7–8 MB/s per upload slot sustained

Note: peak results were achieved together with #436 (uint16 → uint32 speed limits), which removes the 524 Mbps configuration cap. This PR alone still provides significant improvement on connections below that limit.

Recommended configuration for fast connections

For best results, set an explicit MaxUpload value rather than relying on unlimited mode (MaxUpload=0). In unlimited mode aMule ramps up slots slowly based on observed throughput; an explicit value ensures the full slot count is available immediately.

• Stock aMule: MaxUpload=65534 (maximum before the uint16 overflow threshold, ~524 Mbps)
• With Widen speed limit types from uint16 to uint32 #436 applied: MaxUpload=100000 or higher for gigabit connections

Setting MaxUpload to your actual uplink capacity also gives the slot allocation algorithm accurate data to work with.