Current Status (Research Findings)

Item	Current Status
Content server (metadata protocol)	src/network/core/config.cpp NetworkContentServerConnectionString(): environment variable OTTD_CONTENT_SERVER_CS, default content.openttd.org (TCP port 3978)
Download mirror	NetworkContentMirrorUriString(): environment variable OTTD_CONTENT_MIRROR_URI, default https://binaries.openttd.org/bananas
Download method	network_content.cpp DownloadSelectedContentHTTP(): a single POST request with all content IDs → mirror returns a file header list (id,type,filesize,url per line) → serial download of each file one by one (one GET connection per file) → AfterDownload() gunzip + tar extraction
Thread model	HTTP layer (WinHttp) runs in background threads, but file downloads are serialized; no mirror list, no in-game settings, no parallelism

This Feature Implementation

1. New Settings (network_settings.ini + settings_type.h)

• network.content_server (SLE_STR, default empty = use official source)
• network.content_mirrors (SLE_STR, comma-separated multiple mirror URIs, default empty = official mirror)

Priority: environment variable > game setting > official default.

2. Configuration Parsing (src/network/core/config.cpp/h)

• NetworkContentServerConnectionString() reads the setting;
• New NetworkContentMirrorUris() parses comma-separated list (trim whitespace, skip empty items, fallback to official source);
• NetworkContentMirrorUriString() changed to return the first item in the list.

3. Parallel Download (src/network/network_content.h/.cpp)

• New ContentFileDownload (single pending download file: id/type/filesize/url/filename);
• New ContentDownloadSession : HTTPCallback (independent download state and callback per file; IsCancelled links to handler);
• DownloadSelectedContentHTTP(): POST to mirrors[mirror_index] → ParseResponseHeaders() parses all file headers at once → StartDownloadSessions() starts up to 4 parallel sessions (CONTENT_DOWNLOAD_PARALLEL), each session picks the next pending file upon completion;
• Failure retry chain: session failure/mirror request failure → next mirror retry request → all mirrors failed → fallback to legacy TCP protocol (DownloadSelectedContentFallback);
• Graceful cleanup: on failure/cancel, set download_cancelled, wait for all in-flight sessions to finish (OnAllSessionsDone) before retry or fallback, avoiding dangling callbacks;
• ResetMirrorIndex(): new downloads start from the first mirror (called when triggered from GUI).

Involved Files

• src/table/settings/network_settings.ini (2 new settings)
• src/settings_type.h (2 new fields in NetworkSettings)
• src/network/core/config.cpp / config.h (mirror list parsing)
• src/network/network_content.h / .cpp (parallel sessions)
• src/network/network_content_gui.cpp (reset mirror index before download)

Verification Points

1. After filling network.content_mirrors with multiple URIs (comma-separated), content downloads should work and download multiple files in parallel (observe download progress/capture multiple concurrent connections);
2. Network failure/wrong mirror should automatically try the next mirror, finally fallback to legacy protocol;
3. Cancelling during download should not leave .tar.gz partial files;
4. Must be verified on real machine compilation (this repo has no build environment, code not compiled).

Known Limitations

• Parallelism hardcoded to 4 (CONTENT_DOWNLOAD_PARALLEL), can be made a setting later;
• Mirror protocol depends on the official bananas API format (POST id list returns file header list).