simplexmq/spec/modules/Simplex/FileTransfer/Server/Env.md

Simplex.FileTransfer.Server.Env

XFTP server environment: configuration, storage quota tracking, and request routing.

Source: FileTransfer/Server/Env.hs

Non-obvious behavior

1. Startup storage accounting with quota warning

newXFTPServerEnv computes usedStorage by summing file sizes from the in-memory store at startup. If the computed usage exceeds the configured fileSizeQuota, a warning is logged but the server still starts. This allows the server to come up even if it's over quota (e.g., after a quota reduction), relying on expiration to reclaim space.

2. XFTPRequest ADT separates new files from commands

XFTPRequest has three constructors:

• XFTPReqNew: file creation (carries FileInfo, recipient keys, optional basic auth)
• XFTPReqCmd: command on an existing file (carries file ID, FileRec, and the command)
• XFTPReqPing: health check

This separation occurs after credential verification in Server.hs. XFTPReqNew bypasses entity lookup entirely since the file doesn't exist yet.

3. fileTimeout for upload deadline

fileTimeout in XFTPServerConfig sets the maximum time allowed for a single file upload (FPUT). The server wraps the receive operation in timeout fileTimeout. Default is 5 minutes (for 4MB chunks). This prevents slow or stalled uploads from holding server resources indefinitely.