Core Engine

Download Engine

The dlman-core crate is the heart of DLMan. It handles all download operations and is shared between the desktop app and CLI.

Multi-Segment

Split files into up to 32 parallel segments

SQLite Persistence

Progress saved atomically after every chunk

Rate Limiting

Token bucket algorithm for smooth throttling

Queue Scheduler

Time-based start/stop with day-of-week rules

Auto-Retry

Exponential backoff with configurable retries

Crash-Safe

Resume from exact byte position after failures

Multi-Segment Downloads

When you download a file, DLMan splits it into multiple segments that download in parallel. Each segment uses its own HTTP connection with a Range header, writing directly to the correct file offset.

Download Process

Probe

HEAD request to get file size and check Accept-Ranges header

Plan

Calculate segment boundaries based on file size and settings

Spawn

Launch async segment worker tasks, each with its own HTTP connection

Stream

Stream data in 8KB chunks, writing to correct file offset with seek

Progress

Report progress every 100ms via broadcast channels

Complete

All segments done — verify file integrity if checksum available

Segment Sizing

Segment count is automatically calculated based on file size:

File Size	Segments	Per Segment
< 1 MB	1	Full file
1 – 10 MB	2	~50%
10 – 100 MB	4	~25%
100 MB – 1 GB	8	~12.5%
> 1 GB	16	Variable

Pause & Resume

Pausing

Cancel all segment worker tasks
Save progress to SQLite immediately
Record downloaded_bytes per segment

Resuming

Load segment progress from SQLite
Restart workers from last byte position
Use Range: bytes=current-end header

Speed Limiting

DLMan uses a token bucket algorithm for smooth speed limiting. Tokens refill at the rate limit speed, and each segment must acquire tokens before downloading more data.

Per-download

Highest priority — overrides queue and global limits

Per-queue

Applied to all downloads in the queue

Global

App-wide limit across all downloads

Queue Scheduler

The QueueScheduler runs as a background task, checking schedules every 30 seconds. It automatically starts and stops queues based on configured times and active days.

Schedule Check (every 30s)

For each queue with schedule.enabled = true:

·→ Is current day in schedule.days? If not, skip.

·→ Is current time ≥ start_time? Start queue.

·→ Is current time ≥ stop_time? Stop queue.

·→ Calculate countdown to next scheduled start.

Retry Policy

Setting	Value
Max retries	5
Initial delay	1s
Backoff	Exponential (1s, 2s, 4s, 8s, 16s)
Jitter	±10%

Error Handling

All operations return Result<T, DlmanError>. Errors are logged with context, saved to the download record, surfaced to the UI, and retried when possible.

Network

IO

NotFound

InvalidUrl

ResumeNotSupported

Database

Post-Download Actions

When a queue completes all downloads, these actions can trigger:

Notify

Send OS notification

Sleep

Put computer to sleep

Shutdown

Shutdown the computer

Hibernate

Hibernate the computer

RunCommand

Execute a custom shell command

Architecture →

System design overview

Contributing →

How to contribute to DLMan