Protocol Support

Falcon organizes transfer capabilities in layers around one engine: core transfer protocols are enabled by default, P2P and multi-source capabilities run on the same engine, private protocol families are optional compatibility plugins, and object storage plus resource browsing are provided by the storage package. The status below reflects the current codebase and top-level build configuration (FALCON_ENABLE_* in CMakeLists.txt).

Supported protocols

Layer	Protocol	Default	Notes
1 · Core transfer	HTTP/HTTPS	On	V1/libcurl and V2 event-driven engines, resume, segmented downloads, proxies
1 · Core transfer	FTP/FTPS	On	Active/passive modes, REST resume
1 · Core transfer	SFTP	On (requires libssh2)	known_hosts verification, resume
1 · Core transfer	WebDAV	On	dav/davs; the storage layer also provides a WebDAV browser
2 · P2P and multi-source	BitTorrent/Magnet	On (requires libtorrent)	Piece-level P2P, seeding, DHT, NAT port mapping
2 · P2P and multi-source	Metalink	On	RFC 5854 .meta4 / Metalink3 .metalink, multi-mirror P2SP segmentation with pre-publish hash verification
3 · Compatibility plugins	Thunder / QQDL / FlashGet / ED2K / HLS-DASH	Optional	Off by default; enable through FALCON_ENABLE_* as needed
Resource access	S3 / OSS / COS / Kodo / Upyun	On	Object storage (SigV4), MinIO / RustFS private gateways, remote browsing, and resource search

Basic protocols

HTTP/HTTPS

The most common download protocol, with comprehensive Falcon support:

• Resume
• Multi-threaded segmented downloads
• Speed limiting
• Custom HTTP headers
• Proxy support
• Authentication support

Read the full documentation →

FTP/FTPS

Traditional file transfer:

• Active and passive modes
• Anonymous and authenticated login
• FTPS (explicit TLS) support

Read the full documentation →

P2P protocols

BitTorrent

BitTorrent is a P2P capability enabled by default, with libtorrent handling the data plane:

• Magnet links and .torrent files
• DHT (native libtorrent), LSD, UPnP, NAT-PMP
• Optional file selection, seeding (seed-ratio / seed-time)
• Graceful fallback to a pure-C++ experimental mode without libtorrent

Read the full documentation →

ED2K

The codebase contains ED2K-related implementations, but the default build normally disables them:

• File-link support
• Server connections
• Source exchange
• AICH verification

Private protocols

Thunder

The codebase retains private-protocol implementations:

• Classic thunder:// links
• Offline thunderxl:// links

Read the full documentation →

QQDL (QQ Xuanfeng)

Tencent's download protocol:

• Standard qqlink:// links
• Links with a GID

FlashGet

The legacy downloader protocol:

• Full flashget:// format
• Short fg:// format

Streaming protocols

HLS/DASH

The codebase retains HLS/DASH-related implementations:

• .m3u8 playlist parsing
• .mpd manifest recognition
• Segment-by-segment download and merge
• Relative-address resolution inside playlists

Read the full documentation →

Enabling protocols at build time

Control compiled protocols with CMake options (the first six default to ON and the last five to OFF):

cmake -B build \
  -DFALCON_ENABLE_HTTP=ON \
  -DFALCON_ENABLE_FTP=ON \
  -DFALCON_ENABLE_BITTORRENT=ON \
  -DFALCON_ENABLE_SFTP=ON \
  -DFALCON_ENABLE_WEBDAV=ON \
  -DFALCON_ENABLE_METALINK=ON \
  -DFALCON_ENABLE_THUNDER=ON \
  -DFALCON_ENABLE_QQDL=ON \
  -DFALCON_ENABLE_FLASHGET=ON \
  -DFALCON_ENABLE_ED2K=ON \
  -DFALCON_ENABLE_HLS=ON

Missing dependencies degrade gracefully: BitTorrent without libtorrent and SFTP without libssh2 are disabled automatically with a WARNING. HTTP/FTP/WebDAV are provided through libcurl.

Checking supported protocols

The most reliable current method is to inspect the FALCON_ENABLE_* options passed to the build and whether the corresponding plugin was enabled in the configuration log.

Protocol comparison

Protocol	Resource usage	Typical scenario
HTTP/HTTPS	Low	Web and file downloads
FTP	Low	Enterprise file sharing
BitTorrent	High	Large-file distribution
ED2K	Medium	Legacy resource sharing
Thunder/FlashGet	Medium	Chinese-language resources
HLS/DASH	Medium	Video on demand

Speed and stability depend on the origin and network conditions; the protocols themselves do not support a single universal score, so there is no star-rating column.

Choosing a protocol

• Everyday downloads: use HTTP/HTTPS.
• Large files: use BitTorrent.
• Chinese-language resources: use Thunder links.
• Video: use HLS/DASH.