pCloud Sync Library

A C library for pCloud file synchronization, providing a virtual filesystem, binary-protocol API client, bidirectional sync engine, and end-to-end encryption.

Features

• Bidirectional file sync — local-to-remote and remote-to-local synchronization with conflict handling
• Virtual filesystem — FUSE-based mountable filesystem with page cache and on-disk caching
• End-to-end encryption — AES-256-CTR + HMAC-SHA512 per-file encryption, RSA-4096 key exchange
• Multiple SSL backends — wolfSSL, OpenSSL 1.1.x, OpenSSL 3, mbedTLS, SecureTransport
• Cross-platform — Linux, macOS, Windows
• Binary protocol — efficient binary API client for pCloud services

Requirements

Dependency	Purpose
libsqlite3	Persistent state database
libfuse / libosxfuse	Virtual filesystem (FUSE builds only)
libpthread	Threading
zlib	Compression (also bundled as miniz.c)
SSL library	One of: wolfSSL, OpenSSL, mbedTLS, SecureTransport

Compiler: GCC or compatible, C99 (-std=gnu99).

Building

The build system uses GNU Make.

make all              # build psynclib.a (static library, requires USESSL=)
make fs               # build with FUSE filesystem support
make shared           # build shared library (libpsynclib.so / .dylib)
make shared-fs        # build shared library with FUSE support
make cli              # build the CLI test tool (includes FUSE)
make overlay_client   # build overlay icons client (Linux)
make clean            # remove build artifacts

SSL backend selection

When USESSL is omitted, the build system auto-detects the best available SSL provider via pkg-config (trying OpenSSL, then wolfSSL, then mbedTLS; on macOS it falls back to SecureTransport). You can override auto-detection by passing USESSL= explicitly:

Value	Backend
openssl	OpenSSL 1.1.x
openssl3	OpenSSL 3.x
wolfssl	wolfSSL
mbed	mbedTLS 1.3.x (PolarSSL API)
securetransport	SecureTransport (macOS only)

Example:

make fs USESSL=openssl
make all USESSL=mbed

Dependency discovery

Dependencies are discovered via pkg-config by default. If pkg-config is not available or a library is installed in a non-standard location, use the *_INCLUDE_DIR override variables listed below.

Build variables

Variable	Default	Purpose
USESSL	(auto-detected)	SSL backend
SQLITE_INCLUDE_DIR	(pkg-config)	Path to SQLite headers
FUSE_INCLUDE_DIR	(pkg-config)	Path to FUSE headers
OPENSSL_INCLUDE_DIR	(pkg-config)	Path to OpenSSL headers
MBEDTLS_INCLUDE_DIR	(pkg-config)	Path to mbedTLS headers
WOLFSSL_INCLUDE_DIR	(pkg-config)	Path to wolfSSL headers
GCC_OPTIMIZATION_LEVEL	s	GCC -O level (macOS)
DEBUG_LEVEL	(unset)	Debug verbosity: 0 (trace) to 4 (critical)

Installing dependencies

Debian/Ubuntu:

apt install libsqlite3-dev libfuse-dev zlib1g-dev
# Plus one SSL provider:
apt install libssl-dev          # OpenSSL
apt install libwolfssl-dev      # WolfSSL
apt install libmbedtls-dev      # mbedTLS 1.3.x (PolarSSL API) — see note below

Fedora/RHEL:

dnf install sqlite-devel fuse-devel zlib-devel
dnf install openssl-devel       # or wolfssl-devel / mbedtls-devel

Note: The mbed SSL backend targets PolarSSL / mbedTLS 1.3.x, the last version that used the polarssl/ header path and PolarSSL symbol names. Modern distro packages (libmbedtls-dev on Debian/Ubuntu, mbedtls-devel on Fedora) ship mbedTLS 2.x or 3.x, which are not compatible with this backend. If you need mbedTLS, you must build PolarSSL 1.3.x from source. For most users, OpenSSL or wolfSSL are the recommended choices.

macOS (Homebrew):

brew install sqlite3 macfuse
brew install openssl@3          # or wolfssl / mbedtls

API Overview

The public API is declared in psynclib.h. All exported symbols use the psync_ prefix. Functions return 0 on success and -1 on failure unless otherwise noted. All paths are UTF-8.

Key API categories:

• Lifecycle — psync_init(), psync_start_sync(), psync_destroy(), psync_pause(), psync_resume(), psync_stop()
• Authentication — psync_set_user_pass(), psync_set_auth(), psync_logout(), psync_unlink(), psync_tfa_*()
• Sync management — psync_add_sync_by_path_delayed(), psync_change_synctype(), psync_delete_sync(), psync_get_status(), psync_run_localscan()
• Virtual filesystem — psync_fs_start(), psync_fs_stop(), psync_fs_getmountpoint()
• pCloud Encryption (Crypto Folder) — psync_crypto_setup(), psync_crypto_start(), psync_crypto_stop(), psync_crypto_mkdir()
• Folder Invites & Shares — psync_share_folder(), psync_accept_share_request(), psync_remove_share()
• Public/upload links — psync_delete_link(), psync_change_link(), psync_change_upload_link()
• Settings — psync_get_bool_setting(), psync_set_bool_setting(), psync_set_string_setting()
• Contacts & teams — psync_list_contacts(), psync_list_myteams(), psync_account_teamshare()
• File operations — psync_upload_data(), psync_upload_file(), psync_create_remote_folder()

Architecture

PUBLIC API  (psynclib.h)
      |
SYNC ENGINE  (psyncer.c / pdiff.c / plocalscan.c)
      |
 +----+----+
UPLOAD     DOWNLOAD
(pupload)  (pdownload)
      |
NETWORK LAYER  (pnetlibs.c / pasyncnet.c / papi.c)
      |
VIRTUAL FS  (pfs.c / ppagecache.c / pfstasks.c / pfsupload.c)
      |
ENCRYPTION  (pcrypto.c / pfscrypto.c / pssl.c)
      |
DATABASE  (SQLite -- schema in pdatabase.h)

Testing

Tests live in tests/ and use the Check unit testing framework with FFF for mocking. Test build configuration is in tests/Makefile.

Requirements

Install the Check testing framework:

# Fedora/RHEL
sudo dnf install check check-devel

# Debian/Ubuntu
sudo apt-get install check

# macOS
brew install check

Core tests

make check                 # build + run all core tests (plist, ptree, papi)
make test                  # alias for make check

SSL provider tests

Each SSL backend has its own test suite. Run them from tests/:

cd tests
make check-pssl-openssl    # OpenSSL 1.1.x tests
make check-pssl-openssl3   # OpenSSL 3.x tests
make check-pssl-wolfssl    # wolfSSL tests
make check-pssl-mbedtls    # mbedTLS tests
make check-pssl            # run all SSL provider tests

Network integration tests

These tests perform real SSL connections and API calls against pCloud servers:

cd tests
make check-network-openssl3   # OpenSSL 3.x network tests
make check-network             # run all network provider tests

Running a single test

cd tests
make build/check_ptree     # build one test binary
./build/check_ptree        # run it

Exit code is 0 on all-pass, 1 on any failure.

Platform Support

Platform	FS backend	Notes
Linux	libfuse	Overlay icons via D-Bus
macOS	libosxfuse	SecureTransport available; Cocoa integration
Windows	FUSE-compatible driver/layer (WinFsp, cbfs, ...)	COM overlay icons

Platform-specific code lives in pcompat.c.

License

See LICENSE for details.