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IPFS Cache

A C++ wrapper over go-ipfs to store key/value pairs in the IPFS network.

Archived

This project has been split into two parts. The first part has moved into Asio.IPFS project. It contains only the Boost.Asio based bindings to IPFS. The other part with the rest of the code has been moved into Ouinet.

Requirements

To be able to use the IPFS Cache in platforms like Android, where running IPFS as an independent daemon is not a possibility, the wrapper needs to embed IPFS by linking directly with its Go code. Thus the source of go-ipfs is needed to build the main glue between C++ and IPFS. Building that source requires a recent version of Go. To avoid extra system dependencies, the build process automatically downloads the Go system and builds IPFS itself.

In summary, the minimum build dependencies are:

• cmake 3.5+
• g++ capable of C++14
• The Boost library

For Debian, this translates to the following packages:

• build-essential
• cmake
• curl
• libboost-dev
• libboost-system-dev
• libboost-coroutine-dev
• libboost-program-options-dev

The build process is able to compile the IPFS Cache to different platforms with the help of a properly configured cross-compilation environment. If you actually intend to cross-compile you will need proper C/C++ cross-compiler packages, Boost libraries for the target system and a toolchain file for CMake to use them.

To the date, the build process has only been tested on 64-bit GNU/Linux platforms.

Linux cross-compilation example

For building binaries in a Debian Strech machine which are able to run on Raspbian Stretch on the Raspberry Pi:

• Install the gcc-6-arm-linux-gnueabihf and g++-6-arm-linux-gnueabihf packages.

• As indicated in https://wiki.debian.org/Multiarch/HOWTO, add the new architecture with dpkg --add-architecture armhf and update your package list.

• Install the Boost libraries matching the target distribution, with the proper architecture suffix:

  • libboost-system1.62-dev:armhf
  • libboost-coroutine1.62-dev:armhf
  • libboost-program-options1.62-dev:armhf

• Create a toolchain file (e.g. toolchain-linux-armhf-gcc6.cmake) containing:

  set(CMAKE_SYSTEM_NAME Linux)
  set(CMAKE_SYSTEM_PROCESSOR armv6l)
  
  set(CMAKE_C_COMPILER /usr/bin/arm-linux-gnueabihf-gcc-6)
  set(CMAKE_CXX_COMPILER /usr/bin/arm-linux-gnueabihf-g++-6)
  

Android cross-compilation example

For building binaries able to run in Android KitKat and above on ARM processors you will need a Clang/LLVM standalone toolchain created with the Android NDK. Assuming that the NDK is under ~/opt/android-ndk-r15c, you may run:

$ ~/opt/android-ndk-r15c/build/tools/make-standalone-toolchain.sh \
  --platform=android-19 --arch=arm --stl=libc++ \
  --install-dir=$HOME/opt/ndk-android19-arm-libcpp

You will also need to build the Boost libraries for this platform. You may use Boost for Android. Assuming that Boost source is in ~/src/boost/<BOOST_VERSION>, edit doIt.sh and:

• set BOOST_SRC_DIR to $HOME/src/boost
• set BOOST_VERSION to the <BOOST_VERSION> above
• set GOOGLE_DIR to $HOME/opt/android-ndk-r15c
• modify build-boost.sh arguments, set --version=$BOOST_VERSION, --stdlibs="llvm-3.5", --linkage="shared" and --abis to the desired architectures (armeabi-v7a in our example)

Create the llvm-3.5 link as indicated in Boost for Android's readme and run ./doIt.sh to build the Boost libraries. This will create the directory build/boost/<BOOST_VERSION>.

After the previous steps you can use a CMake toolchain file like the following one:

set(CMAKE_SYSTEM_NAME Android)
set(CMAKE_SYSTEM_VERSION 19)
set(CMAKE_ANDROID_ARCH_ABI armeabi-v7a)
set(CMAKE_ANDROID_STANDALONE_TOOLCHAIN $ENV{HOME}/opt/ndk-android19-arm-libcpp)

set(BOOST_INCLUDEDIR /path/to/Boost-for-Android/build/boost/<BOOST_VERSION>/include)
set(BOOST_LIBRARYDIR /path/to/Boost-for-Android/build/boost/<BOOST_VERSION>/libs/${CMAKE_ANDROID_ARCH_ABI}/llvm-3.5)

Building

$ cd <PROJECT ROOT>
$ mkdir build
$ cd build
$ cmake ..
$ make

On success, the build directory shall contain the libipfs-bindings----.so and libipfs-cache----.so shared libraries and two example programs: injector---- and client----. <SYS> is CMake's CMAKE_SYSTEM_NAME (e.g. Linux, Android...) while <PROC> is CMake's CMAKE_SYSTEM_PROCESSOR (e.g. x86_64, armv6l...).

To cross-compile to another system, you may either create a different build directory, or reuse the same directory and just remove the CMakeCache.txt file (thus you can reuse some downloads and build tools). Just remember to point CMake to the proper toolchain file. For the previous Raspbian example:

cmake -DCMAKE_TOOLCHAIN_FILE=/path/to/toolchain-linux-armhf-gcc6.cmake ..
make

This will create the libipfs-cache--Linux--armv6l.so library and similarly named versions of the example programs.

Using the examples

The injector is a program which manipulates the IPFS key/value database. It does so by running a very simplistic HTTP server which listens to requests for adding new (key, value) pairs into the database.

To start the injector listening on the TCP port 8080 start it as so:

$ ./injector --repo <PATH TO IPFS REPOSITORY> -p 8080
Swarm listening on /ip4/127.0.0.1/tcp/4002
Swarm listening on /ip4/<LAN-IP>/tcp/4002
Swarm listening on /ip4/<WAN-IP>/tcp/35038
Swarm listening on /ip4/<WAN-IP>/tcp/4002
Swarm listening on /ip6/::1/tcp/4002
Serving on port 0.0.0.0:8080
IPNS of this database is <DATABASE IPNS>
Starting event loop, press Ctrl-C to exit.

Make a note of the <DATABASE IPNS> string, it is the IPNS address which our client will use to find the database in the IPFS network.

Each IPFS application requires a repository which stores a config file and data being shared on the IPFS network. If the path to the repository doesn't exist, the application will try to create one.

To insert a new (key, value) entry into the database, run the curl command with key and value variables set:

$ curl -d key=my_key -d value=my_value localhost:8080

When this command succeeds, we can have a look at the database by pointing our browser to:

https://ipfs.io/ipns/<DATABASE IPNS>

Which may look something like this:

{"my_key": {"date": "<INSERTION DATE>", "data": ["ipfs:/ipfs/<IPFS CONTENT ID>"]}}

Note that the value is not stored in the database directly, instead, it can be found in the IPFS network under /ipfs/<IPFS CONTENT ID>. We can again look it up with our browser by following the link

https://ipfs.io/ipfs/<IPFS CONTENT ID>

Finally, to find the value of a key using the client example program, one would run it as so:

$ ./client --repo <PATH TO IPFS REPOSITORY> --ipns <DATABASE IPNS> --key my_key