Tools to compute UnixFS IPFS hash.

Author: chriseth

libdevcore/CMakeLists.txt

@@ -12,10 +12,13 @@ set(sources
 	FixedHash.h
 	IndentedWriter.cpp
 	IndentedWriter.h
+	IpfsHash.cpp
+	IpfsHash.h
 	JSON.cpp
 	JSON.h
 	Keccak256.cpp
 	Keccak256.h
+	picosha2.h
 	Result.h
 	StringUtils.cpp
 	StringUtils.h

libdevcore/Exceptions.h

@@ -47,6 +47,7 @@ struct Exception: virtual std::exception, virtual boost::exception
 DEV_SIMPLE_EXCEPTION(InvalidAddress);
 DEV_SIMPLE_EXCEPTION(BadHexCharacter);
 DEV_SIMPLE_EXCEPTION(FileError);
+DEV_SIMPLE_EXCEPTION(DataTooLong);
 
 // error information to be added to exceptions
 using errinfo_invalidSymbol = boost::error_info<struct tag_invalidSymbol, char>;

libdevcore/IpfsHash.cpp

@@ -0,0 +1,93 @@
+/*
+	This file is part of solidity.
+
+	solidity is free software: you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation, either version 3 of the License, or
+	(at your option) any later version.
+
+	solidity is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include <libdevcore/IpfsHash.h>
+
+#include <libdevcore/Exceptions.h>
+#include <libdevcore/picosha2.h>
+#include <libdevcore/CommonData.h>
+
+using namespace std;
+using namespace dev;
+
+namespace
+{
+bytes varintEncoding(size_t _n)
+{
+	bytes encoded;
+	while (_n > 0x7f)
+	{
+		encoded.emplace_back(uint8_t(0x80 | (_n & 0x7f)));
+		_n >>= 7;
+	}
+	encoded.emplace_back(_n);
+	return encoded;
+}
+
+string base58Encode(bytes const& _data)
+{
+	static string const alphabet{"123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz"};
+	bigint data(toHex(_data, HexPrefix::Add));
+	string output;
+	while (data)
+	{
+		output += alphabet[size_t(data % alphabet.size())];
+		data /= alphabet.size();
+	}
+	reverse(output.begin(), output.end());
+	return output;
+}
+}
+
+bytes dev::ipfsHash(string _data)
+{
+	if (_data.length() >= 1024 * 256)
+		BOOST_THROW_EXCEPTION(
+			DataTooLong() <<
+			errinfo_comment("Ipfs hash for large (chunked) files not yet implemented.")
+		);
+
+	bytes lengthAsVarint = varintEncoding(_data.size());
+
+	bytes protobufEncodedData;
+	// Type: File
+	protobufEncodedData += bytes{0x08, 0x02};
+	if (!_data.empty())
+	{
+		// Data (length delimited bytes)
+		protobufEncodedData += bytes{0x12};
+		protobufEncodedData += lengthAsVarint;
+		protobufEncodedData += asBytes(std::move(_data));
+	}
+	// filesize: length as varint
+	protobufEncodedData += bytes{0x18} + lengthAsVarint;
+
+	// PBDag:
+	// Data: (length delimited bytes)
+	size_t protobufLength = protobufEncodedData.size();
+	bytes blockData = bytes{0x0a} + varintEncoding(protobufLength) + std::move(protobufEncodedData);
+	// TODO Handle "large" files with multiple blocks
+
+	// Multihash: sha2-256, 256 bits
+	bytes hash = bytes{0x12, 0x20} + picosha2::hash256(std::move(blockData));
+	return hash;
+}
+
+string dev::ipfsHashBase58(string _data)
+{
+	return base58Encode(ipfsHash(std::move(_data)));
+}

libdevcore/IpfsHash.h

@@ -0,0 +1,37 @@
+/*
+	This file is part of solidity.
+
+	solidity is free software: you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation, either version 3 of the License, or
+	(at your option) any later version.
+
+	solidity is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#pragma once
+
+#include <libdevcore/Common.h>
+
+#include <string>
+
+namespace dev
+{
+
+/// Compute the "ipfs hash" of a file with the content @a _data.
+/// The output will be the multihash of the UnixFS protobuf encoded data.
+/// As hash function it will use sha2-256.
+/// The effect is that the hash should be identical to the one produced by
+/// the command `ipfs add <filename>`.
+bytes ipfsHash(std::string _data);
+
+/// Compute the "ipfs hash" as above, but encoded in base58 as used by ipfs / bitcoin.
+std::string ipfsHashBase58(std::string _data);
+
+}