区块链开源社区、区块链开源心得和区块链二次开发

区块链简介

区块链服务于虚拟货币，区块链技术用个体自己算哈希数来进行货币发行，通过加密技术支持帐户交易，通过分布式通信进行全节点账本同步，提供架构来支持钱包等高级功能。它的出现再次证明计算机和互联网是强大工具，实体世界里的行业模型可以很好地在计算机世界里体现。

锐英源研究过区块链平台多个源代码版本，各个版本都进行了定制开发，客户满意，平台可靠稳定运行。这里分享2个方面的知识点：编译和参数。

区块链源代码编译

区块链是开源的，一般也是用开源的操作系统，现在经常用ubuntu来当区块链的运行平台。在ubuntu下正常的编译步骤如下：

  sudo apt-get update
  sudo apt-get install build-essential libtool autotools-dev automake pkg-config libssl-dev libevent-dev bsdmainutils
  sudo apt-get install libboost-all-dev
  sudo apt-get install git
  sudo apt-get install software-properties-common
  sudo add-apt-repository ppa:bitcoin/bitcoin
  sudo apt-get update
  sudo apt-get install libdb4.8-dev libdb4.8++-dev
  ./autogen.sh 
  ./configure
  make

在ubuntu12下，这些步骤没问题。但是到ubuntu14下，在处理libdb4.8行时，会提示找不到libdb，这时候不要慌，把libdb4.8去掉，变成如下行就可以：

  sudo apt-get install libdb4.8++-dev

安装源在识别时，不能用libdb4.8-dev来找到包，但是用后者就可以，后者也包含libdb4.8-dev，安装后也可以编译出来区块链的可执行文件。这事件的原因就是开源的不全面性造成的，开源世界里遇到变化是常事。

另外要注意操作系统平台的32位或64位情况，一般是用64位平台操作系统才可以运行。

参数

Configuring a blockchain

The parameters of a blockchain are configured after creating the chain by running multichain-util create [chain-name], and before starting the chain by running multichaind [chain-name].
Parameters are set in the params.dat file for each blockchain, which can be modified in any text editor. Once the blockchain is initialized, these parameters cannot be changed. To prevent accidental modification, a hash of the parameters is added to params.dat when the chain starts running. multichain-util create [chain-name]创建区块链后，参数会配置上。
When new nodes attempt to connect to an existing blockchain, they first download a minimal set of blockchain parameters from the existing node, and write them to the params.dat file in the appropriate directory. Once they are granted permission to connect, they are able to download the full set of blockchain parameters.新节点想连接存在的区块链，必须先下载已创建区块链节点机器好的区块链参数。
The parameters for a blockchain can be retrieved using the getblockchainparams API call. getblockchainparams 命令可以查看参数。

Full list of blockchain parameters

Below is a full list of parameters in the params.dat file, grouped by section.

Basic chain parameters

Parameter	Description	Example
chain-protocol	Use multichain for a MultiChain blockchain or bitcoin for a bitcoin-style blockchain with no permissions, native assets or streams.	multichain
chain-description	Textual description of the blockchain for display to users.	Internal chain
root-stream-name	Name of the root stream for general data storage (leave blank for none).	root
root-stream-open	Allow anyone with send permissions to write to the root stream.	true
chain-is-testnet	Whether to set testnet to true in the output of various JSON-RPC API calls. This is for compatibility with Bitcoin Core and does not affect any other testnet-like behavior.	false
target-block-time	Target average number of seconds between blocks, i.e. delay for confirming transactions. If this is below 10 seconds, it is recommended to set mining-turnover low, to minimize the number of forks.	60 (one minute)
maximum-block-size	Maximum number of bytes in each block, to prevent network flooding by a rogue miner.	1000000 (1MB)

Global permissions

Parameter	Description	Example
anyone-can-connect	Apply no restriction to connecting to the network, i.e. nodes do not require connect permissions.	false
anyone-can-send	Apply no restriction to sending transactions, i.e. signing transaction inputs.	false
anyone-can-receive	Apply no restriction to receiving transactions, i.e. appearing in transaction outputs.	false
anyone-can-receive-empty	Apply no restriction to addresses which appear in transaction outputs containing no native currency, assets or other metadata. Only relevant if anyone-can-receive=false. This allows addresses without receivepermission to include a change output in non-asset transactions, e.g. to publish to streams.	true
anyone-can-create	Apply no restriction to creating new streams.	false
anyone-can-issue	Apply no restriction to issuing (creating) new native assets.	false
anyone-can-mine	Apply no restriction to mining blocks for the chain, i.e. confirming transactions.	false
anyone-can-activate	Apply no restriction to changing connect, send and receive permissions of other users.	false
anyone-can-admin	Apply no restriction to changing all permissions of other users.	false
support-miner-precheck	Support advanced miner permission checks by caching the inputs spent by an administrator when setting admin or mine permissions – see permissions management for more information.	true
allow-p2sh-outputs	Allow pay to scripthash outputs, where the redeem script is only revealed when an output is spent. See permissions management for more information about permissions and P2SH addresses.	true
allow-multisig-outputs	Allow multisignature outputs, where more than one address is explicitly listed in a transaction output, and a given number of these addresses are required to sign in order to spend that output. See permissions management for more information about permissions and multisig outputs.	true

Consensus requirements

Parameter	Description	Example
setup-first-blocks	Length of initial setup phase in blocks. During the setup phase, the constraints specified by the other parameters in this section are not applied.块里初始设置阶段的长度。在设置阶段，其它参数不生效。	1440
mining-diversity	Minimum proportion of permitted miners required to participate in round-robin mining to render a valid blockchain, between 0.0 (no constraint) and 1.0 (every permitter miner must participate). Unlike mining-turnover, this is a hard rule which determines whether a blockchain is valid or not.许可矿工最小比例，在循环挖矿来提出一个有效区块链参与时需要	0.5
admin-consensus-admin	Proportion of permitted administrators who must agree to modify the admin privileges for an address, between 0 (no consensus required) and 1 (every admin must agree).	0.5
admin-consensus-activate	Proportion of permitted administrators who must agree to modify the activate privileges for an address, between 0 and 1.	0.5
admin-consensus-mine	Proportion of permitted administrators who must agree to modify mining privileges for an address, between 0 and 1.	0.5
admin-consensus-create	Proportion of permitted administrators who must agree to modify stream creation privileges for an address, between 0 and 1.	0.0
admin-consensus-issue	Proportion of permitted administrators who must agree to modify asset issuing privileges for an address, between 0 and 1.	0.0

Defaults for mining runtime parameters

lock-admin-mine-rounds	Ignore forks that reverse changes in admin or mine permissions after this many (integer) mining rounds have passed. A mining round is defined as mining-diversity multiplied by the number of permitted miners, rounded up. This prevents changes in the blockchain’s governance model from being reversed and can be overridden by each node using the lockadminminerounds runtime parameter.	10
mining-requires-peers	A node will only mine if it is connected to at least one other node. This is ignored during the setup phase or if only one address has mine permissions, and can be overridden by each node using the miningrequirespeers runtime parameter.	true
mine-empty-rounds	If there are no new transactions, stop mining after this many rounds of empty blocks. A mining round is defined as mining-diversity multiplied by the number of permitted miners, rounded up. This reduces disk usage in blockchains with periods of low activity. If negative, continue mining indefinitely. This is ignored during the setup phase or if target-adjust-freq>0, and can be overridden by each node using the mineemptyrounds runtime parameter.	2.5
mining-turnover	A value of 0.0 prefers pure round robin mining between an automatically-discovered subset of the permitted miners, with others stepping in only if a miner fails. In this case the number of active miners will be mining-diversity multiplied by the number of permitted miners, rounded up. A value of 1.0 prefers pure random mining between all permitted miners. Intermediate values set the balance between these two behaviors. Lower values reduce the number of forks, making the blockchain more efficient, but increase the level of mining concentration. Unlike mining-diversity, this is a recommendation rather than a consensus rule, and can be overridden by each node using the miningturnover runtime parameter.	0.5

Native blockchain currency

When creating a blockchain, a fundamental question is whether it should use a native currency (the equivalent of bitcoin as an asset). By default, MultiChain blockchains do not use a native currency. However you may wish to change this to create a market for transactions, whereby transactions bid for inclusion in a block by attaching transaction fees in the native currency, and miners are rewarded with these fees along with block rewards.

Parameter	Description	Example
initial-block-reward	Initial number of native currency units to award the miner of each block, in raw integer units.	0
first-block-reward	Use a different mining reward for the first block only, in raw integer units. Ignored if negative.	-1
reward-halving-interval	Each time this many blocks has passed, halve the per-block miner reward.	52560000
reward-spendable-delay	After a block reward is granted to a miner, the number of blocks until that reward can be spent.	1
minimum-per-output	Minimum quantity of native currency in every transaction output, in raw integer units.	0
maximum-per-output	Maximum quantity of native currency in every transaction output, in raw integer units.	0
minimum-relay-fee	Minimum native currency fee required in order to relay a transaction, in raw integer units. This can be overridden by the minrelaytxfee runtime parameter.	0
native-currency-multiple	How many raw integer units per display unit of the native currency, as used in the JSON-RPC API. For example in the bitcoin network this would be the number of satoshis per bitcoin.	100000000

Advanced mining parameters

Parameter	Description	Example
skip-pow-check	Skip checking whether block hashes demonstrate sufficient proof-of-work.	false
pow-minimum-bits	Minimum/initial proof-of-work difficulty, i.e. the number of leading zero bits in the block hash.	20
target-adjust-freq	Frequency of recalculating proof-of-work difficulty level, measured in seconds. For blockchains which don’t require proof-of-work, use a negative value to prevent recalculation.	86400 (1 day)
allow-min-difficulty-blocks	Ignore the current target difficulty level if blocks are taking too long to appear.	false

Transaction limits

Parameter	Description	Example
only-accept-std-txs	Only accept and relay transactions which qualify as ‘standard’, according to the criteria below.	true
max-std-tx-size	Maximum size of a standard transaction in bytes.	100000 (100k)
max-std-op-returns-count	Maximum number of OP_RETURN outputs (for general data) in standard transactions.	10
max-std-op-return-size	Maximum size of an OP_RETURN metadata output in a standard transaction, in bytes.	4096 (4K)
max-std-op-drops-count	Maximum number of inline OP_DROP metadata elements in a single output in standard transactions.	5
max-std-element-size	Maximum size of data elements in standard transactions, in bytes.	600

Advanced parameters

default-network-port	Default IP port to use for peer-to-peer communications between nodes (can be overridden by each node using the port runtime parameter).	8571
default-rpc-port	Default IP port to use for JSON-RPC calls to multichaind (can be overridden by each node using the rpcport runtime parameter).	8570
chain-name	Blockchain name, which is generally set by a call to multichain-util.	chain1
protocol-version	The version of the chain-protocol protocol used. This can be used to provide backwards compatibility with older versions of MultiChain – see creating a new blockchain.	10007
network-message-start	The four-byte “magic value” sent at the start of each peer-to-peer protocol message.	fddcc6f1
address-pubkeyhash-version address-scripthash-version private-key-version address-checksum-value	These control the formatting of regular addresses, pay-to-scripthash (multisig) addresses and exported private keys. For more information, see address and key format.

Production recommendations

Below is a list of parameters whose values are crucial for long-term production deployments of MultiChain 1.0. (We expect MultiChain 2.0, now in development, to enable many parameters to be changed by administrator consensus in a running blockchain.)

target-block-time	Consider where your validator nodes will be deployed geographically and the latency between those locations. Ensure this value is long enough to enable consensus to be maintained between those nodes at your peak expected throughput. Use pre-production testing to determine a safe value and then add a 50-100% margin of error. This parameter should be tested together with maximum-block-size since larger blocks take longer to propagate.
maximum-block-size	Ensure this is large enough for expected future growth. Use pre-production testing to determine the block sizes for a given workload. Note also that for any given transaction throughput, an increase in target-block-time requires a corresponding proportional increase in maximum-block-size.
anyone-can-mine	Set to false unless you are certain you want to use proof-of-work mining, in which case ensure that target-adjust-freqis a positive number.
anyone-can-admin	Set to false unless you are certain you want any user connected to the blockchain to be able to perform administrative actions, which is a highly unusual case.
support-miner-precheck	Set to true if your blockchain is open to the public, or any participant might be motivated to conduct a denial-of-service attack against the network. (Miner prechecks are performed by MultiChain 1.0 beta 2 or later.)
mining-diversity	Ensure this is above 0.5 to prevent a long-running network split leading to two blockchain forks that can both continue growing in the long term.
admin-consensus-admin admin-consensus-mine	To prevent any possibility of a future conflict between administrators leading to a fork, set these above 0.5. This means there will always be a single clear majority for any governance changes to the chain.
target-adjust-freq	Set to -1 unless you want to use proof-of-work mining in your blockchain, otherwise block creation could become difficult and CPU intensive over time. There is no reason to use proof-of-work in a chain which has permissioned miners who are governed by mining diversity.
max-std-op-return-size	Ensure this is large enough to accommodate the largest piece of data you will ever embed in the blockchain (but note the hard limit of 64 MB). The max-std-tx-size and maximum-block-size should both be at least a few hundred bytes larger than this value.
protocol-version	Set to 10008 or later (assuming your chain-protocol is multichain) so that your blockchain will support upgrading to new protocols in future versions of MultiChain.

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