區塊鏈簡介

　　區塊鏈服務於虛擬貨幣，區塊鏈技術用個體自己算雜湊數來進行貨幣發行，通過加密技術支援帳戶交易，通過分散式通訊進行全節點賬本同步，提供架構來支援錢包等高階功能 。它的出現再次證明計算機和網際網路是強大工具，實體世界裡的行業模型可以很好地在計算機世界裡體現。

　　銳英源研究過區塊鏈平臺多個原始碼版本，各個版本都進行了定製開發，客戶滿意，平臺可靠穩定執行。這裡分享2個方面的知識點：編譯和引數。

　　區塊鏈原始碼編譯

　　區塊鏈是開源的，一般也是用開源的作業系統，現在經常用ubuntu來當區塊鏈的執行平臺。在ubuntu下正常的編譯步驟如下：

　　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，這些步驟沒問題。但是到ubuntu14下，在處理libdb4.8行時，會提示找不到libdb，這時候不要慌，把libdb4.8去掉，變成如下行就可以：

　　sudo apt-get install libdb4.8++-dev

　　安裝源在識別時，不能用libdb4.8-dev來找到包，但是用後者就可以，後者也包含libdb4.8-dev，安裝後也可以編譯出來區塊鏈的可執行檔案。這事件的原因就是開源的不全面性造成的，開源世界裡遇到變化是常事。

　　另外要注意作業系統平臺的32位或64位情況，一般是用64位平臺作業系統才可以執行。

　　引數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]建立區塊鏈後，引數會配置上。

　　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.新節點想連線存在的區塊鏈，必須先下載已建立區塊鏈節點機器好的區塊鏈引數。

　　The parameters for a blockchain can be retrieved using the getblockchainparams API call. getblockchainparams 命令可以檢視引數。

　　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.塊裡初始設定階段的長度。在設定階段，其它引數不生效。

　　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.許可礦工最小比例，在迴圈挖礦來提出一個有效區塊鏈參與時需要

　　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.