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Merge pull request #302 from 8go/patch-73

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rephrase the pipe explanation
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Andreas M. Antonopoulos 2020-07-28 09:30:17 -04:00 committed by GitHub
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@ -205,7 +205,7 @@ The container for Bitcoin Core is +bitcoind+. It is configured to run Bitcoin Co
===== Building the Bitcoin Core Container
Let's start by building and running the bitcoind container. First, we use the +docker build+ command to build it:
Let's start by building and running the +bitcoind+ container. First, we use the +docker build+ command to build it:
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$ cd code/docker
@ -226,7 +226,7 @@ Successfully tagged lnbook/bitcoind:latest
===== Running the Bitcoin Core Container
Next, let's run the bitcoind container and have it mine some blocks. We use the +docker run+ command, with the flags for _interactive (i)_ and _terminal (t)_, and the +name+ argument to give the running container a custom name:
Next, let's run the +bitcoind+ container and have it mine some blocks. We use the +docker run+ command, with the flags for _interactive (i)_ and _terminal (t)_, and the +name+ argument to give the running container a custom name:
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$ docker run -it --name bitcoind lnbook/bitcoind
@ -252,13 +252,13 @@ Mining 1 block every 10 seconds
Balance: 100.00000000
----
As you can see, bitcoind starts up and mines 101 blocks to get the chain started. This is because under the bitcoin consensus rules, newly mined bitcoin is not spendable until 100 blocks have elapsed. By mining 101 blocks, we make the 1st block's coinbase spendable. After that initial mining activity, we mine a new block every 10 seconds, to keep the chain moving forward.
As you can see, bitcoind starts up and mines 101 simulated blocks to get the chain started. This is because under the bitcoin consensus rules, newly mined bitcoin is not spendable until 100 blocks have elapsed. By mining 101 blocks, we make the first block's coinbase spendable. After that initial mining activity, a new block is mined every 10 seconds to keep the chain moving forward.
For now, there are no transactions. But we now have some test bitcoin that has been mined in the wallet and is available to spend. When we connect some Lightning nodes to this chain, we will send some bitcoin to their wallets so that we can open some Lightning channels between the Lightning nodes.
For now, there are no transactions. But we have some test bitcoin that has been mined in the wallet and is available to spend. When we connect some Lightning nodes to this chain, we will send some bitcoin to their wallets so that we can open some Lightning channels between the Lightning nodes.
===== Interacting with the Bitcoin Core Container
In the mean time, we can also interact with the bitcoind container by sending it shell commands. The container is sending a log file to the terminal, displaying the mining process of the bitcoind process. To interact with the shell we can issue commands in another terminal, using the +docker exec+ command. Since we previously named the running container with the +name+ argument, we can refer to it with that name when we run the +docker exec+ command. First, let's run an interactive +bash+ shell:
In the mean time, we can also interact with the +bitcoind+ container by sending it shell commands. The container is sending a log file to the terminal, displaying the mining process of the bitcoind process. To interact with the shell we can issue commands in another terminal, using the +docker exec+ command. Since we previously named the running container with the +name+ argument, we can refer to it by that name when we run the +docker exec+ command. First, let's run an interactive +bash+ shell:
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$ docker exec -it bitcoind /bin/bash
@ -272,9 +272,9 @@ root@e027fd56e31a:/bitcoind# ps x
root@e027fd56e31a:/bitcoind#
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Running the interactive shell puts us "inside" the container and logged in as the +root+ user, as we can see from the new shell prompt +root@e027fd56e31a:/bitcoind#+. If we issue the +ps x+ command to see what processes are running, we see both bitcoind and the script +mine.sh+ are running in the background. To exit this shell, type +CTRL-D+ or +exit+ and you will be returned to your operating system prompt.
Running the interactive shell puts us "inside" the container. It logs in as user +root+, as we can see from the prefix +root@+ in the new shell prompt +root@e027fd56e31a:/bitcoind#+. If we issue the +ps x+ command to see what processes are running, we see both bitcoind and the script +mine.sh+ are running in the background. To exit this shell, type +CTRL-D+ or +exit+ and you will be returned to your operating system prompt.
Instead of running an interactive shell, we can also issue a single command that is executed inside the container, for example to run the +bitcoin-cli+ command, like this:
Instead of running an interactive shell, we can also issue a single command that is executed inside the container. In the following example we run the +bitcoin-cli+ command to obtain information about the current blockchain state:
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$ docker exec bitcoind bitcoin-cli -datadir=/bitcoind getblockchaininfo
@ -290,16 +290,16 @@ $ docker exec bitcoind bitcoin-cli -datadir=/bitcoind getblockchaininfo
$
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As you can see, we need to tell +bitcoin-cli+ where the bitcoind data directory is, with the +datadir+ argument. We can then issue RPC commands to the Bitcoin Core node and get JSON encoded results.
As you can see, we need to tell +bitcoin-cli+ where the bitcoind data directory is by using the +datadir+ argument. We can then issue RPC commands to the Bitcoin Core node and get JSON encoded results.
All the docker containers also have +jq+ installed, which is a command-line JSON encoder/decoder, to help us process JSON on the command-line or from inside scripts. You can send the JSON output of any command to +jq+ using the +|+ character ("pipe" notation). For example, if we pipe the +getblockchaininfo+ JSON result we got above, we can extract the specific field +blocks+ like this:
All our docker containers have +jq+, which is a command-line JSON encoder/decoder, preinstalled. +jq+ helps us to process JSON-formatted data via the command-line or from inside scripts. You can send the JSON output of any command to +jq+ using the +|+ character. This character as well as this operation is called a "pipe". Let's apply a +pipe+ and +jq+ to the previous command as follows:
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$ docker exec bitcoind bitcoin-cli -datadir=/bitcoind getblockchaininfo | jq .blocks
189
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The +jq+ JSON decoder extract the result "189" from the +getblockchaininfo+, which we could use in a subsequent command.
+jq .blocks+ instructs the +jq+ JSON decoder to extract the field +blocks" from the +getblockchaininfo+ result. In our case, it extracts and prints the value of 189 which we could use in a subsequent command.
As you will see in the following sections, we can run several containers and then interact with them individually, issuing commands to extract information (such as the Lightning node public key), or to take an action (open a Lightning channel to another node). The +docker run+ and +docker exec+, together with +jq+ for JSON decoding are all we need to build a working Lightning Network that mixes many different node implementations and allows us to try out various experiments, all on our own computer.