RFC: Sandboxed Bitcoin network ?
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Gabriel L. Somlo via bitcoin-dev
2017-06-21 13:24:09 UTC
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I've been looking for a way to set up a self-contained, sandboxed
network of Bitcoin peer nodes, for testing and experimentation. Think
a bunch of networked VMs, or containers inside a network simulator
like GNS3 (http://gns3.com) or CORE (http://github.com/coreemu/core).

Neither 'main' nor 'test' are feasible, due to hard-coded assumptions
they both make about their respective publicly shared blockchain state.

Right now, that leaves 'regtest' -- however, connecting peers together
over the sandboxed network in regtest mode is a manual process.

After some tinkering, the following changes make 'regtest' behave
similarly to "the real thing", but inside an isolated sandbox network:

diff --git a/src/chainparams.cpp b/src/chainparams.cpp
index 3b42c5f..4345667 100644
--- a/src/chainparams.cpp
+++ b/src/chainparams.cpp
@@ -275,7 +275,7 @@ public:
consensus.nPowTargetTimespan = 14 * 24 * 60 * 60; // two weeks
consensus.nPowTargetSpacing = 10 * 60;
consensus.fPowAllowMinDifficultyBlocks = true;
- consensus.fPowNoRetargeting = true;
+ consensus.fPowNoRetargeting = false;
consensus.nRuleChangeActivationThreshold = 108; // 75% for testchains
consensus.nMinerConfirmationWindow = 144; // Faster than normal for regtest (144 instead of 2016)
consensus.vDeployments[Consensus::DEPLOYMENT_TESTDUMMY].bit = 28;
@@ -307,11 +307,13 @@ public:
assert(genesis.hashMerkleRoot == uint256S("0x4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b"));

vFixedSeeds.clear(); //!< Regtest mode doesn't have any fixed seeds.
+ vFixedSeeds = std::vector<SeedSpec6>(pnSeed6_regtest, pnSeed6_regtest + ARRAYLEN(pnSeed6_regtest));
vSeeds.clear(); //!< Regtest mode doesn't have any DNS seeds.
+ vSeeds.push_back(CDNSSeedData("btc-sandbox.local", "seed.btc-sandbox.local"));

- fDefaultConsistencyChecks = true;
+ fDefaultConsistencyChecks = false;
fRequireStandard = false;
- fMineBlocksOnDemand = true;
+ fMineBlocksOnDemand = false;

checkpointData = (CCheckpointData) {

(not showing the pnSeed6_regtest[] table added to src/chainparamsseeds.h)

Additionally, for this network to behave realistically, I need peers to
actually mine blocks on their own once connected together, so I reverted
commit 8d1de43 and re-added the 'setgenerate' triggered internal miner.

At this point, I have a few questions for the Bitcoin dev community:

1. would a realistic sandbox test mode be interesting enough to make
it worth supporting upstream? (happy to submit patches and do
revisions if there's interest, and a chance for success)

2. if yes, support modifying 'regtest' mode accordingly via some sort of
command line flags, or rather implement a dedicated 'sandbox' mode
with its own CChainParams defaults?

3. finally, would re-inserting the internal 'setgenerate' miner be a
deal breaker?

Any other thoughts and comments also much appreciated!

Thanks much,