dapp testnet: easily spawn a PoA testnet (demo)

This introduces two things:

  * dapp --nix-run which can run programs via Nix.

    For maximum convenience and reliability, we run Geth via Nix,
    so it's downloaded on first run.

  * dapp testnet which runs a 1-node PoA 5s blocktime testnet.

    It uses a private hidden folder in ~/.dapp/testnet which is
    autodeleted when you C-c the `dapp testnet` command.

I've verified that while the testnet is running, I can use `dapp create`
with the exposed localhost RPC.

(You have to set $ETH_FROM to the address of the testnet
genesis account.)

Let's build more convenience features for interacting with
local testnets!

Author: mbrock

libexec/dapp/dapp---nix-run

@@ -0,0 +1,72 @@
+#!/usr/bin/env bash
+# Usage: dapp --nix-run PKG COMMAND...
+# Example:
+#   $ dapp --nix-run go-ethereum geth --version
+#
+# Runs a command with the binaries from a named Nix package in PATH.
+
+# It's basically an implementation of nix-shell(1) but simpler and
+# without actually starting a subshell, and using ~/.dapp/nix as an
+# "indirect GC root."
+
+set -e
+
+have() { command -v "$1" >/dev/null; }
+{ have nix-channel && have nix-env && have nix-shell; } || {
+  echo >&2 "${0##*/}: error: The Nix package manager is required."
+  echo >&2 "${0##*/}: error: See https://dapp.tools for installation instructions."
+  exit 1
+}
+
+channel=$HOME/.nix-defexpr/channels/dapphub
+
+if [[ ! -d "$channel" ]]; then
+  echo >&2 "${0##*/}: DappHub Nix channel not present; adding..."
+  ( set -x; nix-channel --add https://nix.dapphub.com/pkgs/dapphub )
+  ( set -x; nix-channel --update )
+fi
+
+joinpaths() { printf "%s" "$*" | sed 's/ /:/g' ; }
+
+# Let's have a custom directory for semi-temporary files related to
+# Nix packages.  It will contain symlinks to store paths.
+pkgs=$HOME/.dapp/nix/pkgs
+mkdir -p "$pkgs"
+
+attr="$1"; shift
+
+# First step in Nix jargon: instantiate the package as a
+# derivation file.
+#
+# A package is a fully evaluated Nix expression which describes a
+# build product -- a "derivation" which is then saved as a file in
+# the store.
+drvpath=$(nix-instantiate --indirect --add-root "$pkgs"/"$attr".drv \
+                          "$channel" -A "$attr")
+drvpath=$(sed 's/!.*$//' <<<"$drvpath")
+
+# The derivation will have a number of output paths, either of which
+# might contain the ./bin that we're interested in, so we'll accumulate
+# an array of PATH entries to use.
+paths=()
+
+# This while loop gets its stdin from a Nix command; see below.
+while read output; do
+
+  name=$(basename "$output")
+  path="$HOME/.dapp/nix/pkgs/$name"
+  paths+=("$path"/bin)
+
+  if [[ ! -d "$path" ]]; then
+    # The derivation's output paths must be "realised", which in our
+    # case should mean downloading them from the binary cache.
+    echo >&2 "${0##*/}: Need Nix package: $name"
+    nix-store \
+      -Q --indirect --add-root ~/.dapp/nix/pkgs/"$name" \
+      --realise "$output" >/dev/null \
+      2> >(sed 's/^/nix: /' >&2)
+  fi
+
+done < <(nix-store --query "$drvpath")
+
+PATH=$(joinpaths "${paths[@]}"):$PATH "$@"

libexec/dapp/dapp---testnet-launch

@@ -0,0 +1,51 @@
+#!/usr/bin/env bash
+set -e
+
+gethdir=$HOME/.dapp/testnet
+chainid=2000
+while true; do
+  if [[ ! -d "$gethdir/$chainid" ]]; then break; fi
+  chainid=$((chainid + 1))
+done
+
+chaindir="$gethdir/$chainid"
+
+echo >&2 "dapp-testnet: Chain ID: $chainid"
+echo >&2 "dapp-testnet: Database: $chaindir"
+
+mkdir -p "$chaindir"
+
+function clean() { rm -rf "$chaindir"; }
+trap clean EXIT
+
+address=$(
+  geth 2>/dev/null account new --datadir "$chaindir" --password=<(exit) 2>/dev/null \
+    | grep Address | sed 's/Address: {\(.*\)}/\1/')
+
+echo >&2 "dapp-testnet: Whale address: $address"
+echo >&2 "dapp-testnet: RPC URL: http://127.0.0.1:$chainid"
+
+jshon >"$chaindir/genesis.json" \
+  -n {} \
+  -n {} \
+    -n "$chainid" -i chainId \
+    -n 0 -i homesteadBlock \
+    -n 0 -i eip155Block \
+    -n 0 -i eip158Block \
+    -n 0 -i byzantiumBlock \
+    -n {} -n 5 -i period -n 3000 -i epoch -i clique \
+    -i config \
+  -s "0x1" -i difficulty \
+  -s "0x3938700" -i gaslimit \
+  -s "0x3132333400000000000000000000000000000000000000000000000000000000""$address""0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000" -i extraData \
+  -n {} \
+    -n {} -s "0x21e19e0c9bab2400000" -i balance \
+    -i "$address" \
+  -i alloc
+
+geth 2>/dev/null --datadir "$chaindir" init "$chaindir/genesis.json"
+
+geth \
+  --datadir "$chaindir" --mine --rpc --networkid "$chainid" \
+  --minerthreads=1 \
+  --rpcport="$chainid" --unlock="$address" --password=<(exit)

libexec/dapp/dapp-testnet

@@ -0,0 +1,2 @@
+#!/usr/bin/env bash
+dapp --nix-run go-ethereum dapp --testnet-launch