fetch-params.sh

#!/bin/bash

set -eu

if [[ "$OSTYPE" == "darwin"* ]]; then
    PARAMS_DIR="$HOME/Library/Application Support/ZcashParams"
else
    PARAMS_DIR="$HOME/.zcash-params"
fi

SPROUT_PKEY_NAME='sprout-proving.key'
SPROUT_VKEY_NAME='sprout-verifying.key'
SAPLING_SPEND_NAME='sapling-spend.params'
SAPLING_OUTPUT_NAME='sapling-output.params'
SAPLING_SPROUT_GROTH16_NAME='sprout-groth16.params'
SPROUT_URL="https://z.cash/downloads"
SPROUT_IPFS="/ipfs/QmZKKx7Xup7LiAtFRhYsE1M7waXcv9ir9eCECyXAFGxhEo"

SHA256CMD="$(command -v sha256sum || echo shasum)"
SHA256ARGS="$(command -v sha256sum >/dev/null || echo '-a 256')"

WGETCMD="$(command -v wget || echo '')"
IPFSCMD="$(command -v ipfs || echo '')"
CURLCMD="$(command -v curl || echo '')"

# fetch methods can be disabled with ZC_DISABLE_SOMETHING=1
ZC_DISABLE_WGET="${ZC_DISABLE_WGET:-}"
ZC_DISABLE_IPFS="${ZC_DISABLE_IPFS:-}"
ZC_DISABLE_CURL="${ZC_DISABLE_CURL:-}"

function fetch_wget {
    if [ -z "$WGETCMD" ] || ! [ -z "$ZC_DISABLE_WGET" ]; then
        return 1
    fi

    local filename="$1"
    local dlname="$2"

    cat <<EOF

Retrieving (wget): $SPROUT_URL/$filename
EOF

    wget \
        --progress=dot:giga \
        --output-document="$dlname" \
        --continue \
        --retry-connrefused --waitretry=3 --timeout=30 \
        "$SPROUT_URL/$filename"
}

function fetch_ipfs {
    if [ -z "$IPFSCMD" ] || ! [ -z "$ZC_DISABLE_IPFS" ]; then
        return 1
    fi

    local filename="$1"
    local dlname="$2"

    cat <<EOF

Retrieving (ipfs): $SPROUT_IPFS/$filename
EOF

    ipfs get --output "$dlname" "$SPROUT_IPFS/$filename"
}

function fetch_curl {
    if [ -z "$CURLCMD" ] || ! [ -z "$ZC_DISABLE_CURL" ]; then
        return 1
    fi

    local filename="$1"
    local dlname="$2"

    cat <<EOF

Retrieving (curl): $SPROUT_URL/$filename
EOF

    curl \
        --output "$dlname" \
        -# -L -C - \
        "$SPROUT_URL/$filename"

}

function fetch_failure {
    cat >&2 <<EOF

Failed to fetch the Zcash zkSNARK parameters!
Try installing one of the following programs and make sure you're online:

 * ipfs
 * wget
 * curl

EOF
    exit 1
}

function fetch_params {
    local filename="$1"
    local output="$2"
    local dlname="${output}.dl"
    local expectedhash="$3"

    if ! [ -f "$output" ]
    then
        for method in wget ipfs curl failure; do
            if "fetch_$method" "$filename" "$dlname"; then
                echo "Download successful!"
                break
            fi
        done

        "$SHA256CMD" $SHA256ARGS -c <<EOF
$expectedhash  $dlname
EOF

        # Check the exit code of the shasum command:
        CHECKSUM_RESULT=$?
        if [ $CHECKSUM_RESULT -eq 0 ]; then
            mv -v "$dlname" "$output"
        else
            echo "Failed to verify parameter checksums!" >&2
            exit 1
        fi
    fi
}

# Use flock to prevent parallel execution.
function lock() {
    local lockfile=/tmp/fetch_params.lock
    if [[ "$OSTYPE" == "darwin"* ]]; then
        if shlock -f ${lockfile} -p $$; then
            return 0
        else
            return 1
        fi
    else
        # create lock file
        eval "exec 200>$lockfile"
        # acquire the lock
        flock -n 200 \
            && return 0 \
            || return 1
    fi
}

function exit_locked_error {
    echo "Only one instance of fetch-params.sh can be run at a time." >&2
    exit 1
}

function main() {

    lock fetch-params.sh \
    || exit_locked_error

    cat <<EOF
Zcash - fetch-params.sh

This script will fetch the Zcash zkSNARK parameters and verify their
integrity with sha256sum.

If they already exist locally, it will exit now and do nothing else.
EOF

    # Now create PARAMS_DIR and insert a README if necessary:
    if ! [ -d "$PARAMS_DIR" ]
    then
        mkdir -p "$PARAMS_DIR"
        README_PATH="$PARAMS_DIR/README"
        cat >> "$README_PATH" <<EOF
This directory stores common Zcash zkSNARK parameters. Note that it is
distinct from the daemon's -datadir argument because the parameters are
large and may be shared across multiple distinct -datadir's such as when
setting up test networks.
EOF

        # This may be the first time the user's run this script, so give
        # them some info, especially about bandwidth usage:
        cat <<EOF
The complete parameters are currently just under 1.7GB in size, so plan 
accordingly for your bandwidth constraints. If the Sprout parameters are
already present the additional Sapling parameters required are just under 
800MB in size. If the files are already present and have the correct 
sha256sum, no networking is used.

Creating params directory. For details about this directory, see:
$README_PATH

EOF
    fi

    cd "$PARAMS_DIR"

    # Sprout parameters:
    fetch_params "$SPROUT_PKEY_NAME" "$PARAMS_DIR/$SPROUT_PKEY_NAME" "8bc20a7f013b2b58970cddd2e7ea028975c88ae7ceb9259a5344a16bc2c0eef7"
    fetch_params "$SPROUT_VKEY_NAME" "$PARAMS_DIR/$SPROUT_VKEY_NAME" "4bd498dae0aacfd8e98dc306338d017d9c08dd0918ead18172bd0aec2fc5df82"

    # Sapling parameters:
    fetch_params "$SAPLING_SPEND_NAME" "$PARAMS_DIR/$SAPLING_SPEND_NAME" "8e48ffd23abb3a5fd9c5589204f32d9c31285a04b78096ba40a79b75677efc13"
    fetch_params "$SAPLING_OUTPUT_NAME" "$PARAMS_DIR/$SAPLING_OUTPUT_NAME" "2f0ebbcbb9bb0bcffe95a397e7eba89c29eb4dde6191c339db88570e3f3fb0e4"
    fetch_params "$SAPLING_SPROUT_GROTH16_NAME" "$PARAMS_DIR/$SAPLING_SPROUT_GROTH16_NAME" "b685d700c60328498fbde589c8c7c484c722b788b265b72af448a5bf0ee55b50"
}

main
rm -f /tmp/fetch_params.lock
exit 0