Auto merge of #2597 - kpcyrd:fetch-ipfs, r=str4d

Fetch params from ipfs if possible

This patch allows fetch-params to download the params from [ipfs], if it's installed. This reduces the need for a central server and ensures the params are available if the official server ceases to exist.

For now, the default is still wget. If wget exits with an error, the script automatically tries ipfs. To use ipfs instead of wget:

    ZC_DISABLE_WGET=1 ./zcutil/fetch-params.sh

[ipfs]: https://github.com/ipfs/go-ipfs

zcutil/fetch-params.sh

@@ -6,27 +6,83 @@ PARAMS_DIR="$HOME/.zcash-params"
 
 SPROUT_PKEY_NAME='sprout-proving.key'
 SPROUT_VKEY_NAME='sprout-verifying.key'
-SPROUT_PKEY_URL="https://z.cash/downloads/$SPROUT_PKEY_NAME"
-SPROUT_VKEY_URL="https://z.cash/downloads/$SPROUT_VKEY_NAME"
+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 '')"
+
+# fetch methods can be disabled with ZC_DISABLE_SOMETHING=1
+ZC_DISABLE_WGET="${ZC_DISABLE_WGET:-}"
+ZC_DISABLE_IPFS="${ZC_DISABLE_IPFS:-}"
+
+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_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
+
+EOF
+    exit 1
+}
+
 function fetch_params {
-    local url="$1"
+    local filename="$1"
     local output="$2"
     local dlname="${output}.dl"
     local expectedhash="$3"
 
     if ! [ -f "$output" ]
     then
-        echo "Retrieving: $url"
-        wget \
-            --progress=dot:giga \
-            --output-document="$dlname" \
-            --continue \
-            --retry-connrefused --waitretry=3 --timeout=30 \
-            "$url"
+        for method in wget ipfs failure; do
+            if "fetch_$method" "$filename" "$dlname"; then
+                echo "Download successful!"
+                break
+            fi
+        done
 
         "$SHA256CMD" $SHA256ARGS -c <<EOF
 $expectedhash  $dlname
@@ -37,8 +93,8 @@ EOF
         if [ $CHECKSUM_RESULT -eq 0 ]; then
             mv -v "$dlname" "$output"
         else
-           echo "Failed to verify parameter checksums!"
-           exit 1
+            echo "Failed to verify parameter checksums!" >&2
+            exit 1
         fi
     fi
 }
@@ -100,8 +156,8 @@ EOF
 
     cd "$PARAMS_DIR"
 
-    fetch_params "$SPROUT_PKEY_URL" "$PARAMS_DIR/$SPROUT_PKEY_NAME" "8bc20a7f013b2b58970cddd2e7ea028975c88ae7ceb9259a5344a16bc2c0eef7"
-    fetch_params "$SPROUT_VKEY_URL" "$PARAMS_DIR/$SPROUT_VKEY_NAME" "4bd498dae0aacfd8e98dc306338d017d9c08dd0918ead18172bd0aec2fc5df82"
+    fetch_params "$SPROUT_PKEY_NAME" "$PARAMS_DIR/$SPROUT_PKEY_NAME" "8bc20a7f013b2b58970cddd2e7ea028975c88ae7ceb9259a5344a16bc2c0eef7"
+    fetch_params "$SPROUT_VKEY_NAME" "$PARAMS_DIR/$SPROUT_VKEY_NAME" "4bd498dae0aacfd8e98dc306338d017d9c08dd0918ead18172bd0aec2fc5df82"
 }
 
 main