Fixes 4097, improves caching on parameter downloads

zcutil/fetch-params.sh

@@ -13,7 +13,7 @@ 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_URL="https://download.z.cash/downloads"
 SPROUT_IPFS="/ipfs/QmZKKx7Xup7LiAtFRhYsE1M7waXcv9ir9eCECyXAFGxhEo"
 
 SHA256CMD="$(command -v sha256sum || echo shasum)"
@@ -107,13 +107,27 @@ function fetch_params {
 
     if ! [ -f "$output" ]
     then
-        for method in wget ipfs curl failure; do
-            if "fetch_$method" "$filename" "$dlname"; then
-                echo "Download successful!"
-                break
+        for i in 1 2
+        do
+            for method in wget ipfs curl failure; do
+                if "fetch_$method" "${filename}.part.${i}" "${dlname}.part.${i}"; then
+                    echo "Download of part ${i} successful!"
+                    break
+                fi
+            done
+        done
+
+        for i in 1 2
+        do
+            if ! [ -f "${dlname}.part.${i}" ]
+            then
+                fetch_failure
             fi
         done
 
+        cat "${dlname}.part.1" "${dlname}.part.2" > "${dlname}"
+        rm "${dlname}.part.1" "${dlname}.part.2"
+
         "$SHA256CMD" $SHA256ARGS -c <<EOF
 $expectedhash  $dlname
 EOF