Get nft tokens metadata from IPFS support

CHANGELOG.md

@@ -1,6 +1,7 @@
 ## Current
 
 ### Features
+- [#3278](https://github.com/poanetwork/blockscout/pull/3278) - Support of fetching of NFT tokens metadata from IPFS
 - [#3273](https://github.com/poanetwork/blockscout/pull/3273) - Update token metadata at burn/mint events
 - [#3268](https://github.com/poanetwork/blockscout/pull/3268) - Token total supply on-demand fetcher
 - [#3261](https://github.com/poanetwork/blockscout/pull/3261) - Bridged tokens table

apps/explorer/lib/explorer/token/instance_metadata_retriever.ex

@@ -8,6 +8,8 @@ defmodule Explorer.Token.InstanceMetadataRetriever do
   alias Explorer.SmartContract.Reader
   alias HTTPoison.{Error, Response}
 
+  @token_uri "c87b56dd"
+
   @abi [
     %{
       "type" => "function",
@@ -38,7 +40,7 @@ defmodule Explorer.Token.InstanceMetadataRetriever do
 
   def fetch_metadata(contract_address_hash, token_id) do
     # c87b56dd =  keccak256(tokenURI(uint256))
-    contract_functions = %{"c87b56dd" => [token_id]}
+    contract_functions = %{@token_uri => [token_id]}
 
     contract_address_hash
     |> query_contract(contract_functions)
@@ -49,26 +51,26 @@ defmodule Explorer.Token.InstanceMetadataRetriever do
     Reader.query_contract(contract_address_hash, @abi, contract_functions)
   end
 
-  def fetch_json(%{"c87b56dd" => {:ok, [""]}}) do
+  def fetch_json(%{@token_uri => {:ok, [""]}}) do
     {:ok, %{error: @no_uri_error}}
   end
 
-  def fetch_json(%{"c87b56dd" => {:error, "(-32015) VM execution error."}}) do
+  def fetch_json(%{@token_uri => {:error, "(-32015) VM execution error."}}) do
     {:ok, %{error: @no_uri_error}}
   end
 
-  def fetch_json(%{"c87b56dd" => {:ok, ["http://" <> _ = token_uri]}}) do
+  def fetch_json(%{@token_uri => {:ok, ["http://" <> _ = token_uri]}}) do
     fetch_metadata(token_uri)
   end
 
-  def fetch_json(%{"c87b56dd" => {:ok, ["https://" <> _ = token_uri]}}) do
+  def fetch_json(%{@token_uri => {:ok, ["https://" <> _ = token_uri]}}) do
     fetch_metadata(token_uri)
   end
 
-  def fetch_json(%{"c87b56dd" => {:ok, ["data:application/json," <> json]}}) do
+  def fetch_json(%{@token_uri => {:ok, ["data:application/json," <> json]}}) do
     decoded_json = URI.decode(json)
 
-    fetch_json(%{"c87b56dd" => {:ok, [decoded_json]}})
+    fetch_json(%{@token_uri => {:ok, [decoded_json]}})
   rescue
     e ->
       Logger.debug(["Unknown metadata format #{inspect(json)}. error #{inspect(e)}"],
@@ -78,7 +80,12 @@ defmodule Explorer.Token.InstanceMetadataRetriever do
       {:error, json}
   end
 
-  def fetch_json(%{"c87b56dd" => {:ok, [json]}}) do
+  def fetch_json(%{@token_uri => {:ok, ["ipfs://ipfs/" <> ipfs_uid]}}) do
+    ipfs_url = "https://ipfs.io/ipfs/" <> ipfs_uid
+    fetch_metadata(ipfs_url)
+  end
+
+  def fetch_json(%{@token_uri => {:ok, [json]}}) do
     {:ok, json} = decode_json(json)
 
     check_type(json)