From e08b9f7ecc2cff2d6b9f97d6f8e4ba327f8232ab Mon Sep 17 00:00:00 2001
From: zachdaniel <zachary.s.daniel@gmail.com>
Date: Wed, 1 May 2019 10:33:09 -0400
Subject: [PATCH] fix: resolve false positive constructor arguments

---
 CHANGELOG.md                                  |  1 +
 .../smart_contract/solidity/code_compiler.ex  |  6 ++++
 .../lib/explorer/smart_contract/verifier.ex   | 31 ++++++++++++++-----
 .../explorer/smart_contract/verifier_test.exs | 18 ++++++++++-
 4 files changed, 47 insertions(+), 9 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index ed4b8db4d5..ca08e35fee 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -25,6 +25,7 @@
 - [#1885](https://github.com/poanetwork/blockscout/pull/1885) - highlight reserved words in decompiled code
 - [#1896](https://github.com/poanetwork/blockscout/pull/1896) - re-query tokens in top nav automplete
 - [#1881](https://github.com/poanetwork/blockscout/pull/1881) - fix: store solc versions locally for performance
+- [#1875](https://github.com/poanetwork/blockscout/pull/1875) - fix: resolve false positive constructor arguments 
 
 ### Chore
 
diff --git a/apps/explorer/lib/explorer/smart_contract/solidity/code_compiler.ex b/apps/explorer/lib/explorer/smart_contract/solidity/code_compiler.ex
index 72c5bae186..3ded8ba9f1 100644
--- a/apps/explorer/lib/explorer/smart_contract/solidity/code_compiler.ex
+++ b/apps/explorer/lib/explorer/smart_contract/solidity/code_compiler.ex
@@ -63,6 +63,7 @@ defmodule Explorer.SmartContract.Solidity.CodeCompiler do
         }
       }
   """
+  @spec run(Keyword.t()) :: {:ok, map} | {:error, :compilation | :name}
   def run(params) do
     name = Keyword.fetch!(params, :name)
     compiler_version = Keyword.fetch!(params, :compiler_version)
@@ -108,9 +109,14 @@ defmodule Explorer.SmartContract.Solidity.CodeCompiler do
         {:error, %Jason.DecodeError{}} ->
           {:error, :compilation}
 
+        {:error, reason} when reason in [:name, :compilation] ->
+          {:error, reason}
+
         error ->
           parse_error(error)
       end
+    else
+      {:error, :compilation}
     end
   end
 
diff --git a/apps/explorer/lib/explorer/smart_contract/verifier.ex b/apps/explorer/lib/explorer/smart_contract/verifier.ex
index 0fc9f6b21b..746ba610aa 100644
--- a/apps/explorer/lib/explorer/smart_contract/verifier.ex
+++ b/apps/explorer/lib/explorer/smart_contract/verifier.ex
@@ -86,17 +86,32 @@ defmodule Explorer.SmartContract.Verifier do
   In order to discover the bytecode we need to remove the `swarm source` from
   the hash.
 
-  `64` characters to the left of `0029` are the `swarm source`. The rest on
-  the left is the `bytecode` to be validated.
+  For more information on the swarm hash, check out:
+  https://solidity.readthedocs.io/en/v0.5.3/metadata.html#encoding-of-the-metadata-hash-in-the-bytecode
   """
+  def extract_bytecode("0x" <> code) do
+    "0x" <> extract_bytecode(code)
+  end
+
   def extract_bytecode(code) do
-    {bytecode, _swarm_source} =
-      code
-      |> String.split("0029")
-      |> List.first()
-      |> String.split_at(-64)
+    do_extract_bytecode([], String.downcase(code))
+  end
 
-    bytecode
+  defp do_extract_bytecode(extracted, remaining) do
+    case remaining do
+      <<>> ->
+        extracted
+        |> Enum.reverse()
+        |> :binary.list_to_bin()
+
+      "a165627a7a72305820" <> <<_::binary-size(64)>> <> "0029" <> _constructor_arguments ->
+        extracted
+        |> Enum.reverse()
+        |> :binary.list_to_bin()
+
+      <<next::binary-size(2)>> <> rest ->
+        do_extract_bytecode([next | extracted], rest)
+    end
   end
 
   def next_evm_version(current_evm_version) do
diff --git a/apps/explorer/test/explorer/smart_contract/verifier_test.exs b/apps/explorer/test/explorer/smart_contract/verifier_test.exs
index 631c15695e..6786e559df 100644
--- a/apps/explorer/test/explorer/smart_contract/verifier_test.exs
+++ b/apps/explorer/test/explorer/smart_contract/verifier_test.exs
@@ -181,7 +181,7 @@ defmodule Explorer.SmartContract.VerifierTest do
       swarm_source = "3c381c1b48b38d050c54d7ef296ecd411040e19420dfec94772b9c49ae106a0b"
 
       bytecode =
-        "0x608060405234801561001057600080fd5b5060df8061001f6000396000f3006080604052600436106049576000357c0100000000000000000000000000000000000000000000000000000000900463ffffffff16806360fe47b114604e5780636d4ce63c146078575b600080fd5b348015605957600080fd5b5060766004803603810190808035906020019092919050505060a0565b005b348015608357600080fd5b50608a60aa565b6040518082815260200191505060405180910390f35b8060008190555050565b600080549050905600a165627a7a72305820"
+        "0x608060405234801561001057600080fd5b5060df8061001f6000396000f3006080604052600436106049576000357c0100000000000000000000000000000000000000000000000000000000900463ffffffff16806360fe47b114604e5780636d4ce63c146078575b600080fd5b348015605957600080fd5b5060766004803603810190808035906020019092919050505060a0565b005b348015608357600080fd5b50608a60aa565b6040518082815260200191505060405180910390f35b8060008190555050565b600080549050905600"
 
       assert bytecode == Verifier.extract_bytecode(code)
       assert bytecode != code
@@ -189,5 +189,21 @@ defmodule Explorer.SmartContract.VerifierTest do
       assert String.contains?(bytecode, "0029") == false
       assert String.contains?(bytecode, swarm_source) == false
     end
+
+    test "extracts everything to the left of the swarm hash" do
+      code =
+        "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"
+
+      swarm_source = "3c381c1b48b38d050c54d7ef296ecd411040e19420dfec94772b9c49ae106a0b"
+
+      bytecode =
+        "0x608060405234801561001057600080fd5b5060df80610010029f6000396000f3006080604052600436106049576000357c0100000000000000000000000000000000000000000000000000000000900463ffffffff16806360fe47b114604e5780636d4ce63c146078575b600080fd5b348015605957600080fd5b5060766004803603810190808035906020019092919050505060a0565b005b348015608357600080fd5b50608a60aa565b6040518082815260200191505060405180910390f35b8060008190555050565b600080549050905600"
+
+      assert bytecode == Verifier.extract_bytecode(code)
+      assert bytecode != code
+      assert String.contains?(code, bytecode) == true
+      assert String.contains?(bytecode, "0029") == true
+      assert String.contains?(bytecode, swarm_source) == false
+    end
   end
 end