hydraUnstable: patch to support nixUnstable 2.4pre20201205_a5d85d0

Upstream PR: https://github.com/NixOS/hydra/pull/840

pkgs/development/tools/misc/hydra/default.nix

@@ -9,6 +9,9 @@
       rev = "79d34ed7c93af2daf32cf44ee0e3e0768f13f97c";
       sha256 = "1lql899430137l6ghnhyz0ivkayy83fdr087ck2wq3gf1jv8pccj";
     };
+    patches = [
+      ./hydra-nix-receiveContents.patch
+    ];
     nix = nixFlakes;
 
     tests = {

pkgs/development/tools/misc/hydra/hydra-nix-receiveContents.patch

@@ -0,0 +1,18 @@
+Update for https://github.com/NixOS/nix/commit/faa31f40
+
+--- a/src/hydra-queue-runner/nar-extractor.cc
++++ b/src/hydra-queue-runner/nar-extractor.cc
+@@ -48,9 +48,9 @@
+-    void receiveContents(unsigned char * data, size_t len) override
++    void receiveContents(std::string_view data) override
+     {
+         assert(expectedSize);
+         assert(curMember);
+         assert(hashSink);
+-        *curMember->fileSize += len;
+-        (*hashSink)(data, len);
++        *curMember->fileSize += data.size();
++        (*hashSink)(data);
+         if (curMember->contents) {
+-            curMember->contents->append((char *) data, len);
++            curMember->contents->append(data);