don't allocate large buffers on the stack

src/libutil/archive.cc

@@ -31,6 +31,7 @@ static string caseHackSuffix = "~nix~case~hack~";
 
 PathFilter defaultPathFilter = [](const Path &) { return true; };
 
+const size_t BUFFER_SIZE = 65536;
 
 static void dumpContents(const Path & path, size_t size,
     Sink & sink)
@@ -40,14 +41,14 @@ static void dumpContents(const Path & path, size_t size,
     AutoCloseFD fd = open(path.c_str(), O_RDONLY | O_CLOEXEC);
     if (!fd) throw SysError(format("opening file '%1%'") % path);
 
-    unsigned char buf[65536];
+    auto buf = std::make_unique<unsigned char[]>(BUFFER_SIZE);
     size_t left = size;
 
     while (left > 0) {
-        size_t n = left > sizeof(buf) ? sizeof(buf) : left;
-        readFull(fd.get(), buf, n);
+        size_t n = left > BUFFER_SIZE ? BUFFER_SIZE : left;
+        readFull(fd.get(), buf.get(), n);
         left -= n;
-        sink(buf, n);
+        sink(buf.get(), n);
     }
 
     writePadding(size, sink);
@@ -146,14 +147,14 @@ static void parseContents(ParseSink & sink, Source & source, const Path & path)
     sink.preallocateContents(size);
 
     unsigned long long left = size;
-    unsigned char buf[65536];
+    auto buf = std::make_unique<unsigned char[]>(BUFFER_SIZE);
 
     while (left) {
         checkInterrupt();
-        unsigned int n = sizeof(buf);
-        if ((unsigned long long) n > left) n = left;
-        source(buf, n);
-        sink.receiveContents(buf, n);
+        auto n = BUFFER_SIZE;
+        if ((unsigned long long)n > left) n = left;
+        source(buf.get(), n);
+        sink.receiveContents(buf.get(), n);
         left -= n;
     }