Merge branch 'optional-derivation-output-storepath' into ca-derivation-data-types

1 files changed, 13 insertions, 0 deletions

diff --git a/src/libutil/serialise.cc b/src/libutil/serialise.cc
index c8b71188f..00c945113 100644
--- a/src/libutil/serialise.cc
+++ b/src/libutil/serialise.cc
@@ -322,5 +322,18 @@ void StringSink::operator () (const unsigned char * data, size_t len)
     s->append((const char *) data, len);
 }
 
+size_t ChainSource::read(unsigned char * data, size_t len)
+{
+    if (useSecond) {
+        return source2.read(data, len);
+    } else {
+        try {
+            return source1.read(data, len);
+        } catch (EndOfFile &) {
+            useSecond = true;
+            return this->read(data, len);
+        }
+    }
+}
 
 }