Expanded comment in binding.gyp

1 files changed, 4 insertions, 0 deletions

diff --git a/templates/binding.gyp.template b/templates/binding.gyp.template
index 1e5b2ea911..5fcd247442 100644
--- a/templates/binding.gyp.template
+++ b/templates/binding.gyp.template
@@ -46,6 +46,10 @@
     'target_defaults': {
         # Emperically, Node only exports ALPN symbols if its major version is >0.
         # io.js always reports versions >0 and always exports ALPN symbols.
+        # Therefore, Node's major version will be truthy if and only if it
+        # supports ALPN. The output of "node -v" is v[major].[minor].[patch],
+        # like "v4.1.1" in a recent version. We use grep to extract just the
+        # major version. "4", would be the output for the example.
       'defines': [
         'TSI_OPENSSL_ALPN_SUPPORT=<!(node -v | grep -oP "(?<=v)(\d+)(?=\.\d+\.\d+)")'
       ],