new file mode 100644
--- /dev/null
+++ b/stream_js_buffer.t
@@ -0,0 +1,179 @@
+#!/usr/bin/perl
+
+# (C) Dmitry Volyntsev
+# (C) Nginx, Inc.
+
+# Tests for stream njs module, buffer properties.
+
+###############################################################################
+
+use warnings;
+use strict;
+
+use Test::More;
+
+BEGIN { use FindBin; chdir($FindBin::Bin); }
+
+use lib 'lib';
+use Test::Nginx;
+use Test::Nginx::Stream qw/ stream /;
+
+###############################################################################
+
+select STDERR; $| = 1;
+select STDOUT; $| = 1;
+
+my $t = Test::Nginx->new()->has(qw/http proxy rewrite stream stream_return/)
+	->write_file_expand('nginx.conf', <<'EOF');
+
+%%TEST_GLOBALS%%
+
+daemon off;
+
+events {
+}
+
+http {
+    %%TEST_GLOBALS_HTTP%%
+
+    js_import test.js;
+
+    server {
+        listen       127.0.0.1:8080;
+        server_name  localhost;
+
+        location /njs {
+            js_content test.njs;
+        }
+
+        location /p/ {
+            proxy_pass http://127.0.0.1:8085/;
+        }
+
+        location /return {
+            return 200 'RETURN:$http_foo';
+        }
+    }
+}
+
+stream {
+    js_import test.js;
+
+    js_set $type        test.type;
+    js_set $binary_var  test.binary_var;
+
+    server {
+        listen  127.0.0.1:8081;
+        return  $type;
+    }
+
+    server {
+        listen  127.0.0.1:8082;
+        return  $binary_var;
+    }
+
+    server {
+        listen      127.0.0.1:8083;
+        js_preread  test.cb_mismatch;
+        proxy_pass  127.0.0.1:8090;
+    }
+
+    server {
+        listen      127.0.0.1:8084;
+        js_preread  test.cb_mismatch2;
+        proxy_pass  127.0.0.1:8090;
+    }
+
+    server {
+        listen      127.0.0.1:8085;
+        js_filter   test.header_inject;
+        proxy_pass  127.0.0.1:8080;
+    }
+}
+
+EOF
+
+$t->write_file('test.js', <<EOF);
+    function test_njs(r) {
+        r.return(200, njs.version);
+    }
+
+    function type(s) {
+		var v = s.vars.remote_addr;
+		var type = Buffer.isBuffer(v) ? 'buffer' : (typeof v);
+		return type;
+    }
+
+    function binary_var(s) {
+        var test = s.vars.binary_remote_addr.equals(Buffer.from([127,0,0,1]));
+        return test;
+    }
+
+    function cb_mismatch(s) {
+        try {
+            s.on('upload', () => {});
+            s.on('downstream', () => {});
+        } catch (e) {
+            throw new Error(`cb_mismatch:\${e.message}`)
+        }
+    }
+
+    function cb_mismatch2(s) {
+        try {
+            s.on('upstream', () => {});
+            s.on('download', () => {});
+        } catch (e) {
+            throw new Error(`cb_mismatch2:\${e.message}`)
+        }
+    }
+
+    function header_inject(s) {
+        var req = Buffer.from([]);
+
+        s.on('upstream', function(data, flags) {
+            req = Buffer.concat([req, data]);
+
+            var n = req.indexOf('\\n');
+            if (n != -1) {
+                var rest = req.slice(n + 1);
+                req = req.slice(0, n + 1);
+
+                s.send(req, flags);
+                s.send('Foo: foo\\r\\n', flags);
+                s.send(rest, flags);
+
+                s.off('upstream');
+            }
+        });
+    }
+
+    export default {njs: test_njs, type, binary_var, cb_mismatch, cb_mismatch2,
+                    header_inject};
+
+EOF
+
+$t->try_run('no njs ngx')->plan(5);
+
+###############################################################################
+
+TODO: {
+local $TODO = 'not yet'
+	unless http_get('/njs') =~ /^([.0-9]+)$/m && $1 ge '0.5.0';
+
+is(stream('127.0.0.1:' . port(8081))->read(), 'buffer', 'var type');
+is(stream('127.0.0.1:' . port(8082))->read(), 'true', 'binary var');
+
+stream('127.0.0.1:' . port(8083))->io('x');
+stream('127.0.0.1:' . port(8084))->io('x');
+
+like(http_get('/p/return'), qr/RETURN:foo/, 'injected header');
+
+$t->stop();
+
+ok(index($t->read_file('error.log'), 'cb_mismatch:mixing string and buffer')
+   > 0, 'cb mismatch');
+ok(index($t->read_file('error.log'), 'cb_mismatch2:mixing string and buffer')
+   > 0, 'cb mismatch');
+}
+
+###############################################################################