pg-connection-string: avoid clobbering port from queryparams (#2833)

If the connection string is something like:
    postgresql://demo:password@/postgres?host=localhost&port=26258

Then the port from the query parameters should be used. Previously, the
parsing function would end up with a null port, and the default port
would end up being used by the connecetion package.

packages/pg-connection-string/index.js

@@ -38,7 +38,6 @@ function parse(str) {
   config.user = config.user || decodeURIComponent(result.username)
   config.password = config.password || decodeURIComponent(result.password)
 
-  config.port = result.port
   if (result.protocol == 'socket:') {
     config.host = decodeURI(result.pathname)
     config.database = result.searchParams.get('db')
@@ -53,6 +52,10 @@ function parse(str) {
     // Only prepend the hostname to the pathname if it is not a URL encoded Unix socket host.
     result.pathname = hostname + result.pathname
   }
+  if (!config.port) {
+    // Only set the port if there is no equivalent query param.
+    config.port = result.port
+  }
 
   const pathname = result.pathname.slice(1) || null
   config.database = pathname ? decodeURI(pathname) : null

packages/pg-connection-string/test/parse.js

@@ -318,4 +318,10 @@ describe('parse', function () {
     var subject = parse(connectionString)
     subject.keepalives.should.equal('0')
   })
+
+  it('use the port specified in the query parameters', function () {
+    var connectionString = 'postgres:///?host=localhost&port=1234'
+    var subject = parse(connectionString)
+    subject.port.should.equal('1234')
+  })
 })