FSRewriter.scala

// Copyright 2011 Foursquare Labs Inc. All Rights Reserved.

package com.foursquare.snippet

import com.foursquare.lib._
import net.liftweb.common._
import net.liftweb.http._
import net.liftweb.util._
import net.liftweb.util.Helpers._
import scala.xml._

object FSResourceRewriter {
  @volatile var hashCache: Map[String, String] = Map.empty
  def attachResourceId(href: String): String = {
    
    def pathCalc(name:String, hash: String) = {
      if (Props.mode == Props.RunModes.Development) {
        name + "?" + hash + "=_"
      } else {
        s3ResourcePath(name, hash)
      }
    }

    def hash(name:String) = hashCache.get(name) match {
      case Some(hash) => hash
      case None =>
        val hash = LiftRules.doWithResource(name)(is =>{
          StaticResources.md5hash(is)
        }).openOr(Helpers.nextFuncName)
        hashCache += (name->hash)
        hash
    }
    if (!href.startsWith("http")){
      pathCalc(href, hash(href))
    } else {
      href
    }
  }
  
  def s3ResourcePath(name: String, hash: String) = {
    val protocol = if (S.request.exists(IpHelpers.isHttps(_))) "https" else "http"
    protocol + "://4sqstatic.s3.amazonaws.com" + StaticResources.nameHash(name, hash)._1
  }
}

class FSResourceRewriter extends RenderSnippet {
  
  def render(xhtml: NodeSeq): NodeSeq = logTime("FSResourceRewriter"){
    replaceElements(xhtml)
  }
  
  def replaceElements(xhtml: NodeSeq): NodeSeq = {
    xhtml flatMap (_ match {
     case e @ Elem(prefix, "link", attrs, scope, childs @ _*) => 
      attrStr(attrs, "href").map ( href =>
      Elem(prefix, "link",               
        MetaData.update(attrs, 
                        scope, 
                        new UnprefixedAttribute("href", FSResourceRewriter.attachResourceId(href), Null)),
        scope, childs: _*)) openOr e
     case e @ Elem(prefix, "script", attrs, scope, childs @ _*) => 
      attrStr(attrs, "src") map (src =>
      Elem(prefix, "script", 
        MetaData.update(attrs, 
                        scope, 
                        new UnprefixedAttribute("src", FSResourceRewriter.attachResourceId(src), Null)),
        scope, childs: _*)) openOr e
     case e @ Elem(prefix, "img", attrs, scope, childs @ _*) =>
       attrStr(attrs, "src") map (src =>
        Elem(prefix, "img", 
          MetaData.update(attrs, 
                          scope, 
                          new UnprefixedAttribute("src", FSResourceRewriter.attachResourceId(src), Null)),
          scope, childs: _*)) openOr e
     case e @ Elem(prefix, name, attrs, scope, childs @ _*) if !childs.isEmpty => Elem(prefix, name, attrs, scope, childs flatMap replaceElements :_*)
     case e => e
    })
  }
  
  private def attrStr(attrs: MetaData, attr: String): Box[String] = attrs.get(attr) match {
    case None => Empty
    case Some(Nil) => Empty 
    case Some(x) => Full(x.toString)
  }
}