solve the rackup "chicken - egg" problem

with a plain Rack app when config.ru is evaluated it already assumes Rack to be loaded hovewer it's common practice to `bundle exec rackup` such scripts while Bundler loads a version of Rack that might be different than JRuby-Rack's bundled Rack version. 

thus for now we support a magic comment :
# rack.version = ~>1.3.6
...
with "special" support for Bundler as well :
# encoding: UTF-8
# rack.version = bundler
...

Author: kares

src/main/java/org/jruby/rack/DefaultRackApplicationFactory.java

@@ -60,6 +60,11 @@ public RackContext getRackContext() {
     public String getRackupScript() {
         return rackupScript;
     }
+
+    public void setRackupScript(String rackupScript) {
+        this.rackupScript = rackupScript;
+        this.rackupLocation = null;
+    }
 
     /**
      * Initialize this factory using the given context.
@@ -72,7 +77,7 @@ public void init(final RackContext rackContext) {
         // thus does not wrap exceptions into RackExceptions here ...
         // same applies for #newApplication() and #getApplication()
         this.rackContext = (ServletRackContext) rackContext;
-        resolveRackupScript();
+        if ( getRackupScript() == null ) resolveRackupScript();
         this.runtimeConfig = createRuntimeConfig();
         rackContext.log(RackLogger.INFO, runtimeConfig.getVersionString());
         configureDefaults();
@@ -152,6 +157,7 @@ public IRubyObject createApplicationObject(final Ruby runtime) {
             rackContext.log(RackLogger.WARN, "no rackup script found - starting empty Rack application!");
             rackupScript = "";
         }
+        checkAndSetRackVersion(runtime);
         runtime.evalScriptlet("load 'jruby/rack/boot/rack.rb'");
         return createRackServletWrapper(runtime, rackupScript, rackupLocation);
     }
@@ -231,6 +237,31 @@ protected IRubyObject createRackServletWrapper(Ruby runtime, String rackup, Stri
         );
     }
 
+    String checkAndSetRackVersion(final Ruby runtime) {
+        String rackVersion = null;
+        try {
+            rackVersion = IOHelpers.rubyMagicCommentValue(rackupScript, "rack.version:");
+        }
+        catch (Exception e) {
+            rackContext.log(RackLogger.DEBUG, "could not read 'rack.version' magic comment from rackup", e);
+        }
+        if ( rackVersion == null ) {
+            // NOTE: try matching a `require 'bundler/setup'` line ... maybe not ?!
+        }
+        if ( rackVersion != null ) {
+            runtime.evalScriptlet("begin; require 'rubygems'; rescue LoadError; end");
+            if ( rackVersion.equalsIgnoreCase("bundler") ) {
+                runtime.evalScriptlet("require 'bundler/setup'");
+            }
+            else {
+                rackContext.log(RackLogger.DEBUG, "detected 'rack.version' magic comment, " + 
+                        "will use `gem 'rack', '"+ rackVersion +"'`");
+                runtime.evalScriptlet("gem 'rack', '"+ rackVersion +"' if defined? gem");
+            }
+        }
+        return rackVersion;
+    }
+    
     static interface ApplicationObjectFactory {
         IRubyObject create(Ruby runtime) ;
     }

src/main/java/org/jruby/rack/util/IOHelpers.java

@@ -23,10 +23,12 @@
  */
 package org.jruby.rack.util;
 
+import java.io.BufferedReader;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.InputStreamReader;
 import java.io.Reader;
+import java.io.StringReader;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
@@ -41,13 +43,12 @@ public static String inputStreamToString(final InputStream stream)
         throws IOException {
         if ( stream == null ) return null;
 
-        final StringBuilder str = new StringBuilder();
-        int c = stream.read();
-        Reader reader;
+        final StringBuilder str = new StringBuilder(128);
         String coding = "UTF-8";
-        if (c == '#') {     // look for a coding: pragma
+        int c = stream.read();
+        if ( c == '#' ) { // look for a coding: pragma
             str.append((char) c);
-            while ((c = stream.read()) != -1 && c != 10) {
+            while ( (c = stream.read()) != -1 && c != 10 ) {
                 str.append((char) c);
             }
             Pattern pattern = Pattern.compile("coding:\\s*(\\S+)");
@@ -58,13 +59,35 @@ public static String inputStreamToString(final InputStream stream)
         }
 
         str.append((char) c);
-        reader = new InputStreamReader(stream, coding);
+        Reader reader = new InputStreamReader(stream, coding);
 
-        while ((c = reader.read()) != -1) {
+        while ( (c = reader.read()) != -1 ) {
             str.append((char) c);
         }
 
         return str.toString();
     }
+
+    public static String rubyMagicCommentValue(final String script, final String prefix) 
+        throws IOException {
+        
+        final BufferedReader reader = new BufferedReader(new StringReader(script), 80);
+        
+        String line, comment = null; Pattern pattern = null;
+        while ( (line = reader.readLine()) != null ) {
+            if ( line.charAt(0) == '#' ) {
+                if (pattern == null) {
+                    pattern = Pattern.compile(prefix + "\\s*(\\S+)");
+                }
+                Matcher matcher = pattern.matcher(line);
+                if (matcher.find()) {
+                    comment = matcher.group(1); break;
+                }
+            }
+            else break; // (magic) comment expected at the beginning
+        }
+        reader.close();
+        return comment;
+    }
 
 }

src/spec/ruby/rack/application_spec.rb

@@ -6,6 +6,7 @@
 #++
 
 require File.expand_path('spec_helper', File.dirname(__FILE__) + '/..')
+require 'tempfile'
 
 describe org.jruby.rack.DefaultRackApplication, "call" do
 
@@ -327,6 +328,52 @@ def newRuntime() # use the current runtime instead of creating new
         should_eval_as_nil "defined?(::Rack::VERSION)"
       end
 
+      it "loads specified version of rack", :lib => :stub do
+        gem_install_rack_unless_installed '1.3.6'
+        script = "" +
+          "# rack.version: ~>1.3.6\n" +
+          "Proc.new { 'proc-rack-app' }"
+        app_factory.setRackupScript script
+        @runtime = app_factory.new_runtime
+        
+        app_factory.checkAndSetRackVersion(@runtime)
+        @runtime.evalScriptlet "require 'rack'"
+        
+        should_eval_as_eql_to "Rack.release if defined? Rack.release", '1.3'
+        should_eval_as_eql_to "Gem.loaded_specs['rack'].version.to_s", '1.3.6'
+      end
+
+      it "loads bundler with rack", :lib => :stub do
+        gem_install_rack_unless_installed '1.3.6'
+        script = "# encoding: UTF-8\n" +
+          "# rack.version: bundler \n" +
+          "Proc.new { 'proc-rack-app' }"
+        app_factory.setRackupScript script
+        @runtime = app_factory.new_runtime
+        
+        file = Tempfile.new('Gemfile')
+        file << "source 'http://rubygems.org'\n gem 'rack', '1.3.6'"
+        file.flush
+        @runtime.evalScriptlet "ENV['BUNDLE_GEMFILE'] = #{file.path.inspect}"
+        
+        app_factory.checkAndSetRackVersion(@runtime)
+        @runtime.evalScriptlet "require 'rack'"
+        
+        should_not_eval_as_nil "defined?(::Bundler)"
+        should_eval_as_eql_to "Rack.release if defined? Rack.release", '1.3'
+        should_eval_as_eql_to "Gem.loaded_specs['rack'].version.to_s", '1.3.6'
+      end
+      
+      def gem_install_rack_unless_installed(version)
+        begin
+          Gem::Specification.find_by_name 'rack', version
+        rescue Gem::LoadError
+          require 'rubygems/dependency_installer'
+          installer = Gem::DependencyInstaller.new
+          installer.install 'rack', version
+        end
+      end
+      
       # should not matter on 1.7.x due https://github.com/jruby/jruby/pull/123
       if JRUBY_VERSION < '1.7.0'
         it "does not load any features (until load path is adjusted)" do

src/spec/ruby/rack/util_spec.rb

@@ -0,0 +1,51 @@
+# encoding: UTF-8
+#--
+# This source code is available under the MIT license.
+# See the file LICENSE.txt for details.
+#++
+
+require File.expand_path('spec_helper', File.dirname(__FILE__) + '/..')
+
+describe org.jruby.rack.util.IOHelpers do
+  
+  IOHelpers = org.jruby.rack.util.IOHelpers
+  
+  it "reads a stream into a string" do
+    code = "# comment\n" +
+    "puts 'vůl or kôň';\n" +
+    "exit(0)\n"
+    stream = java.io.ByteArrayInputStream.new code.to_java.getBytes('UTF-8')
+    stream = java.io.BufferedInputStream.new(stream, 8)
+    string = IOHelpers.inputStreamToString(stream)
+    expect( string ).to eql "# comment\nputs 'vůl or kôň';\nexit(0)\n"
+  end
+
+#  it "reads a stream into a string with encoding comment" do
+#    code = "# encoding: ISO-8859-1\n" +
+#    "# another comment \n" +
+#    "puts 'vůl or kôň';\n"
+#    #"puts 'v\xC5\xAFl or k\xC3\xB4\xC5\x88';\n"
+#    bytes = java.lang.String.new(code.to_java.getBytes, "UTF-8").getBytes("ISO-8859-1")
+#    stream = java.io.ByteArrayInputStream.new bytes
+#    string = IOHelpers.inputStreamToString(stream)
+#    expect( string ).to eql "# encoding: ISO-8859-1\n# another comment \nputs 'vůl or kôň';\n"
+#  end
+ 
+  it "reads magic comment 1" do
+    code = "# hello: world \n" +
+    "# comment\n" +
+    "exit(0);"
+    string = IOHelpers.rubyMagicCommentValue(code, "hello:")
+    expect( string ).to eql "world"
+  end
+
+  it "reads magic comment 2" do
+    code = "# encoding: UTF-8 \n" +
+    "# comment\n" +
+    "# rack.version: 1.3.6 \n" +
+    "exit(0)\n'42'"
+    string = IOHelpers.rubyMagicCommentValue(code, "rack.version:")
+    expect( string ).to eql "1.3.6"
+  end
+  
+end