When serving output files, intelligently determine the appropriate content-type.

cherry pick 6fa3fda3ed28239cf3ac9720629f9707663aa197 from datajoy.

test/unit/coffee/ContentTypeMapperTests.coffee

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+SandboxedModule = require('sandboxed-module')
+sinon = require('sinon')
+require('chai').should()
+modulePath = require('path').join __dirname, '../../../app/js/ContentTypeMapper'
+
+describe 'ContentTypeMapper', ->
+
+	beforeEach ->
+		@ContentTypeMapper = SandboxedModule.require modulePath
+
+	describe 'map', ->
+
+		it 'should map .txt to text/plain', ->
+			content_type = @ContentTypeMapper.map('example.txt')
+			content_type.should.equal 'text/plain'
+
+		it 'should map .csv to text/csv', ->
+			content_type = @ContentTypeMapper.map('example.csv')
+			content_type.should.equal 'text/csv'
+
+		it 'should map .pdf to application/pdf', ->
+			content_type = @ContentTypeMapper.map('example.pdf')
+			content_type.should.equal 'application/pdf'
+
+		it 'should fall back to octet-stream', ->
+			content_type = @ContentTypeMapper.map('example.unknown')
+			content_type.should.equal 'application/octet-stream'
+
+		describe 'coercing web files to plain text', ->
+
+			it 'should map .js to plain text', ->
+				content_type = @ContentTypeMapper.map('example.js')
+				content_type.should.equal 'text/plain'
+
+			it 'should map .html to plain text', ->
+				content_type = @ContentTypeMapper.map('example.html')
+				content_type.should.equal 'text/plain'
+
+			it 'should map .css to plain text', ->
+				content_type = @ContentTypeMapper.map('example.css')
+				content_type.should.equal 'text/plain'
+
+		describe 'image files', ->
+
+			it 'should map .png to image/png', ->
+				content_type = @ContentTypeMapper.map('example.png')
+				content_type.should.equal 'image/png'
+
+			it 'should map .jpeg to image/jpeg', ->
+				content_type = @ContentTypeMapper.map('example.jpeg')
+				content_type.should.equal 'image/jpeg'