add an optimisation pass for the cached output files

app/coffee/OutputCacheManager.coffee

@@ -5,12 +5,16 @@ Path = require "path"
 logger = require "logger-sharelatex"
 _ = require "underscore"
 
+OutputFileOptimiser = require "./OutputFileOptimiser"
+
 module.exports = OutputCacheManager =
 	CACHE_DIR: '.cache/clsi'
 
 	saveOutputFiles: (outputFiles, target, callback) ->
 		# make a target/build_id directory and
 		# copy all the output files into it
+		# 
+		# TODO: use Path module
 		buildId = 'build-' + Date.now()
 		relDir = OutputCacheManager.CACHE_DIR + '/' + buildId
 		newDir = target + '/' + relDir
@@ -31,7 +35,8 @@ module.exports = OutputCacheManager =
 						else if stats.isFile()
 							#console.log 'isFile: copying'
 							fse.copy src, dst, (err) ->
-								cb(err, newFile)
+								OutputFileOptimiser.optimiseFile src, dst, (err, result) ->
+									cb(err, newFile)
 						else
 							# other filetype - shouldn't happen
 							cb(new Error("output file is not a file"), file)

app/coffee/OutputFileOptimiser.coffee

@@ -0,0 +1,30 @@
+fs = require "fs"
+Path = require "path"
+spawn = require("child_process").spawn
+logger = require "logger-sharelatex"
+
+module.exports = OutputFileOptimiser =
+
+	optimiseFile: (src, dst, callback = (error) ->) ->
+		if src.match(/\.pdf$/)
+			OutputFileOptimiser.optimisePDF src, dst, callback
+		else
+			callback (null)
+
+	optimisePDF: (src, dst, callback = (error) ->) ->
+		tmpOutput = dst + '.opt'
+		args = ["--linearize", src, tmpOutput]
+		logger.log args: args, "running qpdf command"
+
+		proc = spawn("qpdf", args)
+		stdout = ""
+		proc.stdout.on "data", (chunk) ->
+			stdout += chunk.toString()	
+		proc.on "error", callback	
+		proc.on "close", (code) ->
+			if code != 0
+				logger.warn {directory, code}, "qpdf returned error"
+				return callback null
+			fs.rename tmpOutput, dst, (err) ->
+				# could log an error here
+				callback null