If you generate a PDF using iText5 twice you get different results. The creation date, modification date and ID are different. This means that it’s difficult to write a test that is repeatable. It’s also not ideal to mock out the whole PDF generation from a library that’s sole purpose is to manipulate PDF as it gives no confidence the code works.
I decided to read the PDF Reference which documents the PDF format on disk to figure out how to write a binary comparison function that ignores the differences.
Reading the binary data we can see we have this difference:
diff -y <(xxd 1.pdf) <(xxd 2.pdf) | colordiff
Compare PDF Binary data
import java.io._
import java.nio.file.Files
object Main {
def main(args :Array[String]) = {
if (args.length < 2) {
println("usage: scala comparePDFs.scala 1.pdf 2.pdf")
sys.exit(2)
}
println(s"file 1: ${args(0)}")
println(s"file 2: ${args(1)}")
val file1 = fileToByteArray(args(0))
val file2 = fileToByteArray(args(1))
comparePDFs(file1, file2) match {
case true => println("they match")
case false => println("they dont match")
}
}
def fileToByteArray(filename :String) :Array[Byte] = Files.readAllBytes(new File(filename).toPath())
def comparePDFs(file1 :Array[Byte], file2 :Array[Byte]) :Boolean = {
val file1str = new String(file1, "UTF-8")
val file2str = new String(file2, "UTF-8")
val file1cleaned = cleanStr(file1str)
val file2cleaned = cleanStr(file2str)
println(file1cleaned)
println(file2cleaned)
return file1cleaned.equals(file2cleaned)
}
def cleanStr(fileStr :String) :String = {
val idRegex = "/ID \\[.*\\]".r
val creationDateRegex = "/CreationDate(.*)".r
val modifiedDateRegex = "/ModDate(.*)".r
val fileMinusID = idRegex.replaceFirstIn(fileStr, "")
val fileMinusIDAndCreation = creationDateRegex.replaceFirstIn(fileMinusID, "")
val fileMinusIDCreationAndMod = modifiedDateRegex.replaceFirstIn(fileMinusIDAndCreation,"")
return fileMinusIDCreationAndMod
}
}
Not the best code, but hopefully useful.