Help wanted to implement combined download+verify task

[liblit]

Using Gradle 4.6 and gradle-download-task 3.4.0, the vast majority of my downloads have the same general pattern: download a given URL to a given file, then verify that download using a given checksum. I would like to refactor this recurring pattern into a custom task, but I don‘t know how. This is really more of a support question than a bug report, but I hope that you will lend me some wisdom so that I can use gradle-download-task more awesomely.

The following is a representative example of a typical download task:

task downloadJLex {
  outputs.file 'src/JLex/Main.java'  // varies
  doLast {
    download {
      src 'http://www.cs.princeton.edu/~appel/modern/java/JLex/current/Main.java'  // varies
      dest outputs.files.singleFile
      overwrite true
    }
    verifyChecksum {
      src outputs.files.singleFile
      checksum 'fe0cff5db3e2f0f5d67a153cf6c783af'  // varies
    }
  }
}

Other than the task name, three // varies comments above mark the only parts of this pattern vary throughout my project:

1. The output file into which the URL should be saved.
2. The URL to download.
3. The checksum used to verify the download.

My partial, non-working effort to create a custom class consists of the following Gradle code added directly to a subproject's build.gradle:

class VerifiedDownload extends org.gradle.api.DefaultTask {

  @Input String src
  @Input String checksum
  @OutputFile File dest

  @TaskAction
  downloadAndVerify() {
    download {
      src this.src
      dest this.dest
      overwrite true
      onlyIfModified true
    }
    verifyChecksum {
      src this.dest
      checksum this.checksum
    }
  }
}

Unfortunately, my use of download and verifyChecksum is wrong. If I try to instantiate my custom task...

task downloadJLex(type: VerifiedDownload) {
  src 'http://www.cs.princeton.edu/~appel/modern/java/JLex/current/Main.java'
  checksum 'fe0cff5db3e2f0f5d67a153cf6c783af'
  dest file('src/JLex/Main.java')
}

... then Gradle fails, reporting Could not find method download() for arguments [VerifiedDownload$_downloadAndVerify_closure1@49958194] on task ':com.ibm.wala.cast.java.test.data:downloadJLex' of type VerifiedDownload.

I suspect that my use of this.src, this.dest, and this.checksum in the VerifiedDownload constructor may be bogus as well. I am not sure how to access these fields of the current VerifiedDownload task instance versus invoking the src, dest, and checksum methods that would be available inside the download and verifyChecksum if I were using those blocks correctly.

I hope that my intention is clear from the above examples. I would be grateful for any hints as to the right way to turn that intention into working code.

[michel-kraemer]

Please try project.download and project.verifyChecksum instead of download and verifyChecksum.

[liblit]

project.download and project.verifyChecksum worked perfectly. Thank you, @michel-kraemer!