Merge pull request #5653 from FuegoFro/cask_handle_already_downloaded_file

Cask handle already downloaded file

Library/Homebrew/test/cask/cmd/info_spec.rb

@@ -136,4 +136,32 @@ describe Cask::Cmd::Info, :cask do
       Caffeine.app (App)
     EOS
   end
+
+  it "can run be run with a url twice" do
+    expect {
+      described_class.run("https://raw.githubusercontent.com/Homebrew/homebrew-cask" \
+                          "/d0b2c58652ae5eff20a7a4ac93292a08b250912b/Casks/docker.rb")
+      described_class.run("https://raw.githubusercontent.com/Homebrew/homebrew-cask" \
+                          "/d0b2c58652ae5eff20a7a4ac93292a08b250912b/Casks/docker.rb")
+    }.to output(<<~EOS).to_stdout
+      ==> Downloading https://raw.githubusercontent.com/Homebrew/homebrew-cask/d0b2c58652ae5eff20a7a4ac93292a08b250912b/Casks/docker.rb.
+      docker: 2.0.0.2-ce-mac81,30215 (auto_updates)
+      https://www.docker.com/community-edition
+      Not installed
+      ==> Names
+      Docker Community Edition
+      Docker CE
+      ==> Artifacts
+      Docker.app (App)
+      ==> Downloading https://raw.githubusercontent.com/Homebrew/homebrew-cask/d0b2c58652ae5eff20a7a4ac93292a08b250912b/Casks/docker.rb.
+      docker: 2.0.0.2-ce-mac81,30215 (auto_updates)
+      https://www.docker.com/community-edition
+      Not installed
+      ==> Names
+      Docker Community Edition
+      Docker CE
+      ==> Artifacts
+      Docker.app (App)
+    EOS
+  end
 end

Library/Homebrew/utils/curl.rb

@@ -51,10 +51,20 @@ def curl_download(*args, to: nil, **options)
   destination = Pathname(to)
   destination.dirname.mkpath
 
-  continue_at = if destination.exist? &&
+  range_stdout = curl_output("--location", "--range", "0-1",
-                   curl_output("--location", "--range", "0-1",
+                             "--dump-header", "-",
-                               "--write-out", "%{http_code}",
+                             "--write-out", "%{http_code}",
-                               "--output", "/dev/null", *args, **options).stdout.to_i == 206 # Partial Content
+                             "--output", "/dev/null", *args, **options).stdout
+  headers, _, http_status = range_stdout.partition("\r\n\r\n")
+
+  supports_partial_download = http_status.to_i == 206 # Partial Content
+  if supports_partial_download &&
+     destination.exist? &&
+     destination.size == %r{^.*Content-Range: bytes \d+-\d+/(\d+)\r\n.*$}m.match(headers)&.[](1)&.to_i
+    return # We've already downloaded all the bytes
+  end
+
+  continue_at = if destination.exist? && supports_partial_download
     "-"
   else
     0