From b0124c4fb0fea355eb8e94a7a154858aa4d361fc Mon Sep 17 00:00:00 2001
From: Danny Weinberg <danny.weinberg@discordapp.com>
Date: Fri, 1 Feb 2019 14:22:36 -0800
Subject: [PATCH] Cask handle already downloaded file

The current logic for curl_download tries to restart any existing
partial download, but this fails for some servers when the file is
already fully downloaded, returning a status code 416. This updates the
function to check for the file being already downloaded and if so bails
early.

The following command used to fail when run more than once but now works
as expected:
```
brew cask info https://raw.githubusercontent.com/homebrew/homebrew-cask/master/Casks/docker.rb
```
---
 Library/Homebrew/test/cask/cmd/info_spec.rb | 28 +++++++++++++++++++++
 Library/Homebrew/utils/curl.rb              | 18 ++++++++++---
 2 files changed, 42 insertions(+), 4 deletions(-)

diff --git a/Library/Homebrew/test/cask/cmd/info_spec.rb b/Library/Homebrew/test/cask/cmd/info_spec.rb
index 1685b22483..ae5ad215ef 100644
--- a/Library/Homebrew/test/cask/cmd/info_spec.rb
+++ b/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
diff --git a/Library/Homebrew/utils/curl.rb b/Library/Homebrew/utils/curl.rb
index 5b0c5a66db..bcc47d4394 100644
--- a/Library/Homebrew/utils/curl.rb
+++ b/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? &&
-                   curl_output("--location", "--range", "0-1",
-                               "--write-out", "%{http_code}",
-                               "--output", "/dev/null", *args, **options).stdout.to_i == 206 # Partial Content
+  range_stdout = curl_output("--location", "--range", "0-1",
+                             "--dump-header", "-",
+                             "--write-out", "%{http_code}",
+                             "--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