parse_curl_response: Handle duplicate headers

`Curl#parse_curl_response` only includes the last instance of a given
header in its `:headers` hash (replicating pre-existing behavior).
This is a problem for headers like `Set-Cookie`, which can appear more
than once in a response.

This commit addresses the issue by collecting duplicate headers into
an array instead. Headers that only appear once in the response will
still have a string value but headers that appear more than once will
be an array of strings. Whenever headers from `#parse_curl_response`
are used (directly or indirectly), it's important to conditionally
handle the expected types.

Library/Homebrew/test/utils/curl_spec.rb

@@ -112,6 +112,24 @@ describe "Utils::Curl" do
       },
     }
 
+    response_hash[:duplicate_header] = {
+      status_code: "200",
+      status_text: "OK",
+      headers:     {
+        "cache-control"  => "max-age=604800",
+        "content-type"   => "text/html; charset=UTF-8",
+        "date"           => "Wed, 1 Jan 2020 01:23:45 GMT",
+        "expires"        => "Wed, 31 Jan 2020 01:23:45 GMT",
+        "last-modified"  => "Thu, 1 Jan 2019 01:23:45 GMT",
+        "content-length" => "123",
+        "set-cookie"     => [
+          "example1=first",
+          "example2=second; Expires Wed, 31 Jan 2020 01:23:45 GMT",
+          "example3=third",
+        ],
+      },
+    }
+
     response_hash
   }
 
@@ -144,6 +162,13 @@ describe "Utils::Curl" do
       #{response_text[:ok]}
     EOS
 
+    response_text[:duplicate_header] = response_text[:ok].sub(
+      /\r\n\Z/,
+      "Set-Cookie: #{response_hash[:duplicate_header][:headers]["set-cookie"][0]}\r\n" \
+      "Set-Cookie: #{response_hash[:duplicate_header][:headers]["set-cookie"][1]}\r\n" \
+      "Set-Cookie: #{response_hash[:duplicate_header][:headers]["set-cookie"][2]}\r\n\r\n",
+    )
+
     response_text
   }
 
@@ -312,6 +337,7 @@ describe "Utils::Curl" do
     it "returns a correct hash when given HTTP response text" do
       expect(parse_curl_response(response_text[:ok])).to eq(response_hash[:ok])
       expect(parse_curl_response(response_text[:redirection])).to eq(response_hash[:redirection])
+      expect(parse_curl_response(response_text[:duplicate_header])).to eq(response_hash[:duplicate_header])
     end
 
     it "returns an empty hash when given an empty string" do

Library/Homebrew/utils/curl.rb

@@ -484,10 +484,25 @@ module Utils
       response_text = response_text.sub(%r{^HTTP/.* (\d+).*$\s*}, "")
 
       # Create a hash from the header lines
-      response[:headers] =
-        response_text.split("\r\n")
-                     .to_h { |header| header.split(/:\s*/, 2) }
-                     .transform_keys(&:downcase)
+      response[:headers] = {}
+      response_text.split("\r\n").each do |line|
+        header_name, header_value = line.split(/:\s*/, 2)
+        next if header_name.blank?
+
+        header_name = header_name.strip.downcase
+        header_value&.strip!
+
+        case response[:headers][header_name]
+        when nil
+          response[:headers][header_name] = header_value
+        when String
+          response[:headers][header_name] = [response[:headers][header_name], header_value]
+        when Array
+          response[:headers][header_name].push(header_value)
+        end
+
+        response[:headers][header_name]
+      end
 
       response
     end