From c659fe826f54319d93da32d4b11ae6c672df2a65 Mon Sep 17 00:00:00 2001
From: Stephen Paul Weber <singpolyma@singpolyma.net>
Date: Tue, 12 Mar 2019 21:08:12 -0500
Subject: [PATCH] If trying to import from IPFS, fallback to gateway

---
 .rubocop.yml         |  3 ++
 Gemfile              |  1 +
 lib/dhall/ast.rb     |  6 +++-
 lib/dhall/resolve.rb | 72 ++++++++++++++++++++++++++++++++++++++++++--
 test/test_resolve.rb | 30 ++++++++++++++++++
 5 files changed, 108 insertions(+), 4 deletions(-)

diff --git a/.rubocop.yml b/.rubocop.yml
index 890bdce..2298bfa 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -67,6 +67,9 @@ Style/StringLiteralsInInterpolation:
 Style/SymbolArray:
   EnforcedStyle: brackets
 
+Style/WordArray:
+  EnforcedStyle: brackets
+
 Naming/UncommunicativeBlockParamName:
   Enabled: false
 
diff --git a/Gemfile b/Gemfile
index 83fe124..e384e6e 100644
--- a/Gemfile
+++ b/Gemfile
@@ -5,3 +5,4 @@ source "https://rubygems.org"
 gem "cbor"
 gem "promise.rb"
 gem "value_semantics"
+gem "webmock"
diff --git a/lib/dhall/ast.rb b/lib/dhall/ast.rb
index d73af4b..2bb6d0e 100644
--- a/lib/dhall/ast.rb
+++ b/lib/dhall/ast.rb
@@ -572,7 +572,7 @@ module Dhall
 				(uri.scheme == "https" ? Https : Http).new(
 					nil,
 					"#{uri.host}:#{uri.port}",
-					uri.path.split(/\//)[1..-1],
+					*uri.path.split(/\//)[1..-1],
 					uri.query,
 					nil
 				)
@@ -636,6 +636,10 @@ module Dhall
 			def pathname
 				Pathname.new("/").join(*path)
 			end
+
+			def to_uri(scheme, authority)
+				scheme.new(nil, authority, *path, nil, nil)
+			end
 		end
 
 		class RelativePath < Path
diff --git a/lib/dhall/resolve.rb b/lib/dhall/resolve.rb
index 837e541..7b677ff 100644
--- a/lib/dhall/resolve.rb
+++ b/lib/dhall/resolve.rb
@@ -21,7 +21,9 @@ module Dhall
 		ReadHttpSources = lambda do |sources|
 			sources.map do |source|
 				Promise.resolve(nil).then do
-					Net::HTTP.get(source.uri)
+					r = Net::HTTP.get_response(source.uri)
+					raise ImportFailedException, source if r.code != "200"
+					r.body
 				end
 			end
 		end
@@ -32,6 +34,50 @@ module Dhall
 			end
 		end
 
+		class ReadPathAndIPFSSources
+			def initialize(
+				path_reader: ReadPathSources,
+				http_reader: ReadHttpSources,
+				https_reader: http_reader,
+				public_gateway: "cloudflare-ipfs.com"
+			)
+				@path_reader = path_reader
+				@http_reader = http_reader
+				@https_reader = https_reader
+				@public_gateway = public_gateway
+			end
+
+			def call(sources)
+				@path_reader.call(sources).map.with_index do |promise, idx|
+					source = sources[idx]
+					if source.is_a?(Import::AbsolutePath) &&
+					   ["ipfs", "ipns"].include?(source.path.first)
+						gateway_fallback(source, promise)
+					else
+						promise
+					end
+				end
+			end
+
+			def to_proc
+				method(:call).to_proc
+			end
+
+			protected
+
+			def gateway_fallback(source, promise)
+				promise.catch {
+					@http_reader.call([
+						source.to_uri(Import::Http, "localhost:8000")
+					]).first
+				}.catch do
+					@https_reader.call([
+						source.to_uri(Import::Https, @public_gateway)
+					]).first
+				end
+			end
+		end
+
 		class ResolutionSet
 			attr_reader :reader
 
@@ -66,7 +112,7 @@ module Dhall
 			end
 		end
 
-		class Default
+		class Standard
 			def initialize(
 				path_reader: ReadPathSources,
 				http_reader: ReadHttpSources,
@@ -111,7 +157,27 @@ module Dhall
 			end
 		end
 
-		class LocalOnly < Default
+		class Default < Standard
+			def initialize(
+				path_reader: ReadPathSources,
+				http_reader: ReadHttpSources,
+				https_reader: http_reader,
+				ipfs_public_gateway: "cloudflare-ipfs.com"
+			)
+				super(
+					path_reader:  ReadPathAndIPFSSources.new(
+						path_reader:    path_reader,
+						http_reader:    http_reader,
+						https_reader:   https_reader,
+						public_gateway: ipfs_public_gateway
+					),
+					http_reader:  http_reader,
+					https_reader: https_reader
+				)
+			end
+		end
+
+		class LocalOnly < Standard
 			def initialize(path_reader: ReadPathSources)
 				super(
 					path_reader:  path_reader,
diff --git a/test/test_resolve.rb b/test/test_resolve.rb
index 080df84..8b16380 100644
--- a/test/test_resolve.rb
+++ b/test/test_resolve.rb
@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require "base64"
+require "webmock/minitest"
 require "minitest/autorun"
 
 require "dhall/resolve"
@@ -172,6 +173,35 @@ class TestResolve < Minitest::Test
 		assert_equal Dhall::Variable["_"], expr.resolve(@resolver).sync
 	end
 
+	def test_ipfs
+		stub_request(:get, "http://localhost:8000/ipfs/TESTCID")
+			.to_return(status: 200, body: "\x00")
+
+		expr = Dhall::Import.new(
+			nil,
+			Dhall.method(:from_binary),
+			Dhall::Import::AbsolutePath.new("ipfs", "TESTCID")
+		)
+
+		assert_equal Dhall::Variable["_"], expr.resolve.sync
+	end
+
+	def test_ipfs_public_gateway
+		stub_request(:get, "http://localhost:8000/ipfs/TESTCID")
+			.to_return(status: 500)
+
+		stub_request(:get, "https://cloudflare-ipfs.com/ipfs/TESTCID")
+			.to_return(status: 200, body: "\x00")
+
+		expr = Dhall::Import.new(
+			nil,
+			Dhall.method(:from_binary),
+			Dhall::Import::AbsolutePath.new("ipfs", "TESTCID")
+		)
+
+		assert_equal Dhall::Variable["_"], expr.resolve.sync
+	end
+
 	# Sanity check that all expressions can pass through the resolver
 	Pathname.glob(TESTS + "**/*A.dhallb").each do |path|
 		test = path.relative_path_from(TESTS).to_s.sub(/A\.dhallb$/, "")
-- 
2.38.5