CORS header tests for Gateway

- Implements
  https://github.com/ipfs/go-ipfs/pull/2232#issuecomment-173742385
- Separate test suite:
    - we don't want to pollute other gateway tests with CORS headers
    - (as of now) changing headers requires daemon restart anyway

License: MIT
Signed-off-by: Marcin Rataj <lidel@lidel.org>

test/sharness/t0112-gateway-cors.sh

+#!/bin/sh
+#
+# Copyright (c) 2016 Marcin Rataj
+# MIT Licensed; see the LICENSE file in this repository.
+#
+
+test_description="Test HTTP Gateway CORS Support"
+
+test_config_ipfs_cors_headers() {
+    ipfs config --json Gateway.HTTPHeaders.Access-Control-Allow-Origin '["*"]'
+    ipfs config --json Gateway.HTTPHeaders.Access-Control-Allow-Methods '["PUT", "GET", "POST"]'
+    ipfs config --json Gateway.HTTPHeaders.Access-Control-Allow-Headers '["X-Requested-With"]'
+
+    ipfs config --json API.HTTPHeaders.Access-Control-Allow-Origin '["*"]'
+    ipfs config --json API.HTTPHeaders.Access-Control-Allow-Methods '["PUT", "GET", "POST"]'
+    ipfs config --json API.HTTPHeaders.Access-Control-Allow-Headers '["X-Requested-With"]'
+}
+
+. lib/test-lib.sh
+
+test_init_ipfs
+test_config_ipfs_gateway_readonly $ADDR_GWAY
+test_config_ipfs_cors_headers
+test_launch_ipfs_daemon
+
+gwport=$PORT_GWAY
+apiport=$PORT_API
+thash='QmUNLLsPACCz1vLxQVkXqqLX5R1X345qqfHbsf67hvA3Nn'
+
+# Gateway
+
+# HTTP GET Request
+test_expect_success "GET to Gateway succeeds" '
+    curl -svX GET "http://127.0.0.1:$gwport/ipfs/$thash" 2>curl_output
+'
+# GET Response from Gateway should contain CORS headers
+test_expect_success "GET response for Gateway resource looks good" '
+    grep "Access-Control-Allow-Origin:" curl_output &&
+    grep "Access-Control-Allow-Methods:" curl_output &&
+    grep "Access-Control-Allow-Headers:" curl_output
+'
+
+# HTTP OPTIONS Request
+test_expect_success "OPTIONS to Gateway succeeds" '
+    curl -svX OPTIONS "http://127.0.0.1:$gwport/ipfs/$thash" 2>curl_output
+'
+# OPTION Response from Gateway should contain CORS headers
+test_expect_success "OPTIONS response for Gateway resource looks good" '
+    grep "Access-Control-Allow-Origin:" curl_output &&
+    grep "Access-Control-Allow-Methods:" curl_output &&
+    grep "Access-Control-Allow-Headers:" curl_output
+'
+
+# Read-Only API (at the Gateway Port)
+
+# HTTP GET Request
+test_expect_success "GET to API succeeds" '
+    curl -svX GET "http://127.0.0.1:$gwport/api/v0/cat?arg=$thash" 2>curl_output
+'
+# GET Response from the API should NOT contain CORS headers
+# Blacklisting: https://git.io/vzaj2
+# Rationale: https://git.io/vzajX
+test_expect_success "OPTIONS response for API looks good" '
+    grep -q "Access-Control-Allow-" curl_output && false || true
+'
+
+# HTTP OPTIONS Request
+test_expect_success "OPTIONS to API succeeds" '
+    curl -svX OPTIONS "http://127.0.0.1:$gwport/api/v0/cat?arg=$thash" 2>curl_output
+'
+# OPTIONS Response from the API should NOT contain CORS headers
+test_expect_success "OPTIONS response for API looks good" '
+    grep -q "Access-Control-Allow-" curl_output && false || true
+'
+
+test_kill_ipfs_daemon
+
+test_done