Merge pull request #983 from 3scale/routing-policy-configurable-host-…

…header

Routing policy: allow to modify the Host header

CHANGELOG.md

@@ -15,7 +15,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Added
 
 - "Matches" operation that can be used when defining conditionals [PR #975](https://github.com/3scale/apicast/pull/975)
-- New routing policy that selects an upstream based on the request path, a header, a query argument, or a jwt claim [PR #976](https://github.com/3scale/apicast/pull/976), [THREESCALE-1709](https://issues.jboss.org/browse/THREESCALE-1709)
+- New routing policy that selects an upstream based on the request path, a header, a query argument, or a jwt claim [PR #976](https://github.com/3scale/apicast/pull/976), [PR #983](https://github.com/3scale/apicast/pull/983), [THREESCALE-1709](https://issues.jboss.org/browse/THREESCALE-1709)
 - Added "last" attribute in the mapping rules. When set to true indicates that, if the rule matches, APIcast should not try to match the rules placed after this one [PR #982](https://github.com/3scale/apicast/pull/982), [THREESCALE-1344](https://issues.jboss.org/browse/THREESCALE-1344)
 
 ### Changed

gateway/src/apicast/http_proxy.lua

@@ -138,7 +138,7 @@ function _M.request(upstream, proxy_uri)
     local uri = upstream.uri
 
     if uri.scheme == 'http' then -- rewrite the request to use http_proxy
-        upstream.host = uri.host -- to keep correct Host header in case we need to resolve it to IP
+        upstream:use_host_header(uri.host) -- to keep correct Host header in case we need to resolve it to IP
         upstream.servers = resolve_servers(proxy_uri)
         upstream.uri.path = absolute_url(uri)
         upstream:rewrite_request()

gateway/src/apicast/policy/routing/README.md

@@ -320,3 +320,33 @@ configuration that uses that value to route the request:
     }
   }
 ```
+
+## Set the host used in the Host header
+
+By default, when a request is routed, the policy sets the Host header using the
+host of the URL of the rule that matched. However, it is possible to specify a
+different host with the `host_header` attribute. As an example, this is a
+config that specifies `some_host.com` as the host of the Host header:
+```json
+  {
+    "name": "routing",
+    "version": "builtin",
+    "configuration": {
+      "rules": [
+        {
+          "url": "http://example.com",
+          "host_header": "some_host.com",
+          "condition": {
+            "operations": [
+              {
+                "match": "path",
+                "op": "==",
+                "value": "/"
+              }
+            ]
+          }
+        }
+      ]
+    }
+  }
+```

gateway/src/apicast/policy/routing/apicast-policy.json

@@ -130,6 +130,10 @@
             "url": {
               "type": "string"
             },
+            "host_header": {
+              "description": "Host for the Host header. When not specified, defaults to the host of the URL.",
+              "type": "string"
+            },
             "condition": {
               "type": "object",
               "properties": {

gateway/src/apicast/policy/routing/rule.lua

@@ -58,6 +58,7 @@ function _M.new_from_config_rule(config_rule)
 
   if upstream then
     self.url = config_rule.url
+    self.host_header = config_rule.host_header
     self.condition = init_condition(config_rule.condition)
     return self
   else

gateway/src/apicast/policy/routing/upstream_selector.lua

@@ -25,7 +25,13 @@ function _M.select(_, rules, context)
     local cond_is_true = rule.condition:evaluate(context)
 
     if cond_is_true then
-      return Upstream.new(rule.url)
+      local upstream = Upstream.new(rule.url)
+
+      if rule.host_header and rule.host_header ~= '' then
+        upstream:use_host_header(rule.host_header)
+      end
+
+      return upstream
     end
   end
 

gateway/src/apicast/proxy.lua

@@ -191,7 +191,7 @@ function _M.get_upstream(service)
     return nil, err
   end
 
-  upstream.host = service.hostname_rewrite
+  upstream:use_host_header(service.hostname_rewrite)
 
   return upstream
 end

gateway/src/apicast/upstream.lua

@@ -144,6 +144,10 @@ local function host_header(uri)
     end
 end
 
+function _M:use_host_header(host)
+    self.host = host
+end
+
 --- Rewrite request Host header to what is provided in the argument or in the URL.
 function _M:rewrite_request()
     local uri = self.uri

spec/policy/routing/upstream_selector_spec.lua

@@ -101,5 +101,37 @@ describe('UpstreamSelector', function()
         assert.is_nil(upstream)
       end)
     end)
+
+    describe('when a rule that matches has a host for the Host header', function()
+      describe('and it is not empty', function()
+        it('sets the host for the header', function()
+          local rule = {
+            url = 'http://example.com',
+            condition = true_condition,
+            host_header = 'some_host.com'
+          }
+
+          local upstream_selector = UpstreamSelector.new()
+          local upstream = upstream_selector:select({ rule }, {})
+
+          assert.equals(rule.host_header, upstream.host)
+        end)
+      end)
+
+      describe('and it is empty', function()
+        it('does not set the host for the header', function()
+          local rule = {
+            url = 'http://example.com',
+            condition = true_condition,
+            host_header = ''
+          }
+
+          local upstream_selector = UpstreamSelector.new()
+          local upstream = upstream_selector:select({ rule }, {})
+
+          assert.is_nil(upstream.host)
+        end)
+      end)
+    end)
   end)
 end)

spec/upstream_spec.lua

@@ -271,4 +271,18 @@ describe('Upstream', function()
             end)
         end)
     end)
+
+    describe('.use_host_header', function()
+        before_each(stub_ngx_request)
+
+        it('allows to set the host used when setting the Host Header', function()
+            local upstream = Upstream.new('http://example.com')
+            local host = 'http://another_host'
+
+            upstream:use_host_header(host)
+
+            upstream:rewrite_request()
+            assert.spy(ngx.req.set_header).was_called_with('Host', host)
+        end)
+    end)
 end)

t/apicast-policy-routing.t

@@ -1337,3 +1337,61 @@ yay, api backend
 --- error_code: 200
 --- no_error_log
 [error]
+
+=== TEST 20: choosing a Host Header in a routing rule
+--- configuration
+{
+  "services": [
+    {
+      "id": 42,
+      "proxy": {
+        "policy_chain": [
+          {
+            "name": "apicast.policy.routing",
+            "configuration": {
+              "rules": [
+                {
+                  "url": "http://test:$TEST_NGINX_SERVER_PORT",
+                  "host_header": "example.com",
+                  "condition": {
+                    "operations": [
+                      {
+                        "match": "path",
+                        "op": "==",
+                        "value": "/a_path"
+                      }
+                    ]
+                  }
+                }
+              ]
+            }
+          },
+          {
+            "name": "apicast.policy.echo"
+          }
+        ]
+      }
+    }
+  ]
+}
+--- upstream
+  # We need to put the 'host_header' of the rule here.
+  server_name example.com;
+
+  location /a_path {
+     content_by_lua_block {
+       -- Check that the Host header was rewritten as indicated in the policy
+       -- config.
+       local host_header = ngx.req.get_headers()['Host']
+       require('luassert').equals('example.com', host_header)
+
+       ngx.say('yay, api backend');
+     }
+  }
+--- request
+GET /a_path
+--- response_body
+yay, api backend
+--- error_code: 200
+--- no_error_log
+[error]