and Fn::Stringify

README.md

@@ -12,6 +12,7 @@ For example, [`Fn::Include`](#fninclude) provides a convenient way to include fi
 * [`Fn::Flatten`](#fnflatten)
 * [`Fn::Map`](#fnmap)
 * [`Fn::Merge`](#fnmerge)
+* [`Fn::Stringify`](#fnstringify)
 
 Tag-based syntax is available in YAML templates. For example,`Fn::Include` becomes `!Include`.
 
@@ -377,6 +378,29 @@ For example, this allows you to merge objects of your template that have been cr
 }
 ```
 
+## Fn::Stringify
+
+`Fn::Stringify` will take the passed value and transform it to a JSON string. This is useful for parameters that require a JSON document as a string. Using this function, you can keep writing your configuration in YAML and let the function transform it into a JSON string.
+
+Another useful application is the use of this function in a config file passed as `--cli-input-json` parameter.
+
+```
+# myconfig.yml
+
+StackName: MyStack
+TemplateBody: !Stringify { Fn::Include: mytemplate.yml }
+Parameters:
+  - ParameterKey: Foo
+    ParameterValue: Bar
+```
+
+You can then simply run the following command to deploy a stack:
+
+```
+cfn-include myconfig.yml | jq 'del(.Metadata)' > myconfig.json
+aws cloudformation create-stack --cli-input-json file://myconfig.json
+```
+
 ## More Examples
 
 See [/examples](https://github.com/monken/cfn-include/tree/master/examples) for templates that call an API Gateway endpoint to collect AMI IDs for all regions. There is also a good amount of [tests](https://github.com/monken/cfn-include/tree/master/t) that might be helpful.

index.js

@@ -57,6 +57,10 @@ function recurse(base, scope, object) {
       return recurse(base, scope, object["Fn::Merge"]).then(function(json) {
         return _.merge.apply(_, json);
       });
+    } else if (object["Fn::Stringify"]) {
+      return recurse(base, scope, object["Fn::Stringify"]).then(function(json) {
+        return JSON.stringify(json);
+      });
     } else {
       return Promise.props(_.mapValues(object, _.bind(recurse, this, base, scope)))
     }

lib/schema.js

@@ -4,6 +4,8 @@ _ = require('lodash');
 var tags = [
   { short: 'Include', full: 'Fn::Include', type: 'scalar' },
   { short: 'Include', full: 'Fn::Include', type: 'mapping' },
+  { short: 'Stringify', full: 'Fn::Stringify', type: 'sequence' },
+  { short: 'Stringify', full: 'Fn::Stringify', type: 'mapping' },
   { short: 'Map', full: 'Fn::Map', type: 'sequence' },
   { short: 'Flatten', full: 'Fn::Flatten', type: 'sequence' },
   { short: 'Merge', full: 'Fn::Merge', type: 'sequence' },

t/include.js

@@ -12,10 +12,11 @@ var tests = [
   'merge.json',
   'errors.js',
   'yaml.js',
+  'stringify.json',
 ];
 if(process.env['TEST_AWS']) tests.push('s3.json', 'api.js');
 
-//var tests = ['yaml.js'];
+// var tests = [];
 
 tests.forEach(function(file) {
   var tests = require('./tests/' + file);

t/includes/stringify.yml

@@ -0,0 +1 @@
+TemplateBody: !Stringify { Fn::Include: foobar.json }

t/tests/stringify.json

@@ -0,0 +1,33 @@
+{
+  "stringify": [{
+    "name": "basic json",
+    "template": {
+      "Fn::Stringify": {
+        "Fn::Map": [
+          [1, 2, 3], "_"
+        ]
+      }
+    },
+    "output": "[1,2,3]"
+  }, {
+    "name": "array",
+    "template": {
+      "Fn::Stringify": [1,2,3]
+    },
+    "output": "[1,2,3]"
+  }, {
+    "name": "nested includes json",
+    "template": {
+      "Fn::Stringify": {
+        "Fn::Include": "includes/foobar.json"
+      }
+    },
+    "output": "{\"foo\":\"bar\"}"
+  }, {
+    "name": "yaml",
+    "template": {
+      "Fn::Include": "includes/stringify.yml"
+    },
+    "output": { "TemplateBody": "{\"foo\":\"bar\"}" }
+  }]
+}