Add initial support for docker secrets

README.md

@@ -41,6 +41,26 @@ console.log(config);
 - It is possible to change `%` to any other character. Just use `replaceEnv` configuration option.
 - It is possible to use default values when environmental variable is not set.
 
+### Docker secret replacement
+
+/tmp/config.json:
+``` javascript
+{ docks1: "%{DOCKER_SECRET1}", docks2: "%{DOCKER_SECRET2|def}" }
+```
+index.js:
+``` javascript
+var readConfig = require('read-config'),
+    config = readConfig('/tmp/config.json');
+
+console.log(config);
+// If secret file content DOCKER_SECRET1 is 'abc' and DOCKER_SECRET2 is not defined
+//  $ node index.js
+//  { docks1: 'abc', env2: 'def' }
+```
+
+- It is possible to change `#` to any other character. Just use `replaceDockerSecret` configuration option.
+- It is possible to use default values when docker secret is not present.
+
 ### Configuration overriding with system variables
 
 /tmp/config.json:
@@ -225,7 +245,8 @@ All json files are loaded using [JSON5](https://www.npmjs.com/package/json5) lib
     - **optional** - (String/Array, default: []) list of configuration paths that are optional. If any configuration path is not resolved and is not optional it's treated as empty file and no exception is raised.
     - **basedir** - (String/Array, default: []) base directory (or directories) used for searching configuration files. Mind that `basedir` has lower priority than a configuration directory, process basedir, and absolute paths.
     - **replaceEnv** - (Boolean/String, default: false, constraint: A string value must be different than `replaceLocal`) if specified enables environment variable replacement. Expected string value e.g. `%` that will be used to replace all occurrences of `%{...}` with environment variables. You can use default values like: %{a.b.c|some-default-value}.
-    - **replaceLocal** - (Boolean/String, default: '@', constraint: A string value must be different than `replaceEnv`) if specified enables configuration variable replacement. Expected string value e.g. `@` that will be used to replace all occurrences of `@{...}` with configuration variables. You can use default values like: @{a.b.c|some-default-value}.
+    - **replaceDockerSecret** - (Boolean/String, default: false, constraint: A string value must be different than `replaceLocal` and `replaceEnv`) if specified enables docker secret file replacement. Expected string value e.g. `#` that will be used to replace all occurrences of `#{...}` with docker secret file content. You can use default values like: #{DOCKER_SECRET|some-default-value}.
+    - **replaceLocal** - (Boolean/String, default: '@', constraint: A string value must be different than `replaceEnv` and `replaceDockerSecret`) if specified enables configuration variable replacement. Expected string value e.g. `@` that will be used to replace all occurrences of `@{...}` with configuration variables. You can use default values like: @{a.b.c|some-default-value}.
     - **override** - (Boolean/String, default: false) If specified enables configuration overriding with environmental variables like `CONFIG_<propertyName>`.
     - **skipUnresolved** - (Boolean, default: false) `true` blocks error throwing on unresolved variables.
 
@@ -237,6 +258,7 @@ Default **opts** values:
     basedir: null,
     replaceEnv: "%",
     replaceLocal: "@",
+    replaceDockerSecret: "#",
     skipUnresolved: false
 }
 ```

lib/read-config.js

@@ -68,6 +68,7 @@ function defaultOptions(opts) {
         basedir: '.',
         replaceEnv: '%',
         replaceLocal: '@',
+        replaceDockerSecret: '#',
         skipUnresolved: false,
         freeze: false
     }, opts);

lib/resolve/index.js

@@ -3,13 +3,15 @@
 const replaceVariables = require('./replace-variables'),
     override = require('./override'),
     moduleName = '[read-config]',
-    ReadConfigError = require('../read-config-error');
+    ReadConfigError = require('../read-config-error'),
+    secrets = require('./secrets');
 
 module.exports = function(config, opts) {
     opts = opts || {};
     config = override(opts.override, config, process.env);
     config = replaceEnvVariables(config, opts.replaceEnv, opts);
     config = replaceLocalVariables(config, opts.replaceLocal, opts);
+    config = replaceDockerSecrets(config, opts.replaceDockerSecret, opts);
     return config;
 };
 
@@ -36,3 +38,15 @@ function replaceLocalVariables(config, marker, opts) {
         return config;
     }
 }
+
+function replaceDockerSecrets(config, marker, opts) {
+    if (marker) {
+        try {
+            return replaceVariables(marker, config, secrets, opts);
+        } catch (e) {
+            throw new ReadConfigError(`${moduleName} Could not resolve docker secret file. ${e.message}`);
+        }
+    } else {
+        return config;
+    }
+}

lib/resolve/secrets.js

@@ -0,0 +1,19 @@
+'use strict';
+
+const fs = require('fs'),
+    path = require('path'),
+    SECRETS_DIR = '/run/secrets',
+    output = {};
+
+if (fs.existsSync(SECRETS_DIR)) {
+    const files = fs.readdirSync(SECRETS_DIR);
+
+    files.forEach((file) => {
+        const fullPath = path.join(SECRETS_DIR, file),
+            key = file,
+            data = fs.readFileSync(fullPath, 'utf8').toString().trim();
+        output[key] = data;
+    });
+}
+
+module.exports = output;