Property cleanup (#202)

* cleanup property doc; use non-deprecated method for registration

* tweak example

* cleanup doc

* cleanup doc

* cleanup doc

* automatically load built-in external property resolvers

* fix cyclic dependency

Author: Frank Martinez

app/propertyresolver/env.go

@@ -6,11 +6,11 @@ import (
 	"strings"
 
 	"github.com/project-flogo/core/data/property"
-	"github.com/project-flogo/core/engine"
 	"github.com/project-flogo/core/support/log"
 )
 
 const EnvAppPropertyEnvConfigKey = "FLOGO_APP_PROPS_ENV"
+const ResolverNameEnv  = "env"
 
 type PropertyMappings struct {
 	Mappings map[string]string `json:"mappings"`
@@ -36,7 +36,7 @@ func init() {
 				panic("")
 			}
 		}
-		_ = property.RegisterPropertyResolver(resolver)
+		_ = property.RegisterExternalResolver(resolver)
 	}
 }
 
@@ -55,7 +55,7 @@ type EnvVariableValueResolver struct {
 }
 
 func (resolver *EnvVariableValueResolver) Name() string {
-	return engine.PropertyResolverEnv
+	return ResolverNameEnv
 }
 
 func (resolver *EnvVariableValueResolver) LookupValue(key string) (interface{}, bool) {

app/propertyresolver/json.go

@@ -2,12 +2,11 @@ package propertyresolver
 
 import (
 	"encoding/json"
-	"github.com/project-flogo/core/data/property"
-	"github.com/project-flogo/core/engine"
 	"io/ioutil"
 	"os"
 	"strings"
 
+	"github.com/project-flogo/core/data/property"
 	"github.com/project-flogo/core/support/log"
 )
 
@@ -18,6 +17,7 @@ var preload = make(map[string]interface{})
 // Comma separated list of json files overriding default application property values
 // e.g. FLOGO_APP_PROPS_JSON=app1.json,common.json
 const EnvAppPropertyFileConfigKey = "FLOGO_APP_PROPS_JSON"
+const ResolverNameJson = "json"
 
 func init() {
 
@@ -26,7 +26,7 @@ func init() {
 	filePaths := getExternalFiles()
 	if filePaths != "" {
 		// Register value resolver
-		_ = property.RegisterPropertyResolver(&JSONFileValueResolver{})
+		_ = property.RegisterExternalResolver(&JSONFileValueResolver{})
 
 		// preload props from files
 		files := strings.Split(filePaths, ",")
@@ -66,7 +66,7 @@ type JSONFileValueResolver struct {
 }
 
 func (resolver *JSONFileValueResolver) Name() string {
-	return engine.PropertyResolverJson
+	return ResolverNameJson
 }
 
 func (resolver *JSONFileValueResolver) LookupValue(toResolve string) (interface{}, bool) {

data/property/external.go

@@ -17,6 +17,7 @@ var (
 
 // Resolver used to resolve property value from external configuration like env, file etc
 type ExternalResolver interface {
+	// Name of the resolver (e.g., consul)
 	Name() string
 	// Should return value and true if the given key exists in the external configuration otherwise should return nil and false.
 	LookupValue(key string) (interface{}, bool)

docs/properties.md

@@ -72,15 +72,33 @@ Even though the engine itself doesn't support property grouping, this can be acc
 
 These properties can be accessed via `$property[PURCHASE.SERVICE.DB.URL]` or `$property[INVENTORY.SERVICE.DB.URL]`
 
-### Overriding poperties at runtime
+### Overriding properties at runtime
+
+In order to override properties at runtime, you have to enable external property resolvers.
+
+This can be done by setting the `FLOGO_APP_PROP_RESOLVERS` environment variable.  Currently, there are two built-in external
+property resolvers: json(JSON) and env(Environment Variable).
+
+
+```terminal
+FLOGO_APP_PROP_RESOLVERS=env,json ./<app_binary>
+```
 
 You can override app properties at runtime in two ways:
 
-#### Using JSON
+#### Resolver: json
+
+When using the `json` property resolver, you can provide a comma separated list of json files that
+will override the application's existing property values.
+```env
+FLOGO_APP_PROPS_JSON=app1.json,common.json
+```
 
-Define your new value for a given app prop in a json file as shown below:
+**Example**
 
-props.json:
+Let's say you want to override some of your properties.  You will need to define your new value for a given property in your json file.
+
+_props.json_
 
 ```json
 {
@@ -89,60 +107,76 @@ props.json:
 }
 ```
 
-Run the application with the environment variable `FLOGO_APP_PROPS_OVERRIDE` set to `props.json`. For example:
+Now run your application:
 
 ```terminal
-FLOGO_APP_PROPS_OVERRIDE=props.json ./MyApp
+
+export FLOGO_APP_PROPS_JSON=props.json 
+FLOGO_APP_PROP_RESOLVERS=json ./MyApp
 ```
-or
+
+#### Resolver: env
+
+In order to override properties using environment variables, you just need enable the `env` property resolver
 
 ```terminal
-export FLOGO_APP_PROPS_OVERRIDE=props.json 
-./MyApp
+FLOGO_APP_PROP_RESOLVERS=env ./<app_binary>
 ```
 
+**Example**
 
-#### Using Key/Value pair
-
-Run the application with the environment variable `FLOGO_APP_PROPS_OVERRIDE` set to the key/value pairs. For example:
+Let's say you want to override `myprop` property in your app.  You would do the following:
 
 ```terminal
-FLOGO_APP_PROPS_OVERRIDE="MyProp1=This is newvalue,MyProp2=30" ./MyApp
+
+export myprop=bar
+FLOGO_APP_PROP_RESOLVERS=env ./MyApp
 ```
 
-### Working with external configuration management services
 
-You can plug-in your proeprty value resolver to resolve application property values from external configuration management services, such as, Consul, Spring Cloud Config etc. Just implement the following interface and register implementation with the runtime:
+### Custom External Resolver
+
+You can plug-in your own property resolver to resolve application property values from external configuration management services, such as, Consul, Spring Cloud Config etc. Just implement the following interface and register implementation with the runtime:
 
 ```go
-// PropertyValueResolver used to resolve value from external configuration like env, file etc
-type PropertyValueResolver interface {
-	// Should return value and true if the given application property exists in the external configuration otherwise should return nil and false.
-	LookupValue(propertyName string) (interface{}, bool)
+// Resolver used to resolve property value from external configuration like env, file etc
+type ExternalResolver interface {
+	// Name of the resolver (e.g., consul)
+	Name() string
+	// Should return value and true if the given key exists in the external configuration otherwise should return nil and false.
+	LookupValue(key string) (interface{}, bool)
 }
+
 ```
 
 #### Sample Resolver
 
 ```go
 package sampleresolver
 
+import "github.com/project-flogo/core/data/property"
+
+
 type SamplePropertyResolver struct {
 }
 
 func init() {
-  app.RegisterPropertyValueResolver("sampleresolver", &SamplePropertyResolver{})
+  _ = property.RegisterExternalResolver(&SamplePropertyResolver{})
+}
+
+func (resolver *SamplePropertyResolver) Name() string {
+   return "sampleresolver"
 }
 
 func (resolver *SamplePropertyResolver) LookupValue(propertyName string) (interface{}, bool) {
    // Resolve property value
-  return some_value, true
+  return "some_value"", true
 }
 ```
-*Note: In order for your resolver to be loaded in the go code, you need to add an entry to your resolver in the imports section of the the engine.json*
+*Note: In order for your resolver to be loaded in the go code, you need to add an entry to your resolver in the imports section of the engine.json*
 
 
-Set the `FLOGO_APP_PROPS_RESOLVERS` env var to `sampleresolver` while running application. For example:
+Set the `FLOGO_APP_PROP_RESOLVERS` environment variable to `sampleresolver` while running your application. For example:
 
 ```terminal
 FLOGO_APP_PROPS_RESOLVERS=sampleresolver ./<app_binary>

engine/envconfig.go

@@ -6,6 +6,7 @@ import (
 	"strconv"
 	"strings"
 
+	"github.com/project-flogo/core/app/propertyresolver"
 	"github.com/project-flogo/core/data/property"
 	"github.com/project-flogo/core/engine/runner"
 	"github.com/project-flogo/core/support/log"
@@ -32,9 +33,6 @@ const (
 
 	ValueRunnerTypePooled = "POOLED"
 	ValueRunnerTypeDirect = "DIRECT"
-
-	PropertyResolverEnv  = "env"
-	PropertyResolverJson = "json"
 )
 
 func IsSchemaSupportEnabled() bool {
@@ -149,7 +147,7 @@ func GetAppPropertyValueResolvers(logger log.Logger) string {
 		var resolvers, builtinResolvers []string
 
 		for resolver := range property.RegisteredResolvers {
-			if resolver != PropertyResolverEnv && resolver != PropertyResolverJson {
+			if resolver != propertyresolver.ResolverNameEnv && resolver != propertyresolver.ResolverNameJson {
 				resolvers = append(resolvers, resolver)
 			} else {
 				builtinResolvers = append(builtinResolvers, resolver)
@@ -163,7 +161,7 @@ func GetAppPropertyValueResolvers(logger log.Logger) string {
 		}
 
 		if len(builtinResolvers) == 2 { // force priority between the two builtin resolvers
-			builtinResolvers = []string{PropertyResolverEnv, PropertyResolverJson}
+			builtinResolvers = []string{propertyresolver.ResolverNameEnv, propertyresolver.ResolverNameJson}
 		}
 
 		resolvers = append(resolvers, builtinResolvers...)