Add support in the confmap.Resolver to expand embedded config URIs in…

…side configuration.

Signed-off-by: Bogdan Drutu <[email protected]>

CHANGELOG.md

@@ -192,6 +192,7 @@ There isn't a valid core binary for this release. Use v0.57.2 instead.
 - Use OpenCensus `metric` package for process metrics instead of `stats` package (#5486)
 - Update OTLP to v0.18.0 (#5530)
 - Log histogram min/max fields with `logging` exporter (#5520)
+- Add support in the `confmap.Resolver` to expand embedded config URIs inside configuration (#4742)
 
 ### 🧰 Bug fixes 🧰
 

confmap/README.md

@@ -33,39 +33,51 @@ The `Resolver` receives as input a set of `Providers`, a list of `Converters`, a
 `configURI` that will be used to generate the resulting, or effective, configuration in the form of a `Conf`,
 that can be used by code that is oblivious to the usage of `Providers` and `Converters`.
 
+`Providers` are used to provide an entire configuration when the `configURI` is given directly to the `Resolver`,
+or an individual value (partial configuration) when the `configURI` is embedded into the `Conf` as a values using
+the syntax `${configURI}`.
+
 ```terminal
               Resolver                   Provider
-                 │                          │
    Resolve       │                          │
 ────────────────►│                          │
                  │                          │
               ┌─ │        Retrieve          │
               │  ├─────────────────────────►│
-              │  │                          │
+              │  │          Conf            │
               │  │◄─────────────────────────┤
-   foreach    │  │                          │
+  foreach     │  │                          │
   configURI   │  ├───┐                      │
               │  │   │Merge                 │
               │  │◄──┘                      │
+              └─ │                          │
+              ┌─ │        Retrieve          │
+              │  ├─────────────────────────►│
+              │  │    Partial Conf Value    │
+              │  │◄─────────────────────────┤
+  foreach     │  │                          │
+  embedded    │  │                          │
+  configURI   │  ├───┐                      │
+              │  │   │Replace               │
+              │  │◄──┘                      │
               └─ │                          │
                  │            Converter     │
-                 │                │         │
               ┌─ │     Convert    │         │
               │  ├───────────────►│         │
     foreach   │  │                │         │
    Converter  │  │◄───────────────┤         │
               └─ │                          │
                  │                          │
 ◄────────────────┤                          │
-                 │                          │
 ```
 
 The `Resolve` method proceeds in the following steps:
 
 1. Start with an empty "result" of `Conf` type.
 2. For each config URI retrieves individual configurations, and merges it into the "result".
-2. For each "Converter", call "Convert" for the "result".
-4. Return the "result", aka effective, configuration.
+3. For each embedded config URI retrieves individual value, and replaces it into the "result".
+4. For each "Converter", call "Convert" for the "result".
+5. Return the "result", aka effective, configuration.
 
 ### Watching for Updates
 After the configuration was processed, the `Resolver` can be used as a single point to watch for updates in the

confmap/provider.go

@@ -16,6 +16,7 @@ package confmap // import "go.opentelemetry.io/collector/confmap"
 
 import (
 	"context"
+	"fmt"
 )
 
 // Provider is an interface that helps to retrieve a config map and watch for any
@@ -81,7 +82,7 @@ type ChangeEvent struct {
 
 // Retrieved holds the result of a call to the Retrieve method of a Provider object.
 type Retrieved struct {
-	conf      *Conf
+	rawConf   interface{}
 	closeFunc CloseFunc
 }
 
@@ -101,17 +102,39 @@ func WithRetrievedClose(closeFunc CloseFunc) RetrievedOption {
 }
 
 // NewRetrieved returns a new Retrieved instance that contains the data from the raw deserialized config.
-func NewRetrieved(rawConf map[string]interface{}, opts ...RetrievedOption) (Retrieved, error) {
+// The rawConf can be one of the following types:
+//   - Primitives: int, int32, int64, float32, float64, bool, string;
+//   - []interface{};
+//   - map[string]interface{};
+func NewRetrieved(rawConf interface{}, opts ...RetrievedOption) (Retrieved, error) {
+	if err := checkRawConfType(rawConf); err != nil {
+		return Retrieved{}, err
+	}
 	set := retrievedSettings{}
 	for _, opt := range opts {
 		opt(&set)
 	}
-	return Retrieved{conf: NewFromStringMap(rawConf), closeFunc: set.closeFunc}, nil
+	return Retrieved{rawConf: rawConf, closeFunc: set.closeFunc}, nil
 }
 
 // AsConf returns the retrieved configuration parsed as a Conf.
-func (r Retrieved) AsConf() (*Conf, error) {
-	return r.conf, nil
+func (r *Retrieved) AsConf() (*Conf, error) {
+	if r.rawConf == nil {
+		return New(), nil
+	}
+	val, ok := r.rawConf.(map[string]interface{})
+	if !ok {
+		return nil, fmt.Errorf("retrieved value (type=%T) cannot be used as a Conf", r.rawConf)
+	}
+	return NewFromStringMap(val), nil
+}
+
+// AsRaw returns the retrieved configuration parsed as an interface{} which can be one of the following types:
+//   - Primitives: int, int32, int64, float32, float64, bool, string;
+//   - []interface{} - every member follows the same rules as the given interface{};
+//   - map[string]interface{} - every value follows the same rules as the given interface{};
+func (r *Retrieved) AsRaw() (interface{}, error) {
+	return r.rawConf, nil
 }
 
 // Close and release any watchers that Provider.Retrieve may have created.
@@ -129,3 +152,15 @@ func (r Retrieved) Close(ctx context.Context) error {
 
 // CloseFunc a function equivalent to Retrieved.Close.
 type CloseFunc func(context.Context) error
+
+func checkRawConfType(rawConf interface{}) error {
+	if rawConf == nil {
+		return nil
+	}
+	switch rawConf.(type) {
+	case int, int32, int64, float32, float64, bool, string, []interface{}, map[string]interface{}:
+		return nil
+	default:
+		return fmt.Errorf("unsupported type=%T for retrieved config", rawConf)
+	}
+}

confmap/provider/internal/provider.go

@@ -24,7 +24,7 @@ import (
 // * yamlBytes the yaml bytes that will be deserialized.
 // * opts specifies options associated with this Retrieved value, such as CloseFunc.
 func NewRetrievedFromYAML(yamlBytes []byte, opts ...confmap.RetrievedOption) (confmap.Retrieved, error) {
-	var rawConf map[string]interface{}
+	var rawConf interface{}
 	if err := yaml.Unmarshal(yamlBytes, &rawConf); err != nil {
 		return confmap.Retrieved{}, err
 	}

confmap/provider/internal/provider_test.go

@@ -46,10 +46,13 @@ func TestNewRetrievedFromYAMLWithOptions(t *testing.T) {
 
 func TestNewRetrievedFromYAMLInvalidYAMLBytes(t *testing.T) {
 	_, err := NewRetrievedFromYAML([]byte("[invalid:,"))
-	require.Error(t, err)
+	assert.Error(t, err)
 }
 
 func TestNewRetrievedFromYAMLInvalidAsMap(t *testing.T) {
-	_, err := NewRetrievedFromYAML([]byte("string"))
-	require.Error(t, err)
+	ret, err := NewRetrievedFromYAML([]byte("string"))
+	require.NoError(t, err)
+
+	_, err = ret.AsConf()
+	assert.Error(t, err)
 }

confmap/resolver.go

@@ -38,6 +38,8 @@ type Resolver struct {
 	sync.Mutex
 	closers []CloseFunc
 	watcher chan error
+
+	enableExpand bool
 }
 
 // ResolverSettings are the settings to configure the behavior of the Resolver.
@@ -115,28 +117,33 @@ func (mr *Resolver) Resolve(ctx context.Context) (*Conf, error) {
 		// For backwards compatibility:
 		// - empty url scheme means "file".
 		// - "^[A-z]:" also means "file"
-		scheme := "file"
-		if idx := strings.Index(uri, ":"); idx != -1 && !driverLetterRegexp.MatchString(uri) {
-			scheme = uri[:idx]
-		} else {
-			uri = scheme + ":" + uri
-		}
-		p, ok := mr.providers[scheme]
-		if !ok {
-			return nil, fmt.Errorf("scheme %q is not supported for uri %q", scheme, uri)
+		if driverLetterRegexp.MatchString(uri) {
+			uri = "file:" + uri
 		}
-		ret, err := p.Retrieve(ctx, uri, mr.onChange)
+		ret, err := mr.retrieveValue(ctx, location{uri: uri, defaultScheme: "file"})
 		if err != nil {
-			return nil, err
+			return nil, fmt.Errorf("cannot retrieve the configuration: %w", err)
 		}
+		mr.closers = append(mr.closers, ret.Close)
 		retCfgMap, err := ret.AsConf()
 		if err != nil {
 			return nil, err
 		}
 		if err = retMap.Merge(retCfgMap); err != nil {
 			return nil, err
 		}
-		mr.closers = append(mr.closers, ret.Close)
+	}
+
+	if mr.enableExpand {
+		cfgMap := make(map[string]interface{})
+		for _, k := range retMap.AllKeys() {
+			val, err := mr.expandValueRecursively(ctx, retMap.Get(k))
+			if err != nil {
+				return nil, err
+			}
+			cfgMap[k] = val
+		}
+		retMap = NewFromStringMap(cfgMap)
 	}
 
 	// Apply the converters in the given order.
@@ -187,3 +194,82 @@ func (mr *Resolver) closeIfNeeded(ctx context.Context) error {
 	}
 	return err
 }
+
+func (mr *Resolver) expandValueRecursively(ctx context.Context, value interface{}) (interface{}, error) {
+	for i := 0; i < 100; i++ {
+		val, changed, err := mr.expandValue(ctx, value)
+		if err != nil {
+			return nil, err
+		}
+		if !changed {
+			return val, nil
+		}
+		value = val
+	}
+	return nil, errors.New("too many recursive expansions")
+}
+
+func (mr *Resolver) expandValue(ctx context.Context, value interface{}) (interface{}, bool, error) {
+	switch v := value.(type) {
+	case string:
+		// If it doesn't have the format "${scheme:opaque}" no need to expand.
+		if !strings.HasPrefix(v, "${") || !strings.HasSuffix(v, "}") {
+			return value, false, nil
+		}
+		uri := v[2 : len(v)-1]
+		// For backwards compatibility:
+		// - empty scheme means "env".
+		ret, err := mr.retrieveValue(ctx, location{uri: uri, defaultScheme: "env"})
+		if err != nil {
+			return nil, false, err
+		}
+		mr.closers = append(mr.closers, ret.Close)
+		val, err := ret.AsRaw()
+		return val, true, err
+	case []interface{}:
+		nslice := make([]interface{}, 0, len(v))
+		nchanged := false
+		for _, vint := range v {
+			val, changed, err := mr.expandValue(ctx, vint)
+			if err != nil {
+				return nil, false, err
+			}
+			nslice = append(nslice, val)
+			nchanged = nchanged || changed
+		}
+		return nslice, nchanged, nil
+	case map[string]interface{}:
+		nmap := map[string]interface{}{}
+		nchanged := false
+		for mk, mv := range v {
+			val, changed, err := mr.expandValue(ctx, mv)
+			if err != nil {
+				return nil, false, err
+			}
+			nmap[mk] = val
+			nchanged = nchanged || changed
+		}
+		return nmap, nchanged, nil
+	}
+	return value, false, nil
+}
+
+type location struct {
+	uri           string
+	defaultScheme string
+}
+
+func (mr *Resolver) retrieveValue(ctx context.Context, l location) (Retrieved, error) {
+	uri := l.uri
+	scheme := l.defaultScheme
+	if idx := strings.Index(uri, ":"); idx != -1 {
+		scheme = uri[:idx]
+	} else {
+		uri = scheme + ":" + uri
+	}
+	p, ok := mr.providers[scheme]
+	if !ok {
+		return Retrieved{}, fmt.Errorf("scheme %q is not supported for uri %q", scheme, uri)
+	}
+	return p.Retrieve(ctx, uri, mr.onChange)
+}