Collapse AttributeDescriptor into a map<string, AttributeInfo> (#80)

* Remove AttributeDescriptor, collapsing it into a map<string, AttributeInfo> in the AttributeManifest message.

* Add back comments about the requirements for attribute naming that were originally on the AttributeDescriptor message

* Add comments removed from attribute_descriptor.proto to AttributeManifest.

Author: ZackButcher

mixer/v1/config/cfg.proto

@@ -16,12 +16,12 @@ syntax = "proto3";
 
 import "google/protobuf/struct.proto";
 
-import "mixer/v1/config/descriptor/attribute_descriptor.proto";
 import "mixer/v1/config/descriptor/log_entry_descriptor.proto";
 import "mixer/v1/config/descriptor/metric_descriptor.proto";
 import "mixer/v1/config/descriptor/monitored_resource_descriptor.proto";
 import "mixer/v1/config/descriptor/principal_descriptor.proto";
 import "mixer/v1/config/descriptor/quota_descriptor.proto";
+import "mixer/v1/config/descriptor/value_type.proto";
 
 
 package istio.mixer.v1.config;
@@ -119,7 +119,7 @@ message Aspect {
 //
 // In the following example we define a `metrics` adapter using the Mixer's prepackaged
 // prometheus adapter. This adapter doesn't require any parameters.
-// 
+//
 // ```yaml
 // kind: metrics
 // name: prometheus-adapter
@@ -177,9 +177,68 @@ message AttributeManifest {
   // `attributes` kind adapter in Mixer.
   string name = 2;
 
-  // The set of attributes this Istio component will be responsible for
-  // producing at runtime.
-  repeated istio.mixer.v1.config.descriptor.AttributeDescriptor attributes = 3;
+  // AttributeInfo describes the schema of an Istio `Attribute`.
+  //
+  // ## Istio Attributes
+  //
+  // Istio uses `attributes` to describe runtime activities of Istio services.
+  // An Istio attribute carries a specific piece of information about an activity,
+  // such as the error code of an API request, the latency of an API request, or the
+  // original IP address of a TCP connection. The attributes are often generated
+  // and consumed by different services. For example, a frontend service can
+  // generate an authenticated user attribute and pass it to a backend service for
+  // access control purpose.
+  //
+  // To simplify the system and improve developer experience, Istio uses
+  // shared attribute definitions across all components. For example, the same
+  // authenticated user attribute will be used for logging, monitoring, analytics,
+  // billing, access control, auditing. Many Istio components provide their
+  // functionality by collecting, generating, and operating on attributes.
+  // For example, the proxy collects the error code attribute, and the logging
+  // stores it into a log.
+  //
+  // ## Design
+  //
+  // Each Istio attribute must conform to an `AttributeInfo` in an
+  // `AttributeManifest` in the current Istio deployment at runtime. An
+  // [`AttributeInfo`][istio.mixer.v1.config] is used to define an attribute's
+  // metadata: the type of its value and a detailed description that explains
+  // the semantics of the attribute type. Each attribute's name is globally unique;
+  // in other words an attribute name can only appear once across all manifests.
+  //
+  // The runtime presentation of an attribute is intentionally left out of this
+  // specification, because passing attribute using JSON, XML, or Protocol Buffers
+  // does not change the semantics of the attribute. Different implementations
+  // can choose different representations based on their needs.
+  //
+  // ## HTTP Mapping
+  //
+  // Because many systems already have REST APIs, it makes sense to define a
+  // standard HTTP mapping for Istio attributes that are compatible with typical
+  // REST APIs. The design is to map one attribute to one HTTP header, the
+  // attribute name and value becomes the HTTP header name and value. The actual
+  // encoding scheme will be decided later.
+  message AttributeInfo {
+    // Optional. A human-readable description of the attribute's purpose.
+    string description = 1;
+
+    // Required. The type of data carried by this attribute.
+    istio.mixer.v1.config.descriptor.ValueType value_type = 2;
+  }
+  // The set of attributes this Istio component will be responsible for producing at runtime.
+  // We map from attribute name to the attribute's specification. The name of an attribute,
+  // which is how attributes are referred to in aspect configuration, must conform to:
+  //
+  //     Name = IDENT { SEPARATOR IDENT };
+  //
+  // Where `IDENT` must match the regular expression `[a-z][a-z0-9]+` and `SEPARATOR` must
+  // match the regular expression `[\.-]`.
+  //
+  // Attribute names must be unique within a single Istio deployment. The set of canonical
+  // attributes are described at https://istio.io/docs/reference/attribute-vocabulary.html.
+  // Attributes not in that list should be named with a component-specific suffix such as
+  // request.count-my.component
+  map<string, AttributeInfo> attributes = 3;
 }
 
 // Uri represents a properly formed URI.