Make requiresLength a separate trait

Using `requiresLength` as a property of the `streaming` trait no longer
makes sense because event streams should virtually never have a known or
finite length before they begin.

docs/source/spec/core/stream-traits.rst

@@ -12,6 +12,7 @@ once. This includes both streaming binary data and event streams.
     :local:
     :backlinks: none
 
+
 .. _streaming-trait:
 
 -------------------
@@ -30,29 +31,15 @@ Summary
 Trait selector::
     ``:each(blob, union)``
 Value type
-    ``structure``
-
-The value of the ``streaming`` trait is a structure that supports the following
-optional members:
-
-.. list-table::
-    :header-rows: 1
-    :widths: 10 10 80
-
-    * - Property
-      - Type
-      - Description
-    * - requiresLength
-      - ``boolean``
-      - Indicates that the stream must have a known size.
-
-        In an HTTP-based protocol, for instance, this indicates that the
-        ``content-length`` header must be set.
-
-Shapes targeted by this trait MAY NOT be used outside of top level operation
-inputs and operation outputs. Additionally, the ``streaming`` trait is
-*structurally exclusive by target*, meaning only a single member of a
-structure can target a shape marked as ``streaming``.
+    Annotation trait
+Validation
+    * ``streaming`` shapes can only be referenced from top-level members
+      of operation input or output structures.
+    * Structures that contain a member that targets a ``streaming`` shape
+      MUST NOT be targeted by other members.
+    * The ``streaming`` trait is *structurally exclusive by target*, meaning
+      only a single member of a structure can target a shape marked as
+      ``streaming``.
 
 .. tabs::
 
@@ -71,6 +58,37 @@ structure can target a shape marked as ``streaming``.
         @streaming
         blob StreamingBlob
 
+
+.. _requiresLength-trait:
+
+------------------------
+``requiresLength`` trait
+------------------------
+
+Summary
+    Indicates that the streaming blob MUST be finite and has a known size.
+
+    In an HTTP-based protocol, for instance, this trait indicates that the
+    ``Content-Length`` header MUST be sent prior to a client or server
+    sending the payload of a message. This can be useful for services that
+    need to determine if a request will be accepted based on its size or
+    where to store data based on the size of the stream.
+Trait selector::
+    ``blob[trait|streaming]``
+
+    *A blob shape marked with the streaming trait*
+Value type
+    ``structure``
+
+.. tabs::
+
+    .. code-tab:: smithy
+
+        @streaming
+        @requiresLength
+        blob FiniteStreamingBlob
+
+
 .. _event-streams:
 
 -------------

smithy-model/src/main/java/software/amazon/smithy/model/loader/Prelude.java

@@ -77,6 +77,7 @@
 import software.amazon.smithy.model.traits.ReadonlyTrait;
 import software.amazon.smithy.model.traits.ReferencesTrait;
 import software.amazon.smithy.model.traits.RequiredTrait;
+import software.amazon.smithy.model.traits.RequiresLengthTrait;
 import software.amazon.smithy.model.traits.ResourceIdentifierTrait;
 import software.amazon.smithy.model.traits.RetryableTrait;
 import software.amazon.smithy.model.traits.SensitiveTrait;
@@ -183,6 +184,7 @@ public final class Prelude {
             RangeTrait.ID,
             ReadonlyTrait.ID,
             ReferencesTrait.ID,
+            RequiresLengthTrait.ID,
             RequiredTrait.ID,
             ResourceIdentifierTrait.ID,
             RetryableTrait.ID,

smithy-model/src/main/java/software/amazon/smithy/model/traits/RequiresLengthTrait.java

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2020 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License").
+ * You may not use this file except in compliance with the License.
+ * A copy of the License is located at
+ *
+ *  http://aws.amazon.com/apache2.0
+ *
+ * or in the "license" file accompanying this file. This file is distributed
+ * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
+ * express or implied. See the License for the specific language governing
+ * permissions and limitations under the License.
+ */
+
+package software.amazon.smithy.model.traits;
+
+import software.amazon.smithy.model.SourceLocation;
+import software.amazon.smithy.model.shapes.ShapeId;
+
+/**
+ * Indicates that the streaming blob must be finite and has a known size.
+ */
+public final class RequiresLengthTrait extends BooleanTrait {
+    public static final ShapeId ID = ShapeId.from("smithy.api#requiresLength");
+
+    public RequiresLengthTrait(SourceLocation sourceLocation) {
+        super(ID, sourceLocation);
+    }
+
+    public RequiresLengthTrait() {
+        this(SourceLocation.NONE);
+    }
+
+    public static final class Provider extends BooleanTrait.Provider<RequiresLengthTrait> {
+        public Provider() {
+            super(ID, RequiresLengthTrait::new);
+        }
+    }
+}

smithy-model/src/main/java/software/amazon/smithy/model/traits/StreamingTrait.java

@@ -16,43 +16,31 @@
 package software.amazon.smithy.model.traits;
 
 import software.amazon.smithy.model.Model;
-import software.amazon.smithy.model.node.Node;
-import software.amazon.smithy.model.node.ObjectNode;
+import software.amazon.smithy.model.SourceLocation;
 import software.amazon.smithy.model.shapes.MemberShape;
 import software.amazon.smithy.model.shapes.Shape;
 import software.amazon.smithy.model.shapes.ShapeId;
-import software.amazon.smithy.utils.ToSmithyBuilder;
 
 /**
  * Indicates that the the data stored in the shape is very large and should
  * not be stored in memory, or that the size of the data stored in the
  * shape is unknown at the start of a request.
  */
-public final class StreamingTrait extends AbstractTrait implements ToSmithyBuilder<StreamingTrait> {
+public final class StreamingTrait extends BooleanTrait {
     public static final ShapeId ID = ShapeId.from("smithy.api#streaming");
-    private static final String REQUIRES_LENGTH = "requiresLength";
 
-    private final boolean requiresLength;
-
-    private StreamingTrait(Builder builder) {
-        super(ID, builder.getSourceLocation());
-        requiresLength = builder.requiresLength;
+    public StreamingTrait(SourceLocation sourceLocation) {
+        super(ID, sourceLocation);
     }
 
-    /**
-     * Creates a builder for a streaming trait.
-     *
-     * @return Returns the created builder.
-     */
-    public static Builder builder() {
-        return new Builder();
+    public StreamingTrait() {
+        this(SourceLocation.NONE);
     }
 
-    /**
-     * @return Returns true if the stream requires a known length.
-     */
-    public boolean getRequiresLength() {
-        return requiresLength;
+    public static final class Provider extends BooleanTrait.Provider<StreamingTrait> {
+        public Provider() {
+            super(ID, StreamingTrait::new);
+        }
     }
 
     /**
@@ -75,52 +63,4 @@ public static boolean isEventStream(Shape shape) {
     public static boolean isEventStream(Model model, MemberShape member) {
         return isEventStream(model.expectShape(member.getTarget()));
     }
-
-    @Override
-    public Builder toBuilder() {
-        return builder().requiresLength(requiresLength);
-    }
-
-    @Override
-    protected Node createNode() {
-        return requiresLength ? Node.objectNode().withMember(REQUIRES_LENGTH, true) : Node.objectNode();
-    }
-
-    public static final class Provider implements TraitService {
-        @Override
-        public ShapeId getShapeId() {
-            return ID;
-        }
-
-        @Override
-        public StreamingTrait createTrait(ShapeId target, Node value) {
-            ObjectNode node = value.expectObjectNode();
-            return builder().requiresLength(node.getBooleanMemberOrDefault(REQUIRES_LENGTH)).build();
-        }
-    }
-
-    /**
-     * Builds a {@link StreamingTrait} trait.
-     */
-    public static final class Builder extends AbstractTraitBuilder<StreamingTrait, Builder> {
-        private boolean requiresLength;
-
-        private Builder() {}
-
-        @Override
-        public StreamingTrait build() {
-            return new StreamingTrait(this);
-        }
-
-        /**
-         * Indicates if the length of the stream must be known.
-         *
-         * @param requiresLength Set to true to require a known length.
-         * @return Returns the builder.
-         */
-        public Builder requiresLength(boolean requiresLength) {
-            this.requiresLength = requiresLength;
-            return this;
-        }
-    }
 }

smithy-model/src/main/resources/META-INF/services/software.amazon.smithy.model.traits.TraitService

@@ -32,6 +32,7 @@ software.amazon.smithy.model.traits.RangeTrait$Provider
 software.amazon.smithy.model.traits.ReadonlyTrait$Provider
 software.amazon.smithy.model.traits.ReferencesTrait$Provider
 software.amazon.smithy.model.traits.RequiredTrait$Provider
+software.amazon.smithy.model.traits.RequiresLengthTrait$Provider
 software.amazon.smithy.model.traits.ResourceIdentifierTrait$Provider
 software.amazon.smithy.model.traits.RetryableTrait$Provider
 software.amazon.smithy.model.traits.SensitiveTrait$Provider

smithy-model/src/main/resources/software/amazon/smithy/model/loader/prelude-traits.smithy

@@ -315,16 +315,18 @@ structure sensitive {}
 @trait
 string since
 
-/// Indicates that the the data stored in the shape is very large and should not
+/// Indicates that the data stored in the shape is very large and should not
 /// be stored in memory, or that the size of the data stored in the shape is
 /// unknown at the start of a request. If the target is a union then the shape
 /// represents a stream of events.
 @trait(selector: ":each(blob, union)", structurallyExclusive: "target")
 @tags(["diff.error.const"])
-structure streaming {
-    /// Indicates that the stream must have a known size.
-    requiresLength: Boolean,
-}
+structure streaming {}
+
+/// Indicates that the streaming blob must be finite and has a known size.
+@trait(selector: "blob[trait|streaming]")
+@tags(["diff.error.const"])
+structure requiresLength {}
 
 /// Tags a shape with arbitrary tag names that can be used to filter and
 /// group shapes in the model.

smithy-model/src/test/java/software/amazon/smithy/model/traits/StreamingTraitTest.java

@@ -34,6 +34,6 @@ public void loadsTrait() {
 
         assertTrue(trait.isPresent());
         assertThat(trait.get(), instanceOf(StreamingTrait.class));
-        assertThat(trait.get().toNode(), equalTo(Node.objectNode()));
+        assertThat(trait.get().toNode(), equalTo(Node.from(true)));
     }
 }