Add media type parser and mediaType validation

A media type parser is needed to parse Smithy mediaType traits both for
codegen and also for validation.

smithy-model/src/main/java/software/amazon/smithy/model/validation/validators/MediaTypeValidator.java

@@ -0,0 +1,48 @@
+/*
+ * 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.validation.validators;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Optional;
+import software.amazon.smithy.model.Model;
+import software.amazon.smithy.model.shapes.Shape;
+import software.amazon.smithy.model.traits.MediaTypeTrait;
+import software.amazon.smithy.model.validation.AbstractValidator;
+import software.amazon.smithy.model.validation.ValidationEvent;
+import software.amazon.smithy.utils.MediaType;
+
+public final class MediaTypeValidator extends AbstractValidator {
+    @Override
+    public List<ValidationEvent> validate(Model model) {
+        List<ValidationEvent> events = new ArrayList<>();
+        for (Shape shape : model.getShapesWithTrait(MediaTypeTrait.class)) {
+            validateMediaType(shape, shape.expectTrait(MediaTypeTrait.class)).ifPresent(events::add);
+        }
+
+        return events;
+    }
+
+    private Optional<ValidationEvent> validateMediaType(Shape shape, MediaTypeTrait trait) {
+        try {
+            MediaType.from(trait.getValue());
+            return Optional.empty();
+        } catch (RuntimeException e) {
+            return Optional.of(error(shape, trait, String.format(
+                    "Invalid mediaType value, \"%s\": %s", trait.getValue(), e.getMessage())));
+        }
+    }
+}

smithy-model/src/main/resources/META-INF/services/software.amazon.smithy.model.validation.Validator

@@ -15,6 +15,7 @@ software.amazon.smithy.model.validation.validators.HttpQueryTraitValidator
 software.amazon.smithy.model.validation.validators.HttpResponseCodeSemanticsValidator
 software.amazon.smithy.model.validation.validators.HttpUriConflictValidator
 software.amazon.smithy.model.validation.validators.LengthTraitValidator
+software.amazon.smithy.model.validation.validators.MediaTypeValidator
 software.amazon.smithy.model.validation.validators.NoInlineDocumentSupportValidator
 software.amazon.smithy.model.validation.validators.PaginatedTraitValidator
 software.amazon.smithy.model.validation.validators.PrivateAccessValidator

smithy-model/src/test/resources/software/amazon/smithy/model/errorfiles/validators/mediatype-trait.errors

@@ -0,0 +1,7 @@
+[ERROR] smithy.example#Invalid1: Invalid mediaType value, " | MediaType
+[ERROR] smithy.example#Invalid2: Invalid mediaType value, " | MediaType
+[ERROR] smithy.example#Invalid3: Invalid mediaType value, " | MediaType
+[ERROR] smithy.example#Invalid4: Invalid mediaType value, " | MediaType
+[ERROR] smithy.example#Invalid5: Invalid mediaType value, " | MediaType
+[ERROR] smithy.example#Invalid6: Invalid mediaType value, " | MediaType
+[ERROR] smithy.example#Invalid7: Invalid mediaType value, " | MediaType

smithy-model/src/test/resources/software/amazon/smithy/model/errorfiles/validators/mediatype-trait.json

@@ -0,0 +1,71 @@
+{
+    "smithy": "1.0",
+    "shapes": {
+        "smithy.example#Valid1": {
+            "type": "string",
+            "traits": {
+                "smithy.api#mediaType": "application/json"
+            }
+        },
+        "smithy.example#Valid2": {
+            "type": "string",
+            "traits": {
+                "smithy.api#mediaType": "application/foo+json"
+            }
+        },
+        "smithy.example#Valid3": {
+            "type": "string",
+            "traits": {
+                "smithy.api#mediaType": "application/foo+json; bar=baz"
+            }
+        },
+        "smithy.example#Valid4": {
+            "type": "string",
+            "traits": {
+                "smithy.api#mediaType": "application/foo+json; bar=baz; bam=boozled; foo=\"hi\""
+            }
+        },
+        "smithy.example#Invalid1": {
+            "type": "string",
+            "traits": {
+                "smithy.api#mediaType": "application"
+            }
+        },
+        "smithy.example#Invalid2": {
+            "type": "string",
+            "traits": {
+                "smithy.api#mediaType": "application/"
+            }
+        },
+        "smithy.example#Invalid3": {
+            "type": "string",
+            "traits": {
+                "smithy.api#mediaType": "application/json;"
+            }
+        },
+        "smithy.example#Invalid4": {
+            "type": "string",
+            "traits": {
+                "smithy.api#mediaType": "application/json; bar"
+            }
+        },
+        "smithy.example#Invalid5": {
+            "type": "string",
+            "traits": {
+                "smithy.api#mediaType": "application/json; bar="
+            }
+        },
+        "smithy.example#Invalid6": {
+            "type": "string",
+            "traits": {
+                "smithy.api#mediaType": "application/json; bar=,"
+            }
+        },
+        "smithy.example#Invalid7": {
+            "type": "string",
+            "traits": {
+                "smithy.api#mediaType": "application/json; bar=bam;"
+            }
+        }
+    }
+}