Move default MimeMap implementation to frameworks.

This CL topic moves the default MimeMap implementation to frameworks.
Libcore starts with a minimal implementation sufficient to pass
CtsLibcoreTestCases,  but frameworks can inject the real implementation.
Before this CL topic, the data files and logic (MimeMapImpl) were part of
core-*.jar on device; after this CL, they instead live in framework.jar.

Tests from MimeMapTest that check behavior of that default
implementation also move to a non-libcore CTS test.

Specifically, the logic and android.mime.types now live in
frameworks/base/mime. The default implementation is injected
into libcore from RuntimeInit. I chose to use a separate directory
(frameworks/base/mime/) and build java_library target ("mimemap")
in order to keep this as separate as possible from the rest of
frameworks code, to make it as easy as possible to factor this
out into a separate APEX module if we ever choose to do so.

Planned work for follow-up CL:
 1. Make CTS more opinionated, with a plan to assert that all of
    the default mappings are present. How exactly the expectated
    mapping will be bundled in CTS is still TBD.
 2. Add a vendor.mime.types file (defaults to empty) where vendors
    can add additional mappings; I plan to make it such that mappings
    in that file are parsed last but never override any earlier
    mappings, as if each mime type / file extension was prefixed
    with '?'.
 3. Perhaps enforce that public APIs android.webkit.MimeTypeMap
    and java.net.URLConnection.getFileNameMap() behave consistently
    with MimeMap.getDefault().

Test: atest CtsLibcoreTestCases
Test: atest CtsMimeMapTestCases
Bug: 136256059
Change-Id: Ib955699694d24a25c33ef2445443afb7c35ed9e7

1 files changed, 194 insertions, 0 deletions

diff --git a/mime/java/android/content/type/MimeMapImpl.java b/mime/java/android/content/type/MimeMapImpl.java
new file mode 100644
index 000000000000..c904ea3f9b60
--- /dev/null
+++ b/mime/java/android/content/type/MimeMapImpl.java
@@ -0,0 +1,194 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License 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 android.content.type;
+
+import libcore.net.MimeMap;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.regex.Pattern;
+
+/**
+ * Default implementation of {@link MimeMap}, a bidirectional mapping between
+ * MIME types and file extensions.
+ *
+ * This default mapping is loaded from data files that start with some mappings
+ * recognized by IANA plus some custom extensions and overrides.
+ *
+ * @hide
+ */
+public class MimeMapImpl extends MimeMap {
+
+    /**
+     * Creates and returns a new {@link MimeMapImpl} instance that implements.
+     * Android's default mapping between MIME types and extensions.
+     */
+    public static MimeMapImpl createDefaultInstance() {
+        return parseFromResources("/mime.types", "/android.mime.types");
+    }
+
+    private static final Pattern SPLIT_PATTERN = Pattern.compile("\\s+");
+
+    /**
+     * Note: These maps only contain lowercase keys/values, regarded as the
+     * {@link #toLowerCase(String) canonical form}.
+     *
+     * <p>This is the case for both extensions and MIME types. The mime.types
+     * data file contains examples of mixed-case MIME types, but some applications
+     * use the lowercase version of these same types. RFC 2045 section 2 states
+     * that MIME types are case insensitive.
+     */
+    private final Map<String, String> mMimeTypeToExtension;
+    private final Map<String, String> mExtensionToMimeType;
+
+    public MimeMapImpl(Map<String, String> mimeTypeToExtension,
+            Map<String, String> extensionToMimeType) {
+        this.mMimeTypeToExtension = new HashMap<>(mimeTypeToExtension);
+        for (Map.Entry<String, String> entry : mimeTypeToExtension.entrySet()) {
+            checkValidMimeType(entry.getKey());
+            checkValidExtension(entry.getValue());
+        }
+        this.mExtensionToMimeType = new HashMap<>(extensionToMimeType);
+        for (Map.Entry<String, String> entry : extensionToMimeType.entrySet()) {
+            checkValidExtension(entry.getKey());
+            checkValidMimeType(entry.getValue());
+        }
+    }
+
+    private static void checkValidMimeType(String s) {
+        if (MimeMap.isNullOrEmpty(s) || !s.equals(MimeMap.toLowerCase(s))) {
+            throw new IllegalArgumentException("Invalid MIME type: " + s);
+        }
+    }
+
+    private static void checkValidExtension(String s) {
+        if (MimeMap.isNullOrEmpty(s) || !s.equals(MimeMap.toLowerCase(s))) {
+            throw new IllegalArgumentException("Invalid extension: " + s);
+        }
+    }
+
+    static MimeMapImpl parseFromResources(String... resourceNames) {
+        Map<String, String> mimeTypeToExtension = new HashMap<>();
+        Map<String, String> extensionToMimeType = new HashMap<>();
+        for (String resourceName : resourceNames) {
+            parseTypes(mimeTypeToExtension, extensionToMimeType, resourceName);
+        }
+        return new MimeMapImpl(mimeTypeToExtension, extensionToMimeType);
+    }
+
+    /**
+     * An element of a *mime.types file: A MIME type or an extension, with an optional
+     * prefix of "?" (if not overriding an earlier value).
+     */
+    private static class Element {
+        public final boolean keepExisting;
+        public final String s;
+
+        Element(boolean keepExisting, String value) {
+            this.keepExisting = keepExisting;
+            this.s = toLowerCase(value);
+            if (value.isEmpty()) {
+                throw new IllegalArgumentException();
+            }
+        }
+
+        public String toString() {
+            return keepExisting ? ("?" + s) : s;
+        }
+    }
+
+    private static String maybePut(Map<String, String> map, Element keyElement, String value) {
+        if (keyElement.keepExisting) {
+            return map.putIfAbsent(keyElement.s, value);
+        } else {
+            return map.put(keyElement.s, value);
+        }
+    }
+
+    private static void parseTypes(Map<String, String> mimeTypeToExtension,
+            Map<String, String> extensionToMimeType, String resource) {
+        try (BufferedReader r = new BufferedReader(
+                new InputStreamReader(MimeMapImpl.class.getResourceAsStream(resource)))) {
+            String line;
+            while ((line = r.readLine()) != null) {
+                int commentPos = line.indexOf('#');
+                if (commentPos >= 0) {
+                    line = line.substring(0, commentPos);
+                }
+                line = line.trim();
+                // The first time a MIME type is encountered it is mapped to the first extension
+                // listed in its line. The first time an extension is encountered it is mapped
+                // to the MIME type.
+                //
+                // When encountering a previously seen MIME type or extension, then by default
+                // the later ones override earlier mappings (put() semantics); however if a MIME
+                // type or extension is prefixed with '?' then any earlier mapping _from_ that
+                // MIME type / extension is kept (putIfAbsent() semantics).
+                final String[] split = SPLIT_PATTERN.split(line);
+                if (split.length <= 1) {
+                    // Need mimeType + at least one extension to make a mapping.
+                    // "mime.types" files may also contain lines with just a mimeType without
+                    // an extension but we skip them as they provide no mapping info.
+                    continue;
+                }
+                List<Element> lineElements = new ArrayList<>(split.length);
+                for (String s : split) {
+                    boolean keepExisting = s.startsWith("?");
+                    if (keepExisting) {
+                        s = s.substring(1);
+                    }
+                    if (s.isEmpty()) {
+                        throw new IllegalArgumentException("Invalid entry in '" + line + "'");
+                    }
+                    lineElements.add(new Element(keepExisting, s));
+                }
+
+                // MIME type -> first extension (one mapping)
+                // This will override any earlier mapping from this MIME type to another
+                // extension, unless this MIME type was prefixed with '?'.
+                Element mimeElement = lineElements.get(0);
+                List<Element> extensionElements = lineElements.subList(1, lineElements.size());
+                String firstExtension = extensionElements.get(0).s;
+                maybePut(mimeTypeToExtension, mimeElement, firstExtension);
+
+                // extension -> MIME type (one or more mappings).
+                // This will override any earlier mapping from this extension to another
+                // MIME type, unless this extension was prefixed with '?'.
+                for (Element extensionElement : extensionElements) {
+                    maybePut(extensionToMimeType, extensionElement, mimeElement.s);
+                }
+            }
+        } catch (IOException | RuntimeException e) {
+            throw new RuntimeException("Failed to parse " + resource, e);
+        }
+    }
+
+    @Override
+    protected String guessExtensionFromLowerCaseMimeType(String mimeType) {
+        return mMimeTypeToExtension.get(mimeType);
+    }
+
+    @Override
+    protected String guessMimeTypeFromLowerCaseExtension(String extension) {
+        return mExtensionToMimeType.get(extension);
+    }
+}