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/*
* Copyright 2022 Google LLC
*
* 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 com.google.android.libraries.mobiledatadownload.file.backends;
import android.content.Context;
import android.net.Uri;
import android.os.ParcelFileDescriptor;
import android.util.Pair;
import com.google.android.libraries.mobiledatadownload.file.common.MalformedUriException;
import com.google.android.libraries.mobiledatadownload.file.common.internal.Preconditions;
import com.google.android.libraries.mobiledatadownload.file.spi.Backend;
import java.io.Closeable;
import java.io.IOException;
import java.io.InputStream;
/**
* A backend for accessing remote content that uses the Android platform content resolver framework.
* It can be used standalone or as a remote URI resolver within the {@link AndroidFileBackend}.
*
* <p>Usage: <code>
* AndroidFileBackend backend =
* AndroidFileBackend.builder(context)
* .setRemoteBackend(ContentResolverBackend.builder(context).setEmbedded(true).build())
* .build();
* </code>
*
* <p>NOTE: In most cases, you'll want to use the GmsClientBackend for accessing files from GMS
* core. This backend is used to access files from other Apps. Since there are possible security
* concerns with doing so, ContentResolverBackend is restricted to the "content_resolver_allowlist".
* See <internal> for more information.
*/
public final class ContentResolverBackend implements Backend {
private static final String CONTENT_SCHEME = "content";
private final Context context;
private final boolean isEmbedded;
public static Builder builder(Context context) {
return new Builder(context);
}
/** Builder for {@code ContentResolverBackend}. */
public static class Builder {
private final Context context;
private boolean isEmbedded = false;
/** Construct a new builder instance. */
private Builder(Context context) {
this.context = context;
}
/**
* Tells whether this backend is expected to be embedded in another backend. If so, rewrites the
* scheme to "content"; if not, requires that the scheme be "content".
*/
public Builder setEmbedded(boolean isEmbedded) {
this.isEmbedded = isEmbedded;
return this;
}
public ContentResolverBackend build() {
return new ContentResolverBackend(context, isEmbedded);
}
}
private ContentResolverBackend(Context context, boolean isEmbedded) {
this.context = context.getApplicationContext();
this.isEmbedded = isEmbedded;
}
@Override
public String name() {
Preconditions.checkState(!isEmbedded, "Misconfigured embedded backend.");
return CONTENT_SCHEME;
}
@Override
public InputStream openForRead(Uri uri) throws IOException {
Uri contentUri = rewriteAndCheckUri(uri);
return context.getContentResolver().openInputStream(contentUri);
}
@Override
public Pair<Uri, Closeable> openForNativeRead(Uri uri) throws IOException {
Uri contentUri = rewriteAndCheckUri(uri);
ParcelFileDescriptor pfd = context.getContentResolver().openFileDescriptor(contentUri, "r");
return FileDescriptorUri.fromParcelFileDescriptor(pfd);
}
private Uri rewriteAndCheckUri(Uri uri) throws MalformedUriException {
if (isEmbedded) {
return uri.buildUpon().scheme(CONTENT_SCHEME).build();
}
if (!CONTENT_SCHEME.equals(uri.getScheme())) {
throw new MalformedUriException("Expected scheme to be " + CONTENT_SCHEME);
}
return uri;
}
}
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