libbinder: Add binder::Status type

(cherry-pick of 09eb749704afd9e226e1347cb20c90be2016cd21)

This object implements equivalent functionality to the Java logic which
serializes and re-throws exceptions from services.

Bug: 25615695
Test: Integration test for generated AIDL code reveals this to work
      correctly.

Change-Id: I5a57710a148ffbd18a4a2c6f0f4fb6d409e0bf8f

4 files changed, 261 insertions, 16 deletions

diff --git a/include/binder/Status.h b/include/binder/Status.h
new file mode 100644
index 0000000000..04738f8dd1
--- /dev/null
+++ b/include/binder/Status.h
@@ -0,0 +1,121 @@
+/*
+ * Copyright (C) 2015 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.
+ */
+
+#ifndef ANDROID_BINDER_STATUS_H
+#define ANDROID_BINDER_STATUS_H
+
+#include <cstdint>
+
+#include <binder/Parcel.h>
+#include <utils/String8.h>
+
+namespace android {
+namespace binder {
+
+// An object similar in function to a status_t except that it understands
+// how exceptions are encoded in the prefix of a Parcel. Used like:
+//
+//     Parcel data;
+//     Parcel reply;
+//     status_t status;
+//     binder::Status remote_exception;
+//     if ((status = data.writeInterfaceToken(interface_descriptor)) != OK ||
+//         (status = data.writeInt32(function_input)) != OK) {
+//         // We failed to write into the memory of our local parcel?
+//     }
+//     if ((status = remote()->transact(transaction, data, &reply)) != OK) {
+//        // Something has gone wrong in the binder driver or libbinder.
+//     }
+//     if ((status = remote_exception.readFromParcel(reply)) != OK) {
+//         // The remote didn't correctly write the exception header to the
+//         // reply.
+//     }
+//     if (!remote_exception.isOk()) {
+//         // The transaction went through correctly, but the remote reported an
+//         // exception during handling.
+//     }
+//
+class Status final {
+public:
+    // Keep the exception codes in sync with android/os/Parcel.java.
+    enum Exception {
+        EX_NONE = 0,
+        EX_SECURITY = -1,
+        EX_BAD_PARCELABLE = -2,
+        EX_ILLEGAL_ARGUMENT = -3,
+        EX_NULL_POINTER = -4,
+        EX_ILLEGAL_STATE = -5,
+        EX_NETWORK_MAIN_THREAD = -6,
+        EX_UNSUPPORTED_OPERATION = -7,
+        EX_TRANSACTION_FAILED = -8,
+
+        // This is special and Java specific; see Parcel.java.
+        EX_HAS_REPLY_HEADER = -128,
+    };
+
+    // Allow authors to explicitly pick whether their integer is a status_t or
+    // exception code.
+    static Status fromExceptionCode(int32_t exception_code);
+    static Status fromStatusT(status_t status);
+    // A more readable alias for the default constructor.
+    static Status ok();
+
+    Status() = default;
+    Status(int32_t exception_code, const String8& message);
+    Status(int32_t exception_code, const char* message);
+
+
+    // Status objects are copyable and contain just simple data.
+    Status(const Status& status) = default;
+    Status(Status&& status) = default;
+    Status& operator=(const Status& status) = default;
+
+    ~Status() = default;
+
+    // Bear in mind that if the client or service is a Java endpoint, this
+    // is not the logic which will provide/interpret the data here.
+    status_t readFromParcel(const Parcel& parcel);
+    status_t writeToParcel(Parcel* parcel) const;
+
+    // Set one of the pre-defined exception types defined above.
+    void setException(int32_t ex, const String8& message);
+    // A few of the status_t values map to exception codes, but most of them
+    // simply map to "transaction failed."
+    void setFromStatusT(status_t status);
+
+    // Get information about an exception.
+    // Any argument may be given as nullptr.
+    void getException(int32_t* returned_exception,
+                      String8* returned_message) const;
+    int32_t exceptionCode() const  { return mException; }
+    const String8& exceptionMessage() const { return mMessage; }
+
+    bool isOk() const { return mException == EX_NONE; }
+
+    // For logging.
+    String8 toString8() const;
+
+private:
+    // We always write |mException| to the parcel.
+    // If |mException| !=  EX_NONE, we write message as well.
+    int32_t mException = EX_NONE;
+    String8 mMessage;
+};  // class Status
+
+}  // namespace binder
+}  // namespace android
+
+#endif // ANDROID_BINDER_STATUS_H
diff --git a/libs/binder/Android.mk b/libs/binder/Android.mk
index d5860ef6ca..bd432f318a 100644
--- a/libs/binder/Android.mk
+++ b/libs/binder/Android.mk
@@ -36,6 +36,7 @@ sources := \
     PermissionCache.cpp \
     ProcessState.cpp \
     Static.cpp \
+    Status.cpp \
     TextOutput.cpp \
 
 LOCAL_PATH:= $(call my-dir)
diff --git a/libs/binder/Parcel.cpp b/libs/binder/Parcel.cpp
index b8f5436491..1d6ec9e9fe 100644
--- a/libs/binder/Parcel.cpp
+++ b/libs/binder/Parcel.cpp
@@ -23,6 +23,7 @@
 #include <binder/Binder.h>
 #include <binder/BpBinder.h>
 #include <binder/ProcessState.h>
+#include <binder/Status.h>
 #include <binder/TextOutput.h>
 
 #include <errno.h>
@@ -69,9 +70,6 @@ static size_t pad_size(size_t s) {
 // Note: must be kept in sync with android/os/StrictMode.java's PENALTY_GATHER
 #define STRICT_MODE_PENALTY_GATHER (0x40 << 16)
 
-// Note: must be kept in sync with android/os/Parcel.java's EX_HAS_REPLY_HEADER
-#define EX_HAS_REPLY_HEADER -128
-
 // XXX This can be made public if we want to provide
 // support for typed data.
 struct small_flat_data
@@ -1230,7 +1228,8 @@ restart_write:
 
 status_t Parcel::writeNoException()
 {
-    return writeInt32(0);
+    binder::Status status;
+    return status.writeToParcel(this);
 }
 
 void Parcel::remove(size_t /*start*/, size_t /*amt*/)
@@ -1643,18 +1642,9 @@ wp<IBinder> Parcel::readWeakBinder() const
 
 int32_t Parcel::readExceptionCode() const
 {
-  int32_t exception_code = readAligned<int32_t>();
-  if (exception_code == EX_HAS_REPLY_HEADER) {
-    int32_t header_start = dataPosition();
-    int32_t header_size = readAligned<int32_t>();
-    // Skip over fat responses headers.  Not used (or propagated) in
-    // native code
-    setDataPosition(header_start + header_size);
-    // And fat response headers are currently only used when there are no
-    // exceptions, so return no error:
-    return 0;
-  }
-  return exception_code;
+    binder::Status status;
+    status.readFromParcel(*this);
+    return status.exceptionCode();
 }
 
 native_handle* Parcel::readNativeHandle() const
diff --git a/libs/binder/Status.cpp b/libs/binder/Status.cpp
new file mode 100644
index 0000000000..41fff3d4cd
--- /dev/null
+++ b/libs/binder/Status.cpp
@@ -0,0 +1,133 @@
+/*
+ * Copyright (C) 2015 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.
+ */
+
+#include <binder/Status.h>
+
+namespace android {
+namespace binder {
+
+Status Status::fromExceptionCode(int32_t exception_code) {
+    return Status(exception_code, "");
+}
+
+Status Status::fromStatusT(status_t status) {
+    Status ret;
+    ret.setFromStatusT(status);
+    return ret;
+}
+
+Status Status::ok() {
+    return Status();
+}
+
+Status::Status(int32_t exception_code, const String8& message)
+    : mException(exception_code),
+      mMessage(message) {}
+
+Status::Status(int32_t exception_code, const char* message)
+    : mException(exception_code),
+      mMessage(message) {}
+
+status_t Status::readFromParcel(const Parcel& parcel) {
+    status_t status = parcel.readInt32(&mException);
+    if (status != OK) {
+        setFromStatusT(status);
+        return status;
+    }
+
+    // Skip over fat response headers.  Not used (or propagated) in native code.
+    if (mException == EX_HAS_REPLY_HEADER) {
+        // Note that the header size includes the 4 byte size field.
+        const int32_t header_start = parcel.dataPosition();
+        int32_t header_size;
+        status = parcel.readInt32(&header_size);
+        if (status != OK) {
+            setFromStatusT(status);
+            return status;
+        }
+        parcel.setDataPosition(header_start + header_size);
+        // And fat response headers are currently only used when there are no
+        // exceptions, so act like there was no error.
+        mException = EX_NONE;
+    }
+
+    if (mException == EX_NONE) {
+        return status;
+    }
+
+    // The remote threw an exception.  Get the message back.
+    mMessage = String8(parcel.readString16());
+
+    return status;
+}
+
+status_t Status::writeToParcel(Parcel* parcel) const {
+    status_t status = parcel->writeInt32(mException);
+    if (status != OK) { return status; }
+    if (mException == EX_NONE) {
+        // We have no more information to write.
+        return status;
+    }
+    status = parcel->writeString16(String16(mMessage));
+    return status;
+}
+
+void Status::setFromStatusT(status_t status) {
+    switch (status) {
+        case NO_ERROR:
+            mException = EX_NONE;
+            mMessage.clear();
+            break;
+        case UNEXPECTED_NULL:
+            mException = EX_NULL_POINTER;
+            mMessage.setTo("Unexpected null reference in Parcel");
+            break;
+        default:
+            mException = EX_TRANSACTION_FAILED;
+            mMessage.setTo("Transaction failed");
+            break;
+    }
+}
+
+void Status::setException(int32_t ex, const String8& message) {
+    mException = ex;
+    mMessage.setTo(message);
+}
+
+void Status::getException(int32_t* returned_exception,
+                          String8* returned_message) const {
+    if (returned_exception) {
+        *returned_exception = mException;
+    }
+    if (returned_message) {
+        returned_message->setTo(mMessage);
+    }
+}
+
+String8 Status::toString8() const {
+    String8 ret;
+    if (mException == EX_NONE) {
+        ret.append("No error");
+    } else {
+        ret.appendFormat("Status(%d): '", mException);
+        ret.append(String8(mMessage));
+        ret.append("'");
+    }
+    return ret;
+}
+
+}  // namespace binder
+}  // namespace android