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third_party/protobuf/javanano/README.md

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+Protocol Buffers - Google's data interchange format
+===================================================
+
+[![Build Status](https://travis-ci.org/google/protobuf.svg?branch=master)](https://travis-ci.org/google/protobuf)
+
+Copyright 2008 Google Inc.
+
+This directory contains the Java Protocol Buffers Nano runtime library.
+
+Installation - With Maven
+-------------------------
+
+The Protocol Buffers build is managed using Maven.  If you would
+rather build without Maven, see below.
+
+1) Install Apache Maven if you don't have it:
+
+     http://maven.apache.org/
+
+2) Build the C++ code, or obtain a binary distribution of protoc.  If
+   you install a binary distribution, make sure that it is the same
+   version as this package.  If in doubt, run:
+
+     $ protoc --version
+
+   You will need to place the protoc executable in ../src.  (If you
+   built it yourself, it should already be there.)
+
+3) Run the tests:
+
+     $ mvn test
+
+   If some tests fail, this library may not work correctly on your
+   system.  Continue at your own risk.
+
+4) Install the library into your Maven repository:
+
+     $ mvn install
+
+5) If you do not use Maven to manage your own build, you can build a
+   .jar file to use:
+
+     $ mvn package
+
+   The .jar will be placed in the "target" directory.
+
+Installation - Without Maven
+----------------------------
+
+If you would rather not install Maven to build the library, you may
+follow these instructions instead.  Note that these instructions skip
+running unit tests.
+
+1) Build the C++ code, or obtain a binary distribution of protoc.  If
+   you install a binary distribution, make sure that it is the same
+   version as this package.  If in doubt, run:
+
+     $ protoc --version
+
+   If you built the C++ code without installing, the compiler binary
+   should be located in ../src.
+
+2) Invoke protoc to build DescriptorProtos.java:
+
+     $ protoc --java_out=src/main/java -I../src \
+         ../src/google/protobuf/descriptor.proto
+
+3) Compile the code in src/main/java using whatever means you prefer.
+
+4) Install the classes wherever you prefer.
+
+Nano version
+------------
+
+JavaNano is a special code generator and runtime library designed specially for
+resource-restricted systems, like Android. It is very resource-friendly in both
+the amount of code and the runtime overhead. Here is an overview of JavaNano
+features compared with the official Java protobuf:
+
+- No descriptors or message builders.
+- All messages are mutable; fields are public Java fields.
+- For optional fields only, encapsulation behind setter/getter/hazzer/
+  clearer functions is opt-in, which provide proper 'has' state support.
+- For proto2, if not opted in, has state (field presence) is not available.
+  Serialization outputs all fields not equal to their defaults
+  (see important implications below).
+  The behavior is consistent with proto3 semantics.
+- Required fields (proto2 only) are always serialized.
+- Enum constants are integers; protection against invalid values only
+  when parsing from the wire.
+- Enum constants can be generated into container interfaces bearing
+  the enum's name (so the referencing code is in Java style).
+- CodedInputByteBufferNano can only take byte[] (not InputStream).
+- Similarly CodedOutputByteBufferNano can only write to byte[].
+- Repeated fields are in arrays, not ArrayList or Vector. Null array
+  elements are allowed and silently ignored.
+- Full support for serializing/deserializing repeated packed fields.
+- Support  extensions (in proto2).
+- Unset messages/groups are null, not an immutable empty default
+  instance.
+- toByteArray(...) and mergeFrom(...) are now static functions of
+  MessageNano.
+- The 'bytes' type translates to the Java type byte[].
+
+The generated messages are not thread-safe for writes, but may be
+used simultaneously from multiple threads in a read-only manner.
+In other words, an appropriate synchronization mechanism (such as
+a ReadWriteLock) must be used to ensure that a message, its
+ancestors, and descendants are not accessed by any other threads
+while the message is being modified. Field reads, getter methods
+(but not getExtension(...)), toByteArray(...), writeTo(...),
+getCachedSize(), and getSerializedSize() are all considered read-only
+operations.
+
+IMPORTANT: If you have fields with defaults and opt out of accessors
+
+How fields with defaults are serialized has changed. Because we don't
+keep "has" state, any field equal to its default is assumed to be not
+set and therefore is not serialized. Consider the situation where we
+change the default value of a field. Senders compiled against an older
+version of the proto continue to match against the old default, and
+don't send values to the receiver even though the receiver assumes the
+new default value. Therefore, think carefully about the implications
+of changing the default value. Alternatively, turn on accessors and
+enjoy the benefit of the explicit has() checks.
+
+IMPORTANT: If you have "bytes" fields with non-empty defaults
+
+Because the byte buffer is now of mutable type byte[], the default
+static final cannot be exposed through a public field. Each time a
+message's constructor or clear() function is called, the default value
+(kept in a private byte[]) is cloned. This causes a small memory
+penalty. This is not a problem if the field has no default or is an
+empty default.
+
+Nano Generator options
+----------------------
+
+```
+java_package           -> <file-name>|<package-name>
+java_outer_classname   -> <file-name>|<package-name>
+java_multiple_files    -> true or false
+java_nano_generate_has -> true or false [DEPRECATED]
+optional_field_style   -> default or accessors
+enum_style             -> c or java
+ignore_services        -> true or false
+parcelable_messages    -> true or false
+generate_intdefs       -> true or false
+```
+
+**java_package=\<file-name\>|\<package-name\>** (no default)
+
+  This allows overriding the 'java_package' option value
+  for the given file from the command line. Use multiple
+  java_package options to override the option for multiple
+  files. The final Java package for each file is the value
+  of this command line option if present, or the value of
+  the same option defined in the file if present, or the
+  proto package if present, or the default Java package.
+
+**java_outer_classname=\<file-name\>|\<outer-classname\>** (no default)
+
+  This allows overriding the 'java_outer_classname' option
+  for the given file from the command line. Use multiple
+  java_outer_classname options to override the option for
+  multiple files. The final Java outer class name for each
+  file is the value of this command line option if present,
+  or the value of the same option defined in the file if
+  present, or the file name converted to CamelCase. This
+  outer class will nest all classes and integer constants
+  generated from file-scope messages and enums.
+
+**java_multiple_files={true,false}** (no default)
+
+  This allows overriding the 'java_multiple_files' option
+  in all source files and their imported files from the
+  command line. The final value of this option for each
+  file is the value defined in this command line option, or
+  the value of the same option defined in the file if
+  present, or false. This specifies whether to generate
+  package-level classes for the file-scope messages in the
+  same Java package as the outer class (instead of nested
+  classes in the outer class). File-scope enum constants
+  are still generated as integer constants in the outer
+  class. This affects the fully qualified references in the
+  Java code. NOTE: because the command line option
+  overrides the value for all files and their imported
+  files, using this option inconsistently may result in
+  incorrect references to the imported messages and enum
+  constants.
+
+**java_nano_generate_has={true,false}** (default: false)
+
+  DEPRECATED. Use optional_field_style=accessors.
+
+  If true, generates a public boolean variable has\<fieldname\>
+  accompanying each optional or required field (not present for
+  repeated fields, groups or messages). It is set to false initially
+  and upon clear(). If parseFrom(...) reads the field from the wire,
+  it is set to true. This is a way for clients to inspect the "has"
+  value upon parse. If it is set to true, writeTo(...) will ALWAYS
+  output that field (even if field value is equal to its
+  default).
+
+  IMPORTANT: This option costs an extra 4 bytes per primitive field in
+  the message. Think carefully about whether you really need this. In
+  many cases reading the default works and determining whether the
+  field was received over the wire is irrelevant.
+
+**optional_field_style={default,accessors,reftypes}** (default: default)
+
+  Defines the style of the generated code for fields.
+
+  * default
+
+  In the default style, optional fields translate into public mutable
+  Java fields, and the serialization process is as discussed in the
+  "IMPORTANT" section above.
+
+  * accessors
+
+  When set to 'accessors', each optional field is encapsulated behind
+  4 accessors, namely get\<fieldname\>(), set\<fieldname\>(), has\<fieldname\>()
+  and clear\<fieldname\>() methods, with the standard semantics. The hazzer's
+  return value determines whether a field is serialized, so this style is
+  useful when you need to serialize a field with the default value, or check
+  if a field has been explicitly set to its default value from the wire.
+
+  In the 'accessors' style, required and nested message fields are still
+  translated to one public mutable Java field each, repeated fields are still
+  translated to arrays. No accessors are generated for them.
+
+  IMPORTANT: When using the 'accessors' style, ProGuard should always
+  be enabled with optimization (don't use -dontoptimize) and allowing
+  access modification (use -allowaccessmodification). This removes the
+  unused accessors and maybe inline the rest at the call sites,
+  reducing the final code size.
+  TODO(maxtroy): find ProGuard config that would work the best.
+
+  * reftypes
+
+  When set to 'reftypes', each proto field is generated as a public Java
+  field. For primitive types, these fields use the Java reference types
+  such as java.lang.Integer instead of primitive types such as int.
+
+  In the 'reftypes' style, fields are initialized to null (or empty
+  arrays for repeated fields), and their default values are not available.
+  They are serialized over the wire based on equality to null.
+
+  The 'reftypes' mode has some additional cost due to autoboxing and usage
+  of reference types. In practice, many boxed types are cached, and so don't
+  result in object creation. However, references do take slightly more memory
+  than primitives.
+
+  The 'reftypes' mode is useful when you want to be able to serialize fields
+  with default values, or check if a field has been explicitly set to the
+  default over the wire without paying the extra method cost of the
+  'accessors' mode.
+
+  Note that if you attempt to write null to a required field in the reftypes
+  mode, serialization of the proto will cause a NullPointerException. This is
+  an intentional indicator that you must set required fields.
+
+  NOTE
+  optional_field_style=accessors or reftypes cannot be used together with
+  java_nano_generate_has=true. If you need the 'has' flag for any
+  required field (you have no reason to), you can only use
+  java_nano_generate_has=true.
+
+**enum_style={c,java}** (default: c)
+
+  Defines where to put the int constants generated from enum members.
+
+  * c
+
+  Use C-style, so the enum constants are available at the scope where
+  the enum is defined. A file-scope enum's members are referenced like
+  'FileOuterClass.ENUM_VALUE'; a message-scope enum's members are
+  referenced as 'Message.ENUM_VALUE'. The enum name is unavailable.
+  This complies with the Micro code generator's behavior.
+
+  * java
+
+  Use Java-style, so the enum constants are available under the enum
+  name and referenced like 'EnumName.ENUM_VALUE' (they are still int
+  constants). The enum name becomes the name of a public interface, at
+  the scope where the enum is defined. If the enum is file-scope and
+  the java_multiple_files option is on, the interface will be defined
+  in its own file. To reduce code size, this interface should not be
+  implemented and ProGuard shrinking should be used, so after the Java
+  compiler inlines all referenced enum constants into the call sites,
+  the interface remains unused and can be removed by ProGuard.
+
+**ignore_services={true,false}** (default: false)
+
+  Skips services definitions.
+
+  Nano doesn't support services. By default, if a service is defined
+  it will generate a compilation error. If this flag is set to true,
+  services will be silently ignored, instead.
+
+**parcelable_messages={true,false}** (default: false)
+
+  Android-specific option to generate Parcelable messages.
+
+**generate_intdefs={true,false}** (default: false)
+  Android-specific option to generate @IntDef annotations for enums.
+
+  If turned on, an '@IntDef' annotation (a public @interface) will be
+  generated for each enum, and every integer parameter and return
+  value in the generated code meant for this enum will be annotated
+  with it. This interface is generated with the same name and at the
+  same place as the enum members' container interfaces described
+  above under 'enum_style=java', regardless of the enum_style option
+  used. When this is combined with enum_style=java, the interface
+  will be both the '@IntDef' annotation and the container of the enum
+  members; otherwise the interface has an empty body.
+
+  Your app must declare a compile-time dependency on the
+  android-support-annotations library.
+
+  For more information on how these @IntDef annotations help with
+  compile-time type safety, see:
+  https://sites.google.com/a/android.com/tools/tech-docs/support-annotations
+  and
+  https://developer.android.com/reference/android/support/annotation/IntDef.html
+
+
+To use nano protobufs within the Android repo:
+----------------------------------------------
+
+- Set 'LOCAL_PROTOC_OPTIMIZE_TYPE := nano' in your local .mk file.
+  When building a Java library or an app (package) target, the build
+  system will add the Java nano runtime library to the
+  LOCAL_STATIC_JAVA_LIBRARIES variable, so you don't need to.
+- Set 'LOCAL_PROTO_JAVA_OUTPUT_PARAMS := ...' in your local .mk file
+  for any command-line options you need. Use commas to join multiple
+  options. In the nano flavor only, whitespace surrounding the option
+  names and values are ignored, so you can use backslash-newline or
+  '+=' to structure your make files nicely.
+- The options will be applied to *all* proto files in LOCAL_SRC_FILES
+  when you build a Java library or package. In case different options
+  are needed for different proto files, build separate Java libraries
+  and reference them in your main target. Note: you should make sure
+  that, for each separate target, all proto files imported from any
+  proto file in LOCAL_SRC_FILES are included in LOCAL_SRC_FILES. This
+  is because the generator has to assume that the imported files are
+  built using the same options, and will generate code that reference
+  the fields and enums from the imported files using the same code
+  style.
+- Hint: 'include $(CLEAR_VARS)' resets all LOCAL_ variables, including
+  the two above.
+
+To use nano protobufs outside of Android repo:
+----------------------------------------------
+
+- Link with the generated jar file
+  \<protobuf-root\>java/target/protobuf-java-2.3.0-nano.jar.
+- Invoke with --javanano_out, e.g.:
+```
+./protoc '--javanano_out=\
+    java_package=src/proto/simple-data.proto|my_package,\
+    java_outer_classname=src/proto/simple-data.proto|OuterName\
+  :.' src/proto/simple-data.proto
+```
+
+Contributing to nano:
+---------------------
+
+Please add/edit tests in NanoTest.java.
+
+Please run the following steps to test:
+
+- cd external/protobuf
+- ./configure
+- Run "make -j12 check" and verify all tests pass.
+- cd java
+- Run "mvn test" and verify all tests pass.
+- cd ../../..
+- . build/envsetup.sh
+- lunch 1
+- "make -j12 aprotoc libprotobuf-java-2.3.0-nano aprotoc-test-nano-params NanoAndroidTest" and
+  check for build errors.
+- Plug in an Android device or start an emulator.
+- adb install -r out/target/product/generic/data/app/NanoAndroidTest.apk
+- Run:
+  "adb shell am instrument -w com.google.protobuf.nano.test/android.test.InstrumentationTestRunner"
+  and verify all tests pass.
+- repo sync -c -j256
+- "make -j12" and check for build errors
+
+Usage
+-----
+
+The complete documentation for Protocol Buffers is available via the
+web at:
+
+    https://developers.google.com/protocol-buffers/