Protocol Buffers - Google's data interchange format
Copyright 2008 Google Inc.
This directory contains the Objective C Protocol Buffers runtime library.
Requirements
The Objective C implementation requires:
- Objective C 2.0 Runtime (32bit & 64bit iOS, 64bit OS X).
- Xcode 10.3 (or later).
- The library code does not use ARC (for performance reasons), but it all can be called from ARC code.
Installation
The distribution pulled from github includes the sources for both the compiler (protoc) and the runtime (this directory). After cloning the distribution and needed submodules (see the src directory's README), to build the compiler and run the runtime tests, you can use:
$ objectivec/DevTools/full_mac_build.sh
This will generate the src/protoc
binary.
Building
There are two ways to include the Runtime sources in your project:
Add objectivec/*.h
, objectivec/google/protobuf/*.pbobjc.h
, and
objectivec/GPBProtocolBuffers.m
to your project.
or
Add objectivec/*.h
, objectivec/google/protobuf/*.pbobjc.h
,
objectivec/google/protobuf/*.pbobjc.m
, and objectivec/*.m
except for
objectivec/GPBProtocolBuffers.m
to your project.
If the target is using ARC, remember to turn off ARC (-fno-objc-arc
) for the
.m
files.
The files generated by protoc
for the *.proto
files (*.pbobjc.h
and
*.pbobjc.m
) are then also added to the target.
Usage
The objects generated for messages should work like any other Objective C object. They are mutable objects, but if you don't change them, they are safe to share between threads (similar to passing an NSMutableDictionary between threads/queues; as long as no one mutates it, things are fine).
There are a few behaviors worth calling out:
A property that is type NSString* will never return nil. If the value is unset, it will return an empty string (@""). This is inpart to align things with the Protocol Buffers spec which says the default for strings is an empty string, but also so you can always safely pass them to isEqual:/compare:, etc. and have deterministic results.
A property that is type NSData* also won't return nil, it will return an empty data ([NSData data]). The reasoning is the same as for NSString not returning nil.
A property that is another GPBMessage class also will not return nil. If the field wasn't already set, you will get a instance of the correct class. This instance will be a temporary instance unless you mutate it, at which point it will be attached to its parent object. We call this pattern autocreators. Similar to NSString and NSData properties it makes things a little safer when using them with isEqual:/etc.; but more importantly, this allows you to write code that uses Objective C's property dot notation to walk into nested objects and access and/or assign things without having to check that they are not nil and create them each step along the way. You can write this:
- (void)updateRecord:(MyMessage *)msg {
...
// Note: You don't have to check subMessage and otherMessage for nil and
// alloc/init/assign them back along the way.
msg.subMessage.otherMessage.lastName = @"Smith";
...
}
If you want to check if a GPBMessage property is present, there is always as
has\[NAME\]
property to go with the main property to check if it is set.
A property that is of an Array or Dictionary type also provides autocreator behavior and will never return nil. This provides all the same benefits you see for the message properties. Again, you can write:
- (void)updateRecord:(MyMessage *)msg {
...
// Note: Just like above, you don't have to check subMessage and otherMessage
// for nil and alloc/init/assign them back along the way. You also don't have
// to create the siblingsArray, you can safely just append to it.
[msg.subMessage.otherMessage.siblingsArray addObject:@"Pat"];
...
}
If you are inspecting a message you got from some other place (server, disk,
etc), you may want to check if the Array or Dictionary has entries without
causing it to be created for you. For this, there is always a \[NAME\]_Count
property also provided that can return zero or the real count, but won't trigger
the creation.
For primitive type fields (ints, floats, bools, enum) in messages defined in a
.proto
file that use proto2 syntax there are conceptual differences between
having an explicit and default value. You can always get the value of the
property. In the case that it hasn't been set you will get the default. In
cases where you need to know whether it was set explicitly or you are just
getting the default, you can use the has\[NAME\]
property. If the value has
been set, and you want to clear it, you can set the has\[NAME\]
to NO
.
proto3 syntax messages do away with this concept, thus the default values are
never included when the message is encoded.
The Objective C classes/enums can be used from Swift code.
Objective C Generator Proto File Options
objc_class_prefix=<prefix> (no default)
This options allow you to provide a custom prefix for all the symbols generated from a proto file (classes (from message), enums, the Root for extension support).
If not set, the generation options package_to_prefix_mappings_path
and
use_package_as_prefix
(documented below) controls what is used instead. Since
Objective C uses a global namespace for all of its classes, there can be collisions.
use_package_as_prefix=yes
should avoid collisions since proto package are used to
scope/name things in other languages, but this option can be used to get shorter
names instead. Convention is to base the explicit prefix on the proto package.
Objective C Generator protoc
Options
When generating Objective C code, protoc
supports a --objc_opt
argument; the
argument is comma-delimited name/value pairs (key=value,key2=value2). The
keys are used to change the behavior during generation. The currently
supported keys are:
-
generate_for_named_framework
: Thevalue
used for this key will be used when generating the#import
statements in the generated code. Instead of being plain#import "some/path/file.pbobjc.h"
lines, they will be framework based, i.e. -#import <VALUE/file.pbobjc.h>
.NOTE: If this is used with
named_framework_to_proto_path_mappings_path
, then this is effectively the default to use for everything that wasn't mapped by the other. -
named_framework_to_proto_path_mappings_path
: Thevalue
used for this key is a path to a file containing the listing of framework names and proto files. The generator uses this to decide if another proto file referenced should use a framework style import vs. a user level import (#import <FRAMEWORK/file.pbobjc.h>
vs#import "dir/file.pbobjc.h"
).The format of the file is:
- An entry is a line of
frameworkName: file.proto, dir/file2.proto
. - Comments start with
#
. - A comment can go on a line after an entry.
(i.e. -
frameworkName: file.proto # comment
)
Any number of files can be listed for a framework, just separate them with commas.
There can be multiple lines listing the same frameworkName in case it has a lot of proto files included in it; and having multiple lines makes things easier to read.
- An entry is a line of
-
runtime_import_prefix
: Thevalue
used for this key to be used as a prefix on#import
s of runtime provided headers in the generated files. When integrating ObjC protos into a build system, this can be used to avoid having to add the runtime directory to the header search path since the generate#import
will be more complete. -
package_to_prefix_mappings_path
: Thevalue
used for this key is a path to a file containing a list of proto packages and prefixes. The generator will use this to locate which ObjC class prefix to use when generating sources unless theobjc_class_prefix
file option is set. This option can be useful if multiple apps consume a common set of proto files but wish to use a different prefix for the generated sources between them. This option takes precedent over theuse_package_as_prefix
option.The format of the file is:
- An entry is a line of "package=prefix".
- Comments start with
#
. - A comment can go on a line after a expected package/prefix pair. (i.e. - "package=prefix # comment")
- For files that do NOT have a proto package (not recommended), an entry can be made as "no_package:PATH=prefix", where PATH is the path for the .proto file.
-
use_package_as_prefix
andproto_package_prefix_exceptions_path
: Thevalue
foruse_package_as_prefix
can beyes
orno
, and indicates if a prefix should be derived from the proto package for all the symbols for files that don't have theobjc_class_prefix
file option (mentioned above). This helps ensure the symbols are more unique and means there is less chance of ObjC class name collisions.To help in migrating code to using this support,
proto_package_prefix_exceptions_path
can be used to provide the path to a file that contains proto package names (one per line, comments allowed if prefixed with#
). These package won't get the derived prefix, allowing migrations to the behavior one proto package at a time across a code base.use_package_as_prefix
currently defaults tono
(existing behavior), but in the future (as a breaking change), that is likely to change since it helps prepare folks before they end up using a lot of protos and getting a lot of collisions. -
headers_use_forward_declarations
: Thevalue
for this can beyes
orno
, and indicates if the generated headers use forward declarations for Message and Enum types from other .proto files or if the files should be imported into the generated header instead.By using forward declarations, less code is likely to recompile when the files do change, but Swift generally doesn't like forward declarations and will fail to include properties when the concrete definition of the type is known at import time. If your proto usages span modules, this can be a problem.
headers_use_forward_declarations
currently defaults toyes
(existing behavior), but in a future release, that default may change to provide better Swift support by default.
Contributing
Please make updates to the tests along with changes. If just changing the
runtime, the Xcode projects can be used to build and run tests. If your change
also requires changes to the generated code,
objectivec/DevTools/full_mac_build.sh
can be used to easily rebuild and test
changes. Passing -h
to the script will show the addition options that could
be useful.
Documentation
The complete documentation for Protocol Buffers is available via the web at: