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SCons / ProtocBuilder

Generating Protocol Buffers files with SCons

Repositories under version control are the place for code rather than wiki pages, so a Mercurial repository has been created on BitBucket and the code from this page copied into it. The repository is where all evolution of this tool should happen. See also the ToolsIndex page which has more on the tool strategy.

This builder will allow you to generate Google Protocol Buffers .pb.cc, .pb.h, and _pb2.py files using SCons from a .proto source file.

It doesn't currently support Java, but that should be easy to add.

Put this builder/tool file somewhere (next to the SConstruct file or in the Environment's 'toolpath', and call it 'protoc.py'.

#!python 
"""
protoc.py: Protoc Builder for SCons

This Builder invokes protoc to generate C++ and Python
from a .proto file.

NOTE: Java is not currently supported."""

__author__ = "Scott Stafford"

import SCons.Action
import SCons.Builder
import SCons.Defaults
import SCons.Node.FS
import SCons.Util

from SCons.Script import File, Dir

import os.path

protocs = 'protoc'

ProtocAction = SCons.Action.Action('$PROTOCCOM', '$PROTOCCOMSTR')
def ProtocEmitter(target, source, env):
    dirOfCallingSConscript = Dir('.').srcnode()
    env.Prepend(PROTOCPROTOPATH = dirOfCallingSConscript.path)

    source_with_corrected_path = []
    for src in source:
        commonprefix = os.path.commonprefix([dirOfCallingSConscript.path, src.srcnode().path])
        if len(commonprefix)>0:
            source_with_corrected_path.append( src.srcnode().path[len(commonprefix + os.sep):] )
        else:
            source_with_corrected_path.append( src.srcnode().path )

    source = source_with_corrected_path

    for src in source:
        modulename = os.path.splitext(src)[0]

        if env['PROTOCOUTDIR']:
            base = os.path.join(env['PROTOCOUTDIR'] , modulename)
            target.extend( [ base + '.pb.cc', base + '.pb.h' ] )

        if env['PROTOCPYTHONOUTDIR']:
            base = os.path.join(env['PROTOCPYTHONOUTDIR'] , modulename)
            target.append( base + '_pb2.py' )

    try:
        target.append(env['PROTOCFDSOUT'])
    except KeyError:
        pass

    #~ print "PROTOC SOURCE:", [str(s) for s in source]
    #~ print "PROTOC TARGET:", [str(s) for s in target]

    return target, source

ProtocBuilder = SCons.Builder.Builder(action = ProtocAction,
                                   emitter = ProtocEmitter,
                                   srcsuffix = '$PROTOCSRCSUFFIX')

def generate(env):
    """Add Builders and construction variables for protoc to an Environment."""
    try:
        bld = env['BUILDERS']['Protoc']
    except KeyError:
        bld = ProtocBuilder
        env['BUILDERS']['Protoc'] = bld

    env['PROTOC']        = env.Detect(protocs) or 'protoc'
    env['PROTOCFLAGS']   = SCons.Util.CLVar('')
    env['PROTOCPROTOPATH'] = SCons.Util.CLVar('')
    env['PROTOCCOM']     = '$PROTOC ${["-I%s"%x for x in PROTOCPROTOPATH]} $PROTOCFLAGS --cpp_out=$PROTOCCPPOUTFLAGS$PROTOCOUTDIR ${PROTOCPYTHONOUTDIR and ("--python_out="+PROTOCPYTHONOUTDIR) or ""} ${PROTOCFDSOUT and ("-o"+PROTOCFDSOUT) or ""} ${SOURCES}'
    env['PROTOCOUTDIR'] = '${SOURCE.dir}'
    env['PROTOCPYTHONOUTDIR'] = "python"
    env['PROTOCSRCSUFFIX']  = '.proto'

def exists(env):
    return env.Detect(protocs)

Now you should have an env.Protoc() builder that takes .proto as source and emits generated protobuf source.

Here is a sample SConstruct I used (some MSVC/Windows-specific stuff, but the Protoc builder is OS-agnostic.) Note that you must make sure the protoc executable is available in your PATH or it won't be able to execute it.

#!python 
import os

env = Environment(
    ENV = {'PATH' : os.environ['PATH']},
    CPPPATH = ['C:\wc\protobuf-trunk\src' ],
    CPPFLAGS = ['/EHsc', '/MDd'],
    tools=['default', 'protoc']
    )

proto_files = env.Protoc(
    [],
    "config.proto",
    PROTOCPROTOPATH=['.',r'C:\wc\protobuf-trunk\src',],
    PROTOCPYTHONOUTDIR='python', # set to None to not generate python
    PROTOCOUTDIR = 'build', # defaults to same directory as .proto
    # PROTOCCPPOUTFLAGS = "dllexport_decl=PROTOCONFIG_EXPORT:", too
)

env.Program('test', ['test.cpp', proto_files[0]],
    LIBPATH=[r'C:\wc\protobuf-trunk\vsprojects\Debug'],
    LIBS=['libprotobuf.lib'],
    )

-- ScottStafford

Updated