rules/env.bzl

# Copyright (C) 2022 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.

load(":env_variables.bzl", _CAPTURED_ENV_VARS = "CAPTURED_ENV_VARS")

_ALLOWED_SPECIAL_CHARACTERS = [
    "/",
    "_",
    "-",
    "'",
    ".",
    " ",
]

# Since we write the env var value literally into a .bzl file, ensure that the string
# does not contain special characters like '"', '\n' and '\'. Use an allowlist approach
# and check that the remaining string is alphanumeric.
def _validate_env_value(env_var, env_value):
    if env_value == "":
        return
    sanitized_env_value = env_value
    for allowed_char in _ALLOWED_SPECIAL_CHARACTERS:
        sanitized_env_value = sanitized_env_value.replace(allowed_char, "")
    if not sanitized_env_value.isalnum():
        fail("The value of " +
             env_var +
             " can only consist of alphanumeric and " +
             str(_ALLOWED_SPECIAL_CHARACTERS) +
             " characters: " +
             str(env_value))

def _env_impl(rctx):
    captured_env = {}
    for var in _CAPTURED_ENV_VARS:
        value = rctx.os.environ.get(var)
        if value != None:
            _validate_env_value(var, value)
            captured_env[var] = value

    rctx.file("BUILD.bazel", """
exports_files(["env.bzl"])
""")

    rctx.file("env.bzl", """
env = {
    %s
}
""" % "\n    ".join([
        '"%s": "%s",' % (var, value)
        for var, value in captured_env.items()
    ]))

env_repository = repository_rule(
    implementation = _env_impl,
    configure = True,
    local = True,
    environ = _CAPTURED_ENV_VARS,
    doc = "A repository rule to capture environment variables.",
)