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env_provider.go
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env_provider.go
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package config
import (
"os"
"strings"
)
// Redefined in tests
var envVars = func() []string {
return os.Environ()
}
func canonise(key string) string {
k := strings.Replace(key, "_", ".", -1)
k = strings.Replace(k, "..", "_", -1)
return strings.ToLower(k)
}
// EnvProvider reads special FLOW_ preffixed environment variables.
// The contract is:
// * Underscores are being transformed to dots in key part (before the first =).
// * There must be exactly 1 `=` sign.
// * Double underscores are converted to singulars and preserved with no dot-conversion.
type EnvProvider struct {
weight int
registry map[string]Value
ready chan struct{}
prefix string
}
var _ Provider = (*EnvProvider)(nil)
func NewEnvProvider(repo *Repository, weight int) (*EnvProvider, error) {
return NewEnvProviderWithPrefix(repo, weight, "CONFIG_")
}
// NewEnvProvider returns a new instance of EnvProvider.
func NewEnvProviderWithPrefix(repo *Repository, weight int, prefix string) (*EnvProvider, error) {
prov := &EnvProvider{
weight: weight,
ready: make(chan struct{}),
prefix: prefix,
}
repo.RegisterProvider(prov)
return prov, nil
}
// Name returns provider name: env
func (ep *EnvProvider) Name() string { return "env" }
// Depends returns provider dependencies: default
func (ep *EnvProvider) Depends() []string { return []string{"default"} }
// Weight returns provider weight
func (ep *EnvProvider) Weight() int { return ep.weight }
// SetUp takes the list of env vars and canonizes them before registration in
// repo. Env vars are expected to be in form FLOW_<K>=<v>. FLOW_ preffix
// would be cleared out.
func (ep *EnvProvider) SetUp(repo *Repository) error {
defer close(ep.ready)
registry := make(map[string]Value)
var k string
var v interface{}
for _, kv := range envVars() {
if !strings.HasPrefix(kv, ep.prefix) {
continue
}
kv = kv[len(ep.prefix):]
if ix := strings.Index(kv, "="); ix != -1 {
k, v = kv[:ix], kv[ix+1:]
} else {
k, v = kv, true
}
k = canonise(k)
registry[k] = v
if repo != nil {
if err := repo.RegisterKey(NewKey(k), ep); err != nil {
return err
}
}
}
ep.registry = registry
return nil
}
// TearDown is a no-op operation for CliProvider
func (ep *EnvProvider) TearDown(_ *Repository) error { return nil }
// Get is the primary method to fetch values from the provider registry.
func (ep *EnvProvider) Get(key Key) (*KeyValue, bool) {
<-ep.ready
if val, ok := ep.registry[key.String()]; ok {
return &KeyValue{Key: key, Value: val}, ok
}
return nil, false
}