406 lines
9.0 KiB
Markdown
406 lines
9.0 KiB
Markdown
|
# Envconfig
|
||
|
|
|
||
|
|
[](https://pkg.go.dev/mod/github.com/sethvargo/go-envconfig)
|
||
|
|
[](https://github.com/sethvargo/go-envconfig/actions?query=branch%3Amain+-event%3Aschedule)
|
||
|
|
|
||
|
|
Envconfig populates struct field values based on environment variables or
|
||
|
|
arbitrary lookup functions. It supports pre-setting mutations, which is useful
|
||
|
|
for things like converting values to uppercase, trimming whitespace, or looking
|
||
|
|
up secrets.
|
||
|
|
|
||
|
|
**Note:** Versions prior to v0.2 used a different import path. This README and
|
||
|
|
examples are for v0.2+.
|
||
|
|
|
||
|
|
## Usage
|
||
|
|
|
||
|
|
Define a struct with fields using the `env` tag:
|
||
|
|
|
||
|
|
```go
|
||
|
|
type MyConfig struct {
|
||
|
|
Port int `env:"PORT"`
|
||
|
|
Username string `env:"USERNAME"`
|
||
|
|
}
|
||
|
|
```
|
||
|
|
|
||
|
|
Set some environment variables:
|
||
|
|
|
||
|
|
```sh
|
||
|
|
export PORT=5555
|
||
|
|
export USERNAME=yoyo
|
||
|
|
```
|
||
|
|
|
||
|
|
Process it using envconfig:
|
||
|
|
|
||
|
|
```go
|
||
|
|
package main
|
||
|
|
|
||
|
|
import (
|
||
|
|
"context"
|
||
|
|
"log"
|
||
|
|
|
||
|
|
"github.com/sethvargo/go-envconfig"
|
||
|
|
)
|
||
|
|
|
||
|
|
func main() {
|
||
|
|
ctx := context.Background()
|
||
|
|
|
||
|
|
var c MyConfig
|
||
|
|
if err := envconfig.Process(ctx, &c); err != nil {
|
||
|
|
log.Fatal(err)
|
||
|
|
}
|
||
|
|
|
||
|
|
// c.Port = 5555
|
||
|
|
// c.Username = "yoyo"
|
||
|
|
}
|
||
|
|
```
|
||
|
|
|
||
|
|
You can also use nested structs, just remember that any fields you want to
|
||
|
|
process must be public:
|
||
|
|
|
||
|
|
```go
|
||
|
|
type MyConfig struct {
|
||
|
|
Database *DatabaseConfig
|
||
|
|
}
|
||
|
|
|
||
|
|
type DatabaseConfig struct {
|
||
|
|
Port int `env:"PORT"`
|
||
|
|
Username string `env:"USERNAME"`
|
||
|
|
}
|
||
|
|
```
|
||
|
|
|
||
|
|
## Configuration
|
||
|
|
|
||
|
|
Use the `env` struct tag to define configuration.
|
||
|
|
|
||
|
|
### Overwrite
|
||
|
|
|
||
|
|
If overwrite is set, the value will be overwritten if there is an
|
||
|
|
environment variable match regardless if the value is non-zero.
|
||
|
|
|
||
|
|
```go
|
||
|
|
type MyStruct struct {
|
||
|
|
Port int `env:"PORT,overwrite"`
|
||
|
|
}
|
||
|
|
```
|
||
|
|
|
||
|
|
### Required
|
||
|
|
|
||
|
|
If a field is required, processing will error if the environment variable is
|
||
|
|
unset.
|
||
|
|
|
||
|
|
```go
|
||
|
|
type MyStruct struct {
|
||
|
|
Port int `env:"PORT,required"`
|
||
|
|
}
|
||
|
|
```
|
||
|
|
|
||
|
|
It is invalid to have a field as both `required` and `default`.
|
||
|
|
|
||
|
|
### Default
|
||
|
|
|
||
|
|
If an environment variable is not set, the field will be set to the default
|
||
|
|
value. Note that the environment variable must not be set (e.g. `unset PORT`).
|
||
|
|
If the environment variable is the empty string, that counts as a "value" and
|
||
|
|
the default will not be used.
|
||
|
|
|
||
|
|
```go
|
||
|
|
type MyStruct struct {
|
||
|
|
Port int `env:"PORT,default=5555"`
|
||
|
|
}
|
||
|
|
```
|
||
|
|
|
||
|
|
You can also set the default value to another field or value from the
|
||
|
|
environment, for example:
|
||
|
|
|
||
|
|
```go
|
||
|
|
type MyStruct struct {
|
||
|
|
DefaultPort int `env:"DEFAULT_PORT,default=5555"`
|
||
|
|
Port int `env:"OVERRIDE_PORT,default=$DEFAULT_PORT"`
|
||
|
|
}
|
||
|
|
```
|
||
|
|
|
||
|
|
The value for `Port` will default to the value of `DEFAULT_PORT`.
|
||
|
|
|
||
|
|
It is invalid to have a field as both `required` and `default`.
|
||
|
|
|
||
|
|
### Prefix
|
||
|
|
|
||
|
|
For shared, embedded structs, you can define a prefix to use when processing
|
||
|
|
struct values for that embed.
|
||
|
|
|
||
|
|
```go
|
||
|
|
type SharedConfig struct {
|
||
|
|
Port int `env:"PORT,default=5555"`
|
||
|
|
}
|
||
|
|
|
||
|
|
type Server1 struct {
|
||
|
|
// This processes Port from $FOO_PORT.
|
||
|
|
*SharedConfig `env:",prefix=FOO_"`
|
||
|
|
}
|
||
|
|
|
||
|
|
type Server2 struct {
|
||
|
|
// This processes Port from $BAR_PORT.
|
||
|
|
*SharedConfig `env:",prefix=BAR_"`
|
||
|
|
}
|
||
|
|
```
|
||
|
|
|
||
|
|
It is invalid to specify a prefix on non-struct fields.
|
||
|
|
|
||
|
|
### Delimiter
|
||
|
|
|
||
|
|
When parsing maps and slices, a comma (`,`) is the default element delimiter.
|
||
|
|
Define a custom delimiter with `delimiter`:
|
||
|
|
|
||
|
|
```go
|
||
|
|
type MyStruct struct {
|
||
|
|
MyVar map[string]string `env:"MYVAR,delimiter=;"`
|
||
|
|
```
|
||
|
|
|
||
|
|
```bash
|
||
|
|
export MYVAR="a:1;b:2"
|
||
|
|
# map[string]string{"a":"1", "b":"2"}
|
||
|
|
```
|
||
|
|
|
||
|
|
This is especially helpful when your values include the default delimiter
|
||
|
|
character.
|
||
|
|
|
||
|
|
```bash
|
||
|
|
export MYVAR="a:1,2,3;b:4,5"
|
||
|
|
# map[string]string{"a":"1,2,3", "b":"4,5"}
|
||
|
|
```
|
||
|
|
|
||
|
|
### Separator
|
||
|
|
|
||
|
|
When parsing maps, a colon (`:`) is the default key-value separator. Define a
|
||
|
|
separator with `separator`:
|
||
|
|
|
||
|
|
```go
|
||
|
|
type MyStruct struct {
|
||
|
|
MyVar map[string]string `env:"MYVAR,separator=="`
|
||
|
|
}
|
||
|
|
```
|
||
|
|
|
||
|
|
```bash
|
||
|
|
export MYVAR="a=b,c=d"
|
||
|
|
# map[string]string{"a":"b", "c":"d"}
|
||
|
|
```
|
||
|
|
|
||
|
|
This is especially helpful when your keys or values include the default
|
||
|
|
separator character.
|
||
|
|
|
||
|
|
```bash
|
||
|
|
export MYVAR="client=abcd::1/128,backend=abcd::2/128"
|
||
|
|
# map[string]string{"client":"abcd::1/128", "backend":"abcd::2/128"}
|
||
|
|
```
|
||
|
|
|
||
|
|
## Complex Types
|
||
|
|
|
||
|
|
### Durations
|
||
|
|
|
||
|
|
In the environment, `time.Duration` values are specified as a parsable Go
|
||
|
|
duration:
|
||
|
|
|
||
|
|
```go
|
||
|
|
type MyStruct struct {
|
||
|
|
MyVar time.Duration `env:"MYVAR"`
|
||
|
|
}
|
||
|
|
```
|
||
|
|
|
||
|
|
```bash
|
||
|
|
export MYVAR="10m" # 10 * time.Minute
|
||
|
|
```
|
||
|
|
|
||
|
|
### TextUnmarshaler / BinaryUnmarshaler
|
||
|
|
|
||
|
|
Types that implement `TextUnmarshaler` or `BinaryUnmarshaler` are processed as such.
|
||
|
|
|
||
|
|
### json.Unmarshaler
|
||
|
|
|
||
|
|
Types that implement `json.Unmarshaler` are processed as such.
|
||
|
|
|
||
|
|
### gob.Decoder
|
||
|
|
|
||
|
|
Types that implement `gob.Decoder` are processed as such.
|
||
|
|
|
||
|
|
|
||
|
|
### Slices
|
||
|
|
|
||
|
|
Slices are specified as comma-separated values:
|
||
|
|
|
||
|
|
```go
|
||
|
|
type MyStruct struct {
|
||
|
|
MyVar []string `env:"MYVAR"`
|
||
|
|
}
|
||
|
|
```
|
||
|
|
|
||
|
|
```bash
|
||
|
|
export MYVAR="a,b,c,d" # []string{"a", "b", "c", "d"}
|
||
|
|
```
|
||
|
|
|
||
|
|
Note that byte slices are special cased and interpreted as strings from the
|
||
|
|
environment.
|
||
|
|
|
||
|
|
### Maps
|
||
|
|
|
||
|
|
Maps are specified as comma-separated key:value pairs:
|
||
|
|
|
||
|
|
```go
|
||
|
|
type MyStruct struct {
|
||
|
|
MyVar map[string]string `env:"MYVAR"`
|
||
|
|
}
|
||
|
|
```
|
||
|
|
|
||
|
|
```bash
|
||
|
|
export MYVAR="a:b,c:d" # map[string]string{"a":"b", "c":"d"}
|
||
|
|
```
|
||
|
|
|
||
|
|
### Structs
|
||
|
|
|
||
|
|
Envconfig walks the entire struct, including nested structs, so deeply-nested
|
||
|
|
fields are also supported.
|
||
|
|
|
||
|
|
If a nested struct is a pointer type, it will automatically be instantianted to
|
||
|
|
the non-nil value. To change this behavior, see
|
||
|
|
(Initialization)[#Initialization].
|
||
|
|
|
||
|
|
|
||
|
|
### Custom
|
||
|
|
|
||
|
|
You can also define your own decoder for structs (see below).
|
||
|
|
|
||
|
|
|
||
|
|
## Prefixing
|
||
|
|
|
||
|
|
You can define a custom prefix using the `PrefixLookuper`. This will lookup
|
||
|
|
values in the environment by prefixing the keys with the provided value:
|
||
|
|
|
||
|
|
```go
|
||
|
|
type MyStruct struct {
|
||
|
|
MyVar string `env:"MYVAR"`
|
||
|
|
}
|
||
|
|
```
|
||
|
|
|
||
|
|
```go
|
||
|
|
// Process variables, but look for the "APP_" prefix.
|
||
|
|
l := envconfig.PrefixLookuper("APP_", envconfig.OsLookuper())
|
||
|
|
if err := envconfig.ProcessWith(ctx, &c, l); err != nil {
|
||
|
|
panic(err)
|
||
|
|
}
|
||
|
|
```
|
||
|
|
|
||
|
|
```bash
|
||
|
|
export APP_MYVAR="foo"
|
||
|
|
```
|
||
|
|
|
||
|
|
## Initialization
|
||
|
|
|
||
|
|
By default, all pointer fields are initialized (allocated) so they are not
|
||
|
|
`nil`. To disable this behavior, use the tag the field as `noinit`:
|
||
|
|
|
||
|
|
```go
|
||
|
|
type MyStruct struct {
|
||
|
|
// Without `noinit`, DeleteUser would be initialized to the default boolean
|
||
|
|
// value. With `noinit`, if the environment variable is not given, the value
|
||
|
|
// is kept as uninitialized (nil).
|
||
|
|
DeleteUser *bool `env:"DELETE_USER, noinit"`
|
||
|
|
}
|
||
|
|
```
|
||
|
|
|
||
|
|
This also applies to nested fields in a struct:
|
||
|
|
|
||
|
|
```go
|
||
|
|
type ParentConfig struct {
|
||
|
|
// Without `noinit` tag, `Child` would be set to `&ChildConfig{}` whether
|
||
|
|
// or not `FIELD` is set in the env var.
|
||
|
|
// With `noinit`, `Child` would stay nil if `FIELD` is not set in the env var.
|
||
|
|
Child *ChildConfig `env:",noinit"`
|
||
|
|
}
|
||
|
|
|
||
|
|
type ChildConfig struct {
|
||
|
|
Field string `env:"FIELD"`
|
||
|
|
}
|
||
|
|
```
|
||
|
|
|
||
|
|
The `noinit` tag is only applicable for pointer fields. Putting the tag on a
|
||
|
|
non-struct-pointer will return an error.
|
||
|
|
|
||
|
|
|
||
|
|
## Extension
|
||
|
|
|
||
|
|
All built-in types are supported except Func and Chan. If you need to define a
|
||
|
|
custom decoder, implement the `Decoder` interface:
|
||
|
|
|
||
|
|
```go
|
||
|
|
type MyStruct struct {
|
||
|
|
field string
|
||
|
|
}
|
||
|
|
|
||
|
|
func (v *MyStruct) EnvDecode(val string) error {
|
||
|
|
v.field = fmt.Sprintf("PREFIX-%s", val)
|
||
|
|
return nil
|
||
|
|
}
|
||
|
|
|
||
|
|
var _ envconfig.Decoder = (*MyStruct)(nil) // interface check
|
||
|
|
```
|
||
|
|
|
||
|
|
If you need to modify environment variable values before processing, you can
|
||
|
|
specify a custom `Mutator`:
|
||
|
|
|
||
|
|
```go
|
||
|
|
type Config struct {
|
||
|
|
Password `env:"PASSWORD"`
|
||
|
|
}
|
||
|
|
|
||
|
|
func resolveSecretFunc(ctx context.Context, key, value string) (string, error) {
|
||
|
|
if strings.HasPrefix(value, "secret://") {
|
||
|
|
return secretmanager.Resolve(ctx, value) // example
|
||
|
|
}
|
||
|
|
return value, nil
|
||
|
|
}
|
||
|
|
|
||
|
|
var config Config
|
||
|
|
envconfig.ProcessWith(ctx, &config, envconfig.OsLookuper(), resolveSecretFunc)
|
||
|
|
```
|
||
|
|
|
||
|
|
## Testing
|
||
|
|
|
||
|
|
Relying on the environment in tests can be troublesome because environment
|
||
|
|
variables are global, which makes it difficult to parallelize the tests.
|
||
|
|
Envconfig supports extracting data from anything that returns a value:
|
||
|
|
|
||
|
|
```go
|
||
|
|
lookuper := envconfig.MapLookuper(map[string]string{
|
||
|
|
"FOO": "bar",
|
||
|
|
"ZIP": "zap",
|
||
|
|
})
|
||
|
|
|
||
|
|
var config Config
|
||
|
|
envconfig.ProcessWith(ctx, &config, lookuper)
|
||
|
|
```
|
||
|
|
|
||
|
|
Now you can parallelize all your tests by providing a map for the lookup
|
||
|
|
function. In fact, that's how the tests in this repo work, so check there for an
|
||
|
|
example.
|
||
|
|
|
||
|
|
You can also combine multiple lookupers with `MultiLookuper`. See the GoDoc for
|
||
|
|
more information and examples.
|
||
|
|
|
||
|
|
|
||
|
|
## Inspiration
|
||
|
|
|
||
|
|
This library is conceptually similar to [kelseyhightower/envconfig](https://github.com/kelseyhightower/envconfig), with the following
|
||
|
|
major behavioral differences:
|
||
|
|
|
||
|
|
- Adds support for specifying a custom lookup function (such as a map), which
|
||
|
|
is useful for testing.
|
||
|
|
|
||
|
|
- Only populates fields if they contain zero or nil values if `overwrite` is unset.
|
||
|
|
This means you can pre-initialize a struct and any pre-populated fields will not
|
||
|
|
be overwritten during processing.
|
||
|
|
|
||
|
|
- Support for interpolation. The default value for a field can be the value of
|
||
|
|
another field.
|
||
|
|
|
||
|
|
- Support for arbitrary mutators that change/resolve data before type
|
||
|
|
conversion.
|