Modular Golang Struct tags parser that's actually useful.
type Config struct {
Url string `env:"name=URL, type=string"`
Port int `env:"name=PORT, type=port"`
}
type EnvSchema struct {
Name string `tag:"env | get('name')"`
Type string `tag:"env | get('type')"`
}
conf := Config{}
inspector, err := tiq.Inspect(&conf)
for _, field := range inspector.Fields() {
env, err := tiq.Parse[EnvSchema](field)
value := os.Getenv(env.Name)
field.Set(validate(env.Type, value))
}
conf.Url // now set to the value of the URL env var
conf.Port // now set to the value of the PORT env vargo get github.com/AnatoleLucet/tiqtiq is a modular Golang Struct tags parser. It offers a very simple DSL to extract what you need from tags, and multiple APIs to inspect and update user defined structs.
The DSL is designed to be as straightforward as possible for you to pick up and get what's happening at a glance, even if you've never used tiq before.
import (
"github.com/AnatoleLucet/tiq"
)
// User defined struct with tags that can by parsed by the `load()` function.
type Config struct {
Url string `env:"name=URL, type=string, optional"`
Port int `env:"name=PORT, type=port, oneof=8080|3000|5000"`
}
func main() {
conf, err := load(&Config{})
conf.Url // Now set to the value of the URL env var.
conf.Port // Now set to the value of the PORT env var.
}
// Define your schema and how to parse tags
type EnvSchema struct {
// Each field containing a `tag:""` will be evaluated by tiq's DSL to
// extract what you need from the user defined tags.
// See "The DSL" section of the README to learn more.
Name string `tag:"env | get('name')"`
Type string `tag:"env | get('type')"`
Optional bool `tag:"env | has('optional')"`
Oneof []string `tag:"env | get('oneof') | split('|')"`
}
func load[T any](conf *T) (*T, error) {
inspector, err := tiq.Inspect(conf)
for _, field := range inspector.Fields() {
env, err := tiq.Parse[EnvSchema](field)
value := os.Getenv(env.Name)
// Ideally you'd call a function to validate if the value
// is correct according what was parsed in the `env` variable:
// validate(env, value)
// .SetFrom() will convert the value to the target field's type using `github.com/AnatoleLucet/as`.
// Alternatively you could use .Set() to try and set the field's value directly without conversion.
field.SetFrom(value)
}
return conf
}Real world example
If you want to see tiq in action on a real project, checkout environ, another project of mine, powered by tiq!
The DSL is based on ExprLang, a simple but powerful expression language.
Don't try to use functions from the official ExprLang docs, they probably won't work. Instead, take a look at
tiq's function set to find what you need!
# The most simple expression would look like this:
`tag:"123"`
# where `tag:"..."` is the Golang tag tiq will pick up for evaluation,
# and `123` is the DSL expression tiq will evaluate.
# To get a tag's value, simply use the name of the tag you want to get:
`tag:"mytag"`
# it will return `mytag`'s content unaltered (e.g. if given `mytag:"content"`, the expression above will return `content`).
# Once you have the value you want to parse, you can use tiq's function set to extract entries and values from it:
`tag:"get(mytag, 'foo')"`
# here we pass `mytag`'s content to the `get()` function, and try to get the `foo` entry's value from it.
# So when given `mytag:"foo=bar"`, the expression above will return `bar` (the value of the `foo` entry).
# To chain one or more functions together, you can use ExprLang's pipe operator:
`tag:"mytag | get("foo") | default("baz")"`
# the pipe operator will pass the left operand's value as the first parameter the right operand.
# What this means is that `"foo=bar" | get("foo")` is equivalent to `get("foo=bar", "foo")`.
# To learn more about tiq's syntax, check out ExprLang's docs at https://expr-lang.org/docs/getting-started.
# But remember most functions from ExprLang won't work because tiq uses its own functions set (described below).| Name | Description | Usage |
|---|---|---|
get() |
Gets an entry's value from a comma-separated key-value list. | get("foo=1, bar=2", "foo") -> 1 |
first() |
Gets the first entry's value (or key if there's no value) from a comma-separated key-value list. | first("foo=1, bar=2") -> 1 |
last() |
Gets the last entry's value (or key if there's no value) from a comma-separated key-value list. | last("foo=1, bar=2") -> 2 |
nth() |
Gets the nth entry's value (or key if there's no value) from a comma-separated key-value list. | nth("foo=1, bar=2", 0) -> 1 |
has() |
Returns true or false if the entry is present in a comma-separated key-value list. | has("foo=1, bar=2", "bar") -> true |
split() |
Splits a string with the given separator. | split("1|2|3|4", "|") -> [1 2 3 4] |
default() |
Returns a default value if the given value if nil. |
default(nil, "foo") -> "foo" |
The inspector helps you crawl through a struct's fields, read tags from them, and update values accordingly.
inspector, err := tiq.Inspect(&mystruct)
// Get a field by name
field, ok := inspector.Field("Name")
field.Set("value") // update the field's value
field.SetFrom("value") // same as .Set() but converts the value to the field's type if necessary
field.Tag("mytag") // returns the content of `mytag:"content"`
field.Tags() // returns every tags of the field in a map[string]string
// Alternatively you could loop through every field on the struct:
for _, field := range inspector.Fields() {
// field.Set("value")
}The parser is how you retrieve what you want from tags with tiq. It takes a schema and a tiq.Field to parse tags on.
type EnvSchema struct {
Name string `tag:"env | get('name')"`
Optional bool `tag:"env | has('optional')"`
Oneof []string `tag:"env | get('oneof') | split('|')"`
}
env, err := tiq.Parse[EnvSchema](field) // field is usually retrieved via tiq.Inspect
env.Name // if `field` has a tag `env:"name=foo"`, this will be set to "foo", else ""
env.Optional // if `field` has a tag `env:"optional"`, this will be set to true, else false
env.Oneof // if `field` has a tag `env:"oneof=one|two|three"`, this will be set to [one two three], else []A simple static function to get a tag's content from anywhere.
type User struct {
Name string `json:"name,omitempty"`
}
var user User
json, err := tiq.Get(&user, "Name", "json")
json // "name,omitempty"A simple static function to set a field's content from anywhere.
type User struct {
Name string `json:"name,omitempty"`
}
var user User
err := tiq.Set(&user, "Name", "Bob")
user.Name // "Bob"