vieter/src/env/env.v

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Coq
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module env
import os
import toml
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// The prefix that every environment variable should have
const prefix = 'VIETER_'
// The suffix an environment variable in order for it to be loaded from a file
// instead
const file_suffix = '_FILE'
fn get_env_var(field_name string) ?string {
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env_var_name := '$env.prefix$field_name.to_upper()'
env_file_name := '$env.prefix$field_name.to_upper()$env.file_suffix'
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env_var := os.getenv(env_var_name)
env_file := os.getenv(env_file_name)
// If both are missing, we return an empty string
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if env_var == '' && env_file == '' {
return ''
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}
// If they're both set, we report a conflict
if env_var != '' && env_file != '' {
return error('Only one of $env_var_name or $env_file_name can be defined.')
}
// If it's the env var itself, we return it.
// I'm pretty sure this also prevents variable ending in _FILE (e.g.
// VIETER_LOG_FILE) from being mistakingely read as an _FILE suffixed env
// var.
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if env_var != '' {
return env_var
}
// Otherwise, we process the file
return os.read_file(env_file) or {
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error('Failed to read file defined in $env_file_name: ${err.msg()}.')
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}
}
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// load<T> attempts to create an object of type T from the given path to a toml
// file & environment variables. For each field, it will select either a value
// given from an environment variable, a value defined in the config file or a
// configured default if present, in that order.
pub fn load<T>(path string) ?T {
mut res := T{}
if os.exists(path) {
// We don't use reflect here because reflect also sets any fields not
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// in the toml back to their zero value, which we don't want
doc := toml.parse_file(path) ?
$for field in T.fields {
s := doc.value(field.name)
if s !is toml.Null {
$if field.typ is string {
res.$(field.name) = s.string()
} $else $if field.typ is int {
res.$(field.name) = s.int()
}
}
}
}
$for field in T.fields {
env_value := get_env_var(field.name) ?
// The value of an env var will always take precedence over the toml
// file.
if env_value != '' {
$if field.typ is string {
res.$(field.name) = env_value
} $else $if field.typ is int {
res.$(field.name) = env_value.int()
}
}
// Now, we check whether a value is present. If there isn't, that means
// it isn't in the config file, nor is there a default or an env var.
mut has_value := false
$if field.typ is string {
has_value = res.$(field.name) != ''
} $else $if field.typ is int {
has_value = res.$(field.name) != 0
}
if !has_value {
return error("Missing config variable '$field.name' with no provided default. Either add it to the config file or provide it using an environment variable.")
}
}
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return res
}