84 lines
2.2 KiB
Go
84 lines
2.2 KiB
Go
// Package env provides a minimal, dependency-free .env file loader.
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//
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// It reads KEY=VAL pairs from a file and sets them into the process
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// environment using os.Setenv, but only for variables that are NOT already
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// set. This gives the real environment (system env / shell) priority over
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// values in the .env file.
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package env
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import (
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"bufio"
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"fmt"
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"os"
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"strings"
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)
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// DefaultPath is the file LoadEnvDefault reads when no path is given.
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const DefaultPath = ".env"
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// LoadEnvDefault loads environment variables from the default ".env" file
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// in the current working directory.
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func LoadEnvDefault() error {
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return LoadEnv(DefaultPath)
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}
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// LoadEnv reads the file at path line by line and sets each KEY=VALUE pair
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// into the process environment.
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//
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// Rules:
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// - Blank lines and lines starting with '#' (comments) are ignored.
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// - Values may be wrapped in single or double quotes, which are stripped.
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// - A variable already present in the environment is never overridden
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// (system env wins; .env is the lowest priority).
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func LoadEnv(path string) error {
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f, err := os.Open(path)
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if err != nil {
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return err
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}
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defer f.Close()
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scanner := bufio.NewScanner(f)
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for scanner.Scan() {
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line := strings.TrimSpace(scanner.Text())
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if line == "" || strings.HasPrefix(line, "#") {
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continue
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}
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key, value, ok := strings.Cut(line, "=")
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if !ok {
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// Not KEY=VAL format; skip silently.
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continue
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}
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key = strings.TrimSpace(key)
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if key == "" {
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continue
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}
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value = strings.TrimSpace(value)
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value = unquote(value)
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if _, exists := os.LookupEnv(key); exists {
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// System environment wins over .env.
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continue
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}
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if err := os.Setenv(key, value); err != nil {
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return fmt.Errorf("failed to set env var %q: %w", key, err)
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}
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}
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if err := scanner.Err(); err != nil {
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return fmt.Errorf("failed to read %s: %w", path, err)
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}
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return nil
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}
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// unquote strips a single matching pair of surrounding single or double
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// quotes from value, if present. Any other value is returned unchanged.
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func unquote(value string) string {
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if len(value) >= 2 {
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first, last := value[0], value[len(value)-1]
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if (first == '"' && last == '"') || (first == '\'' && last == '\'') {
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return value[1 : len(value)-1]
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}
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}
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return value
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}
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