dotenv.go

package envconfig

import (
	"bufio"
	"fmt"
	"os"
	"strings"
)

// EnvFileLookup returns a lookup function that reads environment variables
// from a .env file. It falls back to OS env if a file is not found.
// The .env file should have lines in the format KEY=VALUE.
// Comments starting with # are ignored.
// Empty lines are ignored.
// Notes:
//   - If both the .env file and OS environment define a key, the OS environment value wins.
//   - Lines like `export KEY=VALUE` are supported.
func EnvFileLookup(filePath string) func(string) (string, bool) {
	envMap := make(map[string]string)

	file, err := os.Open(filePath)
	if err == nil {
		defer func(file *os.File) {
			if err := file.Close(); err != nil {
				_, _ = fmt.Fprintf(os.Stderr, "envconfig: failed to close %q file: %v", filePath, err)
			}
		}(file)

		scanner := bufio.NewScanner(file)
		const (
			initialBufSize = 64 * 1024
			maxBufSize     = 1024 * 1024
		)
		scanner.Buffer(make([]byte, 0, initialBufSize), maxBufSize)
		for scanner.Scan() {
			line := strings.TrimSpace(scanner.Text())

			// Skip empty lines and comments
			if line == "" || strings.HasPrefix(line, "#") {
				continue
			}

			if strings.HasPrefix(line, "export ") {
				line = strings.TrimSpace(strings.TrimPrefix(line, "export "))
			}

			parts := strings.SplitN(line, "=", 2)
			if len(parts) != 2 {
				continue
			}

			key := strings.TrimSpace(parts[0])
			value := strings.TrimSpace(parts[1])

			quoted := false
			if len(value) > 0 && (value[0] == '"' || value[0] == '\'') {
				q := value[0] // " or '

				if idx := strings.LastIndexByte(value, q); idx > 0 {
					inner := value[1:idx]
					rest := strings.TrimSpace(value[idx+1:])

					// If rest starts with a comment, ignore it entirely.
					if rest == "" || strings.HasPrefix(rest, "#") {
						value = inner
						quoted = true
					}
					// If the rest doesn't start with #, we fall through to unquoted handling,
				}
			}

			if !quoted {
				// Remove inline comment for unquoted values: value [space]# comment
				// We do not strip # without prior whitespace to allow "value#partofvalue".
				if idx := strings.Index(value, "#"); idx >= 0 {
					// Only consider as comment if there's whitespace before the '#'
					// e.g., "value # comment", not "value#partofvalue"
					spaceIdx := strings.LastIndexAny(value[:idx], " \t")
					if spaceIdx >= len(value[:idx])-1 {
						value = strings.TrimSpace(value[:idx])
					}
				}
			}

			envMap[key] = value
		}
		if err := scanner.Err(); err != nil {
			_, _ = fmt.Fprintf(os.Stderr, "envconfig: error file scanning %q: %v", filePath, err)
		}
	}

	return func(key string) (string, bool) {
		if value, exists := os.LookupEnv(key); exists {
			return value, true
		}

		if value, exists := envMap[key]; exists {
			return value, true
		}

		return "", false
	}
}