support for docker run environment variables file

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)

opts/envfile.go

@@ -0,0 +1,44 @@
+package opts
+
+import (
+	"bufio"
+	"bytes"
+	"io"
+	"os"
+)
+
+/*
+Read in a line delimited file with environment variables enumerated
+*/
+func ParseEnvFile(filename string) ([]string, error) {
+	fh, err := os.Open(filename)
+	if err != nil {
+		return []string{}, err
+	}
+	var (
+		lines       []string = []string{}
+		line, chunk []byte
+	)
+	reader := bufio.NewReader(fh)
+	line, isPrefix, err := reader.ReadLine()
+
+	for err == nil {
+		if isPrefix {
+			chunk = append(chunk, line...)
+		} else if !isPrefix && len(chunk) > 0 {
+			line = chunk
+			chunk = []byte{}
+		} else {
+			chunk = []byte{}
+		}
+
+		if !isPrefix && len(line) > 0 && bytes.Contains(line, []byte("=")) {
+			lines = append(lines, string(line))
+		}
+		line, isPrefix, err = reader.ReadLine()
+	}
+	if err != nil && err != io.EOF {
+		return []string{}, err
+	}
+	return lines, nil
+}