e2e: read image replacements from file

Signed-off-by: Paul Meyer <[email protected]>

e2e/internal/kuberesource/lookup.go

@@ -0,0 +1,46 @@
+package kuberesource
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"regexp"
+)
+
+var replacementRE = regexp.MustCompile(`(?P<image>[^\s=]+)\s*=\s*(?P<replacement>\S+)`)
+
+// ImageReplacementsFromFile parses the containerlookup file into a map.
+//
+// The file is expected to contain newline-separated pairs of images and their intended
+// replacement, separated by an = sign. Empty lines and lines starting with the pound character
+// are ignored. This file is populated by container image build rules in the justfile.
+func ImageReplacementsFromFile(file io.ReadCloser) (map[string]string, error) {
+	m := make(map[string]string)
+
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		line := scanner.Text()
+		if len(line) == 0 || line[0] == '#' {
+			continue
+		}
+
+		matches := replacementRE.FindStringSubmatch(line)
+		if matches == nil {
+			return nil, fmt.Errorf("invalid image line: %s", line)
+		}
+
+		if replacementRE.SubexpIndex("image") == -1 {
+			return nil, fmt.Errorf("image not found for image line: %s", line)
+		}
+		image := matches[replacementRE.SubexpIndex("image")]
+
+		if replacementRE.SubexpIndex("replacement") == -1 {
+			return nil, fmt.Errorf("replacement not found for image line: %s", line)
+		}
+		replacement := matches[replacementRE.SubexpIndex("replacement")]
+
+		m[image] = replacement
+	}
+
+	return m, nil
+}