build: cache go build & test

Signed-off-by: Anagh Kumar Baranwal <6824881+darthShadow@users.noreply.github.com>

bin/go-test-cache/main.go

@@ -0,0 +1,123 @@
+// This code was copied from:
+// https://github.com/fastly/cli/blob/main/scripts/go-test-cache/main.go
+// which in turn is based on the following script and was generated using AI.
+// https://github.com/airplanedev/blog-examples/blob/main/go-test-caching/update_file_timestamps.py?ref=airplane.ghost.io
+//
+// REFERENCE ARTICLE:
+// https://web.archive.org/web/20240308061717/https://www.airplane.dev/blog/caching-golang-tests-in-ci
+//
+// It updates the mtime of the files to a mtime dervived from the sha1 hash of their contents.
+package main
+
+import (
+	"crypto/sha1"
+	"io"
+	"log"
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+	"time"
+)
+
+const (
+	bufSize    = 65536
+	baseDate   = 1684178360
+	timeFormat = "2006-01-02 15:04:05"
+)
+
+func main() {
+	repoRoot := "."
+	allDirs := make([]string, 0)
+
+	err := filepath.Walk(repoRoot, func(path string, info os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+
+		if info.IsDir() {
+			dirPath := filepath.Join(repoRoot, path)
+			relPath, _ := filepath.Rel(repoRoot, dirPath)
+
+			if strings.HasPrefix(relPath, ".") {
+				return nil
+			}
+
+			allDirs = append(allDirs, dirPath)
+		} else {
+			filePath := filepath.Join(repoRoot, path)
+			relPath, _ := filepath.Rel(repoRoot, filePath)
+
+			if strings.HasPrefix(relPath, ".") {
+				return nil
+			}
+
+			sha1Hash, err := getFileSHA1(filePath)
+			if err != nil {
+				return err
+			}
+
+			modTime := getModifiedTime(sha1Hash)
+
+			log.Printf("Setting modified time of file %s to %s\n", relPath, modTime.Format(timeFormat))
+			err = os.Chtimes(filePath, modTime, modTime)
+			if err != nil {
+				return err
+			}
+		}
+
+		return nil
+	})
+	if err != nil {
+		log.Fatal("Error:", err)
+	}
+
+	sort.Slice(allDirs, func(i, j int) bool {
+		return len(allDirs[i]) > len(allDirs[j]) || (len(allDirs[i]) == len(allDirs[j]) && allDirs[i] < allDirs[j])
+	})
+
+	for _, dirPath := range allDirs {
+		relPath, _ := filepath.Rel(repoRoot, dirPath)
+
+		log.Printf("Setting modified time of directory %s to %s\n", relPath, time.Unix(baseDate, 0).Format(timeFormat))
+		err := os.Chtimes(dirPath, time.Unix(baseDate, 0), time.Unix(baseDate, 0))
+		if err != nil {
+			log.Fatal("Error:", err)
+		}
+	}
+
+	log.Println("Done")
+}
+
+func getFileSHA1(filePath string) (string, error) {
+	file, err := os.Open(filePath)
+	if err != nil {
+		return "", err
+	}
+	defer file.Close()
+
+	// G401: Use of weak cryptographic primitive
+	// Disabling as the hash is used not for security reasons.
+	// The hash is used as a cache key to improve test run times.
+	// #nosec
+	// nosemgrep: go.lang.security.audit.crypto.use_of_weak_crypto.use-of-sha1
+	hash := sha1.New()
+	if _, err := io.CopyBuffer(hash, file, make([]byte, bufSize)); err != nil {
+		return "", err
+	}
+
+	return string(hash.Sum(nil)), nil
+}
+
+func getModifiedTime(sha1Hash string) time.Time {
+	hashBytes := []byte(sha1Hash)
+	lastFiveBytes := hashBytes[:5]
+	lastFiveValue := int64(0)
+
+	for _, b := range lastFiveBytes {
+		lastFiveValue = (lastFiveValue << 8) + int64(b)
+	}
+
+	modTime := baseDate - (lastFiveValue % 10000)
+	return time.Unix(modTime, 0)
+}