adler32 is not nearly unique. switching to sh256 and adding tests

hash/hash.go

@@ -2,13 +2,18 @@ package hash
 
 import (
 	"crypto/md5"
+	"crypto/sha256"
 	"fmt"
-	"hash/adler32"
 	"io"
 	"math/rand"
+	"strings"
 	"time"
 )
 
+func init() {
+	rand.Seed(time.Now().UnixNano())
+}
+
 func Rand64() int64 {
 	return rand.Int63()
 }
@@ -31,7 +36,7 @@ func GetMd5FromBytes(blob []byte) (sum []byte) {
 
 /* get a small, decently unique hash */
 func GetSmallHash() (small_hash string) {
-	h := adler32.New()
-	io.WriteString(h, fmt.Sprintf("%d", time.Now().Unix()))
-	return fmt.Sprintf("%X", h.Sum(nil))
+	h := sha256.New()
+	io.WriteString(h, fmt.Sprintf("%d%d", time.Now().UnixNano(), Rand64()))
+	return strings.ToLower(fmt.Sprintf("%X", h.Sum(nil)[0:9]))
 }

hash/hash_test.go

@@ -3,6 +3,7 @@ package hash
 import (
 	"fmt"
 	"testing"
+  "sort"
 )
 
 func TestRand64(t *testing.T) {
@@ -36,4 +37,15 @@ func TestMd5String(t *testing.T) {
 }
 
 func TestHash(t *testing.T) {
+  seen := []string{}
+  for i := 0; i < 10000; i++ {
+    h := GetSmallHash()
+    j := sort.SearchStrings(seen, h)
+    if len(seen) != 0 && j < len(seen) && h == seen[j] {
+      t.Errorf("there is a non-unique hash after %d attempts [%s and %s]", i, h, seen[j])
+    } else {
+      seen = append(seen, h)
+      sort.Strings(seen)
+    }
+  }
 }