Only bootstrap a compact range once per log

As opposed to doing a new bootstrap with get-proof-by-hash every time
the next root is constructed.  Bootstrapping the compact range from a
get-proof-by-hash query works for the most part, but fails if the log
included a duplicate entry and gives us the index for that instead.  Log
operators with duplicate entries include Cloudflare and Digicert.

If bootstrap fails (unlucky), we try to bootstrap again once the log's
signed tree head moved forward (hoping the last entry has no duplicate).

The more reliable way to bootstrap a compact range would be to use the
get-entry-and-proof endpoint.  This does not work in practise because
some logs are not implementing this endpoint.  Digicert has such logs.

1 files changed, 32 insertions, 0 deletions

diff --git a/internal/ioutil/ioutil.go b/internal/ioutil/ioutil.go
index 7fe6cfc..8e98c65 100644
--- a/internal/ioutil/ioutil.go
+++ b/internal/ioutil/ioutil.go
@@ -1,6 +1,7 @@
 package ioutil
 
 import (
+	"crypto/sha256"
 	"encoding/json"
 	"fmt"
 	"os"
@@ -54,3 +55,34 @@ func DirectoriesExist(paths []string) error {
 	}
 	return nil
 }
+
+func CopyHashes(hashes [][sha256.Size]byte) (ret [][sha256.Size]byte) {
+	for _, hash := range hashes {
+		var dst [sha256.Size]byte
+		copy(dst[:], hash[:])
+		ret = append(ret, dst)
+	}
+	return
+}
+
+func SliceHashes(hashes [][sha256.Size]byte) (ret [][]byte) {
+	for _, hash := range hashes {
+		dst := hash
+		ret = append(ret, dst[:])
+	}
+	return
+}
+
+// UnsliceHashes panics unless all hashes are 32 bytes
+func UnsliceHashes(hashes [][]byte) (ret [][sha256.Size]byte) {
+	for _, hash := range hashes {
+		if got, want := len(hash), sha256.Size; got != want {
+			panic(fmt.Sprintf("bug: invalid hash: size %d", got))
+		}
+
+		var dst [sha256.Size]byte
+		copy(dst[:], hash)
+		ret = append(ret, dst)
+	}
+	return
+}