Add support for hash chaining to detect modifications in postings

The following details of a posting contribute to its hash:

  fullname of account
  string representation of amount

Each posting hashes contributes to the transaction hash, which is compromised
of:

  previous transaction’s hash (as encountered in parsing order)
  actual date
  optional auxiliary date
  optional code
  payee
  hashes of all postings

Note that this means that changes in the “code” or any of the comments

1 files changed, 15 insertions, 0 deletions

diff --git a/src/xact.cc b/src/xact.cc
index 55e816cb..0b9bd9cd 100644
--- a/src/xact.cc
+++ b/src/xact.cc
@@ -581,6 +581,21 @@ bool xact_t::valid() const
   return true;
 }
 
+string xact_t::hash(string nonce) const {
+  std::ostringstream repr;
+  repr << nonce;
+  repr << date();
+  repr << aux_date();
+  repr << code;
+  repr << payee;
+  string hash(repr.str());
+  posts_list all_posts(posts.begin(), posts.end());
+  foreach (post_t * post, all_posts) {
+    hash = post->hash(hash);
+  }
+  return hash;
+}
+
 namespace {
   bool post_pred(expr_t::ptr_op_t op, post_t& post)
   {