From 7b8ade354d41939ee0ac7097cf2fad04df695e6e Mon Sep 17 00:00:00 2001
From: porcuquine <porcuquine@users.noreply.github.com>
Date: Wed, 15 Jul 2020 17:51:44 -0700
Subject: [PATCH] Implement fauxrep2.

---
 filecoin-proofs/src/api/seal.rs               | 24 ++++++++++++++++
 storage-proofs/porep/Cargo.toml               |  1 +
 .../porep/src/stacked/vanilla/proof.rs        | 28 +++++++++++++++++++
 3 files changed, 53 insertions(+)

diff --git a/filecoin-proofs/src/api/seal.rs b/filecoin-proofs/src/api/seal.rs
index 9b9efecb2..d464a1547 100644
--- a/filecoin-proofs/src/api/seal.rs
+++ b/filecoin-proofs/src/api/seal.rs
@@ -807,3 +807,27 @@ pub fn fauxrep_aux<
     commitment[..].copy_from_slice(&comm_r.into_bytes()[..]);
     Ok(commitment)
 }
+
+pub fn fauxrep2<R: AsRef<Path>, S: AsRef<Path>, Tree: 'static + MerkleTreeTrait>(
+    cache_path: R,
+    existing_p_aux_path: S,
+) -> Result<Commitment> {
+    let mut rng = rand::thread_rng();
+
+    let fake_comm_c = <Tree::Hasher as Hasher>::Domain::random(&mut rng);
+
+    let (comm_r, p_aux) =
+        StackedDrg::<Tree, DefaultPieceHasher>::fake_comm_r(fake_comm_c, existing_p_aux_path)?;
+
+    let p_aux_path = cache_path.as_ref().join(CacheKey::PAux.to_string());
+    let mut f_p_aux = File::create(&p_aux_path)
+        .with_context(|| format!("could not create file p_aux={:?}", p_aux_path))?;
+    let p_aux_bytes = serialize(&p_aux)?;
+    f_p_aux
+        .write_all(&p_aux_bytes)
+        .with_context(|| format!("could not write to file p_aux={:?}", p_aux_path))?;
+
+    let mut commitment = [0u8; 32];
+    commitment[..].copy_from_slice(&comm_r.into_bytes()[..]);
+    Ok(commitment)
+}
diff --git a/storage-proofs/porep/Cargo.toml b/storage-proofs/porep/Cargo.toml
index fa0bace7c..38bc3f1ed 100644
--- a/storage-proofs/porep/Cargo.toml
+++ b/storage-proofs/porep/Cargo.toml
@@ -31,6 +31,7 @@ once_cell = "1.3.1"
 neptune = { version = "1.0.1", features = ["gpu"] }
 num_cpus = "1.10.1"
 hex = "0.4.2"
+bincode = "1.1.2"
 byteorder = "1.3.4"
 
 [dev-dependencies]
diff --git a/storage-proofs/porep/src/stacked/vanilla/proof.rs b/storage-proofs/porep/src/stacked/vanilla/proof.rs
index 71f3b8364..38b5d2570 100644
--- a/storage-proofs/porep/src/stacked/vanilla/proof.rs
+++ b/storage-proofs/porep/src/stacked/vanilla/proof.rs
@@ -4,6 +4,7 @@ use std::marker::PhantomData;
 use std::path::{Path, PathBuf};
 use std::sync::{mpsc, Arc, RwLock};
 
+use bincode::deserialize;
 use generic_array::typenum::{self, Unsigned};
 use log::{info, trace};
 use merkletree::merkle::{
@@ -1328,6 +1329,33 @@ impl<'a, Tree: 'static + MerkleTreeTrait, G: 'static + Hasher> StackedDrg<'a, Tr
 
         Ok((comm_r, p_aux))
     }
+
+    pub fn fake_comm_r<R: AsRef<Path>>(
+        tree_c_root: <Tree::Hasher as Hasher>::Domain,
+        existing_p_aux_path: R,
+    ) -> Result<(
+        <Tree::Hasher as Hasher>::Domain,
+        PersistentAux<<Tree::Hasher as Hasher>::Domain>,
+    )> {
+        let existing_p_aux: PersistentAux<<Tree::Hasher as Hasher>::Domain> = {
+            let p_aux_bytes = std::fs::read(&existing_p_aux_path)?;
+
+            deserialize(&p_aux_bytes)
+        }?;
+
+        let existing_comm_r_last = existing_p_aux.comm_r_last;
+
+        // comm_r = H(comm_c || comm_r_last)
+        let comm_r: <Tree::Hasher as Hasher>::Domain =
+            <Tree::Hasher as Hasher>::Function::hash2(&tree_c_root, &existing_comm_r_last);
+
+        let p_aux = PersistentAux {
+            comm_c: tree_c_root,
+            comm_r_last: existing_comm_r_last,
+        };
+
+        Ok((comm_r, p_aux))
+    }
 }
 
 #[cfg(test)]