From 44e4fb0f4e9e9ff9bf6e31c68b626fea2eb7403a Mon Sep 17 00:00:00 2001
From: Rasmus Dahlberg <rasmus.dahlberg@kau.se>
Date: Thu, 22 Oct 2020 20:03:57 +0200
Subject: Added start on get-proof-by-hash code path

If the provided tree size is (mostly) valid the Trillian back-end is
asked to provide an inclusion proof, which is then placed in an
InclusionProofV1 structure and returned as a JSON object.
---
 handler.go | 37 +++++++++++++++++++++++++++++++++++
 type.go    | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 102 insertions(+)

diff --git a/handler.go b/handler.go
index 4d2ace8..57adaf1 100644
--- a/handler.go
+++ b/handler.go
@@ -169,6 +169,43 @@ func getAnchors(ctx context.Context, i *instance, w http.ResponseWriter, r *http
 // getProofByHash provides an inclusion proof based on a given leaf hash
 func getProofByHash(ctx context.Context, i *instance, w http.ResponseWriter, r *http.Request) (int, error) {
 	glog.Info("in getProofByHash")
+	request, err := NewGetProofByHashRequest(r)
+	if err != nil {
+		return http.StatusBadRequest, err
+	}
+
+	trillianRequest := trillian.GetInclusionProofByHashRequest{
+		LogId: i.logID,
+		LeafHash: request.Hash,
+		TreeSize: request.TreeSize,
+		OrderBySequence: true,
+	}
+	trillianResponse, err := i.client.GetInclusionProofByHash(ctx, &trillianRequest)
+	if err != nil {
+		return http.StatusInternalServerError, fmt.Errorf("failed fetching inclusion proof from Trillian backend: %v", err)
+	}
+	// TODO: check the returned tree size in response?
+
+	// Santity check
+	if len(trillianResponse.Proof) == 0 {
+		return http.StatusNotFound, fmt.Errorf("get-proof-by-hash backend returned no proof")
+	}
+	// TODO: verify that proof is valid?
+
+	w.Header().Set("Content-Type", "application/json")
+	data, err := NewGetProofByHashResponse(uint64(request.TreeSize), trillianResponse.Proof[0])
+	if err != nil {
+		return http.StatusInternalServerError, fmt.Errorf("failed creating get-proof-by-hash response: %v", err)
+	}
+	json, err := json.Marshal(data)
+	if err != nil {
+		return http.StatusInternalServerError, fmt.Errorf("failed json-encoding GetProofByHashResponse: %v", err)
+	}
+	_, err = w.Write(json)
+	if err != nil {
+		return http.StatusInternalServerError, fmt.Errorf("failed writing get-entries response: %v", err)
+	}
+
 	return http.StatusOK, nil // TODO
 }
 
diff --git a/type.go b/type.go
index 11fafe1..10ec2bd 100644
--- a/type.go
+++ b/type.go
@@ -95,6 +95,31 @@ func (i ChecksumV1) String() string {
 	return fmt.Sprintf("%v %v", string(i.Package), base64.StdEncoding.EncodeToString(i.Checksum))
 }
 
+type NodeHash struct {
+	Data []byte `tls:"minlen:32,maxlen:255"`
+}
+
+type InclusionProofV1 struct {
+	LogID []byte `tls:"minlen:2,maxlen:127"`
+	TreeSize uint64
+	LeafIndex uint64
+	InclusionPath []NodeHash `tls:"minlen:1,maxlen:65535"`
+}
+
+func NewInclusionProofV1(logID []byte, treeSize uint64, proof *trillian.Proof) InclusionProofV1 {
+	inclusionPath := make([]NodeHash, 0, len(proof.Hashes))
+	for _, hash := range proof.Hashes {
+		inclusionPath = append(inclusionPath, NodeHash{ Data: hash })
+	}
+
+	return InclusionProofV1{
+		LogID: logID,
+		TreeSize: treeSize,
+		LeafIndex: uint64(proof.LeafIndex),
+		InclusionPath: inclusionPath,
+	}
+}
+
 // AddEntryRequest is a collection of add-entry input parameters
 type AddEntryRequest struct {
 	Item        string `json:"item"`
@@ -155,3 +180,43 @@ func NewGetEntriesResponse(leaves []*trillian.LogLeaf) (GetEntriesResponse, erro
 	}
 	return GetEntriesResponse{entries}, nil
 }
+
+type GetProofByHashRequest struct {
+	Hash []byte
+	TreeSize int64
+}
+
+func NewGetProofByHashRequest(httpRequest *http.Request) (*GetProofByHashRequest, error) {
+	var r GetProofByHashRequest
+	var err error
+
+	r.TreeSize, err = strconv.ParseInt(httpRequest.FormValue("tree_size"), 10, 64)
+	if err != nil {
+		return nil, fmt.Errorf("bad tree_size parameter: %v", err)
+	}
+	if r.TreeSize < 0 {
+		return nil, fmt.Errorf("bad tree_size parameter: negative value")
+	}
+	// TODO: check that tree size is not past STH.tree_size
+
+	r.Hash, err = base64.StdEncoding.DecodeString(httpRequest.FormValue("hash"))
+	if err != nil {
+		return nil, fmt.Errorf("bad hash parameter: %v", err)
+	}
+	return &r, nil
+}
+
+type GetProofByHashResponse struct {
+	InclusionProof string `json:"inclusion_proof"`
+}
+
+func NewGetProofByHashResponse(treeSize uint64, inclusionProof *trillian.Proof) (*GetProofByHashResponse, error) {
+	item := NewInclusionProofV1([]byte("TODO: add log ID"), treeSize, inclusionProof)
+	b, err := tls.Marshal(item)
+	if err != nil {
+		return nil, fmt.Errorf("tls marshal failed: %v", err)
+	}
+	return &GetProofByHashResponse{
+		InclusionProof: base64.StdEncoding.EncodeToString(b),
+	}, nil
+}
-- 
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