From 2e90762e3fabf668775b8f8e8b5a037def2a9646 Mon Sep 17 00:00:00 2001
From: Doug Hoyte <doug@hcsw.org>
Date: Fri, 15 Sep 2023 16:13:56 -0400
Subject: [PATCH] C++: protocol version 0

---
 cpp/Negentropy.h     | 60 ++++++++++++++++++++++++++++++++++++--------
 test/cpp/harness.cpp |  6 +++--
 2 files changed, 54 insertions(+), 12 deletions(-)

diff --git a/cpp/Negentropy.h b/cpp/Negentropy.h
index 5abcc11..b0c5ea8 100644
--- a/cpp/Negentropy.h
+++ b/cpp/Negentropy.h
@@ -12,12 +12,14 @@
 #include <limits>
 #include <algorithm>
 #include <stdexcept>
+#include <optional>
 
 #include <openssl/sha.h>
 
 
 namespace negentropy {
 
+const uint64_t PROTOCOL_VERSION_0 = 0x60;
 
 const uint64_t MAX_U64 = std::numeric_limits<uint64_t>::max();
 using err = std::runtime_error;
@@ -27,8 +29,8 @@ enum class Mode {
     Skip = 0,
     Fingerprint = 1,
     IdList = 2,
-    Deprecated = 3,
-    Continuation = 4,
+    Continuation = 3,
+    UnsupportedProtocolVersion = 4,
 };
 
 
@@ -76,6 +78,7 @@ struct Negentropy {
     std::string itemIds;
     bool sealed = false;
     bool isInitiator = false;
+    bool didHandshake = false;
     bool continuationNeeded = false;
     std::deque<OutputRange> pendingOutputs;
 
@@ -117,24 +120,44 @@ struct Negentropy {
 
     std::string initiate() {
         if (!sealed) throw negentropy::err("not sealed");
+        if (didHandshake) throw negentropy::err("can't initiate after reconcile");
         isInitiator = true;
 
         splitRange(0, numItems(), Item(0), Item(MAX_U64), pendingOutputs);
 
-        return buildOutput();
+        auto output = std::move(buildOutput(true).value());
+        return output;
     }
 
     std::string reconcile(std::string_view query) {
         if (isInitiator) throw negentropy::err("initiator not asking for have/need IDs");
+
+        if (!didHandshake) {
+            auto protocolVersion = getByte(query);
+            if (protocolVersion < 0x60 || protocolVersion > 0x6F) throw negentropy::err("invalid negentropy protocol version byte");
+            if (protocolVersion != PROTOCOL_VERSION_0) {
+                std::string o;
+                uint64_t lastTimestampOut = 0;
+                o += encodeBound(Item(PROTOCOL_VERSION_0), lastTimestampOut);
+                o += encodeVarInt(uint64_t(Mode::UnsupportedProtocolVersion));
+                return o;
+            }
+            didHandshake = true;
+        }
+
         std::vector<std::string> haveIds, needIds;
         reconcileAux(query, haveIds, needIds);
-        return buildOutput();
+
+        auto output = std::move(buildOutput(false).value());
+        return output;
     }
 
-    std::string reconcile(std::string_view query, std::vector<std::string> &haveIds, std::vector<std::string> &needIds) {
+    std::optional<std::string> reconcile(std::string_view query, std::vector<std::string> &haveIds, std::vector<std::string> &needIds) {
         if (!isInitiator) throw negentropy::err("non-initiator asking for have/need IDs");
+
         reconcileAux(query, haveIds, needIds);
-        return buildOutput();
+
+        return buildOutput(false);
     }
 
   private:
@@ -241,10 +264,10 @@ struct Negentropy {
 
                     flushIdListOutput();
                 }
-            } else if (mode == Mode::Deprecated) {
-                throw negentropy::err("other side is speaking old negentropy protocol");
             } else if (mode == Mode::Continuation) {
                 continuationNeeded = true;
+            } else if (mode == Mode::UnsupportedProtocolVersion) {
+                throw negentropy::err("server does not support our negentropy protocol version");
             } else {
                 throw negentropy::err("unexpected mode");
             }
@@ -300,11 +323,17 @@ struct Negentropy {
         }
     }
 
-    std::string buildOutput() {
+    std::optional<std::string> buildOutput(bool initialMessage) {
         std::string output;
         Item currBound;
         uint64_t lastTimestampOut = 0;
 
+        if (initialMessage) {
+            if (didHandshake) throw negentropy::err("already built initial message");
+            didHandshake = true;
+            output.push_back(PROTOCOL_VERSION_0);
+        }
+
         std::sort(pendingOutputs.begin(), pendingOutputs.end(), [](const auto &a, const auto &b){ return a.start < b.start; });
 
         while (pendingOutputs.size()) {
@@ -332,11 +361,15 @@ struct Negentropy {
 
         // Server indicates that it has more to send, OR ensure client sends a non-empty message
 
-        if ((!isInitiator && pendingOutputs.size()) || (isInitiator && output.size() == 0 && continuationNeeded)) {
+        if (!isInitiator && pendingOutputs.size()) {
             output += encodeBound(Item(MAX_U64), lastTimestampOut);
             output += encodeVarInt(uint64_t(Mode::Continuation));
         }
 
+        if (isInitiator && output.size() == 0 && !continuationNeeded) {
+            return std::nullopt;
+        }
+
         return output;
     }
 
@@ -362,6 +395,13 @@ struct Negentropy {
 
     // Decoding
 
+    uint8_t getByte(std::string_view &encoded) {
+        if (encoded.size() < 1) throw negentropy::err("parse ends prematurely");
+        uint8_t output = encoded[0];
+        encoded = encoded.substr(1);
+        return output;
+    }
+
     std::string getBytes(std::string_view &encoded, size_t n) {
         if (encoded.size() < n) throw negentropy::err("parse ends prematurely");
         auto res = encoded.substr(0, n);
diff --git a/test/cpp/harness.cpp b/test/cpp/harness.cpp
index e70c880..1912c00 100644
--- a/test/cpp/harness.cpp
+++ b/test/cpp/harness.cpp
@@ -54,15 +54,17 @@ int main() {
 
             if (ne.isInitiator) {
                 std::vector<std::string> have, need;
-                q = ne.reconcile(q, have, need);
+                auto resp = ne.reconcile(q, have, need);
 
                 for (auto &id : have) std::cout << "have," << hoytech::to_hex(id) << "\n";
                 for (auto &id : need) std::cout << "need," << hoytech::to_hex(id) << "\n";
 
-                if (q.size() == 0) {
+                if (!resp) {
                     std::cout << "done" << std::endl;
                     continue;
                 }
+
+                q = *resp;
             } else {
                 q = ne.reconcile(q);
             }