libstore: generatorize protocol serializers

this is cursed. deeply and profoundly cursed. under NO CIRCUMSTANCES
must protocol serializer helpers be applied to temporaries! doing so
will inevitably cause dangling references and cause the entire thing
to crash. we need to do this even so to get rid of boost coroutines,
and likewise to encapsulate the serializers we suffer today at least
a little bit to allow a gradual migration to an actual IPC protocol.

(this isn't a problem that's unique to generators. c++ coroutines in
general cannot safely take references to arbitrary temporaries since
c++ does not have a lifetime system that can make this safe. -sigh-)

Change-Id: I2921ba451e04d86798752d140885d3c5cc08e146

1 files changed, 35 insertions, 38 deletions

diff --git a/src/libstore/worker-protocol.cc b/src/libstore/worker-protocol.cc
index 08c5c6b70..f85fba0ff 100644
--- a/src/libstore/worker-protocol.cc
+++ b/src/libstore/worker-protocol.cc
@@ -28,17 +28,17 @@ std::optional<TrustedFlag> WorkerProto::Serialise<std::optional<TrustedFlag>>::r
     }
 }
 
-void WorkerProto::Serialise<std::optional<TrustedFlag>>::write(const Store & store, WorkerProto::WriteConn conn, const std::optional<TrustedFlag> & optTrusted)
+WireFormatGenerator WorkerProto::Serialise<std::optional<TrustedFlag>>::write(const Store & store, WorkerProto::WriteConn conn, const std::optional<TrustedFlag> & optTrusted)
 {
     if (!optTrusted)
-        conn.to << (uint8_t)0;
+        co_yield (uint8_t)0;
     else {
         switch (*optTrusted) {
         case Trusted:
-            conn.to << (uint8_t)1;
+            co_yield (uint8_t)1;
             break;
         case NotTrusted:
-            conn.to << (uint8_t)2;
+            co_yield (uint8_t)2;
             break;
         default:
             assert(false);
@@ -57,23 +57,23 @@ DerivedPath WorkerProto::Serialise<DerivedPath>::read(const Store & store, Worke
     }
 }
 
-void WorkerProto::Serialise<DerivedPath>::write(const Store & store, WorkerProto::WriteConn conn, const DerivedPath & req)
+WireFormatGenerator WorkerProto::Serialise<DerivedPath>::write(const Store & store, WorkerProto::WriteConn conn, const DerivedPath & req)
 {
     if (GET_PROTOCOL_MINOR(conn.version) >= 30) {
-        conn.to << req.to_string_legacy(store);
+        co_yield req.to_string_legacy(store);
     } else {
         auto sOrDrvPath = StorePathWithOutputs::tryFromDerivedPath(req);
-        std::visit(overloaded {
-            [&](const StorePathWithOutputs & s) {
-                conn.to << s.to_string(store);
+        co_yield std::visit(overloaded {
+            [&](const StorePathWithOutputs & s) -> std::string {
+                return s.to_string(store);
             },
-            [&](const StorePath & drvPath) {
+            [&](const StorePath & drvPath) -> std::string {
                 throw Error("trying to request '%s', but daemon protocol %d.%d is too old (< 1.29) to request a derivation file",
                     store.printStorePath(drvPath),
                     GET_PROTOCOL_MAJOR(conn.version),
                     GET_PROTOCOL_MINOR(conn.version));
             },
-            [&](std::monostate) {
+            [&](std::monostate) -> std::string {
                 throw Error("wanted to build a derivation that is itself a build product, but protocols do not support that. Try upgrading the Nix implementation on the other end of this connection");
             },
         }, sOrDrvPath);
@@ -91,10 +91,10 @@ KeyedBuildResult WorkerProto::Serialise<KeyedBuildResult>::read(const Store & st
     };
 }
 
-void WorkerProto::Serialise<KeyedBuildResult>::write(const Store & store, WorkerProto::WriteConn conn, const KeyedBuildResult & res)
+WireFormatGenerator WorkerProto::Serialise<KeyedBuildResult>::write(const Store & store, WorkerProto::WriteConn conn, const KeyedBuildResult & res)
 {
-    WorkerProto::write(store, conn, res.path);
-    WorkerProto::write(store, conn, static_cast<const BuildResult &>(res));
+    co_yield WorkerProto::write(store, conn, res.path);
+    co_yield WorkerProto::write(store, conn, static_cast<const BuildResult &>(res));
 }
 
 
@@ -120,23 +120,21 @@ BuildResult WorkerProto::Serialise<BuildResult>::read(const Store & store, Worke
     return res;
 }
 
-void WorkerProto::Serialise<BuildResult>::write(const Store & store, WorkerProto::WriteConn conn, const BuildResult & res)
+WireFormatGenerator WorkerProto::Serialise<BuildResult>::write(const Store & store, WorkerProto::WriteConn conn, const BuildResult & res)
 {
-    conn.to
-        << res.status
-        << res.errorMsg;
+    co_yield res.status;
+    co_yield res.errorMsg;
     if (GET_PROTOCOL_MINOR(conn.version) >= 29) {
-        conn.to
-            << res.timesBuilt
-            << res.isNonDeterministic
-            << res.startTime
-            << res.stopTime;
+        co_yield res.timesBuilt;
+        co_yield res.isNonDeterministic;
+        co_yield res.startTime;
+        co_yield res.stopTime;
     }
     if (GET_PROTOCOL_MINOR(conn.version) >= 28) {
         DrvOutputs builtOutputs;
         for (auto & [output, realisation] : res.builtOutputs)
             builtOutputs.insert_or_assign(realisation.id, realisation);
-        WorkerProto::write(store, conn, builtOutputs);
+        co_yield WorkerProto::write(store, conn, builtOutputs);
     }
 }
 
@@ -150,10 +148,10 @@ ValidPathInfo WorkerProto::Serialise<ValidPathInfo>::read(const Store & store, R
     };
 }
 
-void WorkerProto::Serialise<ValidPathInfo>::write(const Store & store, WriteConn conn, const ValidPathInfo & pathInfo)
+WireFormatGenerator WorkerProto::Serialise<ValidPathInfo>::write(const Store & store, WriteConn conn, const ValidPathInfo & pathInfo)
 {
-    WorkerProto::write(store, conn, pathInfo.path);
-    WorkerProto::write(store, conn, static_cast<const UnkeyedValidPathInfo &>(pathInfo));
+    co_yield WorkerProto::write(store, conn, pathInfo.path);
+    co_yield WorkerProto::write(store, conn, static_cast<const UnkeyedValidPathInfo &>(pathInfo));
 }
 
 
@@ -173,18 +171,17 @@ UnkeyedValidPathInfo WorkerProto::Serialise<UnkeyedValidPathInfo>::read(const St
     return info;
 }
 
-void WorkerProto::Serialise<UnkeyedValidPathInfo>::write(const Store & store, WriteConn conn, const UnkeyedValidPathInfo & pathInfo)
+WireFormatGenerator WorkerProto::Serialise<UnkeyedValidPathInfo>::write(const Store & store, WriteConn conn, const UnkeyedValidPathInfo & pathInfo)
 {
-    conn.to
-        << (pathInfo.deriver ? store.printStorePath(*pathInfo.deriver) : "")
-        << pathInfo.narHash.to_string(Base16, false);
-    WorkerProto::write(store, conn, pathInfo.references);
-    conn.to << pathInfo.registrationTime << pathInfo.narSize;
-
-    conn.to
-        << pathInfo.ultimate
-        << pathInfo.sigs
-        << renderContentAddress(pathInfo.ca);
+    co_yield (pathInfo.deriver ? store.printStorePath(*pathInfo.deriver) : "");
+    co_yield pathInfo.narHash.to_string(Base16, false);
+    co_yield WorkerProto::write(store, conn, pathInfo.references);
+    co_yield pathInfo.registrationTime;
+    co_yield pathInfo.narSize;
+
+    co_yield pathInfo.ultimate;
+    co_yield pathInfo.sigs;
+    co_yield renderContentAddress(pathInfo.ca);
 }
 
 }