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, 18 insertions, 14 deletions

diff --git a/src/libstore/common-protocol.cc b/src/libstore/common-protocol.cc
index 456ad2b1f..4e2b2df31 100644
--- a/src/libstore/common-protocol.cc
+++ b/src/libstore/common-protocol.cc
@@ -16,9 +16,9 @@ std::string CommonProto::Serialise<std::string>::read(const Store & store, Commo
     return readString(conn.from);
 }
 
-void CommonProto::Serialise<std::string>::write(const Store & store, CommonProto::WriteConn conn, const std::string & str)
+WireFormatGenerator CommonProto::Serialise<std::string>::write(const Store & store, CommonProto::WriteConn conn, const std::string & str)
 {
-    conn.to << str;
+    co_yield str;
 }
 
 
@@ -27,9 +27,9 @@ StorePath CommonProto::Serialise<StorePath>::read(const Store & store, CommonPro
     return store.parseStorePath(readString(conn.from));
 }
 
-void CommonProto::Serialise<StorePath>::write(const Store & store, CommonProto::WriteConn conn, const StorePath & storePath)
+WireFormatGenerator CommonProto::Serialise<StorePath>::write(const Store & store, CommonProto::WriteConn conn, const StorePath & storePath)
 {
-    conn.to << store.printStorePath(storePath);
+    co_yield store.printStorePath(storePath);
 }
 
 
@@ -38,9 +38,9 @@ ContentAddress CommonProto::Serialise<ContentAddress>::read(const Store & store,
     return ContentAddress::parse(readString(conn.from));
 }
 
-void CommonProto::Serialise<ContentAddress>::write(const Store & store, CommonProto::WriteConn conn, const ContentAddress & ca)
+WireFormatGenerator CommonProto::Serialise<ContentAddress>::write(const Store & store, CommonProto::WriteConn conn, const ContentAddress & ca)
 {
-    conn.to << renderContentAddress(ca);
+    co_yield renderContentAddress(ca);
 }
 
 
@@ -53,9 +53,9 @@ Realisation CommonProto::Serialise<Realisation>::read(const Store & store, Commo
     );
 }
 
-void CommonProto::Serialise<Realisation>::write(const Store & store, CommonProto::WriteConn conn, const Realisation & realisation)
+WireFormatGenerator CommonProto::Serialise<Realisation>::write(const Store & store, CommonProto::WriteConn conn, const Realisation & realisation)
 {
-    conn.to << realisation.toJSON().dump();
+    co_yield realisation.toJSON().dump();
 }
 
 
@@ -64,9 +64,9 @@ DrvOutput CommonProto::Serialise<DrvOutput>::read(const Store & store, CommonPro
     return DrvOutput::parse(readString(conn.from));
 }
 
-void CommonProto::Serialise<DrvOutput>::write(const Store & store, CommonProto::WriteConn conn, const DrvOutput & drvOutput)
+WireFormatGenerator CommonProto::Serialise<DrvOutput>::write(const Store & store, CommonProto::WriteConn conn, const DrvOutput & drvOutput)
 {
-    conn.to << drvOutput.to_string();
+    co_yield drvOutput.to_string();
 }
 
 
@@ -76,9 +76,11 @@ std::optional<StorePath> CommonProto::Serialise<std::optional<StorePath>>::read(
     return s == "" ? std::optional<StorePath> {} : store.parseStorePath(s);
 }
 
-void CommonProto::Serialise<std::optional<StorePath>>::write(const Store & store, CommonProto::WriteConn conn, const std::optional<StorePath> & storePathOpt)
+WireFormatGenerator CommonProto::Serialise<std::optional<StorePath>>::write(const Store & store, CommonProto::WriteConn conn, const std::optional<StorePath> & storePathOpt)
 {
-    conn.to << (storePathOpt ? store.printStorePath(*storePathOpt) : "");
+    return [](std::string s) -> WireFormatGenerator {
+        co_yield s;
+    }(storePathOpt ? store.printStorePath(*storePathOpt) : "");
 }
 
 
@@ -87,9 +89,11 @@ std::optional<ContentAddress> CommonProto::Serialise<std::optional<ContentAddres
     return ContentAddress::parseOpt(readString(conn.from));
 }
 
-void CommonProto::Serialise<std::optional<ContentAddress>>::write(const Store & store, CommonProto::WriteConn conn, const std::optional<ContentAddress> & caOpt)
+WireFormatGenerator CommonProto::Serialise<std::optional<ContentAddress>>::write(const Store & store, CommonProto::WriteConn conn, const std::optional<ContentAddress> & caOpt)
 {
-    conn.to << (caOpt ? renderContentAddress(*caOpt) : "");
+    return [](std::string s) -> WireFormatGenerator {
+        co_yield s;
+    }(caOpt ? renderContentAddress(*caOpt) : "");
 }
 
 }