From 121edecf654ec084274ba1a779c7140082f4115d Mon Sep 17 00:00:00 2001
From: eldritch horrors <pennae@lix.systems>
Date: Sun, 5 May 2024 17:08:59 +0200
Subject: [PATCH] filetransfer: extract decompressor creation

this will be necessary if we want download() to return a source instead
of consuming a sink, which will in turn be needed to remove coroutines.

Change-Id: I34ec241e9bbc5d32fbcd243b244e29c3757533aa
---
 src/libstore/filetransfer.cc | 23 +++++++++++------------
 1 file changed, 11 insertions(+), 12 deletions(-)

diff --git a/src/libstore/filetransfer.cc b/src/libstore/filetransfer.cc
index aa8f4be1d..a0e3fd586 100644
--- a/src/libstore/filetransfer.cc
+++ b/src/libstore/filetransfer.cc
@@ -710,9 +710,8 @@ struct curlFileTransfer : public FileTransfer
         struct State {
             bool done = false, failed = false;
             std::exception_ptr exc;
-            std::string data;
+            std::string data, encoding;
             std::condition_variable avail, request;
-            std::unique_ptr<FinishSink> decompressor;
         };
 
         auto _state = std::make_shared<Sync<State>>();
@@ -736,7 +735,7 @@ struct curlFileTransfer : public FileTransfer
                 state->avail.notify_one();
                 state->request.notify_one();
             }},
-            [_state, &sink](TransferItem & transfer, std::string_view data) {
+            [_state](TransferItem & transfer, std::string_view data) {
                 auto state(_state->lock());
 
                 if (state->failed) {
@@ -744,10 +743,6 @@ struct curlFileTransfer : public FileTransfer
                     throw std::exception{};
                 }
 
-                if (!state->decompressor) {
-                    state->decompressor = makeDecompressionSink(transfer.encoding, sink);
-                }
-
                 /* If the buffer is full, then go to sleep until the calling
                 thread wakes us up (i.e. when it has removed data from the
                 buffer). We don't wait forever to prevent stalling the
@@ -764,11 +759,12 @@ struct curlFileTransfer : public FileTransfer
                 state->avail.notify_one();
             });
 
+        std::unique_ptr<FinishSink> decompressor;
+
         while (true) {
             checkInterrupt();
 
             std::string chunk;
-            FinishSink * sink = nullptr;
 
             /* Grab data if available, otherwise wait for the download
                thread to wake us up. */
@@ -779,8 +775,8 @@ struct curlFileTransfer : public FileTransfer
 
                     if (state->done) {
                         if (state->exc) std::rethrow_exception(state->exc);
-                        if (state->decompressor) {
-                            state->decompressor->finish();
+                        if (decompressor) {
+                            decompressor->finish();
                         }
                         return;
                     }
@@ -791,10 +787,13 @@ struct curlFileTransfer : public FileTransfer
                 }
 
                 chunk = std::move(state->data);
-                sink = state->decompressor.get();
                 /* Reset state->data after the move, since we check data.empty() */
                 state->data = "";
 
+                if (!decompressor) {
+                    decompressor = makeDecompressionSink(state->encoding, sink);
+                }
+
                 state->request.notify_one();
             }
 
@@ -802,7 +801,7 @@ struct curlFileTransfer : public FileTransfer
                if it's blocked on a full buffer. We don't hold the state
                lock while doing this to prevent blocking the download
                thread if sink() takes a long time. */
-            (*sink)(chunk);
+            (*decompressor)(chunk);
         }
     }
 };