chore(tvix/store/protos): add PathInfoService::CalculateNAR() r/5525

Expose the NAR calculation to a separate `CalculateNAR` method, which
responds with the NAR size and sha256 hash.

Contrary to what cl/7618 and cl/7620 initially did, don't add different
other request types.

In the CalculateNARResponse message, there's now some duplication in the
(optional) `narinfo` field of a PathInfo, but I'm not entirely sure if
we want to drop the fields from there yet.

Change-Id: Id797c56e17efedac115fbd43de9dfde9fa1db140
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7663
Reviewed-by: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI

1 files changed, 36 insertions, 7 deletions

diff --git a/tvix/store/protos/rpc_pathinfo.proto b/tvix/store/protos/rpc_pathinfo.proto
index f9710f5722..f37794c291 100644
--- a/tvix/store/protos/rpc_pathinfo.proto
+++ b/tvix/store/protos/rpc_pathinfo.proto
@@ -9,23 +9,42 @@ import "tvix/store/protos/pathinfo.proto";
 option go_package = "code.tvl.fyi/tvix/store/protos;storev1";
 
 service PathInfoService {
-    // Get retrieves a PathInfo object, by using the lookup parameters in
-    // GetPathInfoRequest.
-    // If the PathInfo object contains a DirectoryNode, it needs to be looked
-    // up separately via the DirectoryService, which is purely
-    // content-addressed.
+    // Return a PathInfo message, identified by the decoded nixbase32 part
+    // of a Nix output path.
+    //
+    // To substitute /nix/store/xm35nga2g20mz5sm5l6n8v3bdm86yj83-
+    // cowsay-3.04 the bytes in the request would be
+    // nixbase32dec("xm35nga2g20mz5sm5l6n8v3bdm86yj83").
     rpc Get(GetPathInfoRequest) returns (PathInfo);
 
     // Put uploads a PathInfo object to the remote end. It MUST not return
     // until the PathInfo object has been written on the the remote end.
+    //
     // The remote end MAY check if a potential DirectoryNode has already been
     // uploaded.
+    //
     // Uploading clients SHOULD obviously not steer other machines to try to
     // substitute before from the remote end before having finished uploading
     // PathInfo, Directories and Blobs.
     // The returned PathInfo object MAY contain additional narinfo signatures,
     // but is otherwise left untouched.
     rpc Put(PathInfo) returns (PathInfo);
+
+
+    // Calculate the NAR representation of the contents specified by the
+    // root_node. The calculation SHOULD be cached server-side for subsequent
+    // requests.
+    //
+    // All references (to blobs or Directory messages) MUST already exist in
+    // the store.
+    //
+    // The method can be used to produce a Nix fixed-output path, which
+    // contains the (compressed) sha256 of the NAR content representation in
+    // the root_node name (suffixed with the name).
+    //
+    // It can also be used to calculate arbitrary NAR hashes of output paths,
+    // in case a legacy Nix Binary Cache frontend is provided.
+    rpc CalculateNAR(Node) returns (CalculateNARResponse);
 }
 
 // GetPathInfoRequest describes the lookup parameters that can be used to
@@ -38,7 +57,17 @@ message GetPathInfoRequest {
       // /nix/store/xm35nga2g20mz5sm5l6n8v3bdm86yj83-cowsay-3.04
       // this field would contain nixbase32dec("xm35nga2g20mz5sm5l6n8v3bdm86yj83").
       bytes by_output_hash = 1;
+    };
+}
+
+// CalculateNARResponse is the response returned by the CalculateNAR request.
+//
+// It contains the size of the NAR representation (in bytes), and the sha56
+// digest.
+message CalculateNARResponse {
+    // This size of the NAR file, in bytes.
+    uint32 nar_size = 1;
 
-      // placeholder: by_drv and output name?
-    }
+    // The sha256 of the NAR file representation.
+    bytes nar_sha256 = 2;
 }