buck2: OSS: RE GRPC: actually implement download

Summary:
This function wasn't actually writing the blobs it downloaded, which makes
it definitely not work for pretty much everything we use this for (i.e.
downloading outputs).

This fixes that.

Reviewed By: ndmitchell, themarwhal

Differential Revision: D43310299

fbshipit-source-id: ece6e4684ecc0bd52dddef22bc642c39f00d7b1f

remote_execution/oss/re_grpc/Cargo.toml

@@ -15,6 +15,7 @@ prost = { workspace = true }
 regex = { workspace = true }
 slog = { workspace = true }
 tonic = { workspace = true }
+tokio = { workspace = true }
 
 gazebo_lint.version = "0.1"
 gazebo_lint.optional = true
@@ -23,5 +24,8 @@ gazebo_lint.optional = true
 buck2_core = { workspace = true }
 re_grpc_proto = { path = "../re_grpc_proto" }
 
+[dev-dependencies]
+tempfile = { workspace = true }
+
 [features]
 # @oss-disable: default = ["gazebo_lint"]

remote_execution/oss/re_grpc/TARGETS

@@ -6,6 +6,9 @@ oncall("buck2")
 rust_library(
     name = "remote_execution",
     srcs = glob(["src/**/*.rs"]),
+    test_deps = [
+        "fbsource//third-party/rust:tempfile",
+    ],
     deps = [
         "fbsource//third-party/rust:anyhow",
         "fbsource//third-party/rust:futures",
@@ -14,6 +17,7 @@ rust_library(
         "fbsource//third-party/rust:regex",
         "fbsource//third-party/rust:slog",
         "fbsource//third-party/rust:thiserror",
+        "fbsource//third-party/rust:tokio",
         "fbsource//third-party/rust:tonic",
         "//buck2/app/buck2_core:buck2_core",
         "//buck2/gazebo/dupe:dupe",