test: add optional latency to postgrest-loadtest

This pipes data between client/postgrest and between
postgrest/database through a proxy that adds delay
(github.com/robx/slocat).

default.nix

@@ -41,6 +41,7 @@ let
       allOverlays.postgresql-legacy
       allOverlays.postgresql-future
       (allOverlays.haskell-packages { inherit compiler; })
+      allOverlays.slocat
     ];
 
   # Evaluated expression of the Nixpkgs repository.

nix/README.md

@@ -204,6 +204,9 @@ postgrest-loadtest
 # You can loadtest comparing to a different branch
 postgrest-loadtest-against master
 
+# You can simulate latency client/postgrest and postgrest/database
+PGRST_DELAY=5ms PGDELAY=5ms postgrest-loadtest
+
 # Produce a markdown report to be used on CI
 postgrest-loadtest-report
 ```

nix/overlays/default.nix

@@ -7,4 +7,5 @@
   postgresql-default = import ./postgresql-default.nix;
   postgresql-legacy = import ./postgresql-legacy.nix;
   postgresql-future = import ./postgresql-future.nix;
+  slocat = import ./slocat.nix;
 }

nix/overlays/slocat.nix

@@ -0,0 +1,13 @@
+final: prev:
+{
+  slocat = prev.buildGoModule {
+    name = "slocat";
+    src = prev.fetchFromGitHub {
+      owner = "robx";
+      repo = "slocat";
+      rev = "52e7512c6029fd00483e41ccce260a3b4b9b3b64";
+      sha256 = "sha256-qn6luuh5wqREu3s8RfuMCP5PKdS2WdwPrujRYTpfzQ8=";
+    };
+    vendorSha256 = "sha256-pQpattmS9VmO3ZIQUFn66az8GSmB4IvYhTTCFn6SUmo=";
+  };
+}

nix/tools/loadtest.nix

@@ -60,7 +60,9 @@ let
 
         # shellcheck disable=SC2145
         ${withTools.withPg} --fixtures "$_arg_testdir"/fixtures.sql \
+        ${withTools.withSlowPg} \
         ${withTools.withPgrst} \
+        ${withTools.withSlowPgrst} \
         sh -c "cd \"$_arg_testdir\" && ${runner} -targets targets.http -output \"$abs_output\" \"''${_arg_leftovers[@]}\""
         ${vegeta}/bin/vegeta report -type=text "$_arg_output"
       '';

nix/tools/withTools.nix

@@ -8,6 +8,7 @@
 , lib
 , postgresqlVersions
 , postgrest
+, slocat
 , writeText
 }:
 let
@@ -137,6 +138,81 @@ let
 
   withPg = builtins.head withPgVersions;
 
+  withSlowPg =
+    checkedShellScript
+      {
+        name = "postgrest-with-slow-pg";
+        docs = "Run the given command with simulated high latency postgresql";
+        args =
+          [
+            "ARG_POSITIONAL_SINGLE([command], [Command to run])"
+            "ARG_LEFTOVERS([command arguments])"
+            "ARG_USE_ENV([PGHOST], [], [PG host (socket name)])"
+            "ARG_USE_ENV([PGDELAY], [0ms], [extra PG latency (duration)])"
+          ];
+        positionalCompletion = "_command";
+        inRootDir = true;
+        redirectTixFiles = false;
+        withTmpDir = true;
+      }
+      ''
+        delay="''${PGDELAY:-0ms}"
+        echo "delaying data to/from postgres by $delay"
+
+        REALPGHOST="$PGHOST"
+        export PGHOST="$tmpdir/socket"
+        mkdir -p "$PGHOST"
+
+        ${slocat}/bin/slocat -delay "$delay" -src "$PGHOST/.s.PGSQL.5432" -dst "$REALPGHOST/.s.PGSQL.5432" &
+        SLOCAT_PID=$!
+        # shellcheck disable=SC2317
+        stop_slocat() {
+          kill "$SLOCAT_PID" || true
+          wait "$SLOCAT_PID" || true
+        }
+        trap stop_slocat EXIT
+        sleep 1 # should wait for socket file to appear instead
+
+        ("$_arg_command" "''${_arg_leftovers[@]}")
+      '';
+
+  withSlowPgrst =
+    checkedShellScript
+      {
+        name = "postgrest-with-slow-postgrest";
+        docs = "Run the given command with simulated high latency postgrest";
+        args =
+          [
+            "ARG_POSITIONAL_SINGLE([command], [Command to run])"
+            "ARG_LEFTOVERS([command arguments])"
+            "ARG_USE_ENV([PGRST_SERVER_UNIX_SOCKET], [], [PostgREST host (socket name)])"
+            "ARG_USE_ENV([PGRST_DELAY], [0ms], [extra PostgREST latency (duration)])"
+          ];
+        positionalCompletion = "_command";
+        inRootDir = true;
+        redirectTixFiles = false;
+        withTmpDir = true;
+      }
+      ''
+        delay="''${PGRST_DELAY:-0ms}"
+        echo "delaying data to/from PostgREST by $delay"
+
+        REAL_PGRST_SERVER_UNIX_SOCKET="$PGRST_SERVER_UNIX_SOCKET"
+        export PGRST_SERVER_UNIX_SOCKET="$tmpdir/postgrest.socket"
+
+        ${slocat}/bin/slocat -delay "$delay" -src "$PGRST_SERVER_UNIX_SOCKET" -dst "$REAL_PGRST_SERVER_UNIX_SOCKET" &
+        SLOCAT_PID=$!
+        # shellcheck disable=SC2317
+        stop_slocat() {
+          kill "$SLOCAT_PID" || true
+          wait "$SLOCAT_PID" || true
+        }
+        trap stop_slocat EXIT
+        sleep 1 # should wait for socket file to appear instead
+
+        ("$_arg_command" "''${_arg_leftovers[@]}")
+      '';
+
   withGit =
     let
       name = "postgrest-with-git";
@@ -288,7 +364,7 @@ in
 buildToolbox
 {
   name = "postgrest-with";
-  tools = [ withPgAll withGit withPgrst ] ++ withPgVersions;
+  tools = [ withPgAll withGit withPgrst withSlowPg withSlowPgrst ] ++ withPgVersions;
   # make withTools available for other nix files
-  extra = { inherit withGit withPg withPgAll withPgrst; };
+  extra = { inherit withGit withPg withPgAll withPgrst withSlowPg withSlowPgrst; };
 }