From 6ea6ac8d5784ec65fe4e4d6ec8ebd667951ed2e7 Mon Sep 17 00:00:00 2001
From: Lucas Schwiderski <lucas@lschwiderski.de>
Date: Thu, 29 Aug 2024 11:15:12 +0200
Subject: [PATCH] Allow adding arbitrary buildkit config

Params like `REGISTRY_MIRRORS` don't really scale well to cover
a complex schema like buildkit's toml configuration. Plus, they
can become out-of-date.

A param whose content is written verbatim to the config file
allows defining everything the configuration has to offer, now
and in the future. It also avoids having to add new params one by
one as users request the ability to configure individual values.

Closes: #120
---
 README.md    | 3 +++
 buildkitd.go | 7 +++++++
 types.go     | 2 ++
 3 files changed, 12 insertions(+)

diff --git a/README.md b/README.md
index 7b36732..e05909f 100644
--- a/README.md
+++ b/README.md
@@ -157,6 +157,9 @@ _(As a convention in the list below, all task parameters are specified with a
   (`,`) list of key-value pairs (using syntax `hostname=ip-address`), each
   defining an IP address for resolving some custom hostname.
 
+* `$BUILDKIT_EXTRA_CONFIG` (default empty): a string written verbatim to builkit's
+  TOML config file. See [buildkitd.toml](https://docs.docker.com/build/buildkit/toml-configuration/).
+
 > Note: this is the main pain point with reusable tasks - env vars are kind of
 > an awkward way to configure a task. Once the RFC lands these will turn into a
 > JSON structure similar to configuring `params` on a resource, and task params
diff --git a/buildkitd.go b/buildkitd.go
index a2e65cc..b059c3e 100644
--- a/buildkitd.go
+++ b/buildkitd.go
@@ -173,6 +173,13 @@ func generateConfig(req Request, configPath string) error {
 		return err
 	}
 
+	if len(req.Config.BuildkitExtraConfig) > 0 {
+		_, err = f.WriteString(req.Config.BuildkitExtraConfig)
+		if err != nil {
+			return err
+		}
+	}
+
 	return f.Close()
 }
 
diff --git a/types.go b/types.go
index 8987185..5158b2f 100644
--- a/types.go
+++ b/types.go
@@ -64,6 +64,8 @@ type Config struct {
 
 	BuildkitSecrets map[string]string `json:"buildkit_secrets" envconfig:"optional"`
 
+	BuildkitExtraConfig string `json:"buildkit_extra_config" envconfig:"BUILDKIT_EXTRA_CONFIG,optional"`
+
 	// Unpack the OCI image into Concourse's rootfs/ + metadata.json image scheme.
 	//
 	// Theoretically this would go away if/when we standardize on OCI.