From 34c7a2ff12869730701754a4e67cbf39120b1ced Mon Sep 17 00:00:00 2001
From: Marcos Lilljedahl <marcosnils@gmail.com>
Date: Tue, 5 Apr 2022 12:28:53 -0300
Subject: [PATCH] Automatically set target platform based on client
 architecture

Set the default platform based on the client's OS and architecture. This
function is the same one that buildkit uses (https://github.com/moby/buildkit/blob/master/frontend/dockerfile/builder/build.go#L100-L102) to set the default build target platform

Signed-off-by: Marcos Lilljedahl <marcosnils@gmail.com>
---
 client/client.go        | 32 ++++++++++++++++++++++++++++++++
 plan/plan.go            |  2 +-
 plancontext/context.go  |  4 +---
 plancontext/platform.go | 25 ++++++++++++-------------
 4 files changed, 46 insertions(+), 17 deletions(-)

diff --git a/client/client.go b/client/client.go
index 071ea373..7d109113 100644
--- a/client/client.go
+++ b/client/client.go
@@ -7,12 +7,15 @@ import (
 	"strings"
 	"sync"
 
+	"github.com/containerd/containerd/platforms"
 	"github.com/google/uuid"
 	"go.opentelemetry.io/otel/trace"
 	"golang.org/x/sync/errgroup"
 
 	"github.com/rs/zerolog/log"
 
+	specs "github.com/opencontainers/image-spec/specs-go/v1"
+
 	// Cue
 
 	// buildkit
@@ -78,6 +81,15 @@ func (c *Client) Do(ctx context.Context, pctx *plancontext.Context, fn DoFunc) e
 	lg := log.Ctx(ctx)
 	eg, gctx := errgroup.WithContext(ctx)
 
+	// if platform is set through plan config, skip detection.
+	if !pctx.Platform.IsSet() {
+		p, err := c.detectPlatform(ctx)
+		if err != nil {
+			return err
+		}
+		pctx.Platform.Set(*p)
+	}
+
 	// Spawn print function
 	events := make(chan *bk.SolveStatus)
 	eg.Go(func() error {
@@ -95,6 +107,26 @@ func (c *Client) Do(ctx context.Context, pctx *plancontext.Context, fn DoFunc) e
 	return eg.Wait()
 }
 
+// detectPlatform will try to automatically Buildkit's target platform.
+// If not possible, default platform will be used.
+func (c *Client) detectPlatform(ctx context.Context) (*specs.Platform, error) {
+	w, err := c.c.ListWorkers(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("error detecting platform %w", err)
+	}
+
+	lg := log.Ctx(ctx)
+	if len(w) > 0 && len(w[0].Platforms) > 0 {
+		dPlatform := w[0].Platforms[0]
+		lg.Debug().
+			Str("platform", fmt.Sprintf("%s", dPlatform)).
+			Msg("platform detected automatically")
+		return &dPlatform, nil
+	}
+	defaultPlatform := platforms.DefaultSpec()
+	return &defaultPlatform, nil
+}
+
 func convertCacheOptionEntries(ims []bk.CacheOptionsEntry) []bkgw.CacheOptionsEntry {
 	convertIms := []bkgw.CacheOptionsEntry{}
 
diff --git a/plan/plan.go b/plan/plan.go
index dc4cc0df..6414e443 100644
--- a/plan/plan.go
+++ b/plan/plan.go
@@ -123,7 +123,7 @@ func (p *Plan) configPlatform() error {
 	}
 
 	// Set platform to context
-	err = p.context.Platform.Set(platform)
+	err = p.context.Platform.SetString(platform)
 	if err != nil {
 		return err
 	}
diff --git a/plancontext/context.go b/plancontext/context.go
index 58f6cb79..618dd915 100644
--- a/plancontext/context.go
+++ b/plancontext/context.go
@@ -17,9 +17,7 @@ type Context struct {
 
 func New() *Context {
 	return &Context{
-		Platform: &platformContext{
-			platform: defaultPlatform,
-		},
+		Platform: &platformContext{},
 		FS: &fsContext{
 			store: make(map[string]*FS),
 		},
diff --git a/plancontext/platform.go b/plancontext/platform.go
index 5d12aeab..4ee46b82 100644
--- a/plancontext/platform.go
+++ b/plancontext/platform.go
@@ -5,28 +5,27 @@ import (
 	specs "github.com/opencontainers/image-spec/specs-go/v1"
 )
 
-var (
-	// Default platform.
-	// FIXME: This should be auto detected using buildkit
-	defaultPlatform = specs.Platform{
-		OS:           "linux",
-		Architecture: "amd64",
-	}
-)
-
 type platformContext struct {
-	platform specs.Platform
+	platform *specs.Platform
 }
 
 func (c *platformContext) Get() specs.Platform {
-	return c.platform
+	return *c.platform
 }
 
-func (c *platformContext) Set(platform string) error {
+func (c *platformContext) SetString(platform string) error {
 	p, err := platforms.Parse(platform)
 	if err != nil {
 		return err
 	}
-	c.platform = p
+	c.platform = &p
 	return nil
 }
+
+func (c *platformContext) Set(p specs.Platform) {
+	c.platform = &p
+}
+
+func (c *platformContext) IsSet() bool {
+	return c.platform != nil
+}