From dd2fef8a2dd0de967a61832fcb383ee0434d67e8 Mon Sep 17 00:00:00 2001
From: Andrea Luzzardi <aluzzardi@gmail.com>
Date: Mon, 13 Dec 2021 17:48:32 +0100
Subject: [PATCH] engine.#ReadFile

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>
---
 docs/reference/europa/dagger/engine/README.md | 10 ++++
 plan/task/readfile.go                         | 46 +++++++++++++++++++
 stdlib/europa/dagger/engine/fs.cue            | 10 ++++
 tests/tasks.bats                              |  5 ++
 tests/tasks/readfile/cue.mod/module.cue       |  1 +
 tests/tasks/readfile/cue.mod/pkg/.gitignore   |  3 ++
 tests/tasks/readfile/readfile.cue             | 21 +++++++++
 7 files changed, 96 insertions(+)
 create mode 100644 plan/task/readfile.go
 create mode 100644 stdlib/europa/dagger/engine/fs.cue
 create mode 100644 tests/tasks/readfile/cue.mod/module.cue
 create mode 100644 tests/tasks/readfile/cue.mod/pkg/.gitignore
 create mode 100644 tests/tasks/readfile/readfile.cue

diff --git a/docs/reference/europa/dagger/engine/README.md b/docs/reference/europa/dagger/engine/README.md
index 6bb38f9c..f2ecc560 100644
--- a/docs/reference/europa/dagger/engine/README.md
+++ b/docs/reference/europa/dagger/engine/README.md
@@ -66,6 +66,16 @@ _No input._
 
 _No output._
 
+## engine.#ReadFile
+
+### engine.#ReadFile Inputs
+
+_No input._
+
+### engine.#ReadFile Outputs
+
+_No output._
+
 ## engine.#Secret
 
 A reference to an external secret, for example:  - A password  - A SSH private key  - An API token Secrets are never merged in the Cue tree. They can only be used by a special filesystem mount designed to minimize leak risk.
diff --git a/plan/task/readfile.go b/plan/task/readfile.go
new file mode 100644
index 00000000..cb6a1f25
--- /dev/null
+++ b/plan/task/readfile.go
@@ -0,0 +1,46 @@
+package task
+
+import (
+	"context"
+	"fmt"
+	"io/fs"
+
+	"cuelang.org/go/cue"
+	"go.dagger.io/dagger/compiler"
+	"go.dagger.io/dagger/plancontext"
+	"go.dagger.io/dagger/solver"
+)
+
+func init() {
+	Register("ReadFile", func() Task { return &readFileTask{} })
+}
+
+type readFileTask struct {
+}
+
+func (t *readFileTask) Run(ctx context.Context, pctx *plancontext.Context, s solver.Solver, v *compiler.Value) (*compiler.Value, error) {
+	path, err := v.Lookup("path").String()
+	if err != nil {
+		return nil, err
+	}
+
+	input, err := pctx.FS.FromValue(v.Lookup("input"))
+	if err != nil {
+		return nil, err
+	}
+	inputFS := solver.NewBuildkitFS(input.Result())
+
+	// FIXME: we should create an intermediate image containing only `path`.
+	// That way, on cache misses, we'll only download the layer with the file contents rather than the entire FS.
+	contents, err := fs.ReadFile(inputFS, path)
+	if err != nil {
+		return nil, fmt.Errorf("ReadFile %s: %w", path, err)
+	}
+
+	output := compiler.NewValue()
+	if err := output.FillPath(cue.ParsePath("contents"), string(contents)); err != nil {
+		return nil, err
+	}
+
+	return output, nil
+}
diff --git a/stdlib/europa/dagger/engine/fs.cue b/stdlib/europa/dagger/engine/fs.cue
new file mode 100644
index 00000000..7632d6be
--- /dev/null
+++ b/stdlib/europa/dagger/engine/fs.cue
@@ -0,0 +1,10 @@
+package engine
+
+#ReadFile: {
+	_type: "ReadFile"
+
+	input:    #FS
+	path:     string
+	contents: string
+	output:   #FS
+}
diff --git a/tests/tasks.bats b/tests/tasks.bats
index 2eed09a8..8036dffd 100644
--- a/tests/tasks.bats
+++ b/tests/tasks.bats
@@ -7,4 +7,9 @@ setup() {
 @test "task: #Pull" {
     cd "$TESTDIR"/tasks/pull
     dagger --europa up
+}
+
+@test "task: #ReadFile" {
+    cd "$TESTDIR"/tasks/readfile
+    dagger --europa up
 }
\ No newline at end of file
diff --git a/tests/tasks/readfile/cue.mod/module.cue b/tests/tasks/readfile/cue.mod/module.cue
new file mode 100644
index 00000000..f8af9cef
--- /dev/null
+++ b/tests/tasks/readfile/cue.mod/module.cue
@@ -0,0 +1 @@
+module: ""
diff --git a/tests/tasks/readfile/cue.mod/pkg/.gitignore b/tests/tasks/readfile/cue.mod/pkg/.gitignore
new file mode 100644
index 00000000..2d4dc1ae
--- /dev/null
+++ b/tests/tasks/readfile/cue.mod/pkg/.gitignore
@@ -0,0 +1,3 @@
+# generated by dagger
+alpha.dagger.io
+dagger.lock
diff --git a/tests/tasks/readfile/readfile.cue b/tests/tasks/readfile/readfile.cue
new file mode 100644
index 00000000..65603d6d
--- /dev/null
+++ b/tests/tasks/readfile/readfile.cue
@@ -0,0 +1,21 @@
+package main
+
+import (
+	"alpha.dagger.io/europa/dagger/engine"
+)
+
+engine.#Plan & {
+	actions: {
+		image: engine.#Pull & {
+			source: "alpine:3.15.0@sha256:e7d88de73db3d3fd9b2d63aa7f447a10fd0220b7cbf39803c803f2af9ba256b3"
+		}
+
+		readfile: engine.#ReadFile & {
+			input: image.output
+			path:  "/etc/alpine-release"
+		} & {
+			// assert result
+			contents: "3.15.0\n"
+		}
+	}
+}