tee stdout and stderr for consumers

tfexec/apply.go

@@ -5,7 +5,6 @@ import (
 	"fmt"
 	"os/exec"
 	"strconv"
-	"strings"
 )
 
 type applyConfig struct {
@@ -81,17 +80,7 @@ func (opt *DirOrPlanOption) configureApply(conf *applyConfig) {
 }
 
 func (tf *Terraform) Apply(ctx context.Context, opts ...ApplyOption) error {
-	applyCmd := tf.applyCmd(ctx, opts...)
-
-	var errBuf strings.Builder
-	applyCmd.Stderr = &errBuf
-
-	err := applyCmd.Run()
-	if err != nil {
-		return parseError(err, errBuf.String())
-	}
-
-	return nil
+	return tf.runTerraformCmd(tf.applyCmd(ctx, opts...))
 }
 
 func (tf *Terraform) applyCmd(ctx context.Context, opts ...ApplyOption) *exec.Cmd {

tfexec/cmd.go

@@ -2,6 +2,7 @@ package tfexec
 
 import (
 	"context"
+	"io"
 	"os"
 	"os/exec"
 	"strings"
@@ -100,3 +101,25 @@ func (tf *Terraform) buildTerraformCmd(ctx context.Context, args ...string) *exe
 
 	return cmd
 }
+
+func (tf *Terraform) runTerraformCmd(cmd *exec.Cmd) error {
+	var errBuf strings.Builder
+
+	stdout := tf.stdout
+	if cmd.Stdout != nil {
+		stdout = io.MultiWriter(cmd.Stdout, stdout)
+	}
+	cmd.Stdout = stdout
+
+	stderr := io.MultiWriter(&errBuf, tf.stderr)
+	if cmd.Stderr != nil {
+		stderr = io.MultiWriter(cmd.Stderr, stderr)
+	}
+	cmd.Stderr = stderr
+
+	err := cmd.Run()
+	if err != nil {
+		return parseError(err, errBuf.String())
+	}
+	return nil
+}

tfexec/destroy.go

@@ -5,7 +5,6 @@ import (
 	"fmt"
 	"os/exec"
 	"strconv"
-	"strings"
 )
 
 type destroyConfig struct {
@@ -77,17 +76,7 @@ func (opt *VarOption) configureDestroy(conf *destroyConfig) {
 }
 
 func (tf *Terraform) Destroy(ctx context.Context, opts ...DestroyOption) error {
-	destroyCmd := tf.destroyCmd(ctx, opts...)
-
-	var errBuf strings.Builder
-	destroyCmd.Stderr = &errBuf
-
-	err := destroyCmd.Run()
-	if err != nil {
-		return parseError(err, errBuf.String())
-	}
-
-	return nil
+	return tf.runTerraformCmd(tf.destroyCmd(ctx, opts...))
 }
 
 func (tf *Terraform) destroyCmd(ctx context.Context, opts ...DestroyOption) *exec.Cmd {

tfexec/import.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"os/exec"
 	"strconv"
-	"strings"
 )
 
 type importConfig struct {
@@ -67,18 +66,8 @@ func (opt *VarFileOption) configureImport(conf *importConfig) {
 	conf.varFile = opt.path
 }
 
-func (t *Terraform) Import(ctx context.Context, address, id string, opts ...ImportOption) error {
-	importCmd := t.importCmd(ctx, address, id, opts...)
-
-	var errBuf strings.Builder
-	importCmd.Stderr = &errBuf
-
-	err := importCmd.Run()
-	if err != nil {
-		return parseError(err, errBuf.String())
-	}
-
-	return nil
+func (tf *Terraform) Import(ctx context.Context, address, id string, opts ...ImportOption) error {
+	return tf.runTerraformCmd(tf.importCmd(ctx, address, id, opts...))
 }
 
 func (tf *Terraform) importCmd(ctx context.Context, address, id string, opts ...ImportOption) *exec.Cmd {

tfexec/init.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"fmt"
 	"os/exec"
-	"strings"
 )
 
 type initConfig struct {
@@ -82,18 +81,8 @@ func (opt *VerifyPluginsOption) configureInit(conf *initConfig) {
 	conf.verifyPlugins = opt.verifyPlugins
 }
 
-func (t *Terraform) Init(ctx context.Context, opts ...InitOption) error {
-	initCmd := t.initCmd(ctx, opts...)
-
-	var errBuf strings.Builder
-	initCmd.Stderr = &errBuf
-
-	err := initCmd.Run()
-	if err != nil {
-		return parseError(err, errBuf.String())
-	}
-
-	return nil
+func (tf *Terraform) Init(ctx context.Context, opts ...InitOption) error {
+	return tf.runTerraformCmd(tf.initCmd(ctx, opts...))
 }
 
 func (tf *Terraform) initCmd(ctx context.Context, opts ...InitOption) *exec.Cmd {

tfexec/internal/e2etest/util_test.go

@@ -62,8 +62,14 @@ func runTestVersions(t *testing.T, versions []string, fixtureName string, cb fun
 				}
 			}
 
+			var stdouterr bytes.Buffer
+			tf.SetStdout(&stdouterr)
+			tf.SetStderr(&stdouterr)
+
 			// TODO: capture panics here?
 			cb(t, version.Must(version.NewVersion(tfv)), tf)
+
+			t.Logf("CLI Output:\n%s", stdouterr.String())
 		})
 	}
 }

tfexec/output.go

@@ -5,7 +5,6 @@ import (
 	"context"
 	"encoding/json"
 	"os/exec"
-	"strings"
 )
 
 type outputConfig struct {
@@ -36,17 +35,14 @@ type OutputMeta struct {
 func (tf *Terraform) Output(ctx context.Context, opts ...OutputOption) (map[string]OutputMeta, error) {
 	outputCmd := tf.outputCmd(ctx, opts...)
 
-	var errBuf strings.Builder
 	var outBuf bytes.Buffer
-
-	outputCmd.Stderr = &errBuf
 	outputCmd.Stdout = &outBuf
 
 	outputs := map[string]OutputMeta{}
 
-	err := outputCmd.Run()
+	err := tf.runTerraformCmd(outputCmd)
 	if err != nil {
-		return nil, parseError(err, errBuf.String())
+		return nil, err
 	}
 
 	err = json.Unmarshal(outBuf.Bytes(), &outputs)

tfexec/plan.go

@@ -5,7 +5,6 @@ import (
 	"fmt"
 	"os/exec"
 	"strconv"
-	"strings"
 )
 
 type planConfig struct {
@@ -74,17 +73,7 @@ func (opt *DestroyFlagOption) configurePlan(conf *planConfig) {
 }
 
 func (tf *Terraform) Plan(ctx context.Context, opts ...PlanOption) error {
-	planCmd := tf.planCmd(ctx, opts...)
-
-	var errBuf strings.Builder
-	planCmd.Stderr = &errBuf
-
-	err := planCmd.Run()
-	if err != nil {
-		return parseError(err, errBuf.String())
-	}
-
-	return nil
+	return tf.runTerraformCmd(tf.planCmd(ctx, opts...))
 }
 
 func (tf *Terraform) planCmd(ctx context.Context, opts ...PlanOption) *exec.Cmd {

tfexec/providers_schema.go

@@ -5,25 +5,20 @@ import (
 	"context"
 	"encoding/json"
 	"os/exec"
-	"strings"
 
 	tfjson "github.com/hashicorp/terraform-json"
 )
 
 func (tf *Terraform) ProvidersSchema(ctx context.Context) (*tfjson.ProviderSchemas, error) {
-	var ret tfjson.ProviderSchemas
-
-	var errBuf strings.Builder
-	var outBuf bytes.Buffer
-
 	schemaCmd := tf.providersSchemaCmd(ctx)
 
-	schemaCmd.Stderr = &errBuf
+	var ret tfjson.ProviderSchemas
+	var outBuf bytes.Buffer
 	schemaCmd.Stdout = &outBuf
 
-	err := schemaCmd.Run()
+	err := tf.runTerraformCmd(schemaCmd)
 	if err != nil {
-		return nil, parseError(err, errBuf.String())
+		return nil, err
 	}
 
 	err = json.Unmarshal(outBuf.Bytes(), &ret)

tfexec/show.go

@@ -6,7 +6,6 @@ import (
 	"encoding/json"
 	"fmt"
 	"os/exec"
-	"strings"
 
 	tfjson "github.com/hashicorp/terraform-json"
 )
@@ -17,19 +16,15 @@ func (tf *Terraform) Show(ctx context.Context) (*tfjson.State, error) {
 		return nil, fmt.Errorf("terraform show -json was added in 0.12.0: %w", err)
 	}
 
-	var ret tfjson.State
-
-	var errBuf strings.Builder
-	var outBuf bytes.Buffer
-
 	showCmd := tf.showCmd(ctx)
 
-	showCmd.Stderr = &errBuf
+	var ret tfjson.State
+	var outBuf bytes.Buffer
 	showCmd.Stdout = &outBuf
 
-	err = showCmd.Run()
+	err = tf.runTerraformCmd(showCmd)
 	if err != nil {
-		return nil, parseError(err, errBuf.String())
+		return nil, err
 	}
 
 	err = json.Unmarshal(outBuf.Bytes(), &ret)

tfexec/terraform.go

@@ -2,6 +2,7 @@ package tfexec
 
 import (
 	"fmt"
+	"io"
 	"io/ioutil"
 	"log"
 	"os"
@@ -16,6 +17,8 @@ type Terraform struct {
 	workingDir string
 	env        map[string]string
 
+	stdout  io.Writer
+	stderr  io.Writer
 	logger  *log.Logger
 	logPath string
 
@@ -46,6 +49,8 @@ func NewTerraform(workingDir string, execPath string) (*Terraform, error) {
 		workingDir: workingDir,
 		env:        nil, // explicit nil means copy os.Environ
 		logger:     log.New(ioutil.Discard, "", 0),
+		stdout:     ioutil.Discard,
+		stderr:     ioutil.Discard,
 	}
 
 	return &tf, nil
@@ -71,10 +76,27 @@ func (tf *Terraform) SetEnv(env map[string]string) error {
 	return nil
 }
 
+// SetLogger specifies a logger for tfexec to use.
 func (tf *Terraform) SetLogger(logger *log.Logger) {
 	tf.logger = logger
 }
 
+// SetStdout specifies a writer to stream stdout to for every command.
+//
+// This should be used for information or logging purposes only, not control
+// flow. Any parsing necessary should be added as functionality to this package.
+func (tf *Terraform) SetStdout(w io.Writer) {
+	tf.stdout = w
+}
+
+// SetStderr specifies a writer to stream stderr to for every command.
+//
+// This should be used for information or logging purposes only, not control
+// flow. Any parsing necessary should be added as functionality to this package.
+func (tf *Terraform) SetStderr(w io.Writer) {
+	tf.stderr = w
+}
+
 // SetLogPath sets the TF_LOG_PATH environment variable for Terraform CLI
 // execution.
 func (tf *Terraform) SetLogPath(path string) error {

tfexec/version.go

@@ -42,14 +42,13 @@ func (tf *Terraform) version(ctx context.Context) (*version.Version, map[string]
 	// for that here and fallback to string parsing
 
 	versionCmd := tf.buildTerraformCmd(ctx, "version")
-	var errBuf strings.Builder
+
 	var outBuf bytes.Buffer
-	versionCmd.Stderr = &errBuf
 	versionCmd.Stdout = &outBuf
 
-	err := versionCmd.Run()
+	err := tf.runTerraformCmd(versionCmd)
 	if err != nil {
-		return nil, nil, parseError(err, errBuf.String())
+		return nil, nil, err
 	}
 
 	tfVersion, providerVersions, err := parseVersionOutput(outBuf.String())