Adding support for stdin: scheme for datasources

Signed-off-by: Dave Henderson <[email protected]>

data/datasource.go

@@ -3,6 +3,7 @@ package data
 import (
 	"errors"
 	"fmt"
+	"io"
 	"io/ioutil"
 	"log"
 	"mime"
@@ -22,6 +23,9 @@ import (
 // logFatal is defined so log.Fatal calls can be overridden for testing
 var logFatalf = log.Fatalf
 
+// stdin - for overriding in tests
+var stdin io.Reader
+
 func regExtension(ext, typ string) {
 	err := mime.AddExtensionType(ext, typ)
 	if err != nil {
@@ -43,6 +47,7 @@ func init() {
 	addSourceReader("http", readHTTP)
 	addSourceReader("https", readHTTP)
 	addSourceReader("file", readFile)
+	addSourceReader("stdin", readStdin)
 	addSourceReader("vault", readVault)
 	addSourceReader("consul", readConsul)
 	addSourceReader("consul+http", readConsul)
@@ -157,6 +162,9 @@ func ParseSource(value string) (*Source, error) {
 		srcURL = absURL(f)
 	} else if len(parts) == 2 {
 		alias = parts[0]
+		if parts[1] == "-" {
+			parts[1] = "stdin://"
+		}
 		var err error
 		srcURL, err = url.Parse(parts[1])
 		if err != nil {
@@ -296,6 +304,18 @@ func readFile(source *Source, args ...string) ([]byte, error) {
 	return b, nil
 }
 
+func readStdin(source *Source, args ...string) ([]byte, error) {
+	if stdin == nil {
+		stdin = os.Stdin
+	}
+	b, err := ioutil.ReadAll(stdin)
+	if err != nil {
+		log.Printf("Can't read %v: %#v", stdin, err)
+		return nil, err
+	}
+	return b, nil
+}
+
 func readHTTP(source *Source, args ...string) ([]byte, error) {
 	if source.HC == nil {
 		source.HC = &http.Client{Timeout: time.Second * 5}

data/datasource_test.go

@@ -9,6 +9,7 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"net/url"
+	"strings"
 	"testing"
 
 	"github.com/blang/vfs"
@@ -307,3 +308,23 @@ func TestInclude(t *testing.T) {
 	actual := data.Include("foo")
 	assert.Equal(t, contents, actual)
 }
+
+type errorReader struct{}
+
+func (e errorReader) Read(p []byte) (n int, err error) {
+	return 0, fmt.Errorf("error")
+}
+
+func TestReadStdin(t *testing.T) {
+	defer func() {
+		stdin = nil
+	}()
+	stdin = strings.NewReader("foo")
+	out, err := readStdin(nil)
+	assert.NoError(t, err)
+	assert.Equal(t, []byte("foo"), out)
+
+	stdin = errorReader{}
+	_, err = readStdin(nil)
+	assert.Error(t, err)
+}

docs/content/functions/data.md

@@ -11,7 +11,7 @@ A collection of functions that retrieve, parse, and convert structured data.
 
 Parses a given datasource (provided by the [`--datasource/-d`](#--datasource-d) argument).
 
-Currently, `file://`, `http://`, `https://`, and `vault://` URLs are supported.
+Currently, `file://`, `stdin://`, `http://`, `https://`, and `vault://` URLs are supported.
 
 Currently-supported formats are JSON, YAML, TOML, and CSV.
 
@@ -34,6 +34,25 @@ $ gomplate -d person.json < input.tmpl
 Hello Dave
 ```
 
+### Providing datasources on standard input (`stdin`)
+
+Normally `stdin` is used as the input for the template, but it can also be used
+to provide datasources. To do this, specify a URL with the `stdin:` scheme:
+
+```console
+$ echo 'foo: bar' | gomplate -i '{{(ds "data").foo}}' -d data=stdin:///foo.yaml
+bar
+```
+
+Note that the URL must have a file name with a supported extension in order for
+the input to be correctly parsed. If no parsing is required (i.e. if the data
+is being included verbatim with the include function), just `stdin:` is enough:
+
+```console
+$ echo 'foo' | gomplate -i '{{ include "data" }}' -d data=stdin:
+foo
+```
+
 ### Usage with HTTP data
 
 ```console