Add template provider

.chloggen/template-provider.yaml

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+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: confmap
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Add template provider
+
+# One or more tracking issues or pull requests related to the change
+issues: [8504]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext: |
+  This provider reads and validate template files, but the templates cannot be expanded without an associated template converter.
+
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [api]

confmap/provider/templateprovider/provider.go

@@ -0,0 +1,109 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package templateprovider // import "go.opentelemetry.io/collector/confmap/provider/templateprovider"
+
+import (
+	"context"
+	"fmt"
+	"html/template"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"go.opentelemetry.io/collector/confmap"
+	"go.opentelemetry.io/collector/confmap/provider/internal"
+)
+
+const (
+	schemeName  = "template"
+	templateKey = "template"
+	typeKey     = "type"
+
+	// The template provider will always return the following structure:
+	// {
+	//   "templates": {
+	//     "the_type_of_template": "the_template"
+	//   },
+	// }
+	// This allows multiple templates to be aggreated under the same global key.
+	allTemplatesKey = "templates"
+)
+
+type provider struct{}
+
+// New returns a new confmap.Provider that reads the template from a file.
+//
+// This Provider supports "file" scheme, and can be called with a "uri" that follows:
+//
+//	file-uri		= "template:" local-path
+//	local-path		= [ drive-letter ] file-path
+//	drive-letter	= ALPHA ":"
+//
+// The "file-path" can be relative or absolute, and it can be any OS supported format.
+//
+// Examples:
+// `template:path/to/template` - relative path (unix, windows)
+// `template:/path/to/template` - absolute path (unix, windows)
+// `template:c:/path/to/template` - absolute path including drive-letter (windows)
+// `template:c:\path\to\template` - absolute path including drive-letter (windows)
+func New() confmap.Provider {
+	return &provider{}
+}
+
+func (fmp *provider) Retrieve(_ context.Context, uri string, _ confmap.WatcherFunc) (*confmap.Retrieved, error) {
+	if !strings.HasPrefix(uri, schemeName+":") {
+		return nil, fmt.Errorf("%q uri is not supported by %q provider", uri, schemeName)
+	}
+
+	// Clean the path before using it.
+	content, err := os.ReadFile(filepath.Clean(uri[len(schemeName)+1:]))
+	if err != nil {
+		return nil, fmt.Errorf("unable to read the file %v: %w", uri, err)
+	}
+
+	retrieved, err := internal.NewRetrievedFromYAML(content)
+	if err != nil {
+		return nil, fmt.Errorf("read template %v: %w", uri, err)
+	}
+
+	templateConf, err := retrieved.AsConf()
+	if err != nil {
+		return nil, err
+	}
+
+	if !templateConf.IsSet("type") {
+		return nil, fmt.Errorf("template %v: must have a 'type'", uri)
+	}
+	templateType, ok := templateConf.Get("type").(string)
+	if !ok {
+		return nil, fmt.Errorf("template %v: 'type' must be a string", uri)
+	}
+
+	if !templateConf.IsSet("template") {
+		return nil, fmt.Errorf("template %v: must have a 'template'", uri)
+	}
+
+	rawTemplate, ok := templateConf.Get("template").(string)
+	if !ok {
+		return nil, fmt.Errorf("template %v: 'template' must be a string", uri)
+	}
+
+	if _, err = template.New(templateType).Parse(rawTemplate); err != nil {
+		return nil, fmt.Errorf("template %v: parse as text/template: %w", uri, err)
+	}
+
+	return confmap.NewRetrieved(map[string]any{
+		allTemplatesKey: map[string]any{
+			templateType: rawTemplate,
+		},
+	})
+}
+
+func (*provider) Scheme() string {
+	return schemeName
+}
+
+func (*provider) Shutdown(context.Context) error {
+	return nil
+}

confmap/provider/templateprovider/provider_test.go

@@ -0,0 +1,145 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package templateprovider
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"go.opentelemetry.io/collector/confmap"
+	"go.opentelemetry.io/collector/confmap/confmaptest"
+)
+
+const templateSchemePrefix = schemeName + ":"
+
+func TestValidateProviderScheme(t *testing.T) {
+	assert.NoError(t, confmaptest.ValidateProviderScheme(New()))
+}
+
+func TestEmptyName(t *testing.T) {
+	fp := New()
+	_, err := fp.Retrieve(context.Background(), "", nil)
+	require.Error(t, err)
+	require.NoError(t, fp.Shutdown(context.Background()))
+}
+
+func TestUnsupportedScheme(t *testing.T) {
+	fp := New()
+	_, err := fp.Retrieve(context.Background(), "https://", nil)
+	assert.Error(t, err)
+	assert.NoError(t, fp.Shutdown(context.Background()))
+}
+
+func TestNonExistent(t *testing.T) {
+	fp := New()
+	_, err := fp.Retrieve(context.Background(), templateSchemePrefix+filepath.Join("testdata", "non-existent.yaml"), nil)
+	assert.Error(t, err)
+	_, err = fp.Retrieve(context.Background(), templateSchemePrefix+absolutePath(t, filepath.Join("testdata", "non-existent.yaml")), nil)
+	assert.Error(t, err)
+	require.NoError(t, fp.Shutdown(context.Background()))
+}
+
+func TestInvalidYAML(t *testing.T) {
+	fp := New()
+	_, err := fp.Retrieve(context.Background(), templateSchemePrefix+filepath.Join("testdata", "invalid-yaml.yaml"), nil)
+	assert.Error(t, err)
+	_, err = fp.Retrieve(context.Background(), templateSchemePrefix+absolutePath(t, filepath.Join("testdata", "invalid-yaml.yaml")), nil)
+	assert.Error(t, err)
+	require.NoError(t, fp.Shutdown(context.Background()))
+}
+
+func TestNonMapContent(t *testing.T) {
+	fp := New()
+	_, err := fp.Retrieve(context.Background(), templateSchemePrefix+filepath.Join("testdata", "nonmap.yaml"), nil)
+	assert.ErrorContains(t, err, "cannot be used as a Conf")
+	_, err = fp.Retrieve(context.Background(), templateSchemePrefix+absolutePath(t, filepath.Join("testdata", "nonmap.yaml")), nil)
+	assert.ErrorContains(t, err, "cannot be used as a Conf")
+	require.NoError(t, fp.Shutdown(context.Background()))
+}
+
+func TestMissingType(t *testing.T) {
+	fp := New()
+	_, err := fp.Retrieve(context.Background(), templateSchemePrefix+filepath.Join("testdata", "missing-type.yaml"), nil)
+	assert.ErrorContains(t, err, "must have a 'type'")
+	_, err = fp.Retrieve(context.Background(), templateSchemePrefix+absolutePath(t, filepath.Join("testdata", "missing-type.yaml")), nil)
+	assert.ErrorContains(t, err, "must have a 'type'")
+	require.NoError(t, fp.Shutdown(context.Background()))
+}
+
+func TestNonStringType(t *testing.T) {
+	fp := New()
+	_, err := fp.Retrieve(context.Background(), templateSchemePrefix+filepath.Join("testdata", "nonstring-type.yaml"), nil)
+	assert.ErrorContains(t, err, "type' must be a string")
+	_, err = fp.Retrieve(context.Background(), templateSchemePrefix+absolutePath(t, filepath.Join("testdata", "nonstring-type.yaml")), nil)
+	assert.ErrorContains(t, err, "type' must be a string")
+	require.NoError(t, fp.Shutdown(context.Background()))
+}
+
+func TestMissingTemplate(t *testing.T) {
+	fp := New()
+	_, err := fp.Retrieve(context.Background(), templateSchemePrefix+filepath.Join("testdata", "missing-template.yaml"), nil)
+	assert.ErrorContains(t, err, "must have a 'template'")
+	_, err = fp.Retrieve(context.Background(), templateSchemePrefix+absolutePath(t, filepath.Join("testdata", "missing-template.yaml")), nil)
+	assert.ErrorContains(t, err, "must have a 'template'")
+	require.NoError(t, fp.Shutdown(context.Background()))
+}
+
+func TestNonStringTemplate(t *testing.T) {
+	fp := New()
+	_, err := fp.Retrieve(context.Background(), templateSchemePrefix+filepath.Join("testdata", "nonstring-template.yaml"), nil)
+	assert.ErrorContains(t, err, "template' must be a string")
+	_, err = fp.Retrieve(context.Background(), templateSchemePrefix+absolutePath(t, filepath.Join("testdata", "nonstring-template.yaml")), nil)
+	assert.ErrorContains(t, err, "template' must be a string")
+	require.NoError(t, fp.Shutdown(context.Background()))
+}
+
+func TestInvalidTemplate(t *testing.T) {
+	fp := New()
+	_, err := fp.Retrieve(context.Background(), templateSchemePrefix+filepath.Join("testdata", "invalid-template.yaml"), nil)
+	assert.ErrorContains(t, err, "parse as text/template")
+	_, err = fp.Retrieve(context.Background(), templateSchemePrefix+absolutePath(t, filepath.Join("testdata", "invalid-template.yaml")), nil)
+	assert.ErrorContains(t, err, "parse as text/template")
+	require.NoError(t, fp.Shutdown(context.Background()))
+}
+
+func TestRelativePath(t *testing.T) {
+	fp := New()
+	ret, err := fp.Retrieve(context.Background(), templateSchemePrefix+filepath.Join("testdata", "default-config.yaml"), nil)
+	require.NoError(t, err)
+	retMap, err := ret.AsConf()
+	assert.NoError(t, err)
+	expectedMap := confmap.NewFromStringMap(map[string]any{
+		allTemplatesKey: map[string]any{
+			"my_filelog_template": "filelog:\n  include: {{ .my_file }}\n",
+		},
+	})
+	assert.Equal(t, expectedMap, retMap)
+	assert.NoError(t, fp.Shutdown(context.Background()))
+}
+
+func TestAbsolutePath(t *testing.T) {
+	fp := New()
+	ret, err := fp.Retrieve(context.Background(), templateSchemePrefix+absolutePath(t, filepath.Join("testdata", "default-config.yaml")), nil)
+	require.NoError(t, err)
+	retMap, err := ret.AsConf()
+	assert.NoError(t, err)
+	expectedMap := confmap.NewFromStringMap(map[string]any{
+		allTemplatesKey: map[string]any{
+			"my_filelog_template": "filelog:\n  include: {{ .my_file }}\n",
+		},
+	})
+	assert.Equal(t, expectedMap, retMap)
+	assert.NoError(t, fp.Shutdown(context.Background()))
+}
+
+func absolutePath(t *testing.T, relativePath string) string {
+	dir, err := os.Getwd()
+	require.NoError(t, err)
+	return filepath.Join(dir, relativePath)
+}

confmap/provider/templateprovider/testdata/default-config.yaml

@@ -0,0 +1,4 @@
+type: my_filelog_template
+template: |
+  filelog:
+    include: {{ .my_file }}

confmap/provider/templateprovider/testdata/invalid-template.yaml

@@ -0,0 +1,4 @@
+type: my_filelog_template
+template: |
+  filelog:
+    include: {{

confmap/provider/templateprovider/testdata/invalid-yaml.yaml

@@ -0,0 +1 @@
+[invalid,

confmap/provider/templateprovider/testdata/missing-template.yaml

@@ -0,0 +1 @@
+type: my_filelog_template

confmap/provider/templateprovider/testdata/missing-type.yaml

@@ -0,0 +1,3 @@
+template: |
+  filelog:
+    include: {{ .my_file }}

confmap/provider/templateprovider/testdata/nonmap.yaml

@@ -0,0 +1,2 @@
+- 123
+- 456

confmap/provider/templateprovider/testdata/nonstring-template.yaml

@@ -0,0 +1,2 @@
+type: my_filelog_template
+template: [123,456]

confmap/provider/templateprovider/testdata/nonstring-type.yaml

@@ -0,0 +1,4 @@
+type: [123,456]
+template: |
+  filelog:
+    include: {{ .my_file }}