Implement notifications service with shared messaging and email drivers (#36)

backend/notifications/templates/catalog.go

@@ -0,0 +1,146 @@
+package templates
+
+import (
+	"bytes"
+	"encoding/json"
+	html "html/template"
+	"io"
+	"os"
+	"strings"
+	text "text/template"
+
+	"git.sendico.io/tech/sxchnge/notifications/model"
+	merrors "git.sendico.io/tech/sxchnge/shared/errors"
+)
+
+type Content struct {
+	Subject string `json:"subject"`
+	HTML    string `json:"html"`
+	Text    string `json:"text"`
+}
+type Definition struct {
+	ID            string             `json:"id"`
+	Version       string             `json:"version"`
+	DefaultLocale string             `json:"default_locale"`
+	Parameters    []string           `json:"parameters"`
+	Locales       map[string]Content `json:"locales"`
+}
+type compiled struct {
+	definition Definition
+	locales    map[string]renderers
+}
+type renderers struct {
+	subject, text *text.Template
+	html          *html.Template
+}
+type Catalog struct{ entries map[string]compiled }
+
+func Load(path string) (*Catalog, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, merrors.OpaqueWrap(merrors.ErrInvalidArg, err, "cannot open template catalog")
+	}
+	defer f.Close()
+	var definitions []Definition
+	dec := json.NewDecoder(io.LimitReader(f, 4<<20))
+	dec.DisallowUnknownFields()
+	if err = dec.Decode(&definitions); err != nil {
+		return nil, merrors.OpaqueWrap(merrors.ErrInvalidArg, err, "invalid template catalog")
+	}
+	if err = dec.Decode(new(any)); err != io.EOF {
+		return nil, merrors.InvalidArgument("unexpected template catalog content")
+	}
+	return New(definitions)
+}
+func New(definitions []Definition) (*Catalog, error) {
+	c := &Catalog{entries: map[string]compiled{}}
+	if len(definitions) == 0 {
+		return nil, merrors.InvalidArgument("empty template catalog")
+	}
+	for _, d := range definitions {
+		key := d.ID + "\x00" + d.Version
+		if d.ID == "" || d.Version == "" || strings.ContainsRune(d.ID+d.Version, 0) {
+			return nil, merrors.InvalidArgument("invalid template identity")
+		}
+		if _, ok := c.entries[key]; ok {
+			return nil, merrors.InvalidArgument("duplicate template revision")
+		}
+		if _, ok := d.Locales[d.DefaultLocale]; !ok || d.DefaultLocale == "" {
+			return nil, merrors.InvalidArgument("missing default locale")
+		}
+		params := map[string]string{}
+		for _, p := range d.Parameters {
+			if p == "" {
+				return nil, merrors.InvalidArgument("empty parameter")
+			}
+			if _, ok := params[p]; ok {
+				return nil, merrors.InvalidArgument("duplicate parameter")
+			}
+			params[p] = "sample"
+		}
+		entry := compiled{definition: d, locales: map[string]renderers{}}
+		for locale, content := range d.Locales {
+			s, err := text.New("subject").Option("missingkey=error").Parse(content.Subject)
+			if err != nil {
+				return nil, merrors.InvalidArgument("invalid subject template")
+			}
+			t, err := text.New("text").Option("missingkey=error").Parse(content.Text)
+			if err != nil {
+				return nil, merrors.InvalidArgument("invalid text template")
+			}
+			h, err := html.New("html").Option("missingkey=error").Parse(content.HTML)
+			if err != nil {
+				return nil, merrors.InvalidArgument("invalid HTML template")
+			}
+			entry.locales[locale] = renderers{s, t, h}
+		}
+		c.entries[key] = entry
+		for locale := range d.Locales {
+			if _, err := c.Render(model.Request{TemplateID: d.ID, TemplateVersion: d.Version, Locale: locale, Parameters: params}); err != nil {
+				return nil, err
+			}
+		}
+	}
+	return c, nil
+}
+
+type boundedBuffer struct{ bytes.Buffer }
+
+func (b *boundedBuffer) Write(p []byte) (int, error) {
+	if b.Len()+len(p) > 256<<10 {
+		return 0, merrors.InvalidArgument("rendered content too large")
+	}
+	return b.Buffer.Write(p)
+}
+func (c *Catalog) Render(r model.Request) (model.Email, error) {
+	entry, ok := c.entries[r.TemplateID+"\x00"+r.TemplateVersion]
+	if !ok {
+		return model.Email{}, merrors.NoData("template revision not found")
+	}
+	if len(r.Parameters) != len(entry.definition.Parameters) {
+		return model.Email{}, merrors.InvalidArgument("template parameters do not match")
+	}
+	for _, p := range entry.definition.Parameters {
+		if _, ok := r.Parameters[p]; !ok {
+			return model.Email{}, merrors.InvalidArgument("missing template parameter")
+		}
+	}
+	locale := r.Locale
+	if locale == "" {
+		locale = entry.definition.DefaultLocale
+	}
+	render, ok := entry.locales[locale]
+	if !ok {
+		return model.Email{}, merrors.InvalidArgument("unsupported template locale")
+	}
+	var subject, body, plain boundedBuffer
+	for _, run := range []func() error{func() error { return render.subject.Execute(&subject, r.Parameters) }, func() error { return render.html.Execute(&body, r.Parameters) }, func() error { return render.text.Execute(&plain, r.Parameters) }} {
+		if err := run(); err != nil {
+			return model.Email{}, merrors.OpaqueWrap(merrors.ErrInvalidArg, err, "template rendering failed")
+		}
+	}
+	if subject.Len() == 0 || subject.Len() > 998 || strings.ContainsAny(subject.String(), "\r\n") || (body.Len() == 0 && plain.Len() == 0) {
+		return model.Email{}, merrors.InvalidArgument("invalid rendered email")
+	}
+	return model.Email{Address: r.Address, Subject: subject.String(), HTML: body.String(), Text: plain.String()}, nil
+}