[template]: Add hostPort/serverName templating

internal/template/doc.go

@@ -0,0 +1,18 @@
+// Package template renders the templated fields used by the proxy against
+// per-request values.
+//
+// Templates are ordinary text/template source. They are bound to the context
+// they render against:
+//
+//   - [ParseRouting] yields a template over a [RoutingContext] (local namespace
+//     and metadata), used while routing rules choose an upstream. The remote
+//     namespace is not available here because translation is defined per
+//     upstream.
+//   - [ParseUpstream] yields a template over an [UpstreamContext] (local and
+//     remote namespace, and metadata), used to render the chosen upstream's
+//     hostPort and serverName.
+//
+// A reference to a field absent from the bound context (such as RemoteNamespace
+// in a routing template) fails at parse time. A reference to an absent metadata
+// key renders as the empty string.
+package template

internal/template/template.go

@@ -0,0 +1,96 @@
+package template
+
+import (
+	"fmt"
+	"strings"
+	texttemplate "text/template"
+)
+
+var probeMeta = map[string]string{
+	"dc":        "probe",
+	"x-cluster": "probe",
+}
+
+type (
+	// RoutingContext is available when evaluating routing rules, before an
+	// upstream has been selected. It deliberately omits the remote namespace:
+	// namespace translation is defined per upstream, so the remote name is not
+	// known until routing has chosen one.
+	RoutingContext struct {
+		LocalNamespace string
+		Metadata       map[string]string
+	}
+
+	// UpstreamContext is available when rendering an upstream's hostPort and
+	// serverName, after routing has selected the upstream and the remote
+	// namespace is known.
+	UpstreamContext struct {
+		LocalNamespace  string
+		RemoteNamespace string
+		Metadata        map[string]string
+	}
+
+	// Template is a compiled template bound to the context type T it renders
+	// against. Construct one with [ParseRouting] or [ParseUpstream].
+	Template[T any] struct {
+		tmpl *texttemplate.Template
+		raw  string
+	}
+)
+
+// ParseRouting compiles s into a [Template] rendered against a [RoutingContext].
+// A reference to a field absent from that context (such as RemoteNamespace)
+// fails here rather than at request time.
+func ParseRouting(s string) (*Template[RoutingContext], error) {
+	return parse(s, RoutingContext{LocalNamespace: "probe", Metadata: probeMeta})
+}
+
+// ParseUpstream compiles s into a [Template] rendered against an
+// [UpstreamContext].
+func ParseUpstream(s string) (*Template[UpstreamContext], error) {
+	return parse(s, UpstreamContext{LocalNamespace: "probe", RemoteNamespace: "probe", Metadata: probeMeta})
+}
+
+// Must returns t or panics if err is non-nil. It wraps a Parse call for
+// package-level variables and tests where an invalid template is a programming
+// error.
+func Must[T any](t *Template[T], err error) *Template[T] {
+	if err != nil {
+		panic(err)
+	}
+
+	return t
+}
+
+// Render evaluates the template against ctx. A reference to an absent metadata
+// key renders as the empty string.
+func (t *Template[T]) Render(ctx T) (string, error) {
+	var sb strings.Builder
+	if err := t.tmpl.Execute(&sb, ctx); err != nil {
+		return "", fmt.Errorf("template: render %q: %w", t.raw, err)
+	}
+
+	return sb.String(), nil
+}
+
+// String returns the raw template source.
+func (t *Template[T]) String() string {
+	return t.raw
+}
+
+// parse compiles s and validates it by rendering against probe, surfacing
+// references to unknown fields at parse time. Absent metadata keys render empty
+// under missingkey=zero and so do not trip the check.
+func parse[T any](s string, probe T) (*Template[T], error) {
+	tmpl, err := texttemplate.New("template").Option("missingkey=zero").Parse(s)
+	if err != nil {
+		return nil, fmt.Errorf("template: parse %q: %w", s, err)
+	}
+
+	t := &Template[T]{tmpl: tmpl, raw: s}
+	if _, err := t.Render(probe); err != nil {
+		return nil, err
+	}
+
+	return t, nil
+}

internal/template/template_test.go

@@ -0,0 +1,161 @@
+package template_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/temporalio/temporal-proxy/internal/template"
+)
+
+func TestParseUpstream_Render(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name string
+		tmpl string
+		ctx  template.UpstreamContext
+		want string
+	}{
+		{
+			name: "static string round-trips",
+			tmpl: "localhost:7233",
+			want: "localhost:7233",
+		},
+		{
+			name: "remote namespace in hostPort",
+			tmpl: "{{ .RemoteNamespace }}.acme-cloud.tmprl.cloud:7233",
+			ctx:  template.UpstreamContext{RemoteNamespace: "payments"},
+			want: "payments.acme-cloud.tmprl.cloud:7233",
+		},
+		{
+			name: "remote namespace in serverName",
+			tmpl: "{{ .RemoteNamespace }}.aws.tmprl.cloud",
+			ctx:  template.UpstreamContext{RemoteNamespace: "payments"},
+			want: "payments.aws.tmprl.cloud",
+		},
+		{
+			name: "local namespace",
+			tmpl: "{{ .LocalNamespace }}",
+			ctx:  template.UpstreamContext{LocalNamespace: "orders"},
+			want: "orders",
+		},
+		{
+			name: "metadata dot form",
+			tmpl: "{{ .Metadata.dc }}.internal",
+			ctx:  template.UpstreamContext{Metadata: map[string]string{"dc": "west"}},
+			want: "west.internal",
+		},
+		{
+			name: "metadata index form",
+			tmpl: `{{ index .Metadata "x-cluster" }}`,
+			ctx:  template.UpstreamContext{Metadata: map[string]string{"x-cluster": "c1"}},
+			want: "c1",
+		},
+		{
+			name: "absent metadata key renders empty",
+			tmpl: "{{ .Metadata.dc }}.internal",
+			ctx:  template.UpstreamContext{Metadata: map[string]string{}},
+			want: ".internal",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			tmpl, err := template.ParseUpstream(tt.tmpl)
+			require.NoError(t, err)
+			require.Equal(t, tt.tmpl, tmpl.String())
+
+			got, err := tmpl.Render(tt.ctx)
+			require.NoError(t, err)
+			require.Equal(t, tt.want, got)
+		})
+	}
+}
+
+func TestParseRouting_Render(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name string
+		tmpl string
+		ctx  template.RoutingContext
+		want string
+	}{
+		{
+			name: "local namespace",
+			tmpl: "{{ .LocalNamespace }}",
+			ctx:  template.RoutingContext{LocalNamespace: "orders"},
+			want: "orders",
+		},
+		{
+			name: "metadata index form",
+			tmpl: `{{ index .Metadata "x-cluster" }}`,
+			ctx:  template.RoutingContext{Metadata: map[string]string{"x-cluster": "c1"}},
+			want: "c1",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			tmpl, err := template.ParseRouting(tt.tmpl)
+			require.NoError(t, err)
+
+			got, err := tmpl.Render(tt.ctx)
+			require.NoError(t, err)
+			require.Equal(t, tt.want, got)
+		})
+	}
+}
+
+// A routing template cannot reference RemoteNamespace (it is not known until an
+// upstream is selected); the same template is valid for an upstream.
+func TestRemoteNamespace_scopedToUpstream(t *testing.T) {
+	t.Parallel()
+
+	const tmpl = "{{ .RemoteNamespace }}.acme-cloud.tmprl.cloud:7233"
+
+	_, err := template.ParseRouting(tmpl)
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "RemoteNamespace")
+
+	_, err = template.ParseUpstream(tmpl)
+	require.NoError(t, err)
+}
+
+func TestParse_errors(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name string
+		tmpl string
+	}{
+		{name: "malformed syntax", tmpl: "{{ .LocalNamespace"},
+		{name: "unknown field", tmpl: "{{ .Foo }}.acme.com"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			_, rErr := template.ParseRouting(tt.tmpl)
+			require.Error(t, rErr)
+
+			_, uErr := template.ParseUpstream(tt.tmpl)
+			require.Error(t, uErr)
+		})
+	}
+}
+
+func TestMust(t *testing.T) {
+	t.Parallel()
+
+	require.NotPanics(t, func() { template.Must(template.ParseUpstream("{{ .RemoteNamespace }}.acme.com")) })
+	require.NotPanics(t, func() { template.Must(template.ParseRouting("{{ .LocalNamespace }}")) })
+	require.Panics(t, func() { template.Must(template.ParseRouting("{{ .RemoteNamespace }}")) })
+	require.Panics(t, func() { template.Must(template.ParseUpstream("{{ .Foo }}")) })
+}