feat: enhance BGP template and peer configuration handling. Introduce policies_json parameter for local IP and ASN overrides in BGP speakers. Implement BGP template rendering and update peer configuration to utilize templates, improving flexibility in BGP setup. Add tests for new rendering logic and ensure proper integration with existing configurations.

internal/birdfmt/bgp.go

@@ -5,6 +5,116 @@ import (
 	"strings"
 )
 
+// BGP template names referenced by generated peers (BIRD 2).
+const (
+	BGPTemplateNameV4 = "bgp_template"
+	BGPTemplateNameV6 = "bgp_template_v6"
+)
+
+// BGPTemplatesOptions holds tenant defaults for template bgp bgp_template (+ v6 mirror).
+type BGPTemplatesOptions struct {
+	LocalIPv4      string
+	LocalIPv6      string
+	LocalASN       uint32
+	ExportFilterV4 string
+	ExportFilterV6 string
+}
+
+// RenderBGPTemplates renders two template bgp blocks (IPv4 and IPv6 AFI).
+func RenderBGPTemplates(opts BGPTemplatesOptions) (string, error) {
+	if strings.TrimSpace(opts.LocalIPv4) == "" || strings.TrimSpace(opts.LocalIPv6) == "" {
+		return "", fmt.Errorf("birdfmt: template local IPv4 and IPv6 are required")
+	}
+	if opts.LocalASN == 0 {
+		return "", fmt.Errorf("birdfmt: template local ASN must be non-zero")
+	}
+	exp4 := "all"
+	if strings.TrimSpace(opts.ExportFilterV4) != "" {
+		exp4 = "filter " + strings.TrimSpace(opts.ExportFilterV4)
+	}
+	exp6 := "all"
+	if strings.TrimSpace(opts.ExportFilterV6) != "" {
+		exp6 = "filter " + strings.TrimSpace(opts.ExportFilterV6)
+	}
+	var b strings.Builder
+	fmt.Fprintf(&b, "template bgp %s {\n", BGPTemplateNameV4)
+	b.WriteString("    local ")
+	b.WriteString(strings.TrimSpace(opts.LocalIPv4))
+	fmt.Fprintf(&b, " as %d;\n", opts.LocalASN)
+	b.WriteString("    ipv4 {\n")
+	b.WriteString("        import all;\n")
+	b.WriteString("        export ")
+	b.WriteString(exp4)
+	b.WriteString(";\n")
+	b.WriteString("    };\n")
+	b.WriteString("}\n\n")
+	fmt.Fprintf(&b, "template bgp %s {\n", BGPTemplateNameV6)
+	b.WriteString("    local ")
+	b.WriteString(strings.TrimSpace(opts.LocalIPv6))
+	fmt.Fprintf(&b, " as %d;\n", opts.LocalASN)
+	b.WriteString("    ipv6 {\n")
+	b.WriteString("        import all;\n")
+	b.WriteString("        export ")
+	b.WriteString(exp6)
+	b.WriteString(";\n")
+	b.WriteString("    };\n")
+	b.WriteString("}\n")
+	return b.String(), nil
+}
+
+// BGPPeerFromTemplateOptions describes protocol bgp NAME from TEMPLATE { … }.
+type BGPPeerFromTemplateOptions struct {
+	ProtocolName  string
+	TemplateName  string
+	NeighborIP    string
+	NeighborASN   uint32
+	SourceAddress string
+	// If set, emits "local … as …" before neighbor (overrides template local/ASN for this peer).
+	OverrideLocalIP  string
+	OverrideLocalASN uint32
+}
+
+// RenderProtocolBGPFromTemplate renders protocol bgp … from TEMPLATE { neighbor; multihop; source address; passive; }.
+func RenderProtocolBGPFromTemplate(opts BGPPeerFromTemplateOptions) (string, error) {
+	if strings.TrimSpace(opts.ProtocolName) == "" {
+		return "", fmt.Errorf("birdfmt: protocol name is required")
+	}
+	if strings.TrimSpace(opts.TemplateName) == "" {
+		return "", fmt.Errorf("birdfmt: template name is required")
+	}
+	if strings.TrimSpace(opts.NeighborIP) == "" || strings.TrimSpace(opts.SourceAddress) == "" {
+		return "", fmt.Errorf("birdfmt: neighbor and source address are required")
+	}
+	if opts.NeighborASN == 0 {
+		return "", fmt.Errorf("birdfmt: neighbor ASN must be non-zero")
+	}
+	if opts.OverrideLocalIP != "" && opts.OverrideLocalASN == 0 {
+		return "", fmt.Errorf("birdfmt: override local ASN is required when override local IP is set")
+	}
+
+	var b strings.Builder
+	b.WriteString("protocol bgp ")
+	b.WriteString(strings.TrimSpace(opts.ProtocolName))
+	b.WriteString(" from ")
+	b.WriteString(strings.TrimSpace(opts.TemplateName))
+	b.WriteString(" {\n")
+	if ip := strings.TrimSpace(opts.OverrideLocalIP); ip != "" {
+		b.WriteString("    local ")
+		b.WriteString(ip)
+		fmt.Fprintf(&b, " as %d;\n", opts.OverrideLocalASN)
+	}
+	b.WriteString("    neighbor ")
+	b.WriteString(strings.TrimSpace(opts.NeighborIP))
+	fmt.Fprintf(&b, " as %d;\n", opts.NeighborASN)
+	b.WriteString("    multihop;\n")
+	b.WriteString("    source address ")
+	b.WriteString(strings.TrimSpace(opts.SourceAddress))
+	b.WriteString(";\n")
+	b.WriteString("    passive;\n")
+	b.WriteString("}\n")
+	return b.String(), nil
+}
+
 // BGPPeerIPv4Options describes a single BGP session (BIRD 2, IPv4 AF).
 type BGPPeerIPv4Options struct {
 	ProtocolName string // e.g. evobgp_peer_uplink