fsthttp, internal: add get_addr_dest_ip/port hostcalls

Fixes #121

Author: dgryski

fsthttp/response.go

@@ -5,6 +5,7 @@ package fsthttp
 import (
 	"fmt"
 	"io"
+	"net"
 	"sync"
 
 	"github.com/fastly/compute-sdk-go/internal/abi/fastly"
@@ -32,6 +33,12 @@ type Response struct {
 
 	// Body of the response.
 	Body io.ReadCloser
+
+	// BackendAddrIP is the ip address of the server that sent the response.
+	BackendAddrIP net.IP
+
+	// BackendAddrPort is the port of the server that sent the response.
+	BackendAddrPort uint16
 }
 
 // Cookies parses and returns the cookies set in the Set-Cookie headers.
@@ -62,12 +69,24 @@ func newResponse(req *Request, backend string, abiResp *fastly.HTTPResponse, abi
 		return nil, fmt.Errorf("read header keys: %w", err)
 	}
 
+	addr, err := abiResp.GetAddrDestIP()
+	if err != nil {
+		return nil, fmt.Errorf("get addr dest ip: %w", err)
+	}
+
+	port, err := abiResp.GetAddrDestPort()
+	if err != nil {
+		return nil, fmt.Errorf("get addr dest port: %w", err)
+	}
+
 	return &Response{
-		Request:    req,
-		Backend:    backend,
-		StatusCode: code,
-		Header:     header,
-		Body:       abiBody,
+		Request:         req,
+		Backend:         backend,
+		StatusCode:      code,
+		Header:          header,
+		Body:            abiBody,
+		BackendAddrIP:   addr,
+		BackendAddrPort: port,
 	}, nil
 }
 

internal/abi/fastly/hostcalls_noguest.go

@@ -177,6 +177,14 @@ func (r *HTTPRequest) SetFramingHeadersMode(manual bool) error {
 	return fmt.Errorf("not implemented")
 }
 
+func (r *HTTPResponse) GetAddrDestIP() (net.IP, error) {
+	return nil, fmt.Errorf("not implemented")
+}
+
+func (r *HTTPResponse) GetAddrDestPort() (uint16, error) {
+	return 0, fmt.Errorf("not implemented")
+}
+
 func HandoffWebsocket(backend string) error {
 	return fmt.Errorf("not implemented")
 }

internal/abi/fastly/http_guest.go

@@ -1869,6 +1869,70 @@ func (r *HTTPResponse) SetFramingHeadersMode(manual bool) error {
 	).toError()
 }
 
+// witx:
+//
+//	;;; Hostcall for getting the destination IP used for this request.
+//	;;;
+//	;;; The buffer for the IP address must be 16 bytes.
+//	;;; syntax used in URLs as specified in RFC 3986 section 3.
+//	(@interface func (export "get_addr_dest_ip")
+//		(param $h $response_handle)
+//		;; must be a 16-byte array
+//		(param $addr_octets_out (@witx pointer (@witx char8)))
+//		(result $err (expected $num_bytes (error $fastly_status)))
+//	)
+//
+//go:wasmimport fastly_http_resp get_addr_dest_ip
+//go:noescape
+func fastlyHTTPRespGetAddrDestIP(
+	h responseHandle,
+	addr prim.Pointer[prim.Char8],
+	nWritten prim.Pointer[prim.Usize],
+) FastlyStatus
+
+// GetAddrDestIP
+func (r *HTTPResponse) GetAddrDestIP() (net.IP, error) {
+	buf := prim.NewWriteBuffer(ipBufLen)
+
+	if err := fastlyHTTPRespGetAddrDestIP(
+		r.h,
+		prim.ToPointer(buf.Char8Pointer()),
+		prim.ToPointer(buf.NPointer()),
+	).toError(); err != nil {
+		return nil, err
+	}
+
+	return net.IP(buf.AsBytes()), nil
+}
+
+// witx:
+//
+//	;;; Hostcall for getting the destination port used for this request.
+//	(@interface func (export "get_addr_dest_port")
+//		(param $h $response_handle)
+//		(result $err (expected $port (error $fastly_status)))
+//	)
+//
+//go:wasmimport fastly_http_resp get_addr_dest_port
+//go:noescape
+func fastlyHTTPRespGetAddrDestPort(
+	h responseHandle,
+	port prim.Pointer[prim.U16],
+) FastlyStatus
+
+// GetAddrDestPort
+func (r *HTTPResponse) GetAddrDestPort() (uint16, error) {
+	var port prim.U16
+
+	if err := fastlyHTTPRespGetAddrDestPort(
+		r.h, prim.ToPointer(&port),
+	).toError(); err != nil {
+		return 0, err
+	}
+
+	return uint16(port), nil
+}
+
 // witx:
 //
 //	(module $fastly_uap