library: io: handle retryable errors

Discord client being absent/disconnecting is not fatal to the RPC sender, in cases like that we return ErrAgain and in the case of broken pipe (Discord client going away) also reset the Client state so the caller can choose to retry the operation and therefore initiate a new connection attempt.

Signed-off-by: Ophestra Umiker <cat@ophivana.moe>

io.go

@@ -3,9 +3,11 @@ package rpcfetch
 import (
 	"encoding/binary"
 	"encoding/json"
+	"errors"
 	"net"
 	"os"
 	"strconv"
+	"syscall"
 )
 
 type Client struct {
@@ -33,6 +35,17 @@ func Raw[T any](d *Client, opcode uint32, payload any) (uint32, T, error) {
 
 // Raw writes a raw payload to Discord and returns the response opcode and payload
 func (d *Client) Raw(opcode uint32, payload any) (uint32, []byte, error) {
+	opcodeResp, payloadResp, err := d.raw(opcode, payload)
+	if errors.Is(err, syscall.EPIPE) {
+		// clean up as much as possible
+		_ = d.Close()
+		// advise retry
+		err = ErrAgain
+	}
+	return opcodeResp, payloadResp, err
+}
+
+func (d *Client) raw(opcode uint32, payload any) (uint32, []byte, error) {
 	if err := binary.Write(d.conn, binary.LittleEndian, opcode); err != nil {
 		return 0, nil, err
 	}

io_unix.go

@@ -1,16 +1,25 @@
 package rpcfetch
 
 import (
+	"errors"
+	"io/fs"
 	"net"
 	"time"
 )
 
+var (
+	ErrAgain = errors.New("operation not performed")
+)
+
 func (d *Client) dial() error {
 	if d.dialed {
 		panic("attempted to dial on open client")
 	}
 
 	if conn, err := net.DialTimeout("unix", sockPath()+"/discord-ipc-0", 5*time.Second); err != nil {
+		if errors.Is(err, fs.ErrNotExist) {
+			return ErrAgain
+		}
 		return err
 	} else {
 		d.conn = conn