qbeon/webwire-go

package message

import (
    "fmt"
    "io"

    pld "github.com/qbeon/webwire-go/payload"
)

// WriteMsgReply writes a reply message to the given writer closing it
// eventually
func WriteMsgReply(
    writer io.WriteCloser,
    requestIdentifier []byte,
    payloadEncoding pld.Encoding,
    payloadData []byte,
) error {
    // Verify payload data validity in case of UTF16 encoding
    if payloadEncoding == pld.Utf16 && len(payloadData)%2 != 0 {
        initialErr := fmt.Errorf(
            "invalid UTF16 reply payload data length: %d",
            len(payloadData),
        )
        if err := writer.Close(); err != nil {
            return fmt.Errorf("%s: %s", initialErr, err)
        }
        return initialErr
    }

    // Determine message type from payload encoding type
    msgType := msgTypeReplyBinary
    if payloadEncoding == pld.Utf8 {
        msgType = msgTypeReplyUtf8
    } else if payloadEncoding == pld.Utf16 {
        msgType = msgTypeReplyUtf16
    }

    // Write message type flag
    if _, err := writer.Write(msgType); err != nil {
        if closeErr := writer.Close(); closeErr != nil {
            return fmt.Errorf("%s: %s", err, closeErr)
        }
        return err
    }

    // Write request identifier
    if _, err := writer.Write(requestIdentifier); err != nil {
        if closeErr := writer.Close(); closeErr != nil {
            return fmt.Errorf("%s: %s", err, closeErr)
        }
        return err
    }

    // Write header padding byte if the payload requires proper alignment
    if payloadEncoding == pld.Utf16 {
        if _, err := writer.Write(msgHeaderPadding); err != nil {
            if closeErr := writer.Close(); closeErr != nil {
                return fmt.Errorf("%s: %s", err, closeErr)
            }
            return err
        }
    }

    // Write payload
    if _, err := writer.Write(payloadData); err != nil {
        if closeErr := writer.Close(); closeErr != nil {
            return fmt.Errorf("%s: %s", err, closeErr)
        }
        return err
    }

    return writer.Close()
}