qbeon/webwire-go

package message

import (
    "fmt"
    "io"

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

// WriteMsgSignal writes a named signal message to the given writer closing
// it eventually
func WriteMsgSignal(
    writer io.WriteCloser,
    name []byte,
    payloadEncoding pld.Encoding,
    payloadData []byte,
    safeMode bool,
) error {
    if len(name) > 255 {
        initialErr := fmt.Errorf(
            "unsupported request message name length: %d",
            len(name),
        )
        if err := writer.Close(); err != nil {
            return fmt.Errorf("%s: %s", initialErr, err)
        }
        return initialErr
    }

    // Verify payload data validity in case of UTF16 encoding
    if payloadEncoding == pld.Utf16 && len(payloadData)%2 != 0 {
        initialErr := fmt.Errorf(
            "invalid UTF16 signal payload data length: %d",
            len(payloadData),
        )
        if err := writer.Close(); err != nil {
            return fmt.Errorf("%s: %s", initialErr, err)
        }
        return initialErr
    }

    if safeMode {
        for i := range name {
            char := name[i]
            if char < 32 || char > 126 {
                initialErr := fmt.Errorf(
                    "unsupported character in request name: %s",
                    string(char),
                )
                if err := writer.Close(); err != nil {
                    return fmt.Errorf("%s: %s", initialErr, err)
                }
                return initialErr
            }
        }
    }

    // Determine the message type from the payload encoding type
    msgType := msgTypeSignalBinary
    if payloadEncoding == pld.Utf8 {
        msgType = msgTypeSignalUtf8
    } else if payloadEncoding == pld.Utf16 {
        msgType = msgTypeSignalUtf16
    }

    // 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 name length flag
    if _, err := writer.Write(
        msgNameLenBytes[len(name) : len(name)+1],
    ); err != nil {
        if closeErr := writer.Close(); closeErr != nil {
            return fmt.Errorf("%s: %s", err, closeErr)
        }
        return err
    }

    // Write name (if any)
    if len(name) > 0 {
        if _, err := writer.Write(name); 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 && len(name)%2 != 0 {
        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()
}