Invalid AWN Request Fixer

pkg/ambient/ambienthttp/ambienthttp.go

@@ -0,0 +1,101 @@
+// This package exists purely to override the net.Listener used
+// by the application's http server. This is necessary for certain versions
+// of firmware which errantly put an 0x0a (LF) following PASSKEY for
+// AmbientWeather type http reporting.
+//
+// This needs to be fixed upstream by Ambient Weather and is a complete
+// hack that should never be necessary. Without this, the http server
+// will silently crank back an HTTP:400
+package ambienthttp
+
+import (
+	"bufio"
+	"bytes"
+	"context"
+	"io"
+	"net"
+	"regexp"
+
+	"github.com/rs/zerolog"
+)
+
+// Invalid Request Pattern
+var badReqURI = regexp.MustCompile(`PASSKEY=[^\n&]{16,}$`)
+
+// Listener encapsulates LFStrippingConn to perform
+// infuriating strip of newline character present after PASSKEY
+// sent errantly by specific versions of firmware sending updates
+// in AmbientWeather protocol
+type LFStrippingListener struct {
+	ctx context.Context
+	net.Listener
+}
+
+type LFStrippingConn struct {
+	net.Conn
+	reader io.Reader
+}
+
+func (l *LFStrippingListener) WrapConn(conn net.Conn) net.Conn {
+	buf := new(bytes.Buffer)
+	reader := io.TeeReader(conn, buf)
+
+	scanner := bufio.NewScanner(reader)
+	var newData []byte
+	for scanner.Scan() {
+		line := scanner.Bytes()
+		newData = append(newData, line...)
+
+		// Only restore newline if not a bad request
+		if !badReqURI.Match(line) {
+			newData = append(newData, '\n')
+		}
+	}
+	if scanner.Err() != nil {
+		zerolog.Ctx(l.ctx).Err(scanner.Err()).Send()
+	}
+
+	// Use a multi-reader to prepend the modified request
+	finalReader := io.MultiReader(bytes.NewReader(newData), conn)
+
+	return &LFStrippingConn{
+		Conn:   conn,
+		reader: finalReader,
+	}
+}
+
+func NewLFStrippingListener(ctx context.Context, listen string) net.Listener {
+	// Create the underlying TCP listener
+	rawListener, err := net.Listen("tcp", listen)
+	if err != nil {
+		panic(err)
+	}
+	return &LFStrippingListener{
+		Listener: rawListener,
+		ctx:      ctx,
+	}
+}
+
+// Accept waits for and returns the next connection to the listener.
+func (l *LFStrippingListener) Accept() (net.Conn, error) {
+	conn, err := l.Listener.Accept()
+	if err != nil {
+		return nil, err
+	}
+	return l.WrapConn(conn), nil
+}
+
+// Close closes the listener.
+// Any blocked Accept operations will be unblocked and return errors.
+func (l *LFStrippingListener) Close() error {
+	return l.Listener.Close()
+}
+
+// Addr returns the listener's network address.
+func (l *LFStrippingListener) Addr() net.Addr {
+	return l.Listener.Addr()
+}
+
+func (c *LFStrippingConn) Read(b []byte) (int, error) {
+	return c.reader.Read(b)
+}