merge(third_party/git): Merge squashed git subtree at v2.23.0

Merge commit '1b593e1ea4' as 'third_party/git'

third_party/git/sideband.h

@@ -0,0 +1,29 @@
+#ifndef SIDEBAND_H
+#define SIDEBAND_H
+
+enum sideband_type {
+	SIDEBAND_PROTOCOL_ERROR = -2,
+	SIDEBAND_REMOTE_ERROR = -1,
+	SIDEBAND_FLUSH = 0,
+	SIDEBAND_PRIMARY = 1
+};
+
+/*
+ * Inspects a multiplexed packet read from the remote. If this packet is a
+ * progress packet and thus should not be processed by the caller, returns 0.
+ * Otherwise, returns 1, releases scratch, and sets sideband_type.
+ *
+ * If this packet is SIDEBAND_PROTOCOL_ERROR, SIDEBAND_REMOTE_ERROR, or a
+ * progress packet, also prints a message to stderr.
+ *
+ * scratch must be a struct strbuf allocated by the caller. It is used to store
+ * progress messages split across multiple packets.
+ */
+int demultiplex_sideband(const char *me, char *buf, int len,
+			 int die_on_error,
+			 struct strbuf *scratch,
+			 enum sideband_type *sideband_type);
+
+void send_sideband(int fd, int band, const char *data, ssize_t sz, int packet_max);
+
+#endif