diff --git a/plugin-api.h b/plugin-api.h
index fa67695..f74b069 100644
--- a/plugin-api.h
+++ b/plugin-api.h
@@ -47,22 +47,19 @@ struct service
 	/// Destroy the handle created for the scan
 	void (*scan_free) (void *handle);
 
-	// XXX: maybe force the service to store a reference to the unit?
-
 	/// We have received some data from the peer
-	// FIXME: the dependency on `struct str' is not very good
-	void (*on_data) (void *handle, struct unit *u, struct str *data);
+	void (*on_data) (void *handle, const void *data, size_t len);
 
 	/// Server has closed the connection
-	void (*on_eof) (void *handle, struct unit *u);
+	void (*on_eof) (void *handle);
 
 	// XXX: do we need these at all?  Is there any use for them?
 
 	/// Network or other error has occured
-	void (*on_error) (void *handle, struct unit *u);
+	void (*on_error) (void *handle);
 
 	/// The scan has been aborted
-	void (*on_aborted) (void *handle, struct unit *u);
+	void (*on_aborted) (void *handle);
 };
 
 struct plugin_api
diff --git a/plugins/http.c b/plugins/http.c
index 0bf7378..1aa2bd9 100644
--- a/plugins/http.c
+++ b/plugins/http.c
@@ -48,13 +48,13 @@ struct scan_data
 };
 
 static void
-on_header_read (struct scan_data *data)
+on_header_read (struct scan_data *scan)
 {
-	if (!strcasecmp (data->field.str, "Server"))
+	if (!strcasecmp (scan->field.str, "Server"))
 	{
 		char *info = xstrdup_printf ("%s: %s",
-			"server software", data->value.str);
-		g_data.api->unit_add_info (data->u, info);
+			"server software", scan->value.str);
+		g_data.api->unit_add_info (scan->u, info);
 		free (info);
 	}
 }
@@ -62,15 +62,15 @@ on_header_read (struct scan_data *data)
 static int
 on_header_field (http_parser *parser, const char *at, size_t len)
 {
-	struct scan_data *data = parser->data;
-	if (data->state == STATE_VALUE)
+	struct scan_data *scan = parser->data;
+	if (scan->state == STATE_VALUE)
 	{
-		on_header_read (data);
-		str_reset (&data->field);
-		str_reset (&data->value);
+		on_header_read (scan);
+		str_reset (&scan->field);
+		str_reset (&scan->value);
 	}
-	str_append_data (&data->field, at, len);
-	data->state = STATE_FIELD;
+	str_append_data (&scan->field, at, len);
+	scan->state = STATE_FIELD;
 	return 0;
 }
 
@@ -86,10 +86,10 @@ on_header_value (http_parser *parser, const char *at, size_t len)
 static int
 on_headers_complete (http_parser *parser)
 {
-	struct scan_data *data = parser->data;
+	struct scan_data *scan = parser->data;
 	// We've got this far, this must be an HTTP server
-	g_data.api->unit_set_success (data->u, true);
-	g_data.api->unit_abort (data->u);
+	g_data.api->unit_set_success (scan->u, true);
+	g_data.api->unit_abort (scan->u);
 	return 1;
 }
 
@@ -125,7 +125,7 @@ scan_free (void *handle)
 }
 
 static void
-on_data (void *handle, struct unit *u, struct str *data)
+on_data (void *handle, const void *data, size_t len)
 {
 	static const http_parser_settings http_settings =
 	{
@@ -136,26 +136,23 @@ on_data (void *handle, struct unit *u, struct str *data)
 
 	struct scan_data *scan = handle;
 	http_parser *parser = &scan->parser;
-
-	size_t len = data ? data->len : 0;
-	const char *str = data ? data->str : NULL;
-	size_t n_parsed = http_parser_execute (parser, &http_settings, str, len);
+	size_t n_parsed = http_parser_execute (parser, &http_settings, data, len);
 
 	if (parser->upgrade)
 	{
 		// We should never get here though because `on_headers_complete'
 		// is called first and ends up aborting the unit.
-		g_data.api->unit_add_info (u, "upgrades to a different protocol");
-		g_data.api->unit_abort (u);
+		g_data.api->unit_add_info (scan->u, "upgrades to a different protocol");
+		g_data.api->unit_abort (scan->u);
 	}
 	else if (n_parsed != len && parser->http_errno != HPE_CB_headers_complete)
-		g_data.api->unit_abort (u);
+		g_data.api->unit_abort (scan->u);
 }
 
 static void
-on_eof (void *handle, struct unit *u)
+on_eof (void *handle)
 {
-	on_data (handle, u, NULL);
+	on_data (handle, NULL, 0);
 }
 
 static struct service g_http_service =
diff --git a/plugins/irc.c b/plugins/irc.c
index c0e967d..554c00c 100644
--- a/plugins/irc.c
+++ b/plugins/irc.c
@@ -279,12 +279,10 @@ on_irc_message (const struct irc_message *msg, const char *raw, void *user_data)
 }
 
 static void
-on_data (void *handle, struct unit *u, struct str *data)
+on_data (void *handle, const void *data, size_t len)
 {
-	(void) u;
-
 	struct scan_data *scan = handle;
-	str_append_str (&scan->input, data);
+	str_append_data (&scan->input, data, len);
 	irc_process_buffer (&scan->input, on_irc_message, scan);
 }
 
diff --git a/plugins/ssh.c b/plugins/ssh.c
index cf18c3c..8a1cc3a 100644
--- a/plugins/ssh.c
+++ b/plugins/ssh.c
@@ -32,16 +32,16 @@ g_data;
 
 struct scan_data
 {
+	struct unit *u;                     ///< Scan unit
 	struct str input;                   ///< Input buffer
 };
 
 static void *
 scan_init (struct unit *u)
 {
-	(void) u;
-
 	struct scan_data *scan = xcalloc (1, sizeof *scan);
 	str_init (&scan->input);
+	scan->u = u;
 	return scan;
 }
 
@@ -54,14 +54,14 @@ scan_free (void *handle)
 }
 
 static void
-on_data (void *handle, struct unit *u, struct str *data)
+on_data (void *handle, const void *data, size_t len)
 {
 	// See RFC 4253 -- we check for a valid SSH banner
 	struct scan_data *scan = handle;
-	if (scan->input.len + data->len > 255)
+	if (scan->input.len + len > 255)
 		goto end_scan;
 
-	str_append_str (&scan->input, data);
+	str_append_data (&scan->input, data, len);
 	char *input = scan->input.str;
 	char *nl = strstr (input, "\r\n");
 	if (!nl)
@@ -71,11 +71,11 @@ on_data (void *handle, struct unit *u, struct str *data)
 		goto end_scan;
 
 	*nl = '\0';
-	g_data.api->unit_add_info (u, input);
-	g_data.api->unit_set_success (u, true);
+	g_data.api->unit_add_info (scan->u, input);
+	g_data.api->unit_set_success (scan->u, true);
 
 end_scan:
-	g_data.api->unit_abort (u);
+	g_data.api->unit_abort (scan->u);
 }
 
 static struct service g_ssh_service =
diff --git a/ponymap.c b/ponymap.c
index b53cb83..306830c 100644
--- a/ponymap.c
+++ b/ponymap.c
@@ -518,7 +518,7 @@ unit_abort (struct unit *u)
 	if (u->scan_started)
 	{
 		if (u->service->on_aborted)
-			u->service->on_aborted (u->service_data, u);
+			u->service->on_aborted (u->service_data);
 		u->service->scan_free (u->service_data);
 	}
 
@@ -581,7 +581,7 @@ on_unit_ready (const struct pollfd *pfd, struct unit *u)
 	if (u->read_buffer.len)
 	{
 		struct str *buf = &u->read_buffer;
-		service->on_data (u->service_data, u, buf);
+		service->on_data (u->service_data, buf->str, buf->len);
 		str_remove_slice (buf, 0, buf->len);
 
 		if (u->abortion_requested)
@@ -595,7 +595,7 @@ on_unit_ready (const struct pollfd *pfd, struct unit *u)
 	if (got_eof)
 	{
 		if (service->on_eof)
-			service->on_eof (u->service_data, u);
+			service->on_eof (u->service_data);
 		if (u->abortion_requested || !u->write_buffer.len)
 			goto abort;
 	}
@@ -605,7 +605,7 @@ on_unit_ready (const struct pollfd *pfd, struct unit *u)
 
 error:
 	if (service->on_error)
-		service->on_error (u->service_data, u);
+		service->on_error (u->service_data);
 
 abort:
 	unit_abort (u);