os: add print_lines utility

The code originates from the report_rom server. This patch makes the
code easy to reuse in other components.

repos/os/include/util/print_lines.h

@@ -0,0 +1,96 @@
+/*
+ * \brief  Utility for safely writing multi-line text
+ * \author Norman Feske
+ * \date   2014-01-11
+ */
+
+/*
+ * Copyright (C) 2014 Genode Labs GmbH
+ *
+ * This file is part of the Genode OS framework, which is distributed
+ * under the terms of the GNU General Public License version 2.
+ */
+
+#ifndef _INCLUDE__OS__PRINT_LINES_H_
+#define _INCLUDE__OS__PRINT_LINES_H_
+
+#include <util/string.h>
+
+namespace Genode {
+
+	template <size_t, typename FUNC>
+	static inline void print_lines(char const *, size_t, FUNC const &);
+}
+
+
+/**
+ * Print multi-line string
+ *
+ * \param MAX_LINE_LEN  maximum line length, used to dimension a line buffer
+ *                      on the stack
+ * \param string        character buffer, not necessarily null-terminated
+ * \param len           number of characters to print
+ * \param func          functor called for each line with 'char const *' as
+ *                      argument
+ *
+ * In situations where a string is supplied by an untrusted client, we cannot
+ * simply print the client-provided content as a single string becausewe cannot
+ * expect the client to null-terminate the string properly. The 'Log_multiline'
+ * class outputs the content line by line while keeping track of the content
+ * size.
+ *
+ * The output stops when reaching the end of the buffer or when a null
+ * character is encountered.
+ */
+template <Genode::size_t MAX_LINE_LEN, typename FUNC>
+void Genode::print_lines(char const *string, size_t len, FUNC const &func)
+{
+	/* skip leading line breaks */
+	for (; *string == '\n'; string++);
+
+	/* number of space and tab characters used for indentation */
+	size_t const num_indent_chars =
+		({
+			size_t n = 0;
+			for (; string[n] == ' ' || string[n] == '\t'; n++);
+			n;
+		});
+
+	char const * const first_line = string;
+
+	while (*string && len) {
+
+		/*
+		 * Skip indentation if the pattern is the same as for the first line.
+		 */
+		if (Genode::strcmp(first_line, string, num_indent_chars) == 0)
+			string += num_indent_chars;
+
+		size_t const line_len =
+			({
+				size_t i = 0;
+				for (; string[i] && i < len && string[i] != '\n'; i++);
+
+				/* the newline character belongs to the line */
+				if (string[i] == '\n')
+					i++;
+
+				i;
+			});
+
+		if (!line_len)
+			break;
+
+		/*
+		 * Copy line from (untrusted) caller to local line buffer
+		 */
+		char line_buf[MAX_LINE_LEN];
+		Genode::strncpy(line_buf, string, Genode::min(line_len + 1, sizeof(line_buf)));
+		func(line_buf);
+
+		string += line_len;
+		len    -= line_len;
+	}
+}
+
+#endif /* _INCLUDE__OS__PRINT_LINES_H_ */

repos/os/src/server/report_rom/report_service.h

@@ -18,6 +18,7 @@
 #include <util/arg_string.h>
 #include <report_session/report_session.h>
 #include <root/component.h>
+#include <os/print_lines.h>
 
 /* local includes */
 #include <rom_registry.h>
@@ -41,18 +42,6 @@ struct Report::Session_component : Genode::Rpc_object<Session>, Rom::Writer
 
 		bool &_verbose;
 
-		size_t const _str_line_end(char const * const str, size_t const len)
-		{
-			size_t i = 0;
-			for (; str[i] && i < len && str[i] != '\n'; i++);
-
-			/* the newline character belongs to the line */
-			if (str[i] == '\n')
-				i++;
-
-			return i;
-		}
-
 		Rom::Module &_create_module(Rom::Module::Name const &name)
 		{
 			try {
@@ -62,6 +51,12 @@ struct Report::Session_component : Genode::Rpc_object<Session>, Rom::Writer
 			}
 		}
 
+		static void _log_lines(char const *string, size_t len)
+		{
+			Genode::print_lines<200>(string, len,
+			                         [&] (char const *line) { PLOG("  %s", line); });
+		}
+
 	public:
 
 		Session_component(Rom::Module::Name const &name, size_t buffer_size,
@@ -91,41 +86,8 @@ struct Report::Session_component : Genode::Rpc_object<Session>, Rom::Writer
 			length = Genode::min(length, _ds.size());
 
 			if (_verbose) {
-
 				PLOG("report '%s'", _module.name().string());
-
-				/*
-				 * We cannot simply print the content of the report dataspace
-				 * as one string because we cannot expect the client to null-
-				 * terminate the content properly. Therefore, we output the
-				 * report line by line while keeping track of the dataspace
-				 * size.
-				 */
-
-				/* pointer and length of remaining string */
-				char const *str = _ds.local_addr<char>();
-				size_t      len = length;
-
-				while (*str && len) {
-
-					size_t const line_len = _str_line_end(str, len);
-
-					if (!line_len)
-						break;
-
-					/*
-					 * Copy line from (untrusted) report dataspace to local
-					 * line buffer,
-					 */
-					char line_buf[200];
-					Genode::strncpy(line_buf, str, Genode::min(line_len, sizeof(line_buf)));
-					PLOG("  %s", line_buf);
-
-					str += line_len;
-					len -= line_len;
-				}
-
-				PLOG("\n");
+				_log_lines(_ds.local_addr<char>(), length);
 			}
 
 			_module.write_content(_ds.local_addr<char>(), length);