misc: Add a function to encode newlines

Given a string, the added function encodes existing newline characters
('\n') as the string "\\n" and puts into a given output buffer.

The output buffer must have at least 2 times the length of the input
string plus 1 for the terminating '\0'. In the worst case, each
character can be replaced by 2 characters.

Fixes T189

Signed-off-by: Anderson Toshiyuki Sasaki <ansasaki@redhat.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>

include/libssh/misc.h

@@ -95,5 +95,6 @@ void ssh_log_hexdump(const char *descr, const unsigned char *what, size_t len);
 int ssh_mkdirs(const char *pathname, mode_t mode);
 
 int ssh_quote_file_name(const char *file_name, char *buf, size_t buf_len);
+int ssh_newline_vis(const char *string, char *buf, size_t buf_len);
 
 #endif /* MISC_H_ */

src/misc.c

@@ -1692,4 +1692,47 @@ error:
     return SSH_ERROR;
 }
 
+/**
+ * @internal
+ *
+ * @brief Given a string, encode existing newlines as the string "\\n"
+ *
+ * @param[in]  string   Input string
+ * @param[out] buf      Output buffer. This buffer must be at least (2 *
+ *                      strlen(string)) + 1 long.  In the worst case,
+ *                      each character can be encoded as 2 characters plus the
+ *                      terminating '\0'.
+ * @param[in]  buf_len  Size of the provided output buffer
+ *
+ * @returns SSH_ERROR on error; length of the resulting string not counting the
+ * terminating '\0' otherwise
+ */
+int ssh_newline_vis(const char *string, char *buf, size_t buf_len)
+{
+    const char *in = NULL;
+    char *out = NULL;
+
+    if (string == NULL || buf == NULL || buf_len == 0) {
+        return SSH_ERROR;
+    }
+
+    if ((2 * strlen(string) + 1) > buf_len) {
+        SSH_LOG(SSH_LOG_WARNING, "Buffer too small");
+        return SSH_ERROR;
+    }
+
+    out = buf;
+    for (in = string; *in != '\0'; in++) {
+        if (*in == '\n') {
+            *out++ = '\\';
+            *out++ = 'n';
+        } else {
+            *out++ = *in;
+        }
+    }
+    *out = '\0';
+
+    return out - buf;
+}
+
 /** @} */

tests/unittests/torture_misc.c

@@ -637,6 +637,24 @@ static void torture_ssh_quote_file_name(UNUSED_PARAM(void **state))
     assert_int_equal(rc, SSH_ERROR);
 }
 
+static void torture_ssh_newline_vis(UNUSED_PARAM(void **state))
+{
+    int rc;
+    char buffer[1024];
+
+    rc = ssh_newline_vis("\n", buffer, 1024);
+    assert_int_equal(rc, 2);
+    assert_string_equal(buffer, "\\n");
+
+    rc = ssh_newline_vis("\n\n\n\n", buffer, 1024);
+    assert_int_equal(rc, 8);
+    assert_string_equal(buffer, "\\n\\n\\n\\n");
+
+    rc = ssh_newline_vis("a\nb\n", buffer, 1024);
+    assert_int_equal(rc, 6);
+    assert_string_equal(buffer, "a\\nb\\n");
+}
+
 int torture_run_tests(void) {
     int rc;
     struct CMUnitTest tests[] = {
@@ -656,6 +674,7 @@ int torture_run_tests(void) {
         cmocka_unit_test(torture_timeout_update),
         cmocka_unit_test(torture_ssh_analyze_banner),
         cmocka_unit_test(torture_ssh_dir_writeable),
+        cmocka_unit_test(torture_ssh_newline_vis),
         cmocka_unit_test(torture_ssh_mkdirs),
         cmocka_unit_test(torture_ssh_quote_file_name),
     };