libsmartcols: implement scols_table_print_range_to_string

Reference: https://github.com/karelzak/util-linux/issues/283
Signed-off-by: Igor Gnatenko <i.gnatenko.brain@gmail.com>

libsmartcols/docs/libsmartcols-docs.xml

@@ -9,7 +9,7 @@
     <title>libsmartcols Reference Manual</title>
     <releaseinfo>for libsmartcols version &version;</releaseinfo>
     <copyright>
-      <year>2014-2015</year>
+      <year>2014-2016</year>
       <holder>Karel Zak &lt;kzak@redhat.com&gt;</holder>
     </copyright>
   </bookinfo>

libsmartcols/docs/libsmartcols-sections.txt

@@ -145,6 +145,7 @@ scols_unref_table
 scols_print_table
 scols_print_table_to_string
 scols_table_print_range
+scols_table_print_range_to_string
 </SECTION>
 
 <SECTION>

libsmartcols/src/libsmartcols.h.in

@@ -250,6 +250,10 @@ extern int scols_print_table_to_string(struct libscols_table *tb, char **data);
 extern int scols_table_print_range(	struct libscols_table *tb,
 					struct libscols_line *start,
 					struct libscols_line *end);
+extern int scols_table_print_range_to_string(	struct libscols_table *tb,
+						struct libscols_line *start,
+						struct libscols_line *end,
+						char **data);
 
 #ifdef __cplusplus
 }

libsmartcols/src/libsmartcols.sym

@@ -133,5 +133,6 @@ global:
 	scols_cell_get_flags;
 	scols_cell_set_flags;
 	scols_table_print_range;
+	scols_table_print_range_to_string;
 	scols_table_enable_nolinesep;
 } SMARTCOLS_2.27;

libsmartcols/src/table_print.c

@@ -1351,6 +1351,50 @@ done:
 	return rc;
 }
 
+/**
+ * scols_table_print_range_to_string:
+ * @tb: table
+ * @start: first printed line or NULL to print from the beggin of the table
+ * @end: last printed line or NULL to print all from start.
+ * @data: pointer to the beginning of a memory area to print to
+ *
+ * The same as scols_table_print_range(), but prints to @data instead of
+ * stream.
+ *
+ * Returns: 0, a negative value in case of an error.
+ */
+int scols_table_print_range_to_string(	struct libscols_table *tb,
+					struct libscols_line *start,
+					struct libscols_line *end,
+					char **data)
+{
+#ifdef HAVE_OPEN_MEMSTREAM
+	FILE *stream, *old_stream;
+	size_t sz;
+	int rc;
+
+	if (!tb)
+		return -EINVAL;
+
+	DBG(TAB, ul_debugobj(tb, "printing range to string"));
+
+	/* create a stream for output */
+	stream = open_memstream(data, &sz);
+	if (!stream)
+		return -ENOMEM;
+
+	old_stream = scols_table_get_stream(tb);
+	scols_table_set_stream(tb, stream);
+	rc = scols_table_print_range(tb, start, end);
+	fclose(stream);
+	scols_table_set_stream(tb, old_stream);
+
+	return rc;
+#else
+	return -ENOSYS;
+#endif
+}
+
 /**
  * scols_print_table:
  * @tb: table