lib/buffer: add simple grow-able buffer

The goal is to use it in libmount when generate options strings
and in libsmartcols to replace libscols_buffer.

Signed-off-by: Karel Zak <kzak@redhat.com>

include/buffer.h

@@ -0,0 +1,28 @@
+#ifndef UTIL_LINUX_BUFFER
+#define UTIL_LINUX_BUFFER
+
+#include "c.h"
+
+struct ul_buffer {
+	char *begin;		/* begin of the data */
+	char *end;		/* current end of data */
+
+	size_t sz;		/* allocated space for data */
+	size_t chunksize;
+};
+
+#define UL_INIT_BUFFER { .begin = NULL }
+
+void ul_buffer_reset_data(struct ul_buffer *buf);
+void ul_buffer_free_data(struct ul_buffer *buf);
+int ul_buffer_is_empty(struct ul_buffer *buf);
+void ul_buffer_set_chunksize(struct ul_buffer *buf, size_t sz);
+void ul_buffer_refer_string(struct ul_buffer *buf, char *str);
+int ul_buffer_alloc_data(struct ul_buffer *buf, size_t sz);
+int ul_buffer_append_data(struct ul_buffer *buf, const char *data, size_t sz);
+int ul_buffer_append_string(struct ul_buffer *buf, const char *str);
+int ul_buffer_append_ntimes(struct ul_buffer *buf, size_t n, const char *str);
+int ul_buffer_set_data(struct ul_buffer *buf, const char *data, size_t sz);
+char *ul_buffer_get_data(struct ul_buffer *buf);
+
+#endif /* UTIL_LINUX_BUFFER */

lib/Makemodule.am

@@ -3,6 +3,7 @@ noinst_LTLIBRARIES += libcommon.la
 libcommon_la_CFLAGS = $(AM_CFLAGS)
 libcommon_la_SOURCES = \
 	lib/blkdev.c \
+	lib/buffer.c \
 	lib/canonicalize.c \
 	lib/crc32.c \
 	lib/crc32c.c \
@@ -76,6 +77,7 @@ dist_man_MANS += lib/terminal-colors.d.5
 
 check_PROGRAMS += \
 	test_blkdev \
+	test_buffer \
 	test_canonicalize \
 	test_colors \
 	test_fileutils \
@@ -186,3 +188,6 @@ test_pwdutils_CFLAGS = $(AM_CFLAGS) -DTEST_PROGRAM
 
 test_remove_env_SOURCES = lib/env.c
 test_remove_env_CFLAGS = $(AM_CFLAGS) -DTEST_PROGRAM
+
+test_buffer_SOURCES = lib/buffer.c
+test_buffer_CFLAGS = $(AM_CFLAGS) -DTEST_PROGRAM_BUFFER

lib/buffer.c

@@ -0,0 +1,154 @@
+
+#include "buffer.h"
+
+void ul_buffer_reset_data(struct ul_buffer *buf)
+{
+	if (buf->begin)
+		buf->begin[0] = '\0';
+	buf->end = buf->begin;
+}
+
+void ul_buffer_free_data(struct ul_buffer *buf)
+{
+	assert(buf);
+
+	free(buf->begin);
+	buf->begin = NULL;
+	buf->end = NULL;
+	buf->sz = 0;
+}
+
+void ul_buffer_set_chunksize(struct ul_buffer *buf, size_t sz)
+{
+	buf->chunksize = sz;
+}
+
+int ul_buffer_is_empty(struct ul_buffer *buf)
+{
+	return buf->begin == buf->end;
+}
+
+void ul_buffer_refer_string(struct ul_buffer *buf, char *str)
+{
+	if (buf->sz)
+		ul_buffer_free_data(buf);
+	buf->begin = str;
+	buf->sz = str ? strlen(str) : 0;
+	buf->end = buf->begin + buf->sz;
+}
+
+int ul_buffer_alloc_data(struct ul_buffer *buf, size_t sz)
+{
+	char *tmp;
+	size_t len = 0;
+
+	assert(buf);
+
+	if (sz <= buf->sz)
+		return 0;
+
+	if (buf->end && buf->begin)
+		len = buf->end - buf->begin;
+
+	if (buf->chunksize)
+		sz = ((sz + buf->chunksize) / buf->chunksize) * buf->chunksize + 1;
+
+	tmp = realloc(buf->begin, sz);
+	if (!tmp)
+		return -ENOMEM;
+
+	buf->begin = tmp;
+	buf->end = buf->begin + len;
+	buf->sz = sz;
+
+	return 0;
+}
+
+int ul_buffer_append_data(struct ul_buffer *buf, const char *data, size_t sz)
+{
+	size_t maxsz = 0;
+
+	if (!buf)
+		return -EINVAL;
+	if (!data || !*data)
+		return 0;
+
+	if (buf->begin && buf->end)
+		maxsz = buf->sz - (buf->end - buf->begin);
+
+	if (maxsz <= sz + 1) {
+		int rc = ul_buffer_alloc_data(buf, buf->sz + sz + 1);
+		if (rc)
+			return rc;
+	}
+	memcpy(buf->end, data, sz);
+	buf->end += sz;
+	*buf->end = '\0';	/* make sure it's terminated */
+	return 0;
+}
+
+int ul_buffer_append_string(struct ul_buffer *buf, const char *str)
+{
+	return ul_buffer_append_data(buf, str, strlen(str));
+}
+
+int ul_buffer_append_ntimes(struct ul_buffer *buf, size_t n, const char *str)
+{
+	size_t i;
+	size_t len = strlen(str);
+
+	for (i = 0; len && i < n; i++) {
+		int rc = ul_buffer_append_data(buf, str, len);
+		if (rc)
+			return rc;
+	}
+	return 0;
+}
+
+int ul_buffer_set_data(struct ul_buffer *buf, const char *data, size_t sz)
+{
+	ul_buffer_reset_data(buf);
+	return ul_buffer_append_data(buf, data, sz);
+}
+
+char *ul_buffer_get_data(struct ul_buffer *buf)
+{
+	return buf->begin;
+}
+
+#ifdef TEST_PROGRAM_BUFFER
+int main(void)
+{
+	struct ul_buffer buf = UL_INIT_BUFFER;
+	char *str;
+
+	ul_buffer_set_chunksize(&buf, 16);
+
+	ul_buffer_append_string(&buf, "AAA");
+	ul_buffer_append_data(&buf, "=", 1);
+	ul_buffer_append_string(&buf, "aaa");
+	ul_buffer_append_data(&buf, ",", 1);
+	ul_buffer_append_string(&buf, "BBB");
+	ul_buffer_append_string(&buf, "=");
+	ul_buffer_append_string(&buf, "bbb");
+
+	str = ul_buffer_get_data(&buf);
+	printf("data '%s'\n", str);
+
+	ul_buffer_reset_data(&buf);
+	ul_buffer_append_string(&buf, "This is really long string to test the buffer function.");
+	ul_buffer_append_string(&buf, " YES!");
+	str = ul_buffer_get_data(&buf);
+	printf("data '%s'\n", str);
+
+	ul_buffer_free_data(&buf);
+	str = strdup("foo");
+	ul_buffer_refer_string(&buf, str);
+	ul_buffer_append_data(&buf, ",", 1);
+	ul_buffer_append_string(&buf, "bar");
+	str = ul_buffer_get_data(&buf);
+	printf("data '%s'\n", str);
+
+	ul_buffer_free_data(&buf);
+}
+#endif /* TEST_PROGRAM_BUFFER */