util/string: sprintf_append_realloc to concatenate strings with realloc

Appending string by using sprintf with realloc will be generally
usable and add sprintf_append_realloc() and vsprintf_append_realloc()
to the utility.

These APIs follow realloc about buffer management, i.e., the original
buffer is left untouched if they fail.

Besides, the original buffer is NULL, they are equivalent to
sprintf_alloc() and vsprintf_alloc(), respectively.

Change-Id: I8b69d9640e86e1862ddd3917995bad6f59426b7e
Signed-off-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>
Signed-off-by: Chunyang Hui <chunyang.hui@intel.com>
Signed-off-by: Pawel Wodkowski <pawelx.wodkowski@intel.com>
Reviewed-on: https://review.gerrithub.io/c/436913
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Darek Stojaczyk <dariusz.stojaczyk@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>
Chandler-Test-Pool: SPDK Automated Test System <sys_sgsw@intel.com>

include/spdk/string.h

@@ -69,6 +69,42 @@ char *spdk_sprintf_alloc(const char *format, ...) __attribute__((format(printf,
  */
 char *spdk_vsprintf_alloc(const char *format, va_list args);
 
+/**
+ * Append string using vsprintf with automatic buffer re-allocation.
+ *
+ * The return value is the formatted string, in which the original string in
+ * buffer is unchanged and the specified formatted string is appended.
+ *
+ * The returned string should be passed to free() when no longer needed.
+ *
+ * If buffer is NULL, the call is equivalent to spdk_sprintf_alloc().
+ * If the call fails, the original buffer is left untouched.
+ *
+ * \param buffer Buffer which has a formatted string.
+ * \param format Format for the string to print.
+ *
+ * \return the formatted string on success, or NULL on failure.
+ */
+char *spdk_sprintf_append_realloc(char *buffer, const char *format, ...);
+
+/**
+ * Append string using vsprintf with automatic buffer re-allocation.
+ * The return value is the formatted string, in which the original string in
+ * buffer is unchanged and the specified formatted string is appended.
+ *
+ * The returned string should be passed to free() when no longer needed.
+ *
+ * If buffer is NULL, the call is equivalent to spdk_sprintf_alloc().
+ * If the call fails, the original buffer is left untouched.
+ *
+ * \param buffer Buffer which has a formatted string.
+ * \param format Format for the string to print.
+ * \param args A value that identifies a variable arguments list.
+ *
+ * \return the formatted string on success, or NULL on failure.
+ */
+char *spdk_vsprintf_append_realloc(char *buffer, const char *format, va_list args);
+
 /**
  * Convert string to lowercase in place.
  *

lib/util/string.c

@@ -36,48 +36,55 @@
 #include "spdk/string.h"
 
 char *
-spdk_vsprintf_alloc(const char *format, va_list args)
+spdk_vsprintf_append_realloc(char *buffer, const char *format, va_list args)
 {
 	va_list args_copy;
-	char *buf;
-	size_t bufsize;
-	int rc;
+	char *new_buffer;
+	int orig_size = 0, new_size;
 
-	/* Try with a small buffer first. */
-	bufsize = 32;
-
-	/* Limit maximum buffer size to something reasonable so we don't loop forever. */
-	while (bufsize <= 1024 * 1024) {
-		buf = malloc(bufsize);
-		if (buf == NULL) {
-			return NULL;
+	/* Original buffer size */
+	if (buffer) {
+		orig_size = strlen(buffer);
 	}
 
+	/* Necessary buffer size */
 	va_copy(args_copy, args);
-		rc = vsnprintf(buf, bufsize, format, args_copy);
+	new_size = vsnprintf(NULL, 0, format, args_copy);
 	va_end(args_copy);
 
-		/*
-		 * If vsnprintf() returned a count within our current buffer size, we are done.
-		 * The count does not include the \0 terminator, so rc == bufsize is not OK.
-		 */
-		if (rc >= 0 && (size_t)rc < bufsize) {
-			return buf;
-		}
-
-		/*
-		 * vsnprintf() should return the required space, but some libc versions do not
-		 * implement this correctly, so just double the buffer size and try again.
-		 *
-		 * We don't need the data in buf, so rather than realloc(), use free() and malloc()
-		 * again to avoid a copy.
-		 */
-		free(buf);
-		bufsize *= 2;
-	}
-
+	if (new_size < 0) {
 		return NULL;
 	}
+	new_size += orig_size + 1;
+
+	new_buffer = realloc(buffer, new_size);
+	if (new_buffer == NULL) {
+		return NULL;
+	}
+
+	vsnprintf(new_buffer + orig_size, new_size - orig_size, format, args);
+
+	return new_buffer;
+}
+
+char *
+spdk_sprintf_append_realloc(char *buffer, const char *format, ...)
+{
+	va_list args;
+	char *ret;
+
+	va_start(args, format);
+	ret = spdk_vsprintf_append_realloc(buffer, format, args);
+	va_end(args);
+
+	return ret;
+}
+
+char *
+spdk_vsprintf_alloc(const char *format, va_list args)
+{
+	return spdk_vsprintf_append_realloc(NULL, format, args);
+}
 
 char *
 spdk_sprintf_alloc(const char *format, ...)

test/unit/lib/util/string.c/string_ut.c

@@ -202,6 +202,53 @@ test_parse_capacity(void)
 	CU_ASSERT(rc != 0);
 }
 
+static void
+test_sprintf_append_realloc(void)
+{
+	char *str1, *str2, *str3, *str4;
+
+	/* Test basic functionality. */
+	str1 = spdk_sprintf_alloc("hello world\ngood morning\n" \
+				  "good afternoon\ngood evening\n");
+	SPDK_CU_ASSERT_FATAL(str1 != NULL);
+
+	str2 = spdk_sprintf_append_realloc(NULL, "hello world\n");
+	SPDK_CU_ASSERT_FATAL(str2);
+
+	str2 = spdk_sprintf_append_realloc(str2, "good morning\n");
+	SPDK_CU_ASSERT_FATAL(str2);
+
+	str2 = spdk_sprintf_append_realloc(str2, "good afternoon\n");
+	SPDK_CU_ASSERT_FATAL(str2);
+
+	str2 = spdk_sprintf_append_realloc(str2, "good evening\n");
+	SPDK_CU_ASSERT_FATAL(str2);
+
+	CU_ASSERT(strcmp(str1, str2) == 0);
+
+	free(str1);
+	free(str2);
+
+	/* Test doubling buffer size. */
+	str3 = spdk_sprintf_append_realloc(NULL, "aaaaaaaaaa\n");
+	str3 = spdk_sprintf_append_realloc(str3, "bbbbbbbbbb\n");
+	str3 = spdk_sprintf_append_realloc(str3, "cccccccccc\n");
+
+	str4 = malloc(33 + 1);
+	memset(&str4[0], 'a', 10);
+	str4[10] = '\n';
+	memset(&str4[11], 'b', 10);
+	str4[21] = '\n';
+	memset(&str4[22], 'c', 10);
+	str4[32] = '\n';
+	str4[33] = 0;
+
+	CU_ASSERT(strcmp(str3, str4) == 0);
+
+	free(str3);
+	free(str4);
+}
+
 int
 main(int argc, char **argv)
 {
@@ -221,7 +268,8 @@ main(int argc, char **argv)
 	if (
 		CU_add_test(suite, "test_parse_ip_addr", test_parse_ip_addr) == NULL ||
 		CU_add_test(suite, "test_str_chomp", test_str_chomp) == NULL ||
-		CU_add_test(suite, "test_parse_capacity", test_parse_capacity) == NULL) {
+		CU_add_test(suite, "test_parse_capacity", test_parse_capacity) == NULL ||
+		CU_add_test(suite, "test_sprintf_append_realloc", test_sprintf_append_realloc) == NULL) {
 		CU_cleanup_registry();
 		return CU_get_error();
 	}