Fix convert_case(), introduced in 5c40364.

Check source length before checking for NUL terminator to avoid
reading one byte past the string end. Also fix unreachable bug when
caller does not expect NUL-terminated result.

Add unit test coverage of convert_case() in case_test.c, which makes
it easier to reproduce the valgrind failure.

Discussion: https://postgr.es/m/7a9fd36d-7a38-4dc2-e676-fc939491a95a@gmail.com
Reported-by: Alexander Lakhin

Author: jeff-davis

src/common/unicode/case_test.c

@@ -48,6 +48,9 @@ icu_test_simple(pg_wchar code)
 	}
 }
 
+/*
+ * Exhaustively compare case mappings with the results from ICU.
+ */
 static void
 test_icu(void)
 {
@@ -82,9 +85,100 @@ test_icu(void)
 }
 #endif
 
-/*
- * Exhaustively compare case mappings with the results from libc and ICU.
- */
+static void
+test_strlower(const char *test_string, const char *expected)
+{
+	size_t		src1len = strlen(test_string);
+	size_t		src2len = -1;	/* NUL-terminated */
+	size_t		dst1len = strlen(expected);
+	size_t		dst2len = strlen(expected) + 1; /* NUL-terminated */
+	char	   *src1 = malloc(src1len);
+	char	   *dst1 = malloc(dst1len);
+	char	   *src2 = strdup(test_string);
+	char	   *dst2 = malloc(dst2len);
+	size_t		needed;
+
+	memcpy(src1, test_string, src1len); /* not NUL-terminated */
+
+	/* neither source nor destination are NUL-terminated */
+	memset(dst1, 0x7F, dst1len);
+	needed = unicode_strlower(dst1, dst1len, src1, src1len);
+	if (needed != strlen(expected))
+	{
+		printf("case_test: convert_case test1 FAILURE: needed %zu\n", needed);
+		exit(1);
+	}
+	if (memcmp(dst1, expected, dst1len) != 0)
+	{
+		printf("case_test: convert_case test1 FAILURE: test: '%s' result: '%.*s' expected: '%s'\n",
+			   test_string, (int) dst1len, dst1, expected);
+		exit(1);
+	}
+
+	/* destination is NUL-terminated and source is not */
+	memset(dst2, 0x7F, dst2len);
+	needed = unicode_strlower(dst2, dst2len, src1, src1len);
+	if (needed != strlen(expected))
+	{
+		printf("case_test: convert_case test2 FAILURE: needed %zu\n", needed);
+		exit(1);
+	}
+	if (strcmp(dst2, expected) != 0)
+	{
+		printf("case_test: convert_case test2 FAILURE: test: '%s' result: '%s' expected: '%s'\n",
+			   test_string, dst2, expected);
+		exit(1);
+	}
+
+	/* source is NUL-terminated and destination is not */
+	memset(dst1, 0x7F, dst1len);
+	needed = unicode_strlower(dst1, dst1len, src2, src2len);
+	if (needed != strlen(expected))
+	{
+		printf("case_test: convert_case test3 FAILURE: needed %zu\n", needed);
+		exit(1);
+	}
+	if (memcmp(dst1, expected, dst1len) != 0)
+	{
+		printf("case_test: convert_case test3 FAILURE: test: '%s' result: '%.*s' expected: '%s'\n",
+			   test_string, (int) dst1len, dst1, expected);
+		exit(1);
+	}
+
+	/* both source and destination are NUL-terminated */
+	memset(dst2, 0x7F, dst2len);
+	needed = unicode_strlower(dst2, dst2len, src2, src2len);
+	if (needed != strlen(expected))
+	{
+		printf("case_test: convert_case test4 FAILURE: needed %zu\n", needed);
+		exit(1);
+	}
+	if (strcmp(dst2, expected) != 0)
+	{
+		printf("case_test: convert_case test4 FAILURE: test: '%s' result: '%s' expected: '%s'\n",
+			   test_string, dst2, expected);
+		exit(1);
+	}
+
+	free(src1);
+	free(dst1);
+	free(src2);
+	free(dst2);
+}
+
+static void
+test_convert_case()
+{
+	/* test string with no case changes */
+	test_strlower("√∞", "√∞");
+	/* test string with case changes */
+	test_strlower("ABC", "abc");
+	/* test string with case changes and byte length changes */
+	test_strlower("ȺȺȺ", "ⱥⱥⱥ");
+
+	printf("case_test: convert_case: success\n");
+}
+
 int
 main(int argc, char **argv)
 {
@@ -96,5 +190,6 @@ main(int argc, char **argv)
 	printf("case_test: ICU not available; skipping\n");
 #endif
 
+	test_convert_case();
 	exit(0);
 }

src/common/unicode_case.c

@@ -104,7 +104,7 @@ convert_case(char *dst, size_t dstsize, const char *src, ssize_t srclen,
 	size_t		srcoff = 0;
 	size_t		result_len = 0;
 
-	while (src[srcoff] != '\0' && (srclen < 0 || srcoff < srclen))
+	while ((srclen < 0 || srcoff < srclen) && src[srcoff] != '\0')
 	{
 		pg_wchar	u1 = utf8_to_unicode((unsigned char *) src + srcoff);
 		int			u1len = unicode_utf8len(u1);
@@ -115,15 +115,15 @@ convert_case(char *dst, size_t dstsize, const char *src, ssize_t srclen,
 			pg_wchar	u2 = casemap->simplemap[casekind];
 			pg_wchar	u2len = unicode_utf8len(u2);
 
-			if (result_len + u2len < dstsize)
+			if (result_len + u2len <= dstsize)
 				unicode_to_utf8(u2, (unsigned char *) dst + result_len);
 
 			result_len += u2len;
 		}
 		else
 		{
 			/* no mapping; copy bytes from src */
-			if (result_len + u1len < dstsize)
+			if (result_len + u1len <= dstsize)
 				memcpy(dst + result_len, src + srcoff, u1len);
 
 			result_len += u1len;