From 7b187360e9641c8f664709d3ac50296e3a87b2e0 Mon Sep 17 00:00:00 2001
From: David Goldblatt <davidgoldblatt@fb.com>
Date: Wed, 5 Aug 2020 18:30:34 -0700
Subject: [PATCH] IO: Support 0-padding for unsigned numbers.

---
 src/malloc_io.c       | 28 ++++++++++++++++++++++++++--
 test/unit/malloc_io.c | 10 ++++++++++
 2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/src/malloc_io.c b/src/malloc_io.c
index f5004f0a..59a0cbfc 100644
--- a/src/malloc_io.c
+++ b/src/malloc_io.c
@@ -346,7 +346,11 @@ malloc_vsnprintf(char *str, size_t size, const char *format, va_list ap) {
 	if (!left_justify && pad_len != 0) {				\
 		size_t j;						\
 		for (j = 0; j < pad_len; j++) {				\
-			APPEND_C(' ');					\
+			if (pad_zero) {					\
+				APPEND_C('0');				\
+			} else {					\
+				APPEND_C(' ');				\
+			}						\
 		}							\
 	}								\
 	/* Value. */							\
@@ -418,6 +422,8 @@ malloc_vsnprintf(char *str, size_t size, const char *format, va_list ap) {
 			unsigned char len = '?';
 			char *s;
 			size_t slen;
+			bool first_width_digit = true;
+			bool pad_zero = false;
 
 			f++;
 			/* Flags. */
@@ -454,7 +460,12 @@ malloc_vsnprintf(char *str, size_t size, const char *format, va_list ap) {
 					width = -width;
 				}
 				break;
-			case '0': case '1': case '2': case '3': case '4':
+			case '0':
+				if (first_width_digit) {
+					pad_zero = true;
+				}
+				JEMALLOC_FALLTHROUGH;
+			case '1': case '2': case '3': case '4':
 			case '5': case '6': case '7': case '8': case '9': {
 				uintmax_t uwidth;
 				set_errno(0);
@@ -462,6 +473,7 @@ malloc_vsnprintf(char *str, size_t size, const char *format, va_list ap) {
 				assert(uwidth != UINTMAX_MAX || get_errno() !=
 				    ERANGE);
 				width = (int)uwidth;
+				first_width_digit = false;
 				break;
 			} default:
 				break;
@@ -519,6 +531,18 @@ malloc_vsnprintf(char *str, size_t size, const char *format, va_list ap) {
 				intmax_t val JEMALLOC_CC_SILENCE_INIT(0);
 				char buf[D2S_BUFSIZE];
 
+				/*
+				 * Outputting negative, zero-padded numbers
+				 * would require a nontrivial rework of the
+				 * interaction between the width and padding
+				 * (since 0 padding goes between the '-' and the
+				 * number, while ' ' padding goes either before
+				 * the - or after the number.  Since we
+				 * currently don't ever need 0-padded negative
+				 * numbers, just don't bother supporting it.
+				 */
+				assert(!pad_zero);
+
 				GET_ARG_NUMERIC(val, len);
 				s = d2s(val, (plus_plus ? '+' : (plus_space ?
 				    ' ' : '-')), buf, &slen);
diff --git a/test/unit/malloc_io.c b/test/unit/malloc_io.c
index 1a6e5f63..385f7450 100644
--- a/test/unit/malloc_io.c
+++ b/test/unit/malloc_io.c
@@ -175,6 +175,7 @@ TEST_BEGIN(test_malloc_snprintf) {
 	TEST("_1234_", "_%o_", 01234);
 	TEST("_01234_", "_%#o_", 01234);
 	TEST("_1234_", "_%u_", 1234);
+	TEST("01234", "%05u", 1234);
 
 	TEST("_1234_", "_%d_", 1234);
 	TEST("_ 1234_", "_% d_", 1234);
@@ -183,6 +184,15 @@ TEST_BEGIN(test_malloc_snprintf) {
 	TEST("_-1234_", "_% d_", -1234);
 	TEST("_-1234_", "_%+d_", -1234);
 
+	/*
+	 * Morally, we should test these too, but 0-padded signed types are not
+	 * yet supported.
+	 *
+	 * TEST("01234", "%05", 1234);
+	 * TEST("-1234", "%05d", -1234);
+	 * TEST("-01234", "%06d", -1234);
+	*/
+
 	TEST("_-1234_", "_%d_", -1234);
 	TEST("_1234_", "_%d_", 1234);
 	TEST("_-1234_", "_%i_", -1234);