Merge pull request #503 from arrbee/git-buf-always-cstr

Make git_buf functions always maintain a valid cstr

3 files changed, 113 insertions, 51 deletions

diff --git a/src/buffer.c b/src/buffer.c
index c56a75598..3dff813e3 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -8,13 +8,29 @@
 #include "posix.h"
 #include <stdarg.h>
 
+/* Used as default value for git_buf->ptr so that people can always
+ * assume ptr is non-NULL and zero terminated even for new git_bufs.
+ */
+char git_buf_initbuf[1];
+
 #define ENSURE_SIZE(b, d) \
 	if ((ssize_t)(d) > buf->asize && git_buf_grow(b, (d)) < GIT_SUCCESS)\
 		return;
 
+void git_buf_init(git_buf *buf, size_t initial_size)
+{
+	buf->asize = 0;
+	buf->size = 0;
+	buf->ptr = git_buf_initbuf;
+
+	if (initial_size)
+		git_buf_grow(buf, initial_size);
+}
+
 int git_buf_grow(git_buf *buf, size_t target_size)
 {
 	char *new_ptr;
+	size_t new_size;
 
 	if (buf->asize < 0)
 		return GIT_ENOMEM;
@@ -22,27 +38,56 @@ int git_buf_grow(git_buf *buf, size_t target_size)
 	if (target_size <= (size_t)buf->asize)
 		return GIT_SUCCESS;
 
-	if (buf->asize == 0)
-		buf->asize = target_size;
+	if (buf->asize == 0) {
+		new_size = target_size;
+		new_ptr = NULL;
+	} else {
+		new_size = (size_t)buf->asize;
+		new_ptr = buf->ptr;
+	}
 
 	/* grow the buffer size by 1.5, until it's big enough
 	 * to fit our target size */
-	while (buf->asize < (int)target_size)
-		buf->asize = (buf->asize << 1) - (buf->asize >> 1);
+	while (new_size < target_size)
+		new_size = (new_size << 1) - (new_size >> 1);
 
 	/* round allocation up to multiple of 8 */
-	buf->asize = (buf->asize + 7) & ~7;
+	new_size = (new_size + 7) & ~7;
 
-	new_ptr = git__realloc(buf->ptr, buf->asize);
+	new_ptr = git__realloc(new_ptr, new_size);
 	if (!new_ptr) {
 		buf->asize = -1;
 		return GIT_ENOMEM;
 	}
 
-	buf->ptr = new_ptr;
+	buf->asize = new_size;
+	buf->ptr   = new_ptr;
+
+	/* truncate the existing buffer size if necessary */
+	if (buf->size >= buf->asize)
+		buf->size = buf->asize - 1;
+	buf->ptr[buf->size] = '\0';
+
 	return GIT_SUCCESS;
 }
 
+void git_buf_free(git_buf *buf)
+{
+	if (!buf) return;
+
+	if (buf->ptr != git_buf_initbuf)
+		git__free(buf->ptr);
+
+	git_buf_init(buf, 0);
+}
+
+void git_buf_clear(git_buf *buf)
+{
+	buf->size = 0;
+	if (buf->asize > 0)
+		buf->ptr[0] = '\0';
+}
+
 int git_buf_oom(const git_buf *buf)
 {
 	return (buf->asize < 0);
@@ -53,9 +98,10 @@ void git_buf_set(git_buf *buf, const char *data, size_t len)
 	if (len == 0 || data == NULL) {
 		git_buf_clear(buf);
 	} else {
-		ENSURE_SIZE(buf, len);
+		ENSURE_SIZE(buf, len + 1);
 		memmove(buf->ptr, data, len);
 		buf->size = len;
+		buf->ptr[buf->size] = '\0';
 	}
 }
 
@@ -66,15 +112,17 @@ void git_buf_sets(git_buf *buf, const char *string)
 
 void git_buf_putc(git_buf *buf, char c)
 {
-	ENSURE_SIZE(buf, buf->size + 1);
+	ENSURE_SIZE(buf, buf->size + 2);
 	buf->ptr[buf->size++] = c;
+	buf->ptr[buf->size] = '\0';
 }
 
 void git_buf_put(git_buf *buf, const char *data, size_t len)
 {
-	ENSURE_SIZE(buf, buf->size + len);
+	ENSURE_SIZE(buf, buf->size + len + 1);
 	memmove(buf->ptr + buf->size, data, len);
 	buf->size += len;
+	buf->ptr[buf->size] = '\0';
 }
 
 void git_buf_puts(git_buf *buf, const char *string)
@@ -111,27 +159,25 @@ void git_buf_printf(git_buf *buf, const char *format, ...)
 
 const char *git_buf_cstr(git_buf *buf)
 {
-	if (buf->size + 1 > buf->asize &&
-		git_buf_grow(buf, buf->size + 1) < GIT_SUCCESS)
-		return NULL;
-
-	buf->ptr[buf->size] = '\0';
 	return buf->ptr;
 }
 
-void git_buf_free(git_buf *buf)
+void git_buf_copy_cstr(char *data, size_t datasize, git_buf *buf)
 {
-	if (!buf) return;
+	size_t copylen;
 
-	git__free(buf->ptr);
-	buf->ptr = NULL;
-	buf->asize = 0;
-	buf->size = 0;
-}
+	assert(data && datasize);
 
-void git_buf_clear(git_buf *buf)
-{
-	buf->size = 0;
+	data[0] = '\0';
+
+	if (buf->size == 0 || buf->asize <= 0)
+		return;
+
+	copylen = buf->size;
+	if (copylen > datasize - 1)
+		copylen = datasize - 1;
+	memmove(data, buf->ptr, copylen);
+	data[copylen] = '\0';
 }
 
 void git_buf_consume(git_buf *buf, const char *end)
@@ -140,6 +186,7 @@ void git_buf_consume(git_buf *buf, const char *end)
 		size_t consumed = end - buf->ptr;
 		memmove(buf->ptr, end, buf->size - consumed);
 		buf->size -= consumed;
+		buf->ptr[buf->size] = '\0';
 	}
 }
 
@@ -152,21 +199,12 @@ void git_buf_swap(git_buf *buf_a, git_buf *buf_b)
 
 char *git_buf_take_cstr(git_buf *buf)
 {
-	char *data = NULL;
-
-	if (buf->ptr == NULL)
-		return NULL;
+	char *data = buf->ptr;
 
-	if (buf->size + 1 > buf->asize &&
-		git_buf_grow(buf, buf->size + 1) < GIT_SUCCESS)
+	if (buf->asize <= 0)
 		return NULL;
 
-	data = buf->ptr;
-	data[buf->size] = '\0';
-
-	buf->ptr = NULL;
-	buf->asize = 0;
-	buf->size = 0;
+	git_buf_init(buf, 0);
 
 	return data;
 }
@@ -199,7 +237,7 @@ void git_buf_join_n(git_buf *buf, char separator, int nbuf, ...)
 	}
 	va_end(ap);
 
-	ENSURE_SIZE(buf, buf->size + total_size);
+	ENSURE_SIZE(buf, buf->size + total_size + 1);
 
 	out = buf->ptr + buf->size;
 
@@ -235,6 +273,7 @@ void git_buf_join_n(git_buf *buf, char separator, int nbuf, ...)
 
 	/* set size based on num characters actually written */
 	buf->size = out - buf->ptr;
+	buf->ptr[buf->size] = '\0';
 }
 
 void git_buf_join(
@@ -277,7 +316,7 @@ void git_buf_join(
 
 	if (!add_size) return;
 
-	ENSURE_SIZE(buf, buf->size + add_size);
+	ENSURE_SIZE(buf, buf->size + add_size + 1);
 
 	/* concatenate strings */
 	ptr = buf->ptr + buf->size;
@@ -296,4 +335,5 @@ void git_buf_join(
 
 	/* set size based on num characters actually written */
 	buf->size = ptr - buf->ptr;
+	buf->ptr[buf->size] = '\0';
 }
diff --git a/src/buffer.h b/src/buffer.h
index 2ed9047ca..fa0c7f0b8 100644
--- a/src/buffer.h
+++ b/src/buffer.h
@@ -14,8 +14,11 @@ typedef struct {
 	ssize_t asize, size;
 } git_buf;
 
-#define GIT_BUF_INIT {NULL, 0, 0}
+extern char git_buf_initbuf[];
 
+#define GIT_BUF_INIT { git_buf_initbuf, 0, 0 }
+
+void git_buf_init(git_buf *buf, size_t initial_size);
 int git_buf_grow(git_buf *buf, size_t target_size);
 void git_buf_free(git_buf *buf);
 void git_buf_swap(git_buf *buf_a, git_buf *buf_b);
@@ -42,6 +45,7 @@ void git_buf_join(git_buf *buf, char separator, const char *str_a, const char *s
 
 const char *git_buf_cstr(git_buf *buf);
 char *git_buf_take_cstr(git_buf *buf);
+void git_buf_copy_cstr(char *data, size_t datasize, git_buf *buf);
 
 #define git_buf_PUTS(buf, str) git_buf_put(buf, str, sizeof(str) - 1)
 
diff --git a/tests-clay/core/buffer.c b/tests-clay/core/buffer.c
index bf88a3073..acde8c0a7 100644
--- a/tests-clay/core/buffer.c
+++ b/tests-clay/core/buffer.c
@@ -52,19 +52,19 @@ void test_core_buffer__2(void)
 {
 	git_buf buf = GIT_BUF_INIT;
 	int i;
+	char data[100];
 
 	cl_assert(buf.size == 0);
 
 	/* this must be safe to do */
 	git_buf_free(&buf);
-
 	cl_assert(buf.size == 0);
 	cl_assert(buf.asize == 0);
 
 	/* empty buffer should be empty string */
 	cl_assert_strequal("", git_buf_cstr(&buf));
 	cl_assert(buf.size == 0);
-	cl_assert(buf.asize > 0);
+	/* cl_assert(buf.asize == 0); -- should not assume what git_buf does */
 
 	/* free should set us back to the beginning */
 	git_buf_free(&buf);
@@ -130,6 +130,27 @@ void test_core_buffer__2(void)
 	cl_assert_strequal("", git_buf_cstr(&buf));
 
 	git_buf_free(&buf);
+
+	/* test extracting data into buffer */
+	git_buf_puts(&buf, REP4("0123456789"));
+	cl_assert(git_buf_oom(&buf) == 0);
+
+	git_buf_copy_cstr(data, 100, &buf);
+	cl_assert_strequal(data, REP4("0123456789"));
+	git_buf_copy_cstr(data, 11, &buf);
+	cl_assert_strequal(data, "0123456789");
+	git_buf_copy_cstr(data, 3, &buf);
+	cl_assert_strequal(data, "01");
+	git_buf_copy_cstr(data, 1, &buf);
+	cl_assert_strequal(data, "");
+
+	git_buf_copy_cstr(data, 100, &buf);
+	cl_assert_strequal(data, REP4("0123456789"));
+
+	git_buf_free(&buf);
+
+	git_buf_copy_cstr(data, 100, &buf);
+	cl_assert_strequal(data, "");
 }
 
 /* let's do some tests with larger buffers to push our limits */
@@ -203,10 +224,7 @@ check_buf_append(
 	cl_assert(git_buf_oom(&tgt) == 0);
 	git_buf_puts(&tgt, data_b);
 	cl_assert(git_buf_oom(&tgt) == 0);
-	if (expected_data == NULL)
-		cl_assert(tgt.ptr == NULL);
-	else
-		cl_assert_strequal(expected_data, git_buf_cstr(&tgt));
+	cl_assert_strequal(expected_data, git_buf_cstr(&tgt));
 	cl_assert(tgt.size == expected_size);
 	if (expected_asize > 0)
 		cl_assert(tgt.asize == expected_asize);
@@ -277,15 +295,15 @@ void test_core_buffer__5(void)
 	 */
 
 	check_buf_append("abcdefgh", "/", "abcdefgh/", 9, 16);
-	check_buf_append("abcdefgh", "ijklmno", "abcdefghijklmno", 15, 24);
+	check_buf_append("abcdefgh", "ijklmno", "abcdefghijklmno", 15, 16);
 	check_buf_append("abcdefgh", "ijklmnop", "abcdefghijklmnop", 16, 24);
 	check_buf_append("0123456789", "0123456789",
 					 "01234567890123456789", 20, 24);
 	check_buf_append(REP16("x"), REP16("o"),
 					 REP16("x") REP16("o"), 32, 40);
 
-	check_buf_append(test_4096, "", test_4096, 4096, 6144);
-	check_buf_append(test_4096, test_4096, test_8192, 8192, 9216);
+	check_buf_append(test_4096, "", test_4096, 4096, 4104);
+	check_buf_append(test_4096, test_4096, test_8192, 8192, 9240);
 
 	/* check sequences of appends */
 	check_buf_append_abc("a", "b", "c",
@@ -335,13 +353,13 @@ void test_core_buffer__7(void)
 	b = git_buf_take_cstr(&a);
 
 	cl_assert_strequal("foo", b);
-	cl_assert_strequal(NULL, a.ptr);
+	cl_assert_strequal("", a.ptr);
 	git__free(b);
 
 	b = git_buf_take_cstr(&a);
 
 	cl_assert_strequal(NULL, b);
-	cl_assert_strequal(NULL, a.ptr);
+	cl_assert_strequal("", a.ptr);
 
 	git_buf_free(&a);
 }