Extend git_buf with new utility functions and unit tests.

Add new functions to git_buf for:
* initializing a buffer from a string
* joining one or more strings onto a buffer with separators
* swapping two buffers in place
* extracting data from a git_buf (leaving it empty)

Also, make git_buf_free leave a git_buf back in its initted state,
and slightly tweak buffer allocation sizes and thresholds.

Finally, port unit tests to clay and extend with lots of new tests
for the various git_buf functions.

src/buffer.c

@@ -9,7 +9,7 @@
 #include <stdarg.h>
 
 #define ENSURE_SIZE(b, d) \
-	if ((ssize_t)(d) >= buf->asize && git_buf_grow(b, (d)) < GIT_SUCCESS)\
+	if ((ssize_t)(d) > buf->asize && git_buf_grow(b, (d)) < GIT_SUCCESS)\
 		return;
 
 int git_buf_grow(git_buf *buf, size_t target_size)
@@ -19,6 +19,9 @@ int git_buf_grow(git_buf *buf, size_t target_size)
 	if (buf->asize < 0)
 		return GIT_ENOMEM;
 
+	if (target_size <= (size_t)buf->asize)
+		return GIT_SUCCESS;
+
 	if (buf->asize == 0)
 		buf->asize = target_size;
 
@@ -27,6 +30,9 @@ int git_buf_grow(git_buf *buf, size_t target_size)
 	while (buf->asize < (int)target_size)
 		buf->asize = (buf->asize << 1) - (buf->asize >> 1);
 
+	/* round allocation up to multiple of 8 */
+	buf->asize = (buf->asize + 7) & ~7;
+
 	new_ptr = git__realloc(buf->ptr, buf->asize);
 	if (!new_ptr) {
 		buf->asize = -1;
@@ -42,6 +48,22 @@ int git_buf_oom(const git_buf *buf)
 	return (buf->asize < 0);
 }
 
+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);
+		memmove(buf->ptr, data, len);
+		buf->size = len;
+	}
+}
+
+void git_buf_sets(git_buf *buf, const char *string)
+{
+	git_buf_set(buf, string, string ? strlen(string) : 0);
+}
+
 void git_buf_putc(git_buf *buf, char c)
 {
 	ENSURE_SIZE(buf, buf->size + 1);
@@ -51,13 +73,14 @@ void git_buf_putc(git_buf *buf, char c)
 void git_buf_put(git_buf *buf, const char *data, size_t len)
 {
 	ENSURE_SIZE(buf, buf->size + len);
-	memcpy(buf->ptr + buf->size, data, len);
+	memmove(buf->ptr + buf->size, data, len);
 	buf->size += len;
 }
 
 void git_buf_puts(git_buf *buf, const char *string)
 {
-	git_buf_put(buf, string, strlen(string));
+	if (string != NULL)
+		git_buf_put(buf, string, strlen(string));
 }
 
 void git_buf_printf(git_buf *buf, const char *format, ...)
@@ -88,7 +111,8 @@ 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)
+	if (buf->size + 1 > buf->asize &&
+		git_buf_grow(buf, buf->size + 1) < GIT_SUCCESS)
 		return NULL;
 
 	buf->ptr[buf->size] = '\0';
@@ -97,7 +121,14 @@ const char *git_buf_cstr(git_buf *buf)
 
 void git_buf_free(git_buf *buf)
 {
-	git__free(buf->ptr);
+	if (buf) {
+		if (buf->ptr) {
+			git__free(buf->ptr);
+			buf->ptr = NULL;
+		}
+		buf->asize = 0;
+		buf->size = 0;
+	}
 }
 
 void git_buf_clear(git_buf *buf)
@@ -107,7 +138,104 @@ void git_buf_clear(git_buf *buf)
 
 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;
+	if (end > buf->ptr && end <= buf->ptr + buf->size) {
+		size_t consumed = end - buf->ptr;
+		memmove(buf->ptr, end, buf->size - consumed);
+		buf->size -= consumed;
+	}
+}
+
+void git_buf_swap(git_buf *buf_a, git_buf *buf_b)
+{
+	git_buf t = *buf_a;
+	*buf_a = *buf_b;
+	*buf_b = t;
 }
+
+char *git_buf_take_cstr(git_buf *buf)
+{
+	char *data = NULL;
+
+	if (buf->ptr == NULL)
+		return NULL;
+
+	if (buf->size + 1 > buf->asize &&
+		git_buf_grow(buf, buf->size + 1) < GIT_SUCCESS)
+		return NULL;
+
+	data = buf->ptr;
+	data[buf->size] = '\0';
+
+	buf->ptr = NULL;
+	buf->asize = 0;
+	buf->size = 0;
+
+	return data;
+}
+
+void git_buf_join(git_buf *buf, char separator, int nbuf, ...)
+{
+	/* Make two passes to avoid multiple reallocation */
+
+	va_list ap;
+	int i;
+	int total_size = 0;
+	char *out;
+
+	if (buf->size > 0 && buf->ptr[buf->size - 1] != separator)
+		++total_size; /* space for initial separator */
+
+	va_start(ap, nbuf);
+	for (i = 0; i < nbuf; ++i) {
+		const char* segment;
+		int segment_len;
+
+		segment = va_arg(ap, const char *);
+		if (!segment)
+			continue;
+
+		segment_len = strlen(segment);
+		total_size += segment_len;
+		if (segment_len == 0 || segment[segment_len - 1] != separator)
+			++total_size; /* space for separator */
+	}
+	va_end(ap);
+
+	ENSURE_SIZE(buf, buf->size + total_size);
+
+	out = buf->ptr + buf->size;
+
+	/* append separator to existing buf if needed */
+	if (buf->size > 0 && out[-1] != separator)
+		*out++ = separator;
+
+	va_start(ap, nbuf);
+	for (i = 0; i < nbuf; ++i) {
+		const char* segment;
+		int segment_len;
+
+		segment = va_arg(ap, const char *);
+		if (!segment)
+			continue;
+
+		/* skip leading separators */
+		if (out > buf->ptr && out[-1] == separator)
+			while (*segment == separator) segment++;
+
+		/* copy over next buffer */
+		segment_len = strlen(segment);
+		if (segment_len > 0) {
+			memmove(out, segment, segment_len);
+			out += segment_len;
+		}
+
+		/* append trailing separator (except for last item) */
+		if (i < nbuf - 1 && out > buf->ptr && out[-1] != separator)
+			*out++ = separator;
+	}
+	va_end(ap);
+
+	/* set size based on num characters actually written */
+	buf->size = out - buf->ptr;
+}
+

src/buffer.h

@@ -17,15 +17,30 @@ typedef struct {
 #define GIT_BUF_INIT {NULL, 0, 0}
 
 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);
+
+/**
+ * Any function that writes to a git_buf can fail due to memory allocation
+ * issues.  If one fails, the git_buf will be marked with an OOM error and
+ * further calls to modify the buffer will fail.  You just check
+ * git_buf_oom() at the end of your sequence and it will be true if you ran
+ * out of memory at any point with that buffer.
+ */
 int git_buf_oom(const git_buf *buf);
+
+void git_buf_set(git_buf *buf, const char *data, size_t len);
+void git_buf_sets(git_buf *buf, const char *string);
 void git_buf_putc(git_buf *buf, char c);
 void git_buf_put(git_buf *buf, const char *data, size_t len);
 void git_buf_puts(git_buf *buf, const char *string);
 void git_buf_printf(git_buf *buf, const char *format, ...) GIT_FORMAT_PRINTF(2, 3);
-const char *git_buf_cstr(git_buf *buf);
-void git_buf_free(git_buf *buf);
 void git_buf_clear(git_buf *buf);
 void git_buf_consume(git_buf *buf, const char *end);
+void git_buf_join(git_buf *buf, char separator, int nbuf, ...);
+
+const char *git_buf_cstr(git_buf *buf);
+char *git_buf_take_cstr(git_buf *buf);
 
 #define git_buf_PUTS(buf, str) git_buf_put(buf, str, sizeof(str) - 1)
 

tests-clay/clay_libgit2.h

@@ -25,4 +25,20 @@
  */
 #define cl_git_fail(expr) cl_must_fail(expr)
 
+/**
+ * Wrapper for string comparison that knows about nulls.
+ */
+#define cl_assert_strequal(a,b) \
+	cl_assert_strequal_internal(a,b,__FILE__,__LINE__)
+
+GIT_INLINE(void) cl_assert_strequal_internal(const char *a, const char *b, const char *file, int line)
+{
+	int match = (a == NULL || b == NULL) ? (a == b) : (strcmp(a, b) == 0);
+	if (!match) {
+		char buf[4096];
+		snprintf(buf, 4096, "'%s' != '%s'", a, b);
+		clay__assert(0, file, line, buf, "Strings do not match", 1);
+	}
+}
+
 #endif