git-apply: parse the diff headers (both traditional and new)

.. and print out the information. This sets up all the pathname
information, and whether it's a new file, deleted file, rename,
copy or whatever.

It's slowly getting to the point where it all comes together,
and we can actually apply all the information that we've gathered.

Author: Linus Torvalds

apply.c

@@ -21,9 +21,18 @@
 static int merge_patch = 1;
 static const char apply_usage[] = "git-apply <patch>";
 
+/*
+ * Various "current state", notably line numbers and what
+ * file (and how) we're patching right now.. The "is_xxxx"
+ * things are flags, where -1 means "don't know yet".
+ */
 static int linenr = 1;
+static int old_mode, new_mode;
+static char *old_name, *new_name, *def_name;
+static int is_rename, is_copy, is_new, is_delete;
 
 #define CHUNKSIZE (8192)
+#define SLOP (16)
 
 static void *read_patch_file(int fd, unsigned long *sizep)
 {
@@ -48,6 +57,15 @@ static void *read_patch_file(int fd, unsigned long *sizep)
 		size += nr;
 	}
 	*sizep = size;
+
+	/*
+	 * Make sure that we have some slop in the buffer
+	 * so that we can do speculative "memcmp" etc, and
+	 * see to it that it is NUL-filled.
+	 */
+	if (alloc < size + SLOP)
+		buffer = xrealloc(buffer, size + SLOP);
+	memset(buffer + size, 0, SLOP);
 	return buffer;
 }
 
@@ -62,48 +80,200 @@ static unsigned long linelen(char *buffer, unsigned long size)
 	return len;
 }
 
-static int match_word(const char *line, const char *match)
+static int is_dev_null(const char *str)
+{
+	return !memcmp("/dev/null", str, 9) && isspace(str[9]);
+}
+
+static char * find_name(const char *line, char *def, int p_value)
 {
+	int len;
+	const char *start = line;
+	char *name;
+
 	for (;;) {
-		char c = *match++;
-		if (!c)
+		char c = *line;
+		if (isspace(c))
 			break;
-		if (*line++ != c)
-			return 0;
+		line++;
+		if (c == '/' && !--p_value)
+			start = line;
+	}
+	if (!start)
+		return def;
+	len = line - start;
+	if (!len)
+		return def;
+
+	/*
+	 * Generally we prefer the shorter name, especially
+	 * if the other one is just a variation of that with
+	 * something else tacked on to the end (ie "file.orig"
+	 * or "file~").
+	 */
+	if (def) {
+		int deflen = strlen(def);
+		if (deflen < len && !strncmp(start, def, deflen))
+			return def;
 	}
-	return *line == ' ';
+
+	name = xmalloc(len + 1);
+	memcpy(name, start, len);
+	name[len] = 0;
+	free(def);
+	return name;
+}
+
+/*
+ * Get the name etc info from the --/+++ lines of a traditional patch header
+ *
+ * NOTE! This hardcodes "-p1" behaviour in filename detection.
+ */
+static int parse_traditional_patch(const char *first, const char *second)
+{
+	int p_value = 1;
+	char *name;
+
+	first += 4;	// skip "--- "
+	second += 4;	// skip "+++ "
+	if (is_dev_null(first)) {
+		is_new = 1;
+		name = find_name(second, def_name, p_value);
+	} else if (is_dev_null(second)) {
+		is_delete = 1;
+		name = find_name(first, def_name, p_value);
+	} else {
+		name = find_name(first, def_name, p_value);
+		name = find_name(second, name, p_value);
+	}
+	if (!name)
+		die("unable to find filename in patch at line %d", linenr);
+	old_name = name;
+	new_name = name;
+}
+
+static int gitdiff_hdrend(const char *line)
+{
+	return -1;
+}
+
+static int gitdiff_oldname(const char *line)
+{
+	if (!old_name)
+		old_name = find_name(line, NULL, 1);
+	return 0;
+}
+
+static int gitdiff_newname(const char *line)
+{
+	if (!new_name)
+		new_name = find_name(line, NULL, 1);
+	return 0;
+}
+
+static int gitdiff_oldmode(const char *line)
+{
+	old_mode = strtoul(line, NULL, 8);
+	return 0;
+}
+
+static int gitdiff_newmode(const char *line)
+{
+	new_mode = strtoul(line, NULL, 8);
+	return 0;
+}
+
+static int gitdiff_delete(const char *line)
+{
+	is_delete = 1;
+	return gitdiff_oldmode(line);
+}
+
+static int gitdiff_newfile(const char *line)
+{
+	is_new = 1;
+	return gitdiff_newmode(line);
+}
+
+static int gitdiff_copysrc(const char *line)
+{
+	is_copy = 1;
+	old_name = find_name(line, NULL, 0);
+	return 0;
+}
+
+static int gitdiff_copydst(const char *line)
+{
+	is_copy = 1;
+	new_name = find_name(line, NULL, 0);
+	return 0;
+}
+
+static int gitdiff_renamesrc(const char *line)
+{
+	is_rename = 1;
+	old_name = find_name(line, NULL, 0);
+	return 0;
+}
+
+static int gitdiff_renamedst(const char *line)
+{
+	is_rename = 1;
+	new_name = find_name(line, NULL, 0);
+	return 0;
+}
+
+static int gitdiff_similarity(const char *line)
+{
+	return 0;
 }
 
 /* Verify that we recognize the lines following a git header */
-static int parse_git_header(char *line, unsigned int size)
+static int parse_git_header(char *line, int len, unsigned int size)
 {
-	unsigned long offset, len;
+	unsigned long offset;
+
+	/* A git diff has explicit new/delete information, so we don't guess */
+	is_new = 0;
+	is_delete = 0;
+
+	line += len;
+	size -= len;
+	linenr++;
+	for (offset = len ; size > 0 ; offset += len, size -= len, line += len, linenr++) {
+		static const struct opentry {
+			const char *str;
+			int (*fn)(const char *);
+		} optable[] = {
+			{ "@@ -", gitdiff_hdrend },
+			{ "--- ", gitdiff_oldname },
+			{ "+++ ", gitdiff_newname },
+			{ "old mode ", gitdiff_oldmode },
+			{ "new mode ", gitdiff_newmode },
+			{ "deleted file mode ", gitdiff_delete },
+			{ "new file mode ", gitdiff_newfile },
+			{ "copy from ", gitdiff_copysrc },
+			{ "copy to ", gitdiff_copydst },
+			{ "rename from ", gitdiff_renamesrc },
+			{ "rename to ", gitdiff_renamedst },
+			{ "similarity index ", gitdiff_similarity },
+		};
+		int i;
 
-	for (offset = 0 ; size > 0 ; offset += len, size -= len, line += len, linenr++) {
 		len = linelen(line, size);
-		if (!len)
-			break;
-		if (line[len-1] != '\n')
-			return -1;
-		if (len < 4)
+		if (!len || line[len-1] != '\n')
 			break;
-		if (!memcmp(line, "@@ -", 4))
-			return offset;
-		if (match_word(line, "new file mode"))
-			continue;
-		if (match_word(line, "deleted file mode"))
-			continue;
-		if (match_word(line, "copy"))
-			continue;
-		if (match_word(line, "rename"))
-			continue;
-		if (match_word(line, "similarity index"))
-			continue;
-		break;
+		for (i = 0; i < sizeof(optable) / sizeof(optable[0]); i++) {
+			const struct opentry *p = optable + i;
+			int oplen = strlen(p->str);
+			if (len < oplen || memcmp(p->str, line, oplen))
+				continue;
+			if (p->fn(line + oplen) < 0)
+				return offset;
+		}
 	}
 
-	/* We want either a patch _or_ something real */
-	return offset ? :-1;
+	return offset;
 }
 
 static int parse_num(const char *line, int len, int offset, const char *expect, unsigned long *p)
@@ -159,6 +329,10 @@ static int find_header(char *line, unsigned long size, int *hdrsize)
 {
 	unsigned long offset, len;
 
+	is_rename = is_copy = 0;
+	is_new = is_delete = -1;
+	old_mode = new_mode = -1;
+	def_name = old_name = new_name = NULL;
 	for (offset = 0; size > 0; offset += len, size -= len, line += len, linenr++) {
 		unsigned long nextlen;
 
@@ -190,11 +364,11 @@ static int find_header(char *line, unsigned long size, int *hdrsize)
 		 * or mode change, so we handle that specially
 		 */
 		if (!memcmp("diff --git ", line, 11)) {
-			int git_hdr_len = parse_git_header(line + len, size - len);
+			int git_hdr_len = parse_git_header(line, len, size);
 			if (git_hdr_len < 0)
 				continue;
 
-			*hdrsize = len + git_hdr_len;
+			*hdrsize = git_hdr_len;
 			return offset;
 		}
 
@@ -212,6 +386,7 @@ static int find_header(char *line, unsigned long size, int *hdrsize)
 			continue;
 
 		/* Ok, we'll consider it a patch */
+		parse_traditional_patch(line, line+len);
 		*hdrsize = len + nextlen;
 		linenr += 2;
 		return offset;
@@ -237,6 +412,11 @@ static int apply_fragment(char *line, unsigned long size)
 	oldlines = pos[1];
 	newlines = pos[3];
 
+	if (is_new < 0 && (pos[0] || oldlines))
+		is_new = 0;
+	if (is_delete < 0 && (pos[1] || newlines))
+		is_delete = 0;
+
 	/* Parse the thing.. */
 	line += len;
 	size -= len;
@@ -294,6 +474,12 @@ static int apply_chunk(char *buffer, unsigned long size)
 	header = buffer + offset;
 
 printf("Found header:\n%.*s\n\n", hdrsize, header);
+printf("Rename: %d\n", is_rename);
+printf("Copy:   %d\n", is_copy);
+printf("New:    %d\n", is_new);
+printf("Delete: %d\n", is_delete);
+printf("Mode:   %o->%o\n", old_mode, new_mode);
+printf("Name:   '%s'->'%s'\n", old_name, new_name);
 
 	patch = header + hdrsize;
 	patchsize = apply_single_patch(patch, size - offset - hdrsize);