git-apply: find offset fragments, and really apply them

This applies the fragments in memory, but doesn't actually
write the results out to the files yet. But we now do all the
difficult parts, the rest is just basically writing the
results out and updating the index.

apply.c

@@ -773,19 +773,20 @@ static int read_old_data(struct stat *st, const char *path, void *buf, unsigned
 
 static int find_offset(const char *buf, unsigned long size, const char *fragment, unsigned long fragsize, int line)
 {
-	unsigned long start;
+	int i;
+	unsigned long start, backwards, forwards;
 
 	if (fragsize > size)
 		return -1;
 
 	start = 0;
 	if (line > 1) {
-		line--;
 		unsigned long offset = 0;
-		while (start + offset <= size) {
+		i = line-1;
+		while (offset + fragsize <= size) {
 			if (buf[offset++] == '\n') {
 				start = offset;
-				if (!--line)
+				if (!--i)
 					break;
 			}
 		}
@@ -795,14 +796,61 @@ static int find_offset(const char *buf, unsigned long size, const char *fragment
 	if (!memcmp(buf + start, fragment, fragsize))
 		return start;
 
+	/*
+	 * There's probably some smart way to do this, but I'll leave
+	 * that to the smart and beautiful people. I'm simple and stupid.
+	 */
+	backwards = start;
+	forwards = start;
+	for (i = 0; ; i++) {
+		unsigned long try;
+		int n;
+
+		/* "backward" */
+		if (i & 1) {
+			if (!backwards) {
+				if (forwards + fragsize > size)
+					break;
+				continue;
+			}
+			do {
+				--backwards;
+			} while (backwards && buf[backwards-1] != '\n');
+			try = backwards;
+		} else {
+			while (forwards + fragsize <= size) {
+				if (buf[forwards++] == '\n')
+					break;
+			}
+			try = forwards;
+		}
+
+		if (try + fragsize > size)
+			continue;
+		if (memcmp(buf + try, fragment, fragsize))
+			continue;
+		n = (i >> 1)+1;
+		if (i & 1)
+			n = -n;
+		fprintf(stderr, "Fragment applied at offset %d\n", n);
+		return try;
+	}
+
 	/*
 	 * We should start searching forward and backward.
 	 */
 	return -1;
 }
 
-static int apply_one_fragment(char *buf, unsigned long *sizep, unsigned long *bufsizep, struct fragment *frag)
+struct buffer_desc {
+	char *buffer;
+	unsigned long size;
+	unsigned long alloc;
+};
+
+static int apply_one_fragment(struct buffer_desc *desc, struct fragment *frag)
 {
+	char *buf = desc->buffer;
 	const char *patch = frag->patch;
 	int offset, size = frag->size;
 	char *old = xmalloc(size);
@@ -848,9 +896,21 @@ static int apply_one_fragment(char *buf, unsigned long *sizep, unsigned long *bu
 		size -= len;
 	}
 
-	offset = find_offset(buf, *sizep, old, oldsize, frag->newpos);
+	offset = find_offset(buf, desc->size, old, oldsize, frag->newpos);
 	if (offset >= 0) {
-		printf("found at offset %d\n", offset);
+		int diff = newsize - oldsize;
+		unsigned long size = desc->size + diff;
+		unsigned long alloc = desc->alloc;
+
+		if (size > alloc) {
+			alloc = size + 8192;
+			desc->alloc = alloc;
+			buf = xrealloc(buf, alloc);
+			desc->buffer = buf;
+		}
+		desc->size = size;
+		memmove(buf + offset + newsize, buf + offset + oldsize, size - offset - newsize);
+		memcpy(buf + offset, new, newsize);
 		offset = 0;
 	}
 
@@ -859,12 +919,12 @@ static int apply_one_fragment(char *buf, unsigned long *sizep, unsigned long *bu
 	return offset;
 }
 
-static int apply_fragments(char *buf, unsigned long *sizep, unsigned long *bufsizep, struct patch *patch)
+static int apply_fragments(struct buffer_desc *desc, struct patch *patch)
 {
 	struct fragment *frag = patch->fragments;
 
 	while (frag) {
-		if (apply_one_fragment(buf, sizep, bufsizep, frag) < 0)
+		if (apply_one_fragment(desc, frag) < 0)
 			return error("patch failed: %s:%d", patch->old_name, frag->oldpos);
 		frag = frag->next;
 	}
@@ -872,18 +932,25 @@ static int apply_fragments(char *buf, unsigned long *sizep, unsigned long *bufsi
 
 static int apply_data(struct patch *patch, struct stat *st)
 {
-	unsigned long size, bufsize;
-	void *buf;
+	char *buf;
+	unsigned long size, alloc;
+	struct buffer_desc desc;
 
 	if (!patch->old_name || !patch->fragments)
 		return 0;
 	size = st->st_size;
-	bufsize = size + 16;
-	buf = xmalloc(bufsize);
-	if (read_old_data(st, patch->old_name, buf, bufsize) != size)
+	alloc = size + 8192;
+	buf = xmalloc(alloc);
+	if (read_old_data(st, patch->old_name, buf, alloc) != size)
 		return error("read of %s failed", patch->old_name);
-	if (apply_fragments(buf, &size, &bufsize, patch) < 0)
+
+	desc.size = size;
+	desc.alloc = alloc;
+	desc.buffer = buf;
+	if (apply_fragments(&desc, patch) < 0)
 		return -1;
+	patch->result = desc.buffer;
+	patch->resultsize = desc.size;
 	return 0;
 }