patch: replace it with toybox's implementation

Signed-off-by: Rob Landley <rob@landley.net>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 555 insertions, 270 deletions

diff --git a/editors/patch.c b/editors/patch.c
index 62477af16..7f3234e66 100644
--- a/editors/patch.c
+++ b/editors/patch.c
@@ -1,306 +1,591 @@
-/* vi: set sw=4 ts=4: */
-/*
- *  busybox patch applet to handle the unified diff format.
- *  Copyright (C) 2003 Glenn McGrath
+/* Adapted from toybox's patch. */
+
+/* vi: set sw=4 ts=4:
+ *
+ * patch.c - Apply a "universal" diff.
  *
- *  Licensed under the GPL v2 or later, see the file LICENSE in this tarball.
+ * Copyright 2007 Rob Landley <rob@landley.net>
  *
- *  This applet is written to work with patches generated by GNU diff,
- *  where there is equivalent functionality busybox patch shall behave
- *  as per GNU patch.
+ * see http://www.opengroup.org/onlinepubs/009695399/utilities/patch.html
+ * (But only does -u, because who still cares about "ed"?)
  *
- *  There is a SUSv3 specification for patch, however it looks to be
- *  incomplete, it doesnt even mention unified diff format.
- *  http://www.opengroup.org/onlinepubs/007904975/utilities/patch.html
+ * TODO:
+ * -b backup
+ * -l treat all whitespace as a single space
+ * -N ignore already applied
+ * -d chdir first
+ * -D define wrap #ifdef and #ifndef around changes
+ * -o outfile output here instead of in place
+ * -r rejectfile write rejected hunks to this file
  *
- *  Issues
- *   - Non-interactive
- *   - Patches must apply cleanly or patch (not just one hunk) will fail.
- *   - Reject file isnt saved
- */
+ * -E remove empty files --remove-empty-files
+ * -f force (no questions asked)
+ * -F fuzz (number, default 2)
+ * [file] which file to patch
+
+USE_PATCH(NEWTOY(patch, USE_TOYBOX_DEBUG("x")"up#i:R", TOYFLAG_USR|TOYFLAG_BIN))
+
+config PATCH
+	bool "patch"
+	default y
+	help
+	  usage: patch [-i file] [-p depth] [-Ru]
+
+	  Apply a unified diff to one or more files.
 
+	  -i	Input file (defaults=stdin)
+	  -p	number of '/' to strip from start of file paths (default=all)
+	  -R	Reverse patch.
+	  -u	Ignored (only handles "unified" diffs)
+
+	  This version of patch only handles unified diffs, and only modifies
+	  a file when all all hunks to that file apply.  Patch prints failed
+	  hunks to stderr, and exits with nonzero status if any hunks fail.
+
+	  A file compared against /dev/null (or with a date <= the epoch) is
+	  created/deleted as appropriate.
+*/
 #include "libbb.h"
 
-static unsigned copy_lines(FILE *src_stream, FILE *dst_stream, unsigned lines_count)
+struct double_list {
+	struct double_list *next;
+	struct double_list *prev;
+	char *data;
+};
+
+// Return the first item from the list, advancing the list (which must be called
+// as &list)
+static
+void *TOY_llist_pop(void *list)
 {
-	while (src_stream && lines_count) {
-		char *line;
-		line = xmalloc_fgets(src_stream);
-		if (line == NULL) {
-			break;
-		}
-		if (fputs(line, dst_stream) == EOF) {
-			bb_perror_msg_and_die("error writing to new file");
+	// I'd use a void ** for the argument, and even accept the typecast in all
+	// callers as documentation you need the &, except the stupid compiler
+	// would then scream about type-punned pointers.  Screw it.
+	void **llist = (void **)list;
+	void **next = (void **)*llist;
+	*llist = *next;
+
+	return (void *)next;
+}
+
+// Free all the elements of a linked list
+// if freeit!=NULL call freeit() on each element before freeing it.
+static
+void TOY_llist_free(void *list, void (*freeit)(void *data))
+{
+	while (list) {
+		void *pop = TOY_llist_pop(&list);
+		if (freeit) freeit(pop);
+		else free(pop);
+
+		// End doubly linked list too.
+		if (list==pop) break;
+	}
+}
+
+// Add an entry to the end off a doubly linked list
+static
+struct double_list *dlist_add(struct double_list **list, char *data)
+{
+	struct double_list *line = xmalloc(sizeof(struct double_list));
+
+	line->data = data;
+	if (*list) {
+		line->next = *list;
+		line->prev = (*list)->prev;
+		(*list)->prev->next = line;
+		(*list)->prev = line;
+	} else *list = line->next = line->prev = line;
+
+	return line;
+}
+
+// Ensure entire path exists.
+// If mode != -1 set permissions on newly created dirs.
+// Requires that path string be writable (for temporary null terminators).
+static
+void xmkpath(char *path, int mode)
+{
+	char *p, old;
+	mode_t mask;
+	int rc;
+	struct stat st;
+
+	for (p = path; ; p++) {
+		if (!*p || *p == '/') {
+			old = *p;
+			*p = rc = 0;
+			if (stat(path, &st) || !S_ISDIR(st.st_mode)) {
+				if (mode != -1) {
+					mask = umask(0);
+					rc = mkdir(path, mode);
+					umask(mask);
+				} else rc = mkdir(path, 0777);
+			}
+			*p = old;
+			if(rc) bb_perror_msg_and_die("mkpath '%s'", path);
 		}
-		free(line);
-		lines_count--;
+		if (!*p) break;
+	}
+}
+
+// Slow, but small.
+static
+char *get_rawline(int fd, long *plen, char end)
+{
+	char c, *buf = NULL;
+	long len = 0;
+
+	for (;;) {
+		if (1>read(fd, &c, 1)) break;
+		if (!(len & 63)) buf=xrealloc(buf, len+65);
+		if ((buf[len++]=c) == end) break;
+	}
+	if (buf) buf[len]=0;
+	if (plen) *plen = len;
+
+	return buf;
+}
+
+static
+char *get_line(int fd)
+{
+	long len;
+	char *buf = get_rawline(fd, &len, '\n');
+
+	if (buf && buf[--len]=='\n') buf[len]=0;
+
+	return buf;
+}
+
+// Copy the rest of in to out and close both files.
+static
+void xsendfile(int in, int out)
+{
+	long len;
+	char buf[4096];
+
+	if (in<0) return;
+	for (;;) {
+		len = safe_read(in, buf, 4096);
+		if (len<1) break;
+		xwrite(out, buf, len);
+	}
+}
+
+// Copy the rest of the data and replace the original with the copy.
+static
+void replace_tempfile(int fdin, int fdout, char **tempname)
+{
+	char *temp = xstrdup(*tempname);
+
+	temp[strlen(temp)-6]=0;
+	if (fdin != -1) {
+		xsendfile(fdin, fdout);
+		xclose(fdin);
 	}
-	return lines_count;
+	xclose(fdout);
+	rename(*tempname, temp);
+	free(*tempname);
+	free(temp);
+	*tempname = NULL;
+}
+
+// Open a temporary file to copy an existing file into.
+static
+int copy_tempfile(int fdin, char *name, char **tempname)
+{
+	struct stat statbuf;
+	int fd;
+
+	*tempname = xasprintf("%sXXXXXX", name);
+	fd = mkstemp(*tempname);
+	if(-1 == fd) bb_perror_msg_and_die("no temp file");
+
+	// Set permissions of output file
+	fstat(fdin, &statbuf);
+	fchmod(fd, statbuf.st_mode);
+
+	return fd;
+}
+
+// Abort the copy and delete the temporary file.
+static
+void delete_tempfile(int fdin, int fdout, char **tempname)
+{
+	close(fdin);
+	close(fdout);
+	unlink(*tempname);
+	free(*tempname);
+	*tempname = NULL;
+}
+
+
+
+struct globals {
+	char *infile;
+	long prefix;
+
+	struct double_list *current_hunk;
+	long oldline, oldlen, newline, newlen, linenum;
+	int context, state, filein, fileout, filepatch, hunknum;
+	char *tempname;
+
+	// was toys.foo:
+	int exitval;
+};
+#define TT (*ptr_to_globals)
+#define INIT_TT() do { \
+	SET_PTR_TO_GLOBALS(xzalloc(sizeof(TT))); \
+} while (0)
+
+
+//bbox had: "p:i:RN"
+#define FLAG_STR "Rup:i:x"
+/* FLAG_REVERSE must be == 1! Code uses this fact. */
+#define FLAG_REVERSE (1 << 0)
+#define FLAG_u       (1 << 1)
+#define FLAG_PATHLEN (1 << 2)
+#define FLAG_INPUT   (1 << 3)
+//non-standard:
+#define FLAG_DEBUG   (1 << 4)
+
+// Dispose of a line of input, either by writing it out or discarding it.
+
+// state < 2: just free
+// state = 2: write whole line to stderr
+// state = 3: write whole line to fileout
+// state > 3: write line+1 to fileout when *line != state
+
+#define PATCH_DEBUG (option_mask32 & FLAG_DEBUG)
+
+static void do_line(void *data)
+{
+	struct double_list *dlist = (struct double_list *)data;
+
+	if (TT.state>1 && *dlist->data != TT.state)
+		fdprintf(TT.state == 2 ? 2 : TT.fileout,
+			"%s\n", dlist->data+(TT.state>3 ? 1 : 0));
+
+	if (PATCH_DEBUG) fdprintf(2, "DO %d: %s\n", TT.state, dlist->data);
+
+	free(dlist->data);
+	free(data);
+}
+
+static void finish_oldfile(void)
+{
+	if (TT.tempname) replace_tempfile(TT.filein, TT.fileout, &TT.tempname);
+	TT.fileout = TT.filein = -1;
 }
 
-/* If patch_level is -1 it will remove all directory names
- * char *line must be greater than 4 chars
- * returns NULL if the file doesnt exist or error
- * returns malloc'ed filename
- * NB: frees 1st argument!
- */
-static char *extract_filename(char *line, int patch_level, const char *pat)
+static void fail_hunk(void)
 {
-	char *temp = NULL, *filename_start_ptr = line + 4;
-
-	if (strncmp(line, pat, 4) == 0) {
-		/* Terminate string at end of source filename */
-		line[strcspn(line, "\t\n\r")] = '\0';
-
-		/* Skip over (patch_level) number of leading directories */
-		while (patch_level--) {
-			temp = strchr(filename_start_ptr, '/');
-			if (!temp)
-				break;
-			filename_start_ptr = temp + 1;
+	if (!TT.current_hunk) return;
+	TT.current_hunk->prev->next = 0;
+
+	fdprintf(2, "Hunk %d FAILED %ld/%ld.\n", TT.hunknum, TT.oldline, TT.newline);
+	TT.exitval = 1;
+
+	// If we got to this point, we've seeked to the end.  Discard changes to
+	// this file and advance to next file.
+
+	TT.state = 2;
+	TOY_llist_free(TT.current_hunk, do_line);
+	TT.current_hunk = NULL;
+	delete_tempfile(TT.filein, TT.fileout, &TT.tempname);
+	TT.state = 0;
+}
+
+// Given a hunk of a unified diff, make the appropriate change to the file.
+// This does not use the location information, but instead treats a hunk
+// as a sort of regex.  Copies data from input to output until it finds
+// the change to be made, then outputs the changed data and returns.
+// (Finding EOF first is an error.)  This is a single pass operation, so
+// multiple hunks must occur in order in the file.
+
+static int apply_one_hunk(void)
+{
+	struct double_list *plist, *buf = NULL, *check;
+	int matcheof = 0, reverse = option_mask32 & FLAG_REVERSE, backwarn = 0;
+
+	// Break doubly linked list so we can use singly linked traversal function.
+	TT.current_hunk->prev->next = NULL;
+
+	// Match EOF if there aren't as many ending context lines as beginning
+	for (plist = TT.current_hunk; plist; plist = plist->next) {
+		if (plist->data[0]==' ') matcheof++;
+		else matcheof = 0;
+		if (PATCH_DEBUG) fdprintf(2, "HUNK:%s\n", plist->data);
+	}
+	matcheof = matcheof < TT.context;
+
+	if (PATCH_DEBUG) fdprintf(2,"MATCHEOF=%c\n", matcheof ? 'Y' : 'N');
+
+	// Loop through input data searching for this hunk.  Match all context
+	// lines and all lines to be removed until we've found the end of a
+	// complete hunk.
+	plist = TT.current_hunk;
+	buf = NULL;
+	if (TT.context) for (;;) {
+		char *data = get_line(TT.filein);
+
+		TT.linenum++;
+
+		// Figure out which line of hunk to compare with next.  (Skip lines
+		// of the hunk we'd be adding.)
+		while (plist && *plist->data == "+-"[reverse]) {
+			if (data && !strcmp(data, plist->data+1)) {
+				if (!backwarn) {
+					fdprintf(2,"Possibly reversed hunk %d at %ld\n",
+						TT.hunknum, TT.linenum);
+					backwarn++;
+				}
+			}
+			plist = plist->next;
 		}
-		temp = xstrdup(filename_start_ptr);
+
+		// Is this EOF?
+		if (!data) {
+			if (PATCH_DEBUG) fdprintf(2, "INEOF\n");
+
+			// Does this hunk need to match EOF?
+			if (!plist && matcheof) break;
+
+			// File ended before we found a place for this hunk.
+			fail_hunk();
+			goto done;
+		} else if (PATCH_DEBUG) fdprintf(2, "IN: %s\n", data);
+		check = dlist_add(&buf, data);
+
+		// Compare this line with next expected line of hunk.
+		// todo: teach the strcmp() to ignore whitespace.
+
+		// A match can fail because the next line doesn't match, or because
+		// we hit the end of a hunk that needed EOF, and this isn't EOF.
+
+		// If match failed, flush first line of buffered data and
+		// recheck buffered data for a new match until we find one or run
+		// out of buffer.
+
+		for (;;) {
+			if (!plist || strcmp(check->data, plist->data+1)) {
+				// Match failed.  Write out first line of buffered data and
+				// recheck remaining buffered data for a new match.
+
+				if (PATCH_DEBUG)
+					fdprintf(2, "NOT: %s\n", plist->data);
+
+				TT.state = 3;
+				check = TOY_llist_pop(&buf);
+				check->prev->next = buf;
+				buf->prev = check->prev;
+				do_line(check);
+				plist = TT.current_hunk;
+
+				// If we've reached the end of the buffer without confirming a
+				// match, read more lines.
+				if (check==buf) {
+					buf = 0;
+					break;
+				}
+				check = buf;
+			} else {
+				if (PATCH_DEBUG)
+					fdprintf(2, "MAYBE: %s\n", plist->data);
+				// This line matches.  Advance plist, detect successful match.
+				plist = plist->next;
+				if (!plist && !matcheof) goto out;
+				check = check->next;
+				if (check == buf) break;
+			}
+		}
+	}
+out:
+	// We have a match.  Emit changed data.
+	TT.state = "-+"[reverse];
+	TOY_llist_free(TT.current_hunk, do_line);
+	TT.current_hunk = NULL;
+	TT.state = 1;
+done:
+	if (buf) {
+		buf->prev->next = NULL;
+		TOY_llist_free(buf, do_line);
 	}
-	free(line);
-	return temp;
+
+	return TT.state;
 }
 
+// Read a patch file and find hunks, opening/creating/deleting files.
+// Call apply_one_hunk() on each hunk.
+
+// state 0: Not in a hunk, look for +++.
+// state 1: Found +++ file indicator, look for @@
+// state 2: In hunk: counting initial context lines
+// state 3: In hunk: getting body
+
 int patch_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int patch_main(int argc UNUSED_PARAM, char **argv)
 {
-	struct stat saved_stat;
-	char *patch_line;
-	FILE *patch_file;
-	int patch_level;
-	int ret = 0;
-	char plus = '+';
-	unsigned opt;
-	enum {
-		OPT_R = (1 << 2),
-		OPT_N = (1 << 3),
-		/*OPT_f = (1 << 4), ignored */
-		/*OPT_E = (1 << 5), ignored, this is the default */
-		/*OPT_g = (1 << 6), ignored */
-		OPT_dry_run = (1 << 7) * ENABLE_LONG_OPTS,
-	};
-
-	xfunc_error_retval = 2;
-	{
-		const char *p = "-1";
-		const char *i = "-"; /* compat */
-#if ENABLE_LONG_OPTS
-		static const char patch_longopts[] ALIGN1 =
-			"strip\0"                 Required_argument "p"
-			"input\0"                 Required_argument "i"
-			"reverse\0"               No_argument       "R"
-			"forward\0"               No_argument       "N"
-		/* "Assume user knows what [s]he is doing, do not ask any questions": */
-			"force\0"                 No_argument       "f" /*ignored*/
-# if ENABLE_DESKTOP
-			"remove-empty-files\0"    No_argument       "E" /*ignored*/
-		/* "Controls actions when a file is under RCS or SCCS control,
-		 * and does not exist or is read-only and matches the default version,
-		 * or when a file is under ClearCase control and does not exist..."
-		 * IOW: rather obscure option.
-		 * But Gentoo's portage does use -g0 */
-			"get\0"                   Required_argument "g" /*ignored*/
-# endif
-			"dry-run\0"               No_argument       "\xfd"
-# if ENABLE_DESKTOP
-			"backup-if-mismatch\0"    No_argument       "\xfe" /*ignored*/
-			"no-backup-if-mismatch\0" No_argument       "\xff" /*ignored*/
-# endif
-			;
-		applet_long_options = patch_longopts;
-#endif
-		/* -f,-E,-g are ignored */
-		opt = getopt32(argv, "p:i:RN""fEg:", &p, &i, NULL);
-		if (opt & OPT_R)
-			plus = '-';
-		patch_level = xatoi(p); /* can be negative! */
-		patch_file = xfopen_stdin(i);
-	}
+	int opts;
+	int reverse, state = 0;
+	char *oldname = NULL, *newname = NULL;
+	char *opt_p, *opt_i;
+
+	INIT_TT();
+
+	opts = getopt32(argv, FLAG_STR, &opt_p, &opt_i);
+	reverse = opts & FLAG_REVERSE;
+	TT.prefix = (opts & FLAG_PATHLEN) ? xatoi(opt_p) : 0; // can be negative!
+	if (opts & FLAG_INPUT) TT.filepatch = xopen(opt_i, O_RDONLY);
+	TT.filein = TT.fileout = -1;
 
-	patch_line = xmalloc_fgetline(patch_file);
-	while (patch_line) {
-		FILE *src_stream;
-		FILE *dst_stream;
-		//char *old_filename;
-		char *new_filename;
-		char *backup_filename = NULL;
-		unsigned src_cur_line = 1;
-		unsigned dst_cur_line = 0;
-		unsigned dst_beg_line;
-		unsigned bad_hunk_count = 0;
-		unsigned hunk_count = 0;
-		smallint copy_trailing_lines_flag = 0;
-
-		/* Skip everything upto the "---" marker
-		 * No need to parse the lines "Only in <dir>", and "diff <args>"
-		 */
-		do {
-			/* Extract the filename used before the patch was generated */
-			new_filename = extract_filename(patch_line, patch_level, "--- ");
-			// was old_filename above
-			patch_line = xmalloc_fgetline(patch_file);
-			if (!patch_line) goto quit;
-		} while (!new_filename);
-		free(new_filename); // "source" filename is irrelevant
-
-		new_filename = extract_filename(patch_line, patch_level, "+++ ");
-		if (!new_filename) {
-			bb_error_msg_and_die("invalid patch");
+	// Loop through the lines in the patch
+	for(;;) {
+		char *patchline;
+
+		patchline = get_line(TT.filepatch);
+		if (!patchline) break;
+
+		// Other versions of patch accept damaged patches,
+		// so we need to also.
+		if (!*patchline) {
+			free(patchline);
+			patchline = xstrdup(" ");
 		}
 
-		/* Get access rights from the file to be patched */
-		if (stat(new_filename, &saved_stat) != 0) {
-			char *slash = strrchr(new_filename, '/');
-			if (slash) {
-				/* Create leading directories */
-				*slash = '\0';
-				bb_make_directory(new_filename, -1, FILEUTILS_RECUR);
-				*slash = '/';
+		// Are we assembling a hunk?
+		if (state >= 2) {
+			if (*patchline==' ' || *patchline=='+' || *patchline=='-') {
+				dlist_add(&TT.current_hunk, patchline);
+
+				if (*patchline != '+') TT.oldlen--;
+				if (*patchline != '-') TT.newlen--;
+
+				// Context line?
+				if (*patchline==' ' && state==2) TT.context++;
+				else state=3;
+
+				// If we've consumed all expected hunk lines, apply the hunk.
+
+				if (!TT.oldlen && !TT.newlen) state = apply_one_hunk();
+				continue;
 			}
-			src_stream = NULL;
-			saved_stat.st_mode = 0644;
-		} else if (!(opt & OPT_dry_run)) {
-			backup_filename = xasprintf("%s.orig", new_filename);
-			xrename(new_filename, backup_filename);
-			src_stream = xfopen_for_read(backup_filename);
-		} else
-			src_stream = xfopen_for_read(new_filename);
-
-		if (opt & OPT_dry_run) {
-			dst_stream = xfopen_for_write("/dev/null");
-		} else {
-			dst_stream = xfopen_for_write(new_filename);
-			fchmod(fileno(dst_stream), saved_stat.st_mode);
+			fail_hunk();
+			state = 0;
+			continue;
 		}
 
-		printf("patching file %s\n", new_filename);
-
-		/* Handle all hunks for this file */
-		patch_line = xmalloc_fgets(patch_file);
-		while (patch_line) {
-			unsigned count;
-			unsigned src_beg_line;
-			unsigned hunk_offset_start;
-			unsigned src_last_line = 1;
-			unsigned dst_last_line = 1;
-
-			if ((sscanf(patch_line, "@@ -%d,%d +%d,%d", &src_beg_line, &src_last_line, &dst_beg_line, &dst_last_line) < 3)
-			 && (sscanf(patch_line, "@@ -%d +%d,%d", &src_beg_line, &dst_beg_line, &dst_last_line) < 2)
-			) {
-				/* No more hunks for this file */
-				break;
-			}
-			if (plus != '+') {
-				/* reverse patch */
-				unsigned tmp = src_last_line;
-				src_last_line = dst_last_line;
-				dst_last_line = tmp;
-				tmp = src_beg_line;
-				src_beg_line = dst_beg_line;
-				dst_beg_line = tmp;
+		// Open a new file?
+		if (!strncmp("--- ", patchline, 4) || !strncmp("+++ ", patchline, 4)) {
+			char *s, **name = reverse ? &newname : &oldname;
+			int i;
+
+			if (*patchline == '+') {
+				name = reverse ? &oldname : &newname;
+				state = 1;
 			}
-			hunk_count++;
-
-			if (src_beg_line && dst_beg_line) {
-				/* Copy unmodified lines upto start of hunk */
-				/* src_beg_line will be 0 if it's a new file */
-				count = src_beg_line - src_cur_line;
-				if (copy_lines(src_stream, dst_stream, count)) {
-					bb_error_msg_and_die("bad src file");
-				}
-				src_cur_line += count;
-				dst_cur_line += count;
-				copy_trailing_lines_flag = 1;
+
+			free(*name);
+			finish_oldfile();
+
+			// Trim date from end of filename (if any).  We don't care.
+			for (s = patchline+4; *s && *s!='\t'; s++)
+				if (*s=='\\' && s[1]) s++;
+			i = atoi(s);
+			if (i>1900 && i<=1970)
+				*name = xstrdup("/dev/null");
+			else {
+				*s = 0;
+				*name = xstrdup(patchline+4);
 			}
-			src_last_line += hunk_offset_start = src_cur_line;
-			dst_last_line += dst_cur_line;
-
-			while (1) {
-				free(patch_line);
-				patch_line = xmalloc_fgets(patch_file);
-				if (patch_line == NULL)
-					break; /* EOF */
-				if (!*patch_line) {
-					/* whitespace-damaged patch with "" lines */
-					free(patch_line);
-					patch_line = xstrdup(" ");
+
+			// We defer actually opening the file because svn produces broken
+			// patches that don't signal they want to create a new file the
+			// way the patch man page says, so you have to read the first hunk
+			// and _guess_.
+
+		// Start a new hunk?
+		} else if (state == 1 && !strncmp("@@ -", patchline, 4)) {
+			int i;
+
+			i = sscanf(patchline+4, "%ld,%ld +%ld,%ld", &TT.oldline,
+						&TT.oldlen, &TT.newline, &TT.newlen);
+			if (i != 4)
+				bb_error_msg_and_die("corrupt hunk %d at %ld", TT.hunknum, TT.linenum);
+
+			TT.context = 0;
+			state = 2;
+
+			// If this is the first hunk, open the file.
+			if (TT.filein == -1) {
+				int oldsum, newsum, del = 0;
+				char *s, *name;
+
+ 				oldsum = TT.oldline + TT.oldlen;
+				newsum = TT.newline + TT.newlen;
+
+				name = reverse ? oldname : newname;
+
+				// We're deleting oldname if new file is /dev/null (before -p)
+				// or if new hunk is empty (zero context) after patching
+				if (!strcmp(name, "/dev/null") || !(reverse ? oldsum : newsum))
+				{
+					name = reverse ? newname : oldname;
+					del++;
 				}
-				if ((*patch_line != '-') && (*patch_line != '+')
-				 && (*patch_line != ' ')
-				) {
-					break; /* End of hunk */
+
+				// handle -p path truncation.
+				for (i=0, s = name; *s;) {
+					if ((option_mask32 & FLAG_PATHLEN) && TT.prefix == i) break;
+					if (*(s++)=='/') {
+						name = s;
+						i++;
+					}
 				}
-				if (*patch_line != plus) { /* '-' or ' ' */
-					char *src_line = NULL;
-					if (src_cur_line == src_last_line)
-						break;
-					if (src_stream) {
-						src_line = xmalloc_fgets(src_stream);
-						if (src_line) {
-							int diff = strcmp(src_line, patch_line + 1);
-							src_cur_line++;
-							free(src_line);
-							if (diff)
-								src_line = NULL;
+
+				if (del) {
+					printf("removing %s\n", name);
+					xunlink(name);
+					state = 0;
+				// If we've got a file to open, do so.
+				} else if (!(option_mask32 & FLAG_PATHLEN) || i <= TT.prefix) {
+					// If the old file was null, we're creating a new one.
+					if (!strcmp(oldname, "/dev/null") || !oldsum) {
+						printf("creating %s\n", name);
+						s = strrchr(name, '/');
+						if (s) {
+							*s = 0;
+							xmkpath(name, -1);
+							*s = '/';
 						}
+						TT.filein = xopen3(name, O_CREAT|O_EXCL|O_RDWR, 0666);
+					} else {
+						printf("patching file %s\n", name);
+						TT.filein = xopen(name, O_RDWR);
 					}
-					/* Do not patch an already patched hunk with -N */
-					if (src_line == 0 && (opt & OPT_N)) {
-						continue;
-					}
-					if (!src_line) {
-						bb_error_msg("hunk #%u FAILED at %u", hunk_count, hunk_offset_start);
-						bad_hunk_count++;
-						break;
-					}
-					if (*patch_line != ' ') { /* '-' */
-						continue;
-					}
+					TT.fileout = copy_tempfile(TT.filein, name, &TT.tempname);
+					TT.linenum = 0;
+					TT.hunknum = 0;
 				}
-				if (dst_cur_line == dst_last_line)
-					break;
-				fputs(patch_line + 1, dst_stream);
-				dst_cur_line++;
-			} /* end of while loop handling one hunk */
-		} /* end of while loop handling one file */
-
-		/* Cleanup last patched file */
-		if (copy_trailing_lines_flag) {
-			copy_lines(src_stream, dst_stream, (unsigned)(-1));
-		}
-		if (src_stream) {
-			fclose(src_stream);
-		}
-		fclose(dst_stream);
-		if (bad_hunk_count) {
-			ret = 1;
-			bb_error_msg("%u out of %u hunk FAILED", bad_hunk_count, hunk_count);
-		} else {
-			/* It worked, we can remove the backup */
-			if (backup_filename) {
-				unlink(backup_filename);
-			}
-			if (!(opt & OPT_dry_run)
-			 && ((dst_cur_line == 0) || (dst_beg_line == 0))
-			) {
-				/* The new patched file is empty, remove it */
-				xunlink(new_filename);
-				// /* old_filename and new_filename may be the same file */
-				// unlink(old_filename);
 			}
+
+			TT.hunknum++;
+
+			continue;
 		}
-		free(backup_filename);
-		//free(old_filename);
-		free(new_filename);
-	} /* end of "while there are patch lines" */
- quit:
-	/* 0 = SUCCESS
-	 * 1 = Some hunks failed
-	 * 2 = More serious problems (exited earlier)
-	 */
-	return ret;
+
+		// If we didn't continue above, discard this line.
+		free(patchline);
+	}
+
+	finish_oldfile();
+
+	if (ENABLE_FEATURE_CLEAN_UP) {
+		close(TT.filepatch);
+		free(oldname);
+		free(newname);
+	}
+
+	return TT.exitval;
 }