package patch

R=r
http://go/go-review/1018043

src/pkg/patch/apply.go

@@ -0,0 +1,54 @@
+// Copyright 2009 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package patch
+
+import "os"
+
+// An Op is a single operation to execute to apply a patch.
+type Op struct {
+	Verb	Verb;	// action
+	Src	string;	// source file
+	Dst	string;	// destination file
+	Mode	int;	// mode for destination (if non-zero)
+	Data	[]byte;	// data for destination (if non-nil)
+}
+
+// Apply applies the patch set to the files named in the patch set,
+// constructing an in-memory copy of the new file state.
+// It is the client's job to write the changes to the file system
+// if desired.
+//
+// The function readFile should return the contents of the named file.
+// Typically this function will be io.ReadFile.
+//
+func (set *Set) Apply(readFile func(string) ([]byte, os.Error)) ([]Op, os.Error) {
+	op := make([]Op, len(set.File));
+
+	for i, f := range set.File {
+		o := &op[i];
+		o.Verb = f.Verb;
+		o.Src = f.Src;
+		o.Dst = f.Dst;
+		o.Mode = f.NewMode;
+		if f.Diff != NoDiff || o.Verb != Edit {
+			// Clients assume o.Data == nil means no data diff.
+			// Start with a non-nil data.
+			var old []byte = make([]byte, 0);	// not nil
+			var err os.Error;
+			if f.Src != "" {
+				old, err = readFile(f.Src);
+				if err != nil {
+					return nil, &os.PathError{string(f.Verb), f.Src, err};
+				}
+			}
+			o.Data, err = f.Diff.Apply(old);
+			if err != nil {
+				return nil, &os.PathError{string(f.Verb), f.Src, err};
+			}
+		}
+	}
+
+	return op, nil;
+}