mime: Remove an allocation in word decoding.
This fixes a TODO in (*WordDecoder).Decode by replacing a call to strings.Split with
simple prefix/suffix checking and some custom slicing.
Benchmark results:
benchmark old ns/op new ns/op delta
BenchmarkQEncodeWord-8 740 693 -6.35%
BenchmarkQDecodeWord-8 1291 727 -43.69%
BenchmarkQDecodeHeader-8 1194 767 -35.76%
benchmark old allocs new allocs delta
BenchmarkQEncodeWord-8 1 1 +0.00%
BenchmarkQDecodeWord-8 3 2 -33.33%
BenchmarkQDecodeHeader-8 3 2 -33.33%
benchmark old bytes new bytes delta
BenchmarkQEncodeWord-8 48 48 +0.00%
BenchmarkQDecodeWord-8 128 48 -62.50%
BenchmarkQDecodeHeader-8 128 48 -62.50%
Change-Id: I2d6844c75ec2e2b79be2e49b7fc4ca320b7e84e5
Reviewed-on: https://go-review.googlesource.com/14432
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/src/mime/encodedword.go b/src/mime/encodedword.go
index 3b414dd..db4b5f4 100644
--- a/src/mime/encodedword.go
+++ b/src/mime/encodedword.go
@@ -194,12 +194,24 @@
// Decode decodes an RFC 2047 encoded-word.
func (d *WordDecoder) Decode(word string) (string, error) {
- fields := strings.Split(word, "?") // TODO: remove allocation?
- if len(fields) != 5 || fields[0] != "=" || fields[4] != "=" || len(fields[2]) != 1 {
+ if !strings.HasPrefix(word, "=?") || !strings.HasSuffix(word, "?=") || strings.Count(word, "?") != 4 {
+ return "", errInvalidWord
+ }
+ word = word[2 : len(word)-2]
+
+ // split delimits the first 2 fields
+ split := strings.IndexByte(word, '?')
+ // the field after split must only be one byte
+ if word[split+2] != '?' {
return "", errInvalidWord
}
- content, err := decode(fields[2][0], fields[3])
+ // split word "UTF-8?q?ascii" into "UTF-8", 'q', and "ascii"
+ charset := word[:split]
+ encoding := word[split+1]
+ text := word[split+3:]
+
+ content, err := decode(encoding, text)
if err != nil {
return "", err
}
@@ -207,7 +219,7 @@
buf := getBuffer()
defer putBuffer(buf)
- if err := d.convert(buf, fields[1], content); err != nil {
+ if err := d.convert(buf, charset, content); err != nil {
return "", err
}
