io/ioutil: clean-up of ReadAll and ReadFile

Make ReadAll use the same mechanism as ReadFile.

R=r
CC=golang-dev
https://golang.org/cl/4279041

diff --git a/src/pkg/io/ioutil/ioutil.go b/src/pkg/io/ioutil/ioutil.go
index fb3fdcda1e673b6da62ad5de96e5e13cbc9b95b5..7e3b44e55c599da2f52a363f4a276d5c332ecd06 100644 (file)
--- a/src/pkg/io/ioutil/ioutil.go
+++ b/src/pkg/io/ioutil/ioutil.go
@@ -13,11 +13,17 @@ import (
        "sort"
 )
 
+// readAll reads from r until an error or EOF and returns the data it read
+// from the internal buffer allocated with a specified capacity.
+func readAll(r io.Reader, capacity int64) ([]byte, os.Error) {
+       buf := bytes.NewBuffer(make([]byte, 0, capacity))
+       _, err := buf.ReadFrom(r)
+       return buf.Bytes(), err
+}
+
 // ReadAll reads from r until an error or EOF and returns the data it read.
 func ReadAll(r io.Reader) ([]byte, os.Error) {
-       var buf bytes.Buffer
-       _, err := io.Copy(&buf, r)
-       return buf.Bytes(), err
+       return readAll(r, bytes.MinRead)
 }
 
 // ReadFile reads the file named by filename and returns the contents.
@@ -34,16 +40,12 @@ func ReadFile(filename string) ([]byte, os.Error) {
        if err == nil && fi.Size < 2e9 { // Don't preallocate a huge buffer, just in case.
                n = fi.Size
        }
-       // Add a little extra in case Size is zero, and to avoid another allocation after
-       // Read has filled the buffer.
-       n += bytes.MinRead
-       // Pre-allocate the correct size of buffer, then set its size to zero.  The
-       // Buffer will read into the allocated space cheaply.  If the size was wrong,
-       // we'll either waste some space off the end or reallocate as needed, but
+       // As initial capacity for readAll, use n + a little extra in case Size is zero,
+       // and to avoid another allocation after Read has filled the buffer.  The readAll
+       // call will read into its allocated internal buffer cheaply.  If the size was
+       // wrong, we'll either waste some space off the end or reallocate as needed, but
        // in the overwhelmingly common case we'll get it just right.
-       buf := bytes.NewBuffer(make([]byte, 0, n))
-       _, err = buf.ReadFrom(f)
-       return buf.Bytes(), err
+       return readAll(f, n+bytes.MinRead)
 }
 
 // WriteFile writes data to a file named by filename.