all: remove public named return values when useless

Named returned values should only be used on public funcs and methods
when it contributes to the documentation.

Named return values should not be used if they're only saving the
programmer a few lines of code inside the body of the function,
especially if that means there's stutter in the documentation or it
was only there so the programmer could use a naked return
statement. (Naked returns should not be used except in very small
functions)

This change is a manual audit & cleanup of public func signatures.

Signatures were not changed if:

* the func was private (wouldn't be in public godoc)
* the documentation referenced it
* the named return value was an interesting name. (i.e. it wasn't
  simply stutter, repeating the name of the type)

There should be no changes in behavior. (At least: none intended)

Change-Id: I3472ef49619678fe786e5e0994bdf2d9de76d109
Reviewed-on: https://go-review.googlesource.com/20024
Run-TryBot: Brad Fitzpatrick <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Andrew Gerrand <[email protected]>

doc/effective_go.html

@@ -239,9 +239,9 @@ <h2 id="commentary">Commentary</h2>
 </p>
 
 <pre>
-// Compile parses a regular expression and returns, if successful, a Regexp
-// object that can be used to match against text.
-func Compile(str string) (regexp *Regexp, err error) {
+// Compile parses a regular expression and returns, if successful,
+// a Regexp that can be used to match against text.
+func Compile(str string) (*Regexp, error) {
 </pre>
 
 <p>

src/archive/zip/reader.go

@@ -153,19 +153,18 @@ func (f *File) DataOffset() (offset int64, err error) {
 
 // Open returns a ReadCloser that provides access to the File's contents.
 // Multiple files may be read concurrently.
-func (f *File) Open() (rc io.ReadCloser, err error) {
+func (f *File) Open() (io.ReadCloser, error) {
 	bodyOffset, err := f.findBodyOffset()
 	if err != nil {
-		return
+		return nil, err
 	}
 	size := int64(f.CompressedSize64)
 	r := io.NewSectionReader(f.zipr, f.headerOffset+bodyOffset, size)
 	dcomp := f.zip.decompressor(f.Method)
 	if dcomp == nil {
-		err = ErrAlgorithm
-		return
+		return nil, ErrAlgorithm
 	}
-	rc = dcomp(r)
+	var rc io.ReadCloser = dcomp(r)
 	var desr io.Reader
 	if f.hasDataDescriptor() {
 		desr = io.NewSectionReader(f.zipr, f.headerOffset+bodyOffset+size, dataDescriptorLen)
@@ -176,7 +175,7 @@ func (f *File) Open() (rc io.ReadCloser, err error) {
 		f:    f,
 		desr: desr,
 	}
-	return
+	return rc, nil
 }
 
 type checksumReader struct {

src/bufio/bufio.go

@@ -220,15 +220,15 @@ func (b *Reader) Read(p []byte) (n int, err error) {
 
 // ReadByte reads and returns a single byte.
 // If no byte is available, returns an error.
-func (b *Reader) ReadByte() (c byte, err error) {
+func (b *Reader) ReadByte() (byte, error) {
 	b.lastRuneSize = -1
 	for b.r == b.w {
 		if b.err != nil {
 			return 0, b.readErr()
 		}
 		b.fill() // buffer is empty
 	}
-	c = b.buf[b.r]
+	c := b.buf[b.r]
 	b.r++
 	b.lastByte = int(c)
 	return c, nil
@@ -395,12 +395,12 @@ func (b *Reader) ReadLine() (line []byte, isPrefix bool, err error) {
 // ReadBytes returns err != nil if and only if the returned data does not end in
 // delim.
 // For simple uses, a Scanner may be more convenient.
-func (b *Reader) ReadBytes(delim byte) (line []byte, err error) {
+func (b *Reader) ReadBytes(delim byte) ([]byte, error) {
 	// Use ReadSlice to look for array,
 	// accumulating full buffers.
 	var frag []byte
 	var full [][]byte
-
+	var err error
 	for {
 		var e error
 		frag, e = b.ReadSlice(delim)
@@ -442,10 +442,9 @@ func (b *Reader) ReadBytes(delim byte) (line []byte, err error) {
 // ReadString returns err != nil if and only if the returned data does not end in
 // delim.
 // For simple uses, a Scanner may be more convenient.
-func (b *Reader) ReadString(delim byte) (line string, err error) {
+func (b *Reader) ReadString(delim byte) (string, error) {
 	bytes, err := b.ReadBytes(delim)
-	line = string(bytes)
-	return line, err
+	return string(bytes), err
 }
 
 // WriteTo implements io.WriterTo.

src/bytes/buffer.go

@@ -293,14 +293,14 @@ func (b *Buffer) Next(n int) []byte {
 
 // ReadByte reads and returns the next byte from the buffer.
 // If no byte is available, it returns error io.EOF.
-func (b *Buffer) ReadByte() (c byte, err error) {
+func (b *Buffer) ReadByte() (byte, error) {
 	b.lastRead = opInvalid
 	if b.off >= len(b.buf) {
 		// Buffer is empty, reset to recover space.
 		b.Truncate(0)
 		return 0, io.EOF
 	}
-	c = b.buf[b.off]
+	c := b.buf[b.off]
 	b.off++
 	b.lastRead = opRead
 	return c, nil

src/bytes/reader.go

@@ -63,14 +63,14 @@ func (r *Reader) ReadAt(b []byte, off int64) (n int, err error) {
 	return
 }
 
-func (r *Reader) ReadByte() (b byte, err error) {
+func (r *Reader) ReadByte() (byte, error) {
 	r.prevRune = -1
 	if r.i >= int64(len(r.s)) {
 		return 0, io.EOF
 	}
-	b = r.s[r.i]
+	b := r.s[r.i]
 	r.i++
-	return
+	return b, nil
 }
 
 func (r *Reader) UnreadByte() error {

src/crypto/dsa/dsa.go

@@ -52,7 +52,7 @@ const numMRTests = 64
 
 // GenerateParameters puts a random, valid set of DSA parameters into params.
 // This function can take many seconds, even on fast machines.
-func GenerateParameters(params *Parameters, rand io.Reader, sizes ParameterSizes) (err error) {
+func GenerateParameters(params *Parameters, rand io.Reader, sizes ParameterSizes) error {
 	// This function doesn't follow FIPS 186-3 exactly in that it doesn't
 	// use a verification seed to generate the primes. The verification
 	// seed doesn't appear to be exported or used by other code and
@@ -87,9 +87,8 @@ func GenerateParameters(params *Parameters, rand io.Reader, sizes ParameterSizes
 
 GeneratePrimes:
 	for {
-		_, err = io.ReadFull(rand, qBytes)
-		if err != nil {
-			return
+		if _, err := io.ReadFull(rand, qBytes); err != nil {
+			return err
 		}
 
 		qBytes[len(qBytes)-1] |= 1
@@ -101,9 +100,8 @@ GeneratePrimes:
 		}
 
 		for i := 0; i < 4*L; i++ {
-			_, err = io.ReadFull(rand, pBytes)
-			if err != nil {
-				return
+			if _, err := io.ReadFull(rand, pBytes); err != nil {
+				return err
 			}
 
 			pBytes[len(pBytes)-1] |= 1
@@ -142,7 +140,7 @@ GeneratePrimes:
 		}
 
 		params.G = g
-		return
+		return nil
 	}
 }
 

src/crypto/ecdsa/ecdsa.go

@@ -96,17 +96,17 @@ func randFieldElement(c elliptic.Curve, rand io.Reader) (k *big.Int, err error)
 }
 
 // GenerateKey generates a public and private key pair.
-func GenerateKey(c elliptic.Curve, rand io.Reader) (priv *PrivateKey, err error) {
+func GenerateKey(c elliptic.Curve, rand io.Reader) (*PrivateKey, error) {
 	k, err := randFieldElement(c, rand)
 	if err != nil {
-		return
+		return nil, err
 	}
 
-	priv = new(PrivateKey)
+	priv := new(PrivateKey)
 	priv.PublicKey.Curve = c
 	priv.D = k
 	priv.PublicKey.X, priv.PublicKey.Y = c.ScalarBaseMult(k.Bytes())
-	return
+	return priv, nil
 }
 
 // hashToInt converts a hash value to an integer. There is some disagreement

src/crypto/rsa/pkcs1v15.go

@@ -24,31 +24,32 @@ type PKCS1v15DecryptOptions struct {
 	SessionKeyLen int
 }
 
-// EncryptPKCS1v15 encrypts the given message with RSA and the padding scheme from PKCS#1 v1.5.
-// The message must be no longer than the length of the public modulus minus 11 bytes.
+// EncryptPKCS1v15 encrypts the given message with RSA and the padding
+// scheme from PKCS#1 v1.5.  The message must be no longer than the
+// length of the public modulus minus 11 bytes.
 //
-// The rand parameter is used as a source of entropy to ensure that encrypting
-// the same message twice doesn't result in the same ciphertext.
+// The rand parameter is used as a source of entropy to ensure that
+// encrypting the same message twice doesn't result in the same
+// ciphertext.
 //
-// WARNING: use of this function to encrypt plaintexts other than session keys
-// is dangerous. Use RSA OAEP in new protocols.
-func EncryptPKCS1v15(rand io.Reader, pub *PublicKey, msg []byte) (out []byte, err error) {
+// WARNING: use of this function to encrypt plaintexts other than
+// session keys is dangerous. Use RSA OAEP in new protocols.
+func EncryptPKCS1v15(rand io.Reader, pub *PublicKey, msg []byte) ([]byte, error) {
 	if err := checkPub(pub); err != nil {
 		return nil, err
 	}
 	k := (pub.N.BitLen() + 7) / 8
 	if len(msg) > k-11 {
-		err = ErrMessageTooLong
-		return
+		return nil, ErrMessageTooLong
 	}
 
 	// EM = 0x00 || 0x02 || PS || 0x00 || M
 	em := make([]byte, k)
 	em[1] = 2
 	ps, mm := em[2:len(em)-len(msg)-1], em[len(em)-len(msg):]
-	err = nonZeroRandomBytes(ps, rand)
+	err := nonZeroRandomBytes(ps, rand)
 	if err != nil {
-		return
+		return nil, err
 	}
 	em[len(em)-len(msg)-1] = 0
 	copy(mm, msg)
@@ -57,8 +58,7 @@ func EncryptPKCS1v15(rand io.Reader, pub *PublicKey, msg []byte) (out []byte, er
 	c := encrypt(new(big.Int), pub, m)
 
 	copyWithLeftPad(em, c.Bytes())
-	out = em
-	return
+	return em, nil
 }
 
 // DecryptPKCS1v15 decrypts a plaintext using RSA and the padding scheme from PKCS#1 v1.5.
@@ -69,19 +69,18 @@ func EncryptPKCS1v15(rand io.Reader, pub *PublicKey, msg []byte) (out []byte, er
 // learn whether each instance returned an error then they can decrypt and
 // forge signatures as if they had the private key. See
 // DecryptPKCS1v15SessionKey for a way of solving this problem.
-func DecryptPKCS1v15(rand io.Reader, priv *PrivateKey, ciphertext []byte) (out []byte, err error) {
+func DecryptPKCS1v15(rand io.Reader, priv *PrivateKey, ciphertext []byte) ([]byte, error) {
 	if err := checkPub(&priv.PublicKey); err != nil {
 		return nil, err
 	}
 	valid, out, index, err := decryptPKCS1v15(rand, priv, ciphertext)
 	if err != nil {
-		return
+		return nil, err
 	}
 	if valid == 0 {
 		return nil, ErrDecryption
 	}
-	out = out[index:]
-	return
+	return out[index:], nil
 }
 
 // DecryptPKCS1v15SessionKey decrypts a session key using RSA and the padding scheme from PKCS#1 v1.5.
@@ -103,7 +102,7 @@ func DecryptPKCS1v15(rand io.Reader, priv *PrivateKey, ciphertext []byte) (out [
 // a random value was used (because it'll be different for the same ciphertext)
 // and thus whether the padding was correct. This defeats the point of this
 // function. Using at least a 16-byte key will protect against this attack.
-func DecryptPKCS1v15SessionKey(rand io.Reader, priv *PrivateKey, ciphertext []byte, key []byte) (err error) {
+func DecryptPKCS1v15SessionKey(rand io.Reader, priv *PrivateKey, ciphertext []byte, key []byte) error {
 	if err := checkPub(&priv.PublicKey); err != nil {
 		return err
 	}
@@ -114,7 +113,7 @@ func DecryptPKCS1v15SessionKey(rand io.Reader, priv *PrivateKey, ciphertext []by
 
 	valid, em, index, err := decryptPKCS1v15(rand, priv, ciphertext)
 	if err != nil {
-		return
+		return err
 	}
 
 	if len(em) != k {
@@ -125,7 +124,7 @@ func DecryptPKCS1v15SessionKey(rand io.Reader, priv *PrivateKey, ciphertext []by
 
 	valid &= subtle.ConstantTimeEq(int32(len(em)-index), int32(len(key)))
 	subtle.ConstantTimeCopy(valid, key, em[len(em)-len(key):])
-	return
+	return nil
 }
 
 // decryptPKCS1v15 decrypts ciphertext using priv and blinds the operation if
@@ -213,21 +212,23 @@ var hashPrefixes = map[crypto.Hash][]byte{
 	crypto.RIPEMD160: {0x30, 0x20, 0x30, 0x08, 0x06, 0x06, 0x28, 0xcf, 0x06, 0x03, 0x00, 0x31, 0x04, 0x14},
 }
 
-// SignPKCS1v15 calculates the signature of hashed using RSASSA-PKCS1-V1_5-SIGN from RSA PKCS#1 v1.5.
-// Note that hashed must be the result of hashing the input message using the
-// given hash function. If hash is zero, hashed is signed directly. This isn't
+// SignPKCS1v15 calculates the signature of hashed using
+// RSASSA-PKCS1-V1_5-SIGN from RSA PKCS#1 v1.5.  Note that hashed must
+// be the result of hashing the input message using the given hash
+// function. If hash is zero, hashed is signed directly. This isn't
 // advisable except for interoperability.
 //
-// If rand is not nil then RSA blinding will be used to avoid timing side-channel attacks.
+// If rand is not nil then RSA blinding will be used to avoid timing
+// side-channel attacks.
 //
-// This function is deterministic. Thus, if the set of possible messages is
-// small, an attacker may be able to build a map from messages to signatures
-// and identify the signed messages. As ever, signatures provide authenticity,
-// not confidentiality.
-func SignPKCS1v15(rand io.Reader, priv *PrivateKey, hash crypto.Hash, hashed []byte) (s []byte, err error) {
+// This function is deterministic. Thus, if the set of possible
+// messages is small, an attacker may be able to build a map from
+// messages to signatures and identify the signed messages. As ever,
+// signatures provide authenticity, not confidentiality.
+func SignPKCS1v15(rand io.Reader, priv *PrivateKey, hash crypto.Hash, hashed []byte) ([]byte, error) {
 	hashLen, prefix, err := pkcs1v15HashInfo(hash, len(hashed))
 	if err != nil {
-		return
+		return nil, err
 	}
 
 	tLen := len(prefix) + hashLen
@@ -248,30 +249,28 @@ func SignPKCS1v15(rand io.Reader, priv *PrivateKey, hash crypto.Hash, hashed []b
 	m := new(big.Int).SetBytes(em)
 	c, err := decryptAndCheck(rand, priv, m)
 	if err != nil {
-		return
+		return nil, err
 	}
 
 	copyWithLeftPad(em, c.Bytes())
-	s = em
-	return
+	return em, nil
 }
 
 // VerifyPKCS1v15 verifies an RSA PKCS#1 v1.5 signature.
 // hashed is the result of hashing the input message using the given hash
 // function and sig is the signature. A valid signature is indicated by
 // returning a nil error. If hash is zero then hashed is used directly. This
 // isn't advisable except for interoperability.
-func VerifyPKCS1v15(pub *PublicKey, hash crypto.Hash, hashed []byte, sig []byte) (err error) {
+func VerifyPKCS1v15(pub *PublicKey, hash crypto.Hash, hashed []byte, sig []byte) error {
 	hashLen, prefix, err := pkcs1v15HashInfo(hash, len(hashed))
 	if err != nil {
-		return
+		return err
 	}
 
 	tLen := len(prefix) + hashLen
 	k := (pub.N.BitLen() + 7) / 8
 	if k < tLen+11 {
-		err = ErrVerification
-		return
+		return ErrVerification
 	}
 
 	c := new(big.Int).SetBytes(sig)

src/crypto/rsa/pss.go

@@ -246,7 +246,7 @@ func (opts *PSSOptions) saltLength() int {
 // Note that hashed must be the result of hashing the input message using the
 // given hash function. The opts argument may be nil, in which case sensible
 // defaults are used.
-func SignPSS(rand io.Reader, priv *PrivateKey, hash crypto.Hash, hashed []byte, opts *PSSOptions) (s []byte, err error) {
+func SignPSS(rand io.Reader, priv *PrivateKey, hash crypto.Hash, hashed []byte, opts *PSSOptions) ([]byte, error) {
 	saltLength := opts.saltLength()
 	switch saltLength {
 	case PSSSaltLengthAuto:
@@ -260,8 +260,8 @@ func SignPSS(rand io.Reader, priv *PrivateKey, hash crypto.Hash, hashed []byte,
 	}
 
 	salt := make([]byte, saltLength)
-	if _, err = io.ReadFull(rand, salt); err != nil {
-		return
+	if _, err := io.ReadFull(rand, salt); err != nil {
+		return nil, err
 	}
 	return signPSSWithSalt(rand, priv, hash, hashed, salt)
 }