Map io.EOF errors to io.ErrUnexpectedEOF

io.EOF is never expected during valid usage. In addition, database/sql
uses io.EOF as a sentinal value that all rows from a query have been
received.

See https://github.com/jackc/pgx/issues/662.

frontend.go

@@ -58,12 +58,19 @@ func (f *Frontend) Send(msg FrontendMessage) error {
 	return err
 }
 
+func translateEOFtoErrUnexpectedEOF(err error) error {
+	if err == io.EOF {
+		return io.ErrUnexpectedEOF
+	}
+	return err
+}
+
 // Receive receives a message from the backend.
 func (f *Frontend) Receive() (BackendMessage, error) {
 	if !f.partialMsg {
 		header, err := f.cr.Next(5)
 		if err != nil {
-			return nil, err
+			return nil, translateEOFtoErrUnexpectedEOF(err)
 		}
 
 		f.msgType = header[0]
@@ -73,7 +80,7 @@ func (f *Frontend) Receive() (BackendMessage, error) {
 
 	msgBody, err := f.cr.Next(f.bodyLen)
 	if err != nil {
-		return nil, err
+		return nil, translateEOFtoErrUnexpectedEOF(err)
 	}
 
 	f.partialMsg = false

frontend_test.go

@@ -1,10 +1,11 @@
 package pgproto3_test
 
 import (
-	"errors"
+	"io"
 	"testing"
 
 	"github.com/jackc/pgproto3/v2"
+	"github.com/stretchr/testify/assert"
 )
 
 type interruptReader struct {
@@ -13,7 +14,7 @@ type interruptReader struct {
 
 func (ir *interruptReader) Read(p []byte) (n int, err error) {
 	if len(ir.chunks) == 0 {
-		return 0, errors.New("no data")
+		return 0, io.EOF
 	}
 
 	n = copy(p, ir.chunks[0])
@@ -56,3 +57,24 @@ func TestFrontendReceiveInterrupted(t *testing.T) {
 		t.Fatalf("unexpected msg: %v", msg)
 	}
 }
+
+func TestFrontendReceiveUnexpectedEOF(t *testing.T) {
+	t.Parallel()
+
+	server := &interruptReader{}
+	server.push([]byte{'Z', 0, 0, 0, 5})
+
+	frontend := pgproto3.NewFrontend(pgproto3.NewChunkReader(server), nil)
+
+	msg, err := frontend.Receive()
+	if err == nil {
+		t.Fatal("expected err")
+	}
+	if msg != nil {
+		t.Fatalf("did not expect msg, but %v", msg)
+	}
+
+	msg, err = frontend.Receive()
+	assert.Nil(t, msg)
+	assert.Equal(t, io.ErrUnexpectedEOF, err)
+}

go.mod

@@ -5,4 +5,5 @@ go 1.12
 require (
 	github.com/jackc/chunkreader/v2 v2.0.0
 	github.com/jackc/pgio v1.0.0
+	github.com/stretchr/testify v1.4.0
 )

go.sum

@@ -1,4 +1,14 @@
+github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/jackc/chunkreader/v2 v2.0.0 h1:DUwgMQuuPnS0rhMXenUtZpqZqrR/30NWY+qQvTpSvEs=
 github.com/jackc/chunkreader/v2 v2.0.0/go.mod h1:odVSm741yZoC3dpHEUXIqA9tQRhFrgOHwnPIn9lDKlk=
 github.com/jackc/pgio v1.0.0 h1:g12B9UwVnzGhueNavwioyEEpAmqMe1E/BN9ES+8ovkE=
 github.com/jackc/pgio v1.0.0/go.mod h1:oP+2QK2wFfUWgr+gxjoBH9KGBb31Eio69xUb0w5bYf8=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.4.0 h1:2E4SXV/wtOkTonXsotYi4li6zVWxYlZuYNCXe9XRJyk=
+github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v2 v2.2.2 h1:ZCJp+EgiOT7lHqUV2J862kp8Qj64Jo6az82+3Td9dZw=
+gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=