From 68d6d1c77950d01d5b693a997c048c15386c7032 Mon Sep 17 00:00:00 2001
From: Jack Christensen <jack@jackchristensen.com>
Date: Sat, 26 Jan 2019 10:21:16 -0600
Subject: [PATCH] Properly abort CopyFrom on reader error

---
 pgconn/pgconn.go      | 45 ++++++++++++++++++++-------------------
 pgproto3/copy_fail.go | 49 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 73 insertions(+), 21 deletions(-)
 create mode 100644 pgproto3/copy_fail.go

diff --git a/pgconn/pgconn.go b/pgconn/pgconn.go
index e8baffa2..d8ec6b07 100644
--- a/pgconn/pgconn.go
+++ b/pgconn/pgconn.go
@@ -876,34 +876,37 @@ func (pgConn *PgConn) CopyFrom(ctx context.Context, r io.Reader, sql string) (Co
 	buf = make([]byte, 0, 65536)
 	buf = append(buf, 'd')
 	sp := len(buf)
-	for {
-		n, err := r.Read(buf[5:cap(buf)])
-		if err == io.EOF && n == 0 {
-			break
-		}
-		buf = buf[0 : n+5]
-		pgio.SetInt32(buf[sp:], int32(n+4))
+	var readErr error
+	for readErr == nil {
+		n, readErr = r.Read(buf[5:cap(buf)])
+		if n > 0 {
+			buf = buf[0 : n+5]
+			pgio.SetInt32(buf[sp:], int32(n+4))
 
-		_, err = pgConn.conn.Write(buf)
-		if err != nil {
-			// Partially sent messages are a fatal error for the connection. If nothing was sent it might be possible to
-			// recover the connection with a CopyFail, but that could be rather complicated and error prone. Simpler just to
-			// close the connection.
-			pgConn.conn.Close()
-			pgConn.closed = true
+			_, err = pgConn.conn.Write(buf)
+			if err != nil {
+				// Partially sent messages are a fatal error for the connection. If nothing was sent it might be possible to
+				// recover the connection with a CopyFail, but that could be rather complicated and error prone. Simpler just to
+				// close the connection.
+				pgConn.conn.Close()
+				pgConn.closed = true
 
-			cleanupContextDeadline()
-			<-pgConn.controller
+				cleanupContextDeadline()
+				<-pgConn.controller
 
-			return "", preferContextOverNetTimeoutError(ctx, err)
+				return "", preferContextOverNetTimeoutError(ctx, err)
+			}
 		}
 	}
 
-	// Send copy done
 	buf = buf[:0]
-	copyDone := &pgproto3.CopyDone{}
-	buf = copyDone.Encode(buf)
-
+	if readErr == io.EOF {
+		copyDone := &pgproto3.CopyDone{}
+		buf = copyDone.Encode(buf)
+	} else {
+		copyFail := &pgproto3.CopyFail{Error: readErr.Error()}
+		buf = copyFail.Encode(buf)
+	}
 	_, err = pgConn.conn.Write(buf)
 	if err != nil {
 		pgConn.conn.Close()
diff --git a/pgproto3/copy_fail.go b/pgproto3/copy_fail.go
new file mode 100644
index 00000000..432a311b
--- /dev/null
+++ b/pgproto3/copy_fail.go
@@ -0,0 +1,49 @@
+package pgproto3
+
+import (
+	"bytes"
+	"encoding/json"
+
+	"github.com/jackc/pgx/pgio"
+)
+
+type CopyFail struct {
+	Error string
+}
+
+func (*CopyFail) Frontend() {}
+func (*CopyFail) Backend()  {}
+
+func (dst *CopyFail) Decode(src []byte) error {
+	idx := bytes.IndexByte(src, 0)
+	if idx != len(src)-1 {
+		return &invalidMessageFormatErr{messageType: "CopyFail"}
+	}
+
+	dst.Error = string(src[:idx])
+
+	return nil
+}
+
+func (src *CopyFail) Encode(dst []byte) []byte {
+	dst = append(dst, 'C')
+	sp := len(dst)
+	dst = pgio.AppendInt32(dst, -1)
+
+	dst = append(dst, src.Error...)
+	dst = append(dst, 0)
+
+	pgio.SetInt32(dst[sp:], int32(len(dst[sp:])))
+
+	return dst
+}
+
+func (src *CopyFail) MarshalJSON() ([]byte, error) {
+	return json.Marshal(struct {
+		Type  string
+		Error string
+	}{
+		Type:  "CopyFail",
+		Error: src.Error,
+	})
+}