jsonio: Fix parse errors on EOF

Fix an issue with jsonio.Reader where parse errors occurring at the end
of an input (EOF) are often ignored or return an ambiguous EOF error.

pkg/jsonlexer/lexer.go

@@ -160,6 +160,9 @@ func (l *Lexer) readString() Token {
 		c, err := l.br.ReadByte()
 		if err != nil {
 			l.err = err
+			if err == io.EOF {
+				l.err = errors.New("unexpected end of JSON input")
+			}
 			return TokenErr
 		}
 		l.buf = append(l.buf, c)

zio/jsonio/reader.go

@@ -2,6 +2,7 @@ package jsonio
 
 import (
 	"bufio"
+	"errors"
 	"fmt"
 	"io"
 
@@ -149,7 +150,11 @@ func (r *Reader) readNameValuePair(t jsonlexer.Token) error {
 
 func (r *Reader) error(t jsonlexer.Token, msg string) error {
 	if t == jsonlexer.TokenErr {
-		return r.lexer.Err()
+		err := r.lexer.Err()
+		if err == io.EOF {
+			return errors.New("unexpected end of JSON input")
+		}
+		return err
 	}
 	return fmt.Errorf("invalid character %q %s", r.lexer.Buf()[0], msg)
 }

zio/jsonio/ztests/unexpected-input-end.yaml

@@ -0,0 +1,28 @@
+script: |
+  while IFS= read -r line; do
+    ! echo "$line" | zq -i json -
+  done < errors.txt
+
+inputs:
+  - name: errors.txt
+    data: |
+      "3
+      ["3",
+      ["3"
+      {"foo":
+      {"foo":"bar",
+      {"foo":"bar"
+      {"foo":"bar
+
+outputs:
+  - name: stderr
+    data: |
+      stdio:stdin: unexpected end of JSON input
+      stdio:stdin: unexpected end of JSON input
+      stdio:stdin: unexpected end of JSON input
+      stdio:stdin: unexpected end of JSON input
+      stdio:stdin: unexpected end of JSON input
+      stdio:stdin: unexpected end of JSON input
+      stdio:stdin: unexpected end of JSON input
+  - name: stdout
+    data: ""