From 88530a7944a47ea7619ee42384d597179405bf54 Mon Sep 17 00:00:00 2001
From: Megan Marsh <megan@hashicorp.com>
Date: Fri, 8 Nov 2019 12:34:36 -0800
Subject: [PATCH 1/2] if someone logs a line longer than 65*1024 bytes before
 it contains a newline, the default ScanLines func in bufio.Scanner can't
 handle it. Copy that func and add a conditional to clear buffer and continue
 scanning in this situation.

---
 log.go | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/log.go b/log.go
index 1a6722235..021de1f4e 100644
--- a/log.go
+++ b/log.go
@@ -2,6 +2,7 @@ package main
 
 import (
 	"bufio"
+	"bytes"
 	"fmt"
 	"io"
 	"os"
@@ -30,6 +31,8 @@ func logOutput() (logOutput io.Writer, err error) {
 			// calls.
 			r, w := io.Pipe()
 			scanner := bufio.NewScanner(r)
+			scanner.Split(ScanLinesSmallerThanBuffer)
+
 			go func(scanner *bufio.Scanner) {
 				for scanner.Scan() {
 					if strings.Contains(scanner.Text(), "ui:") {
@@ -47,3 +50,39 @@ func logOutput() (logOutput io.Writer, err error) {
 
 	return
 }
+
+// The below functions come from bufio.Scanner with a small tweak, to fix an
+// edgecase where the default ScanFunc fails: sometimes, if someone tries to
+// log a line that is longer than 64*1024 bytes long before it contains a
+// newline, the ScanLine will continue to return, requesting more data from the
+// buffer, which can't increase in size anymore, causing a hang.
+func dropCR(data []byte) []byte {
+	if len(data) > 0 && data[len(data)-1] == '\r' {
+		return data[0 : len(data)-1]
+	}
+	return data
+}
+
+func ScanLinesSmallerThanBuffer(data []byte, atEOF bool) (advance int, token []byte, err error) {
+	if atEOF && len(data) == 0 {
+		return 0, nil, nil
+	}
+	if i := bytes.IndexByte(data, '\n'); i >= 0 {
+		// We have a full newline-terminated line.
+		return i + 1, dropCR(data[0:i]), nil
+	}
+	// If we're at EOF, we have a final, non-terminated line. Return it.
+	if atEOF {
+		return len(data), dropCR(data), nil
+	}
+
+	// Our tweak:
+	// Buffer is full, so we can't get more data. Just return what we have as
+	// its own token so we can keep going, even though there's no newline.
+	if len(data)+1 >= bufio.MaxScanTokenSize {
+		return len(data), data[0 : len(data)-1], nil
+	}
+
+	// Request more data.
+	return 0, nil, nil
+}

From 60cf4f60140a89a2feee3072bd93f7faeaae5bc0 Mon Sep 17 00:00:00 2001
From: Megan Marsh <megan@hashicorp.com>
Date: Mon, 11 Nov 2019 09:19:35 -0800
Subject: [PATCH 2/2] log errors in scanner and manually close logging pipe if
 we hit an error in the scanner

---
 log.go | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/log.go b/log.go
index 021de1f4e..ff12c94c0 100644
--- a/log.go
+++ b/log.go
@@ -43,6 +43,10 @@ func logOutput() (logOutput io.Writer, err error) {
 					}
 					os.Stderr.WriteString(fmt.Sprint(scanner.Text() + "\n"))
 				}
+				if err := scanner.Err(); err != nil {
+					os.Stderr.WriteString(err.Error())
+					w.Close()
+				}
 			}(scanner)
 			logOutput = w
 		}