Milo: Limit text field to 256 characters

milo/api/resp/build.go

Index: milo/api/resp/build.go
diff --git a/milo/api/resp/build.go b/milo/api/resp/build.go
index 174f328f23bcb78db9c004d9d3f524c70170d9aa..e92c94b8825d4d550b8bb471fea5722f36cfe593 100644
--- a/milo/api/resp/build.go
+++ b/milo/api/resp/build.go
@@ -285,11 +285,18 @@ func NewLink(label, url string) *Link {
 }
 
 func (comp *BuildComponent) toModelSummary() model.Summary {
+	text := comp.Text
+	// Max length for a datastore text field is 1500 char, but for summary purposes
+	// we don't really need anything much longer than 200 char or so.

[dnj, 2017/08/03 16:28:20]

s/200/256?

[Ryan Tseng, 2017/08/03 16:32:58]

I was trying to highlight the inexact nature of what the max len could be, but I
guess that deters.

+	const maxTextLen = 256
+	if len(text) > maxTextLen {
+		text = text[0:256]

[dnj, 2017/08/03 16:28:20]

nit: can just do text[:256].

However, there is a problem here, namely that "text" can be unicode, in which
case this may slice a UTF8 rune in half.

Since the GAE limit is bytes, you want up to 256 bytes worth of runes. This
walks over each rune in the string and records the last rune offset whose
position is <256.

sliceIdx := 0
for idx, r := range text {
  if idx > 256 {
    break
  }
  sliceIdx = idx
}
text = text[:sliceIdx]

[Ryan Tseng, 2017/08/03 16:32:58]

Weird, Go used to complain if I did [:number]

done.

+	}
 	return model.Summary{
 		Status: comp.Status,
 		Start:  comp.Started,
 		End:    comp.Finished,
-		Text:   comp.Text,
+		Text:   text,
 	}
 }