Milo: Limit text field to 256 characters

milo/api/resp/build.go

 // Copyright 2015 The LUCI Authors.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //      http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
@@ skipping 267 matching lines @@
         // Alias, if true, means that this link is an [alias link].
         Alias bool `json:",omitempty"`
 }
 
 // NewLink does just about what you'd expect.
 func NewLink(label, url string) *Link {
         return &Link{Link: model.Link{Label: label, URL: url}}
 }
 
 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,
         }
 }
 
 // SummarizeTo summarizes the data into a given model.BuildSummary.
 func (rb *MiloBuild) SummarizeTo(c context.Context, bs *model.BuildSummary) error {
         bs.Summary = rb.Summary.toModelSummary()
         if rb.Summary.Status == model.Running {
                 // Assume the last step is the current step.
                 if len(rb.Components) > 0 {
                         cs := rb.Components[len(rb.Components)-1]
@@ skipping 27 matching lines @@
                 }
                 if rb.SourceStamp.Changelist != nil {
                         bs.Patches = append(bs.Patches, model.PatchInfo{
                                 Link:        rb.SourceStamp.Changelist.Link,
                                 AuthorEmail: rb.SourceStamp.AuthorEmail,
                         })
                 }
         }
         return nil
 }