Increase Channel Purpose length to 250, and add channel field length handling code to the slack importer (#4458)

* Increase Channel Purpose length to 250.

This commit increases the maxmimum length of the channel purpose field
to 250, including the database migration necessary.

It also adds a method to the Slack importer to check the lengths of
channel properties before importing, and truncate them if necessary.

Fixes #4168

* Fix database migration.

1 files changed, 12 insertions, 8 deletions

diff --git a/model/channel.go b/model/channel.go
index 7dee079c5..2ad257ccc 100644
--- a/model/channel.go
+++ b/model/channel.go
@@ -10,10 +10,14 @@ import (
 )
 
 const (
-	CHANNEL_OPEN    = "O"
-	CHANNEL_PRIVATE = "P"
-	CHANNEL_DIRECT  = "D"
-	DEFAULT_CHANNEL = "town-square"
+	CHANNEL_OPEN                   = "O"
+	CHANNEL_PRIVATE                = "P"
+	CHANNEL_DIRECT                 = "D"
+	DEFAULT_CHANNEL                = "town-square"
+	CHANNEL_DISPLAY_NAME_MAX_RUNES = 64
+	CHANNEL_NAME_MAX_LENGTH        = 64
+	CHANNEL_HEADER_MAX_RUNES       = 1024
+	CHANNEL_PURPOSE_MAX_RUNES      = 250
 )
 
 type Channel struct {
@@ -75,11 +79,11 @@ func (o *Channel) IsValid() *AppError {
 		return NewLocAppError("Channel.IsValid", "model.channel.is_valid.update_at.app_error", nil, "id="+o.Id)
 	}
 
-	if utf8.RuneCountInString(o.DisplayName) > 64 {
+	if utf8.RuneCountInString(o.DisplayName) > CHANNEL_DISPLAY_NAME_MAX_RUNES {
 		return NewLocAppError("Channel.IsValid", "model.channel.is_valid.display_name.app_error", nil, "id="+o.Id)
 	}
 
-	if len(o.Name) > 64 {
+	if len(o.Name) > CHANNEL_NAME_MAX_LENGTH {
 		return NewLocAppError("Channel.IsValid", "model.channel.is_valid.name.app_error", nil, "id="+o.Id)
 	}
 
@@ -91,11 +95,11 @@ func (o *Channel) IsValid() *AppError {
 		return NewLocAppError("Channel.IsValid", "model.channel.is_valid.type.app_error", nil, "id="+o.Id)
 	}
 
-	if utf8.RuneCountInString(o.Header) > 1024 {
+	if utf8.RuneCountInString(o.Header) > CHANNEL_HEADER_MAX_RUNES {
 		return NewLocAppError("Channel.IsValid", "model.channel.is_valid.header.app_error", nil, "id="+o.Id)
 	}
 
-	if utf8.RuneCountInString(o.Purpose) > 128 {
+	if utf8.RuneCountInString(o.Purpose) > CHANNEL_PURPOSE_MAX_RUNES {
 		return NewLocAppError("Channel.IsValid", "model.channel.is_valid.purpose.app_error", nil, "id="+o.Id)
 	}