Unclear message text when message property is too long

[pmokeev]

Summary

When I'm trying to post a message which contains mattermost.PostMessageMaxRunesV2 + 1 of symbols, I receive "invalid message" error, which is definitely unclear what is exactly invalid in my message. I see that the code contains a check for the length of the message which is being sent, but then it maps to "Invalid message" message using i18 json files, the text of which seems too general. Moreover, searching for more codebase I found that there is another message error, which specifies information about message length.

So my proposal is to rename model.post.is_valid.msg.app_error error to something like model.post.is_valid.message_length.app_error and the mapping message to Post Message property is longer than the maximum permitted length.

Steps to reproduce

import (
	"context"
	"strings"

	mattermost "github.com/mattermost/mattermost/server/public/model"
)

func main() {
	mattermostClient := mattermost.NewAPIv4Client("http://localhost:8065")
	mattermostClient.SetToken("SOME_TOKEN")

	msg := mattermost.Post{
		ChannelId: "SOME_CHANNEL_ID",
		Message:   strings.Repeat("!", mattermost.PostMessageMaxRunesV2+1),
	}

	_, _, err := mattermostClient.CreatePost(context.TODO(), &msg)
	if err != nil {
		panic(err)
	}
}

Expected behavior

panic: Post Message property is longer than the maximum permitted length.

Observed behavior (that appears unintentional)

panic: Invalid message.

Possible fixes

• Rename model.post.is_valid.msg.app_error to model.post.is_valid.message_length.app_error
• Rename Invalid message mapping error text to Post Message property is longer than the maximum permitted length.

WDYT? I can create a PR by my own to solve this issue.

[pmokeev]

It seems that model.draft.is_valid.msg.app_error has similar behaviour - Link

[amyblais]

Feel free to open a PR for this!