proposal: strconv: add a version of QuoteToASCII that doesn't add quotes

[the80srobot]

I'd like to propose exporting the function strconv.quoteWith.

Use case 1: strconv.QuoteWith(s, 0, true, false) to ASCII-escape a string without adding quotes. One might want to do this for terminal output or to escape filenames.

Use case 2: strconv.QuoteWith(s, '\'', false, false) to single-quote a string.

As an additional extension, consider making strconv.QuoteWith accept a func(rune)bool instead of two bool values. It would then be used like this:

Use case 1: strconv.QuoteWith(s, 0, func(r rune) bool { return !IsPrint(r) })
Use case 2: strconv.QuoteWith(s, 0, nil)

[ianlancetaylor]

It would help to give a use case. Thanks.

[tmthrgd]

You can do this already with strings.Trim like this:

s = strings.Trim(strconv.QuoteToASCII(s), `"`)

Try this playground example: https://play.golang.org/p/l-LKg504RDu

[the80srobot]

My immediate use case is that I have a daemon that uploads log files in batches. It assigns each batch a human-readable source identifier (derived from the source file name). For ease of debugging and sysadmin tasks, it's helpful for the identifiers to be visible and readable in two contexts: a downstream processing system, and temporary on-disk spooling.

Escaping the string lets the program preserve identifier readability, while using them for filenames and downstream primary keys. The proposed API change would let me define a function that decides which runes need escaping. (The current solution hex-encodes the identifiers instead.)

[ccbrown]

You can do this already with strings.Trim like this:

s = strings.Trim(strconv.QuoteToASCII(s), `"`)

It's not quite as simple as this. This doesn't work for strings ending in quotes, e.g. `"`.

[tmthrgd]

@ccbrown Ah, good catch. Still this should work without any new API:

s = strconv.QuoteToASCII(s)
s = s[1:len(s)-1]

[rsc]

There's already a lot of API around quoting. Given that the existing API must stay, it does not seem particularly compelling to add new API to avoid @tmthrgd's suggestion of just slicing off the quotes.

Does this come up often enough, in a large enough variety of programs, to merit being in the standard library?

[rsc]

Given the lack of a compelling use case and how easy it is to write two lines of code instead, this seems like a likely decline.

Leaving open for a week for final comments.