proposal: crypto, hash: add WriteString support

[josharian]

Add WriteString to crypto/sha1, crypto/sha256, hash/crc64, etc. Similar to #11805. Probably easy pickings.

[josharian]

And see CL 20524 for a place this would get used.

[sctb]

Initial CL submitted. I expect it's not quite there yet; glad to make any changes necessary.

[gopherbot]

CL https://golang.org/cl/22422 mentions this issue.

[minux]

My thought on this issue: If you want high performance hashing, then using strings is very probable already a mistake (the string must come from somewhere else, so it gets converted from []byte in the first place.) But if the string does not come from outside (I/O), then it's still better to use []byte directly. Could you please given a real scenarios where you want WriteString support on a crypto.Hash while still care about the utmost performance? While I agree that WriteString support on io.MultiWriter is fine, adding WriteString support to all io.Writer implementations doesn't look necessary esp. if doesn't bring enough performance improvement.

[josharian]

I think you're probably right. Before abandoning this, I'd like to do a bit of research in my Go corpus, but that might take a while.

[Scratch-net]

Having WriteString might indirectly suggest using it to hash passwords, which is a very, very bad idea.