all: add support for shielding hostcalls

[dgryski]

No description provided.

[dgryski]

Blocked on fastly/Viceroy#504 with shielding support for CI.

[cceckman-at-fastly]

Hiding cacheKey is the only thing that I feel strongly about, others are just nits / opinions.

[dgryski]

PTAL

[cee-dub]

My feedback was addressed :)

[cee-dub]

This is reserving the ability to add options later and not break the public API?

[dgryski]

Yes. There was an (unexported) option in the Rust SDK that I copied over, but have since removed.

[dgryski]

Last minute fixup; changed the info target parsing code but at the same time removed the API calls that were checking they worked. (Spoiler: it didn't..)

[cee-dub]

Force pushes make it hard to tell what changed (I'd be fine with a squashed merge at the end for this OSS repo, though!)

[dgryski]

Yeah, I realized afterwards that this kind of fixup probably should have been a separate commit and then squashed at merge time.
Basically there was an off-by-one in the new code because I changed my mind about stripping the initial zero or not.

diff --git a/internal/abi/fastly/shielding_guest.go b/internal/abi/fastly/shielding_guest.go
index a7ab34d..9103242 100644
--- a/internal/abi/fastly/shielding_guest.go
+++ b/internal/abi/fastly/shielding_guest.go
@@ -58,7 +58,7 @@ func ShieldingShieldInfo(name string) (*ShieldInfo, error) {
        info.me = bufb[0] == 1

        if !info.me {
-               // extract targets
+               // strip first null byte and extract targets
                vals := bytes.Split(bufb[1:], []byte{0})

                // ensure we got what we expected
@@ -66,8 +66,8 @@ func ShieldingShieldInfo(name string) (*ShieldInfo, error) {
                        return nil, FastlyStatusBadAlign.toError()
                }

-               info.target = string(vals[1])
-               info.sslTarget = string(vals[2])
+               info.target = string(vals[0])
+               info.sslTarget = string(vals[1])
        }

[cee-dub]

I just explored this in the playground (current code) and LGTM.