tool/go: add wrapper to download and use go.toolchain.rev go version.

Also update build_dist.sh and build_docker.sh to use the wrapper.

Signed-off-by: Maisem Ali <maisem@tailscale.com>

build_dist.sh

@@ -45,4 +45,4 @@ EOF
 	exit 0
 fi
 
-exec go build -ldflags "-X tailscale.com/version.Long=${LONG} -X tailscale.com/version.Short=${SHORT} -X tailscale.com/version.GitCommit=${GIT_HASH}" "$@"
+exec ./tool/go build -ldflags "-X tailscale.com/version.Long=${LONG} -X tailscale.com/version.Short=${SHORT} -X tailscale.com/version.GitCommit=${GIT_HASH}" "$@"

build_docker.sh

@@ -19,6 +19,9 @@
 
 set -eu
 
+# Use the "go" binary from the "tool" directory (which is github.com/tailscale/go)
+export PATH=$PWD/tool:$PATH
+
 eval $(./build_dist.sh shellvars)
 DEFAULT_TAGS="v${VERSION_SHORT},v${VERSION_MINOR}"
 DEFAULT_REPOS="tailscale/tailscale,ghcr.io/tailscale/tailscale"

tool/go

@@ -0,0 +1,89 @@
+#!/bin/sh
+#
+# This script acts like the "go" command, but uses Tailscale's
+# currently-desired version from https://github.com/tailscale/go,
+# downloading it first if necessary.
+
+set -eu
+
+log() {
+    echo "$@" >&2
+}
+
+DEFAULT_TOOLCHAIN_DIR="${HOME}/.cache/tailscale-go"
+TOOLCHAIN="${TOOLCHAIN-${DEFAULT_TOOLCHAIN_DIR}}"
+TOOLCHAIN_GO="${TOOLCHAIN}/bin/go"
+read -r REV < "$(dirname "$0")/../go.toolchain.rev"
+
+# Fast, quiet path, when Tailscale is already current.
+if [ -e "${TOOLCHAIN_GO}" ]; then
+    short_hash=$("${TOOLCHAIN_GO}" version | sed 's/.*-ts//; s/ .*//')
+    case $REV in
+    "$short_hash"*)
+        unset GOROOT
+        exec "${TOOLCHAIN_GO}" "$@"
+    esac
+fi
+
+# This works for linux and darwin, which is sufficient
+# (we do not build tailscale-go for other targets).
+GOOS=$(uname -s | tr A-Z a-z)
+ARCH="$(uname -m)"
+if [ "$ARCH" = "aarch64" ]; then
+    # Go uses the name "arm64".
+    ARCH="arm64"
+elif [ "$ARCH" = "x86_64" ]; then
+    # Go uses the name "amd64".
+    ARCH="amd64"
+fi
+
+get_cached() {
+    if [ ! -d "$TOOLCHAIN" ]; then
+        mkdir -p "$TOOLCHAIN"
+    fi
+
+    archive="$TOOLCHAIN-$REV.tar.gz"
+    mark="$TOOLCHAIN.extracted"
+    extracted=
+    [ ! -e "$mark" ] || read -r extracted junk <$mark
+
+    if [ "$extracted" = "$REV" ] && [ -e "${TOOLCHAIN_GO}" ]; then
+        # already ok
+        log "Go toolchain '$REV' already extracted."
+        return 0
+    fi
+
+    rm -f "$archive.new" "$TOOLCHAIN.extracted"
+    if [ ! -e "$archive" ]; then
+            log "Need to download go '$REV'."
+            if [ "$ARCH" = "amd64" ]; then
+                # For historic reasons, the tailscale/go amd64 release artifacts don't
+                # have the arch in their name.
+                BUILD="$GOOS"
+            else
+                BUILD="$GOOS-$ARCH"
+            fi
+            curl -f -L -o "$archive.new" "https://github.com/tailscale/go/releases/download/build-${REV}/${BUILD}.tar.gz"
+            rm -f "$archive"
+            mv "$archive.new" "$archive"
+    fi
+
+    log "Extracting tailscale/go rev '$REV'" >&2
+    log "  into '$TOOLCHAIN'." >&2
+    rm -rf "$TOOLCHAIN"
+    mkdir -p "$TOOLCHAIN"
+    (cd "$TOOLCHAIN" && tar --strip-components=1 -xf "$archive")
+    echo "$REV" >$mark
+}
+
+if [ "${REV}" = "SKIP" ] ||
+   [ "${GOOS}" != "darwin" -a "${GOOS}" != "linux" ] ||
+   [ "${ARCH}" != "amd64" -a "${ARCH}" != "arm64" ]; then
+    # Use whichever go is available
+    exec go "$@"
+else
+    get_cached
+fi
+
+unset GOROOT
+exec "${TOOLCHAIN_GO}" "$@"