Add resolvers check to CI

.github/workflows/resolverscheck.sh

@@ -0,0 +1,71 @@
+#! /bin/sh
+
+DNSLOOKUP_VERSION=1.4.5
+
+case "$(uname -ms)" in
+Darwin\ x86_64) DNSLOOKUP_ARCH=darwin-amd64 ;;
+Linux\ x86_64) DNSLOOKUP_ARCH=linux-amd64 ;;
+*)
+    echo "Unsupported platform" >&2
+    exit 2
+    ;;
+esac
+
+RESOLVERS_LIST="v3/public-resolvers.md"
+
+ERROR_LOG=".error-log"
+: >"$ERROR_LOG"
+
+if [ ! -x "${DNSLOOKUP_ARCH}/dnslookup" ]; then
+    curl -sL https://github.com/ameshkov/dnslookup/releases/download/v${DNSLOOKUP_VERSION}/dnslookup-${DNSLOOKUP_ARCH}-v${DNSLOOKUP_VERSION}.tar.gz | tar xzpf - || exit 1
+fi
+PATH="$(pwd)/${DNSLOOKUP_ARCH}:$PATH"
+
+try_resolver() {
+    ERROR_LOG_TMP=".errors"
+    resolver_name="$1"
+    stamp="$2"
+    if dnslookup one.net "$line" >/dev/null 2>&1; then
+        echo "pass: ${resolver_name}"
+    elif dnslookup one.net "$line" >/dev/null 2>&1; then
+        echo "pass: ${resolver_name} (1 retry)"
+    elif dnslookup one.net "$line" >/dev/null 2>&1; then
+        echo "pass: ${resolver_name} (2 retries)"
+    elif dnslookup one.net "$line" >/dev/null 2>"$ERROR_LOG_TMP"; then
+        echo "pass: ${resolver_name} (3 retries)"
+    else
+        if grep -Eq "(no route|unreachable)" "$ERROR_LOG_TMP"; then
+            echo "ipv6: ${resolver_name}"
+        else
+            (
+                echo "* FAILED: ${resolver_name}"
+                echo "$stamp"
+                cat "$ERROR_LOG_TMP"
+                echo
+            ) >>"$ERROR_LOG"
+            return 1
+        fi
+    fi
+}
+
+resolver_name=""
+while read -r line; do
+    case "$line" in
+    \#\#\ *)
+        resolver_name=$(echo "$line" | sed 's/^## *//')
+        continue
+        ;;
+    sdns:*)
+        try_resolver "$resolver_name" "$line"
+        ;;
+    esac
+done <"$RESOLVERS_LIST"
+
+if [ -s "$ERROR_LOG" ]; then
+    exec 1>&2
+    echo
+    echo "** FAILURES **"
+    echo
+    cat "$ERROR_LOG"
+    exit 1
+fi

.github/workflows/resolverscheck.yml

@@ -0,0 +1,17 @@
+name: resolverscheck
+
+on:
+  push:
+    branches: [next, ci]
+  pull_request:
+    branches: [next, ci]
+  workflow_dispatch:
+
+jobs:
+  resolverscheck:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: resolvers check
+        run: .github/workflows/resolverscheck.sh