rcp.sh: curl wrapper for easier RPC calls

Signed-off-by: Jakub Sokołowski <jakub@status.im>

MAILSERVER.md

@@ -46,8 +46,13 @@ There's two simple ways to verify your Mailserver is up and running.
 
 By making an HTTP request to the metrics port(`9090` by default) you can check if you Mailserver is receiving envelopes:
 ```sh
- $ curl -s localhost:9090/metrics | grep '^whisper_envelopes_received_total'
-whisper_envelopes_received_total 123
+ > curl -sS localhost:9090/metrics | grep '^waku_envelopes_received_total'
+waku_envelopes_received_total 123
+```
+Or numbers and types of peers connected:
+```sh
+ > curl -sS localhost:9090/metrics | grep '^p2p_peers_count'
+p2p_peers_count{platform="linux-amd64",type="Statusd",version="v0.79.0"} 3
 ```
 
 ## JSON RPC Calls
@@ -55,10 +60,16 @@ whisper_envelopes_received_total 123
 The JSON RPC port (`8545` by default) allows you to manage your node.
 You can list connected peers by doing:
 ```sh
- $ export DATA='{"jsonrpc":"2.0","method":"admin_peers", "params": [], "id":1}'
- $ curl -s -H 'content-type: application/json' -d $DATA localhost:8545 \
-     | jq -r '.result[].network.remoteAddress'
+ > export RPC_HOST=localhost RPC_PORT=8545
+ > _assets/scripts/rpc.sh admin_peers | jq -r '.result[].network.remoteAddress'
 34.68.132.118:30305
 134.209.136.123:30305
 178.128.141.249:443
 ```
+Where [`rpc.sh`](./_assets/scripts/rpc.sh) is simply a thin wrapper around `curl`.
+
+You can use it to easily add peers too:
+```sh
+ > _assets/scripts/rpc.sh admin_addPeer enode://7aa648d6e855950b2e3d3bf220c496e0cae4adfddef3e1e6062e6b177aec93bc6cdcf1282cb40d1656932ebfdd565729da440368d7c4da7dbd4d004b1ac02bf8@178.128.142.26:443
+{"jsonrpc": "2.0", "id": 1, "result": true}
+```

_assets/scripts/rpc.sh

@@ -0,0 +1,38 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+RPC_HOST="${RPC_HOST:-localhost}"
+RPC_PORT="${RPC_PORT:-8545}"
+RPC_URL="${RPC_URL:-http://${RPC_HOST}:${RPC_PORT}/}"
+
+METHOD="$1"
+shift
+PARAMS=("$@")
+
+if [[ -z "${METHOD}" ]]; then
+    echo "No method specified!" >&2
+    exit 1
+fi
+# Parameter expansion trick to avoid var unbound error.
+if [[ -z "${PARAMS-}" ]]; then
+    PARAMS_STR=''
+else
+    PARAMS_STR=$(printf '%s\",\"' "${PARAMS[@]}")
+    PARAMS_STR="\"${PARAMS_STR%%\",\"}\""
+fi
+
+PAYLOAD="{
+  \"id\": 1,
+  \"jsonrpc\": \"2.0\",
+  \"method\": \"${METHOD}\",
+  \"params\": [${PARAMS_STR}]
+}"
+
+OUT=$(
+    curl --fail --show-error --silent \
+        -H "Content-type:application/json" \
+        -X POST --data "${PAYLOAD}" \
+        "${RPC_URL}"
+)
+
+echo "${OUT}" | jq .