feat: monitor ethernet link speed

install.sh

@@ -31,12 +31,21 @@ fi
 # but ignored by the monitor and never exposed as monitor configuration.
 python3 - <<'PY'
 from pathlib import Path
-import configparser
-p=Path('/etc/pigway-pi-control.conf');c=configparser.ConfigParser();c.read(p)
-with p.open('a') as f:
-    for section,values in {'device':{'identifier':'auto','name':'auto'},'plugins':{},'api':{'bind':'0.0.0.0','port':'6001','log_limit':'200'}}.items():
-        if not c.has_section(section):
-            f.write('\n['+section+']\n'+''.join(k+' = '+v+'\n' for k,v in values.items()))
+import configparser,re
+p=Path('/etc/pigway-pi-control.conf');text=p.read_text();c=configparser.ConfigParser();c.read_string(text)
+for section,values in {'device':{'identifier':'auto','name':'auto'},'plugins':{},
+                       'alerts':{'ethernet_min_speed_mbps':'1000','ethernet_speed_seconds':'15'},
+                       'api':{'bind':'0.0.0.0','port':'6001','log_limit':'200'}}.items():
+    if not c.has_section(section):
+        text=text.rstrip()+'\n\n['+section+']\n'+''.join(k+' = '+v+'\n' for k,v in values.items())
+    else:
+        missing={k:v for k,v in values.items() if not c.has_option(section,k)}
+        if missing:
+            start=re.search(rf'(?mi)^\[{re.escape(section)}\][ \t]*$',text).end()
+            following=re.search(r'(?m)^\[[^\]\r\n]+\]',text[start:])
+            end=start+(following.start() if following else len(text)-start)
+            text=text[:end].rstrip()+'\n'+''.join(k+' = '+v+'\n' for k,v in missing.items())+'\n'+text[end:].lstrip('\n')
+p.write_text(text)
 PY
 if [ ! -s /etc/pigway-pi-control-api.token ]; then
   (umask 077; python3 -c 'import secrets; print(secrets.token_urlsafe(32))' > /etc/pigway-pi-control-api.token)