Harden history parsing and single-point chart rendering

src/web_server.cpp

@@ -252,6 +252,40 @@ static String history_date_from_epoch(uint32_t ts_utc) {
   return String(buf);
 }
 
+static bool history_parse_u32_field(const char *start, size_t len, uint32_t &out) {
+  if (!start || len == 0 || len >= 16) {
+    return false;
+  }
+  char buf[16];
+  memcpy(buf, start, len);
+  buf[len] = '\0';
+
+  char *end = nullptr;
+  unsigned long value = strtoul(buf, &end, 10);
+  if (end == buf || *end != '\0' || value > static_cast<unsigned long>(UINT32_MAX)) {
+    return false;
+  }
+  out = static_cast<uint32_t>(value);
+  return true;
+}
+
+static bool history_parse_float_field(const char *start, size_t len, float &out) {
+  if (!start || len == 0 || len >= 24) {
+    return false;
+  }
+  char buf[24];
+  memcpy(buf, start, len);
+  buf[len] = '\0';
+
+  char *end = nullptr;
+  float value = strtof(buf, &end);
+  if (end == buf || *end != '\0') {
+    return false;
+  }
+  out = value;
+  return true;
+}
+
 static bool history_open_next_file() {
   if (!g_history.active || g_history.done || g_history.error) {
     return false;
@@ -274,40 +308,32 @@ static bool history_parse_line(const char *line, uint32_t &ts_out, float &p_out)
   if (!line || line[0] < '0' || line[0] > '9') {
     return false;
   }
+
   const char *comma1 = strchr(line, ',');
   if (!comma1) {
     return false;
   }
-  char ts_buf[16];
+
-  size_t ts_len = static_cast<size_t>(comma1 - line);
+  uint32_t ts = 0;
-  if (ts_len >= sizeof(ts_buf)) {
+  if (!history_parse_u32_field(line, static_cast<size_t>(comma1 - line), ts)) {
-    return false;
-  }
-  memcpy(ts_buf, line, ts_len);
-  ts_buf[ts_len] = '\0';
-  char *end = nullptr;
-  uint32_t ts = static_cast<uint32_t>(strtoul(ts_buf, &end, 10));
-  if (end == ts_buf) {
     return false;
   }
+
   const char *comma2 = strchr(comma1 + 1, ',');
   if (!comma2) {
     return false;
   }
+
+  float p = 0.0f;
+  if (!history_parse_float_field(comma1 + 1, static_cast<size_t>(comma2 - (comma1 + 1)), p)) {
     const char *p_start = comma2 + 1;
     const char *p_end = strchr(p_start, ',');
-  char p_buf[16];
     size_t p_len = p_end ? static_cast<size_t>(p_end - p_start) : strlen(p_start);
-  if (p_len == 0 || p_len >= sizeof(p_buf)) {
+    if (!history_parse_float_field(p_start, p_len, p)) {
       return false;
     }
-  memcpy(p_buf, p_start, p_len);
-  p_buf[p_len] = '\0';
-  char *endp = nullptr;
-  float p = strtof(p_buf, &endp);
-  if (endp == p_buf) {
-    return false;
   }
+
   ts_out = ts;
   p_out = p;
   return true;
@@ -649,10 +675,11 @@ static void handle_sender() {
       html += "if(min===max){min=0;}";
       html += "ctx.strokeStyle='#333';ctx.lineWidth=1;ctx.beginPath();";
       html += "let first=true;";
+      html += "const xDen=series.length>1?(series.length-1):1;";
       html += "for(let i=0;i<series.length;i++){";
       html += "const v=series[i][1];";
       html += "if(v===null)continue;";
-      html += "const x=(i/(series.length-1))* (w-2) + 1;";
+      html += "const x=series.length>1?((i/xDen)*(w-2)+1):(w/2);";
       html += "const y=h-2-((v-min)/(max-min))*(h-4);";
       html += "if(first){ctx.moveTo(x,y);first=false;} else {ctx.lineTo(x,y);} }";
       html += "ctx.stroke();";