feat(webserver): add support for chunked HTTP responses Fixes #5080

libraries/WebServer/examples/ChunkWriting/ChunkWriting.ino

@@ -0,0 +1,75 @@
+/*
+ * This example demonstrates how to send an HTTP response using chunks
+ * It will create an HTTP Server (port 80) associated with an a MDNS service
+ * Access the HTTP server using a Web Browser:
+ * URL can be composed using the MDNS name "esp32_chunk_resp.local"
+ * http://esp32_chunk_resp.local/
+ * or the IP Address that will be printed out, such as for instance 192.168.1.10
+ * http://192.168.1.10/
+ *
+ * ESP32 Server response can also be viewed using the curl command:
+ * curl -i esp32_chunk_resp.local:80
+ * curl -i --raw esp32_chunk_resp.local:80
+ */
+
+#include <WiFi.h>
+#include <NetworkClient.h>
+#include <WebServer.h>
+#include <ESPmDNS.h>
+
+const char *ssid = "........";
+const char *password = "........";
+
+WebServer server(80);
+
+void handleChunks() {
+  uint8_t countDown = 10;
+  server.chunkResponseBegin();
+  char countContent[8];
+  while (countDown) {
+    sprintf(countContent, "%d...\r\n", countDown--);
+    server.chunkWrite(countContent, strlen(countContent));
+    // count down shall show up in the browser only after about 5 seconds when finishing the whole transmission
+    // using "curl -i esp32_chunk_resp.local:80", it will show the count down as it sends each chunk
+    delay(500);
+  }
+  server.chunkWrite("DONE!", 5);
+  server.chunkResponseEnd();
+}
+
+void setup(void) {
+  Serial.begin(115200);
+  WiFi.mode(WIFI_STA);
+  WiFi.begin(ssid, password);
+  Serial.println("");
+
+  // Wait for connection
+  while (WiFi.status() != WL_CONNECTED) {
+    delay(500);
+    Serial.print(".");
+  }
+  Serial.println("");
+  Serial.print("Connected to ");
+  Serial.println(ssid);
+  Serial.print("IP address: ");
+  Serial.println(WiFi.localIP());
+
+  // Use the URL: http://esp32_chunk_resp.local/
+  if (MDNS.begin("esp32_chunk_resp")) {
+    Serial.println("MDNS responder started");
+  }
+
+  server.on("/", handleChunks);
+
+  server.onNotFound([]() {
+    server.send(404, "text/plain", "Page not found");
+  });
+
+  server.begin();
+  Serial.println("HTTP server started");
+}
+
+void loop(void) {
+  server.handleClient();
+  delay(2);  //allow the cpu to switch to other tasks
+}

libraries/WebServer/examples/ChunkWriting/ci.json

@@ -0,0 +1,6 @@
+{
+  "requires_any": [
+    "CONFIG_SOC_WIFI_SUPPORTED=y",
+    "CONFIG_ESP_WIFI_REMOTE_ENABLED=y"
+  ]
+}

libraries/WebServer/src/WebServer.cpp

@@ -551,6 +551,76 @@ void WebServer::enableETag(bool enable, ETagFunction fn) {
   _eTagFunction = fn;
 }
 
+void WebServer::chunkResponseBegin(const char *contentType) {
+  if (_chunkedResponseActive) {
+    log_e("Already in chunked response mode");
+    return;
+  }
+
+  if (strchr(contentType, '\r') || strchr(contentType, '\n')) {
+    log_e("Invalid character in content type");
+    return;
+  }
+
+  _chunkedResponseActive = true;
+  _chunkedClient = _currentClient;
+
+  _contentLength = CONTENT_LENGTH_UNKNOWN;
+
+  String header;
+  _prepareHeader(header, 200, contentType, 0);
+  _currentClientWrite(header.c_str(), header.length());
+
+  _chunkedResponseActive = true;
+  _chunkedClient = _currentClient;
+}
+
+void WebServer::chunkWrite(const char *data, size_t length) {
+  if (!_chunkedResponseActive) {
+    log_e("Chunked response has not been started");
+    return;
+  }
+
+  char chunkSize[11];
+  snprintf(chunkSize, sizeof(chunkSize), "%zx\r\n", length);
+
+  if (_chunkedClient.write(chunkSize) != strlen(chunkSize)) {
+    log_e("Failed to write chunk size");
+    _chunkedResponseActive = false;
+    return;
+  }
+
+  if (_chunkedClient.write((const uint8_t *)data, length) != length) {
+    log_e("Failed to write chunk data");
+    _chunkedResponseActive = false;
+    return;
+  }
+
+  if (_chunkedClient.write("\r\n") != 2) {
+    log_e("Failed to write chunk terminator");
+    _chunkedResponseActive = false;
+    return;
+  }
+}
+
+void WebServer::chunkResponseEnd() {
+  if (!_chunkedResponseActive) {
+    log_e("Chunked response has not been started");
+    return;
+  }
+
+  if (_chunkedClient.write("0\r\n\r\n", 5) != 5) {
+    log_e("Failed to write terminating chunk");
+  }
+
+  _chunkedClient.flush();
+  _chunkedResponseActive = false;
+  _chunked = false;
+  _chunkedClient = NetworkClient();
+
+  _clearResponseHeaders();
+}
+
 void WebServer::_prepareHeader(String &response, int code, const char *content_type, size_t contentLength) {
   _responseCode = code;
 

libraries/WebServer/src/WebServer.h

@@ -115,6 +115,10 @@ class WebServer {
   const String AuthTypeDigest = F("Digest");
   const String AuthTypeBasic = F("Basic");
 
+  void chunkResponseBegin(const char *contentType = "text/plain");
+  void chunkWrite(const char *data, size_t length);
+  void chunkResponseEnd();
+
   /* Callbackhandler for authentication. The extra parameters depend on the
    * HTTPAuthMethod mode:
    *
@@ -241,6 +245,10 @@ class WebServer {
 
   static String responseCodeToString(int code);
 
+private:
+  bool _chunkedResponseActive = false;
+  NetworkClient _chunkedClient;  // Store by value, no dangling pointer
+
 protected:
   virtual size_t _currentClientWrite(const char *b, size_t l) {
     return _currentClient.write(b, l);