fix: oom exceptions for OPDS, KOSync, and OTA via wolfssl (#2475)

2026-07-12 01:53:26 +03:00
parent 1f5669a08a
commit 3e627112f6
13 changed files with 413 additions and 233 deletions
@@ -2,10 +2,10 @@

 #include <ArduinoJson.h>
 #include <Logging.h>
-#include <esp_crt_bundle.h>
-#include <esp_http_client.h>
+#include <SecureHttpClient.h>
+#include <base64.h>

-#include <ctime>
+#include <string>

 #include "KOReaderCredentialStore.h"

@@ -16,82 +16,35 @@ namespace {
 constexpr char DEVICE_NAME[] = "CrossPoint";
 constexpr char DEVICE_ID[] = "crosspoint-reader";

-// Small TLS buffers to fit in ESP32-C3's limited heap (~46KB free after WiFi).
-// KOSync payloads are tiny JSON (<1KB), so 2KB buffers are sufficient.
-// Default 16KB buffers cause OOM during TLS handshake.
-constexpr int HTTP_BUF_SIZE = 2048;
-
-// Cloudflare tunnels send a 3-cert Google Trust Services chain. During the TLS handshake
-// mbedTLS makes many small allocations that collectively consume ~48KB of heap. With only
-// ~50KB free after WiFi connects, the session drove min-free-ever down to 2600 bytes before
-// failing with MBEDTLS_ERR_X509_ALLOC_FAILED (-0x2880). Check total free heap (not max
-// contiguous block) because the failure mode is aggregate exhaustion, not one large alloc.
+// KOSync's TLS-1.3 servers can't be reached through the precompiled system
+// mbedTLS (TLS 1.3 is stubbed out), so requests run over wolfSSL via
+// SecureHttpClient. The handshake still needs working heap; gate on it. wolfSSL's
+// footprint is smaller than mbedTLS's old ~48KB peak, but keep a conservative
+// floor. Check both total free heap and largest contiguous block so fragmented
+// heap does not fall through into a failed TLS allocation path.
 constexpr uint32_t MIN_HEAP_FOR_TLS = 55000;

-// Response buffer for reading HTTP body
-struct ResponseBuffer {
-  char* data = nullptr;
-  int len = 0;
-  int capacity = 0;
-
-  ~ResponseBuffer() { free(data); }
-
-  bool ensure(int size) {
-    if (size <= capacity) return true;
-    char* newData = (char*)realloc(data, size);
-    if (!newData) return false;
-    data = newData;
-    capacity = size;
-    return true;
-  }
-};
-
-// HTTP event handler to collect response body
-esp_err_t httpEventHandler(esp_http_client_event_t* evt) {
-  auto* buf = static_cast<ResponseBuffer*>(evt->user_data);
-  if (evt->event_id == HTTP_EVENT_ON_DATA && buf) {
-    if (buf->ensure(buf->len + evt->data_len + 1)) {
-      memcpy(buf->data + buf->len, evt->data, evt->data_len);
-      buf->len += evt->data_len;
-      buf->data[buf->len] = '\0';
-    } else {
-      LOG_ERR("KOSync", "Response buffer allocation failed (%d bytes)", evt->data_len);
-    }
-  }
-  return ESP_OK;
+// Apply the shared KOSync auth headers after begin(). x-auth-* is the native
+// KOSync scheme; Basic auth is added for Calibre-Web-Automated compatibility.
+void applyAuthHeaders(freeink::SecureHttpClient& http) {
+  http.addHeader("Accept", "application/vnd.koreader.v1+json");
+  http.addHeader("x-auth-user", KOREADER_STORE.getUsername());
+  http.addHeader("x-auth-key", KOREADER_STORE.getMd5Password());
+  const std::string credentials = KOREADER_STORE.getUsername() + ":" + KOREADER_STORE.getPassword();
+  const String encoded = base64::encode(credentials.c_str());
+  http.addHeader("Authorization", std::string("Basic ") + encoded.c_str());
 }

-// Create configured esp_http_client with small TLS buffers
-esp_http_client_handle_t createClient(const char* url, ResponseBuffer* buf,
-                                      esp_http_client_method_t method = HTTP_METHOD_GET) {
-  esp_http_client_config_t config = {};
-  config.url = url;
-  config.event_handler = httpEventHandler;
-  config.user_data = buf;
-  config.method = method;
-  config.timeout_ms = 15000;
-  config.buffer_size = HTTP_BUF_SIZE;
-  config.buffer_size_tx = HTTP_BUF_SIZE;
-  config.crt_bundle_attach = esp_crt_bundle_attach;
-
-  // HTTP Basic Auth for Calibre-Web-Automated compatibility
-  config.username = KOREADER_STORE.getUsername().c_str();
-  config.password = KOREADER_STORE.getPassword().c_str();
-  config.auth_type = HTTP_AUTH_TYPE_BASIC;
-
-  esp_http_client_handle_t client = esp_http_client_init(&config);
-  if (!client) return nullptr;
-
-  // KOSync auth headers
-  if (esp_http_client_set_header(client, "Accept", "application/vnd.koreader.v1+json") != ESP_OK ||
-      esp_http_client_set_header(client, "x-auth-user", KOREADER_STORE.getUsername().c_str()) != ESP_OK ||
-      esp_http_client_set_header(client, "x-auth-key", KOREADER_STORE.getMd5Password().c_str()) != ESP_OK) {
-    LOG_ERR("KOSync", "Failed to set auth headers");
-    esp_http_client_cleanup(client);
-    return nullptr;
+// True when free heap is too low to risk a TLS handshake.
+bool insufficientHeap() {
+  const uint32_t freeHeap = ESP.getFreeHeap();
+  const uint32_t maxAllocHeap = ESP.getMaxAllocHeap();
+  if (freeHeap < MIN_HEAP_FOR_TLS || maxAllocHeap < MIN_HEAP_FOR_TLS) {
+    LOG_ERR("KOSync", "Insufficient heap for TLS handshake: %u bytes free, %u max alloc (need %u)", freeHeap,
+            maxAllocHeap, MIN_HEAP_FOR_TLS);
+    return true;
  }
-
-  return client;
+  return false;
 }
 }  // namespace

@@ -102,26 +55,24 @@ KOReaderSyncClient::Error KOReaderSyncClient::authenticate() {
    return NO_CREDENTIALS;
  }

-  std::string url = KOREADER_STORE.getBaseUrl() + "/users/auth";
-  const uint32_t freeHeap = ESP.getFreeHeap();
-  LOG_DBG("KOSync", "Authenticating: %s (heap: %u)", url.c_str(), (unsigned)freeHeap);
-  if (freeHeap < MIN_HEAP_FOR_TLS) {
-    LOG_ERR("KOSync", "Insufficient heap for TLS handshake: %u bytes free (need %u)", freeHeap, MIN_HEAP_FOR_TLS);
-    return LOW_MEMORY;
+  const std::string url = KOREADER_STORE.getBaseUrl() + "/users/auth";
+  LOG_DBG("KOSync", "Authenticating: %s (heap: %u)", url.c_str(), (unsigned)ESP.getFreeHeap());
+  if (insufficientHeap()) return LOW_MEMORY;
+
+  freeink::SecureHttpClient http;
+  http.setInsecure();
+  if (!http.begin(url)) {
+    LOG_ERR("KOSync", "Bad URL: %s", url.c_str());
+    return NETWORK_ERROR;
  }
-
-  ResponseBuffer buf;
-  esp_http_client_handle_t client = createClient(url.c_str(), &buf);
-  if (!client) return NETWORK_ERROR;
-
-  esp_err_t err = esp_http_client_perform(client);
-  const int httpCode = esp_http_client_get_status_code(client);
+  applyAuthHeaders(http);
+  const int httpCode = http.GET();
+  http.end();
  lastHttpCode = httpCode;
-  esp_http_client_cleanup(client);

-  LOG_DBG("KOSync", "Auth response: %d (err: %d)", httpCode, err);
+  LOG_DBG("KOSync", "Auth response: %d", httpCode);

-  if (err != ESP_OK) return NETWORK_ERROR;
+  if (httpCode <= 0) return NETWORK_ERROR;
  if (httpCode == 200) return OK;
  if (httpCode == 401) return AUTH_FAILED;
  return SERVER_ERROR;
@@ -135,30 +86,31 @@ KOReaderSyncClient::Error KOReaderSyncClient::getProgress(const std::string& doc
    return NO_CREDENTIALS;
  }

-  std::string url = KOREADER_STORE.getBaseUrl() + "/syncs/progress/" + documentHash;
-  const uint32_t freeHeap = ESP.getFreeHeap();
-  LOG_DBG("KOSync", "Getting progress: %s (heap: %u)", url.c_str(), (unsigned)freeHeap);
-  if (freeHeap < MIN_HEAP_FOR_TLS) {
-    LOG_ERR("KOSync", "Insufficient heap for TLS handshake: %u bytes free (need %u)", freeHeap, MIN_HEAP_FOR_TLS);
-    return LOW_MEMORY;
+  const std::string url = KOREADER_STORE.getBaseUrl() + "/syncs/progress/" + documentHash;
+  LOG_DBG("KOSync", "Getting progress: %s (heap: %u)", url.c_str(), (unsigned)ESP.getFreeHeap());
+  if (insufficientHeap()) return LOW_MEMORY;
+
+  freeink::SecureHttpClient http;
+  http.setInsecure();
+  if (!http.begin(url)) {
+    LOG_ERR("KOSync", "Bad URL: %s", url.c_str());
+    return NETWORK_ERROR;
+  }
+  applyAuthHeaders(http);
+  const int httpCode = http.GET();
+  lastHttpCode = httpCode;
+
+  LOG_DBG("KOSync", "Get progress response: %d", httpCode);
+
+  if (httpCode <= 0) {
+    http.end();
+    return NETWORK_ERROR;
  }

-  ResponseBuffer buf;
-  esp_http_client_handle_t client = createClient(url.c_str(), &buf);
-  if (!client) return NETWORK_ERROR;
-
-  esp_err_t err = esp_http_client_perform(client);
-  const int httpCode = esp_http_client_get_status_code(client);
-  lastHttpCode = httpCode;
-  esp_http_client_cleanup(client);
-
-  LOG_DBG("KOSync", "Get progress response: %d (err: %d)", httpCode, err);
-
-  if (err != ESP_OK) return NETWORK_ERROR;
-
-  if (httpCode == 200 && buf.data) {
+  if (httpCode == 200) {
    JsonDocument doc;
-    const DeserializationError error = deserializeJson(doc, buf.data);
+    const DeserializationError error = deserializeJson(doc, http.getString().c_str());
+    http.end();

    if (error) {
      LOG_ERR("KOSync", "JSON parse failed: %s", error.c_str());
@@ -176,6 +128,7 @@ KOReaderSyncClient::Error KOReaderSyncClient::getProgress(const std::string& doc
    return OK;
  }

+  http.end();
  if (httpCode == 401) return AUTH_FAILED;
  if (httpCode == 404) return NOT_FOUND;
  return SERVER_ERROR;
@@ -188,13 +141,9 @@ KOReaderSyncClient::Error KOReaderSyncClient::updateProgress(const KOReaderProgr
    return NO_CREDENTIALS;
  }

-  std::string url = KOREADER_STORE.getBaseUrl() + "/syncs/progress";
-  const uint32_t freeHeap = ESP.getFreeHeap();
-  LOG_DBG("KOSync", "Updating progress: %s (heap: %u)", url.c_str(), (unsigned)freeHeap);
-  if (freeHeap < MIN_HEAP_FOR_TLS) {
-    LOG_ERR("KOSync", "Insufficient heap for TLS handshake: %u bytes free (need %u)", freeHeap, MIN_HEAP_FOR_TLS);
-    return LOW_MEMORY;
-  }
+  const std::string url = KOREADER_STORE.getBaseUrl() + "/syncs/progress";
+  LOG_DBG("KOSync", "Updating progress: %s (heap: %u)", url.c_str(), (unsigned)ESP.getFreeHeap());
+  if (insufficientHeap()) return LOW_MEMORY;

  // Build JSON body
  JsonDocument doc;
@@ -209,25 +158,21 @@ KOReaderSyncClient::Error KOReaderSyncClient::updateProgress(const KOReaderProgr

  LOG_DBG("KOSync", "Request body: %s", body.c_str());

-  ResponseBuffer buf;
-  esp_http_client_handle_t client = createClient(url.c_str(), &buf, HTTP_METHOD_PUT);
-  if (!client) return NETWORK_ERROR;
-
-  if (esp_http_client_set_header(client, "Content-Type", "application/json") != ESP_OK ||
-      esp_http_client_set_post_field(client, body.c_str(), body.length()) != ESP_OK) {
-    LOG_ERR("KOSync", "Failed to set request body");
-    esp_http_client_cleanup(client);
+  freeink::SecureHttpClient http;
+  http.setInsecure();
+  if (!http.begin(url)) {
+    LOG_ERR("KOSync", "Bad URL: %s", url.c_str());
    return NETWORK_ERROR;
  }
-
-  esp_err_t err = esp_http_client_perform(client);
-  const int httpCode = esp_http_client_get_status_code(client);
+  applyAuthHeaders(http);
+  http.addHeader("Content-Type", "application/json");
+  const int httpCode = http.sendRequest("PUT", body);
+  http.end();
  lastHttpCode = httpCode;
-  esp_http_client_cleanup(client);

-  LOG_DBG("KOSync", "Update progress response: %d (err: %d)", httpCode, err);
+  LOG_DBG("KOSync", "Update progress response: %d", httpCode);

-  if (err != ESP_OK) return NETWORK_ERROR;
+  if (httpCode <= 0) return NETWORK_ERROR;
  if (httpCode == 200 || httpCode == 202) return OK;
  if (httpCode == 401) return AUTH_FAILED;
  return SERVER_ERROR;
@@ -5,6 +5,17 @@

 #include <cstring>

+namespace {
+constexpr size_t ENTRY_STORAGE_CAPACITY = 64;
+constexpr size_t MAX_ENTRIES = ENTRY_STORAGE_CAPACITY - 2;
+constexpr size_t MAX_TITLE_CHARS = 160;
+constexpr size_t MAX_AUTHOR_CHARS = 120;
+constexpr size_t MAX_ID_CHARS = 128;
+constexpr size_t MAX_HREF_CHARS = 768;
+constexpr size_t MAX_SEARCH_TEMPLATE_CHARS = 768;
+constexpr size_t MAX_PAGE_URL_CHARS = 768;
+}  // namespace
+
 OpdsParser::OpdsParser() {
  parser = XML_ParserCreate(nullptr);
  if (!parser) {
@@ -12,6 +23,7 @@ OpdsParser::OpdsParser() {
    LOG_DBG("OPDS", "Couldn't allocate memory for parser");
    return;
  }
+  entries.reserve(ENTRY_STORAGE_CAPACITY);
  XML_SetUserData(parser, this);
  XML_SetElementHandler(parser, startElement, endElement);
  XML_SetCharacterDataHandler(parser, characterData);
@@ -71,6 +83,8 @@ void OpdsParser::clear() {
  currentEntry = OpdsEntry{};
  currentText.clear();
  inEntry = inTitle = inAuthor = inAuthorName = inId = false;
+  collectCurrentEntry = false;
+  feedTruncated = false;
 }

 std::vector<OpdsEntry> OpdsParser::getBooks() const {
@@ -88,9 +102,33 @@ const char* OpdsParser::findAttribute(const XML_Char** atts, const char* name) {
  return nullptr;
 }

+void OpdsParser::assignBounded(std::string& target, const char* value, const size_t maxLen) {
+  if (!value) {
+    target.clear();
+    return;
+  }
+  target.assign(value, strnlen(value, maxLen));
+}
+
+void OpdsParser::appendBounded(std::string& target, const char* value, const size_t len, const size_t maxLen) {
+  if (target.size() >= maxLen) return;
+  const size_t remaining = maxLen - target.size();
+  target.append(value, len < remaining ? len : remaining);
+}
+
 void XMLCALL OpdsParser::startElement(void* userData, const XML_Char* name, const XML_Char** atts) {
  auto* self = static_cast<OpdsParser*>(userData);

+  if (strcmp(name, "entry") == 0 || strstr(name, ":entry") != nullptr) {
+    self->inEntry = true;
+    self->collectCurrentEntry = self->entries.size() < MAX_ENTRIES;
+    self->feedTruncated = self->feedTruncated || !self->collectCurrentEntry;
+    self->currentEntry = OpdsEntry{};
+    self->currentText.clear();
+    self->inTitle = self->inAuthor = self->inAuthorName = self->inId = false;
+    return;
+  }
+
  if (strcmp(name, "link") == 0 || strstr(name, ":link") != nullptr) {
    const char* href = findAttribute(atts, "href");
    if (href) {
@@ -98,17 +136,16 @@ void XMLCALL OpdsParser::startElement(void* userData, const XML_Char* name, cons
      const char* type = findAttribute(atts, "type");

      if (rel && strcmp(rel, "search") == 0) {
-        std::string sHref(href);
-        if (sHref.find("{searchTerms}") != std::string::npos) {
-          self->searchTemplate = sHref;
+        if (strstr(href, "{searchTerms}") != nullptr) {
+          assignBounded(self->searchTemplate, href, MAX_SEARCH_TEMPLATE_CHARS);
        }
      } else if (rel && strcmp(rel, "next") == 0 && !self->inEntry) {
-        self->nextPageUrl = href;
+        assignBounded(self->nextPageUrl, href, MAX_PAGE_URL_CHARS);
      } else if (rel && strcmp(rel, "previous") == 0 && !self->inEntry) {
-        self->prevPageUrl = href;
+        assignBounded(self->prevPageUrl, href, MAX_PAGE_URL_CHARS);
      }

-      if (self->inEntry) {
+      if (self->inEntry && self->collectCurrentEntry) {
        if (rel && type && strstr(rel, "opds-spec.org/acquisition") != nullptr &&
            strcmp(type, "application/epub+zip") == 0) {
          // Prefer plain EPUB links over derived formats when multiple
@@ -119,25 +156,19 @@ void XMLCALL OpdsParser::startElement(void* userData, const XML_Char* name, cons
                                            self->currentEntry.href.find("/epub/") != std::string::npos);
          if (self->currentEntry.type != OpdsEntryType::BOOK || (isPlainEpub && !alreadyHasPlainEpub)) {
            self->currentEntry.type = OpdsEntryType::BOOK;
-            self->currentEntry.href = href;
+            assignBounded(self->currentEntry.href, href, MAX_HREF_CHARS);
          }
        } else if (type && strstr(type, "application/atom+xml") != nullptr) {
          if (self->currentEntry.type != OpdsEntryType::BOOK) {
            self->currentEntry.type = OpdsEntryType::NAVIGATION;
-            self->currentEntry.href = href;
+            assignBounded(self->currentEntry.href, href, MAX_HREF_CHARS);
          }
        }
      }
    }
  }

-  if (strcmp(name, "entry") == 0 || strstr(name, ":entry") != nullptr) {
-    self->inEntry = true;
-    self->currentEntry = OpdsEntry{};
-    return;
-  }
-
-  if (!self->inEntry) return;
+  if (!self->inEntry || !self->collectCurrentEntry) return;

  if (strcmp(name, "title") == 0 || strstr(name, ":title") != nullptr) {
    self->inTitle = true;
@@ -157,10 +188,11 @@ void XMLCALL OpdsParser::endElement(void* userData, const XML_Char* name) {
  auto* self = static_cast<OpdsParser*>(userData);

  if (strcmp(name, "entry") == 0 || strstr(name, ":entry") != nullptr) {
-    if (!self->currentEntry.title.empty() && !self->currentEntry.href.empty()) {
+    if (self->collectCurrentEntry && !self->currentEntry.title.empty() && !self->currentEntry.href.empty()) {
      self->entries.push_back(self->currentEntry);
    }
    self->inEntry = false;
+    self->collectCurrentEntry = false;
  } else if (self->inEntry) {
    if (strcmp(name, "title") == 0 || strstr(name, ":title") != nullptr) {
      if (self->inTitle) self->currentEntry.title = self->currentText;
@@ -179,7 +211,12 @@ void XMLCALL OpdsParser::endElement(void* userData, const XML_Char* name) {

 void XMLCALL OpdsParser::characterData(void* userData, const XML_Char* s, const int len) {
  auto* self = static_cast<OpdsParser*>(userData);
-  if (self->inTitle || self->inAuthorName || self->inId) {
-    self->currentText.append(s, len);
+  if (!self->collectCurrentEntry) return;
+  if (self->inTitle) {
+    appendBounded(self->currentText, s, len, MAX_TITLE_CHARS);
+  } else if (self->inAuthorName) {
+    appendBounded(self->currentText, s, len, MAX_AUTHOR_CHARS);
+  } else if (self->inId) {
+    appendBounded(self->currentText, s, len, MAX_ID_CHARS);
  }
 }
@@ -61,6 +61,7 @@ class OpdsParser final : public Print {
  void flush() override;

  bool error() const;
+  bool truncated() const { return feedTruncated; }

  operator bool() { return !error(); }

@@ -93,6 +94,8 @@ class OpdsParser final : public Print {
  std::string prevPageUrl;
  // Helper to find attribute value
  static const char* findAttribute(const XML_Char** atts, const char* name);
+  static void assignBounded(std::string& target, const char* value, size_t maxLen);
+  static void appendBounded(std::string& target, const char* value, size_t len, size_t maxLen);

  XML_Parser parser = nullptr;
  std::vector<OpdsEntry> entries;
@@ -105,6 +108,8 @@ class OpdsParser final : public Print {
  bool inAuthor = false;
  bool inAuthorName = false;
  bool inId = false;
+  bool collectCurrentEntry = false;

  bool errorOccured = false;
+  bool feedTruncated = false;
 };
@@ -37,6 +37,19 @@ build_flags =
  -DPNG_MAX_BUFFERED_PIXELS=16416
  -DFREEINK_DEVICE_X4=1
  -DFREEINK_DEVICE_X3=1
+  -DFREEINK_NET_WOLFSSL=1
+  -DWOLFSSL_USER_SETTINGS
+  -DWOLFSSL_OPTIONS_H
+  -DWOLFSSL_CLIENT_EXAMPLE
+  -DWOLFSSL_TLS13
+  -DWOLFSSL_SP_RISCV32
+  -DHAVE_TLS_EXTENSIONS
+  -DHAVE_SUPPORTED_CURVES
+  -DHAVE_HKDF
+  -DHAVE_FFDHE_2048
+  -DHAVE_CURVE25519
+  -DWC_RSA_PSS
+  -DHAVE_SNI
  -Wno-bidi-chars
  -Wl,--wrap=panic_print_backtrace,--wrap=panic_abort,--wrap=bootloader_common_check_efuse_blk_validity
  -fno-exceptions
@@ -51,6 +64,7 @@ board_build.flash_size = 16MB
 board_build.partitions = partitions.csv

 extra_scripts =
+  pre:scripts/patch_wolfssl.py
  pre:scripts/build_html.py
  pre:scripts/gen_i18n.py
  pre:scripts/git_branch.py
@@ -65,6 +79,7 @@ lib_deps =
  SDCardManager=symlink://freeink-sdk/libs/hardware/SDCardManager
  BoardConfig=symlink://freeink-sdk/libs/hardware/BoardConfig
  PowerManager=symlink://freeink-sdk/libs/hardware/PowerManager
+  SecureNet=symlink://freeink-sdk/libs/network/SecureNet
  FreeInkUI=symlink://freeink-sdk/libs/ui/FreeInkUI
  Icons=symlink://freeink-sdk/libs/assets/Icons
  bblanchon/ArduinoJson @ 7.4.2
@@ -72,6 +87,10 @@ lib_deps =
  bitbank2/PNGdec @ 1.1.6
  https://github.com/bitbank2/JPEGDEC.git#86282979224c8a32fd51e091ed5a35b0c699a52b
  links2004/WebSockets @ 2.7.3
+  wolfssl/Arduino-wolfSSL @ 5.7.2
+
+lib_ignore =
+  BLE

 [env:default]
 extends = base
@@ -0,0 +1,29 @@
+from pathlib import Path
+
+Import("env")
+
+
+PROJECT_DIR = Path(env.subst("$PROJECT_DIR"))
+MARKER = "/* CrossPoint wolfSSL compatibility overrides */"
+OVERRIDES = f"""
+
+{MARKER}
+#undef NO_DH
+#ifndef HAVE_FFDHE_2048
+#define HAVE_FFDHE_2048
+#endif
+#undef FP_MAX_BITS
+#define FP_MAX_BITS 16384
+"""
+
+
+def patch_user_settings(path: Path) -> None:
+    text = path.read_text()
+    if MARKER in text:
+        text = text.split(MARKER, 1)[0].rstrip()
+    path.write_text(text + OVERRIDES + "\n")
+    print(f"Patched wolfSSL settings: {path.relative_to(PROJECT_DIR)}")
+
+
+for settings in PROJECT_DIR.glob(".pio/libdeps/*/Arduino-wolfSSL/src/user_settings.h"):
+    patch_user_settings(settings)
@@ -1,5 +1,6 @@
 #include "OpdsBookBrowserActivity.h"

+#include <Arduino.h>
 #include <GfxRenderer.h>
 #include <I18n.h>
 #include <Logging.h>
@@ -19,7 +20,9 @@

 namespace {
 constexpr int PAGE_ITEMS = 23;
-}
+constexpr int DOWNLOAD_PROGRESS_STEP_PERCENT = 5;
+constexpr unsigned long DOWNLOAD_PROGRESS_MIN_UPDATE_MS = 5000;
+}  // namespace

 void OpdsBookBrowserActivity::onEnter() {
  Activity::onEnter();
@@ -193,7 +196,7 @@ void OpdsBookBrowserActivity::fetchFeed(const std::string& path) {
    return;
  }

-  std::string url = (path.find("http") == 0) ? path : UrlUtils::buildUrl(server.url, path);
+  std::string url = UrlUtils::buildUrl(server.url, path);
  LOG_DBG("OPDS", "Fetching: %s", url.c_str());
  OpdsParser parser;
  {
@@ -216,14 +219,19 @@ void OpdsBookBrowserActivity::fetchFeed(const std::string& path) {
  searchTemplate = parser.getSearchTemplate();
  const auto& nextUrl = parser.getNextPageUrl();
  const auto& prevUrl = parser.getPrevPageUrl();
+  const bool feedTruncated = parser.truncated();
  entries = std::move(parser).getEntries();

+  entries.reserve(entries.size() + (prevUrl.empty() ? 0 : 1) + (nextUrl.empty() ? 0 : 1));
  if (!prevUrl.empty()) {
    entries.insert(entries.begin(), OpdsEntry{OpdsEntryType::NAVIGATION, tr(STR_PREV_PAGE), "", prevUrl, ""});
  }
  if (!nextUrl.empty()) {
    entries.push_back(OpdsEntry{OpdsEntryType::NAVIGATION, tr(STR_NEXT_PAGE), "", nextUrl, ""});
  }
+  if (feedTruncated) {
+    LOG_INF("OPDS", "Feed truncated to fit memory");
+  }

  selectorIndex = 0;
  state = entries.empty() ? BrowserState::ERROR : BrowserState::BROWSING;
@@ -231,6 +239,8 @@ void OpdsBookBrowserActivity::fetchFeed(const std::string& path) {
  requestUpdate();
 }

+void OpdsBookBrowserActivity::releaseEntries() { std::vector<OpdsEntry>().swap(entries); }
+
 void OpdsBookBrowserActivity::navigateToEntry(const OpdsEntry& entry) {
  navigationHistory.push_back(currentPath);
  // Resolve to a full URL so sub-sub-navigation retains parent path context
@@ -239,7 +249,7 @@ void OpdsBookBrowserActivity::navigateToEntry(const OpdsEntry& entry) {

  state = BrowserState::LOADING;
  statusMessage = tr(STR_LOADING);
-  entries.clear();
+  releaseEntries();
  selectorIndex = 0;
  requestUpdate(true);
  fetchFeed(currentPath);
@@ -253,7 +263,7 @@ void OpdsBookBrowserActivity::navigateBack() {
    navigationHistory.pop_back();
    state = BrowserState::LOADING;
    statusMessage = tr(STR_LOADING);
-    entries.clear();
+    releaseEntries();
    selectorIndex = 0;
    requestUpdate();
    fetchFeed(currentPath);
@@ -273,12 +283,22 @@ void OpdsBookBrowserActivity::downloadBook(const OpdsEntry& book) {
      "/" + StringUtils::sanitizeFilename((book.author.empty() ? "" : book.author + " - ") + book.title) + ".epub";
  LOG_DBG("OPDS", "Downloading: %s -> %s", downloadUrl.c_str(), filename.c_str());

+  int lastRenderedPercent = -1;
+  unsigned long lastProgressUpdateMs = 0;
  const auto result = HttpDownloader::downloadToFile(
      downloadUrl, filename,
-      [this](const size_t downloaded, const size_t total) {
+      [this, &lastRenderedPercent, &lastProgressUpdateMs](const size_t downloaded, const size_t total) {
        downloadProgress = downloaded;
        downloadTotal = total;
+        const int percent = total > 0 ? static_cast<int>(static_cast<uint64_t>(downloaded) * 100 / total) : 0;
+        const unsigned long now = millis();
+        if (percent >= 100 || lastRenderedPercent < 0 ||
+            percent >= lastRenderedPercent + DOWNLOAD_PROGRESS_STEP_PERCENT ||
+            now - lastProgressUpdateMs >= DOWNLOAD_PROGRESS_MIN_UPDATE_MS) {
+          lastRenderedPercent = percent;
+          lastProgressUpdateMs = now;
          requestUpdate(true);
+        }
      },
      nullptr, server.username, server.password);

@@ -286,6 +306,7 @@ void OpdsBookBrowserActivity::downloadBook(const OpdsEntry& book) {
    clearBookCache(filename);
    state = BrowserState::BROWSING;
  } else {
+    LOG_ERR("OPDS", "Download failed: %d", static_cast<int>(result));
    state = BrowserState::ERROR;
    errorMessage = tr(STR_DOWNLOAD_FAILED);
  }
@@ -340,6 +361,8 @@ void OpdsBookBrowserActivity::performSearch(const std::string& query) {

  state = BrowserState::LOADING;
  statusMessage = tr(STR_LOADING);
+  releaseEntries();
+  selectorIndex = 0;
  requestUpdate(true);
  fetchFeed(url);
 }
@@ -46,6 +46,7 @@ class OpdsBookBrowserActivity final : public Activity {
  void launchWifiSelection();
  void onWifiSelectionComplete(bool connected);
  void fetchFeed(const std::string& path);
+  void releaseEntries();
  void navigateToEntry(const OpdsEntry& entry);
  void navigateBack();
  void downloadBook(const OpdsEntry& book);
@@ -4,27 +4,34 @@
 #include <Logging.h>
 #include <Memory.h>
 #include <base64.h>
-#include <esp_crt_bundle.h>
-#include <esp_http_client.h>

-#include <cstring>
 #include <functional>
 #include <string>

+#if defined(FREEINK_NET_WOLFSSL)
+#include <SecureHttpClient.h>
+
+extern "C" void wolfSSL_Arduino_Serial_Print(const char* const msg) { LOG_DBG("WOLFSSL", "%s", msg); }
+#else
+#include <esp_crt_bundle.h>
+#include <esp_http_client.h>
+#endif
+
 namespace {
-// RX holds the response headers. 4096 fits real OPDS servers; GitHub's release
-// CDN sends more and logs HTTP_HEADER "Buffer length is small", but that's
-// non-fatal: the headers we read (Location, Content-Length) come first and
-// survive. Smaller keeps contiguous heap free while WiFi and TLS are up. TX
-// only carries our GET; the body streams in READ_CHUNK pieces.
-constexpr int HTTP_RX_BUF = 4096;
-constexpr int HTTP_TX_BUF = 1024;
+#if !defined(FREEINK_NET_WOLFSSL)
+// RX holds the response headers. Smaller buffers leave enough contiguous heap
+// for mbedTLS on redirect-heavy OPDS feeds while still preserving the headers
+// we read directly (Location, Content-Length).
+constexpr int HTTP_RX_BUF = 2048;
+constexpr int HTTP_TX_BUF = 512;
+#endif
 // Per-socket-op timeout. Some OPDS download endpoints are slow to send headers
 // (>15s) and chunked catalogs stall mid-body, so 15s killed them. 60s gives
 // slow servers room. esp_http_client's timeout_ms is uint32, so unlike Arduino
 // HTTPClient's uint16 setTimeout it doesn't silently truncate.
 constexpr int HTTP_TIMEOUT_MS = 60000;
-constexpr size_t READ_CHUNK = 2048;
+constexpr size_t READ_CHUNK = 1024;
+constexpr int MAX_REDIRECTS = 5;

 struct Sink {
  std::function<bool(const uint8_t*, size_t)> write;  // returns false to abort the transfer
@@ -38,6 +45,68 @@ bool isRedirect(int status) {
  return status == 301 || status == 302 || status == 303 || status == 307 || status == 308;
 }

+#if defined(FREEINK_NET_WOLFSSL)
+HttpDownloader::DownloadError runGetWolf(const std::string& startUrl, const std::string& username,
+                                         const std::string& password, Sink& sink) {
+  std::string url = startUrl;
+
+  for (int hop = 0; hop <= MAX_REDIRECTS; ++hop) {
+    freeink::SecureHttpClient http;
+    http.setTimeout(HTTP_TIMEOUT_MS);
+    http.setInsecure();
+    if (!http.begin(url)) {
+      LOG_ERR("HTTP", "wolfSSL bad URL: %s", url.c_str());
+      return HttpDownloader::HTTP_ERROR;
+    }
+    http.addHeader("User-Agent", "CrossPoint-ESP32-" CROSSPOINT_VERSION);
+    if (!username.empty() && !password.empty()) {
+      const std::string credentials = username + ":" + password;
+      const String encoded = base64::encode(credentials.c_str());
+      http.addHeader("Authorization", std::string("Basic ") + encoded.c_str());
+    }
+
+    LOG_DBG("HTTP", "wolfSSL GET: %s", url.c_str());
+    const int status = http.GET(
+        [&http, &sink](const uint8_t* data, size_t len) {
+          if (http.getStatus() != 200) return true;
+          if (sink.total == 0 && http.hasContentLength()) sink.total = http.getContentLength();
+          if (!sink.write(data, len)) return false;
+          sink.downloaded += len;
+          if (sink.progress && sink.total > 0) sink.progress(sink.downloaded, sink.total);
+          return true;
+        },
+        [&sink]() { return sink.cancelFlag && *sink.cancelFlag; });
+
+    if (http.aborted()) return HttpDownloader::ABORTED;
+    if (status < 0) {
+      LOG_ERR("HTTP", "wolfSSL request failed: %s", url.c_str());
+      return HttpDownloader::HTTP_ERROR;
+    }
+    if (isRedirect(status)) {
+      const std::string location = http.getHeader("location");
+      if (location.empty() || !freeink::SecureHttpClient::resolveUrl(url, location, url)) {
+        LOG_ERR("HTTP", "wolfSSL bad redirect: %d", status);
+        return HttpDownloader::HTTP_ERROR;
+      }
+      continue;
+    }
+    if (status != 200) {
+      LOG_ERR("HTTP", "wolfSSL unexpected status: %d", status);
+      return HttpDownloader::HTTP_ERROR;
+    }
+    if (http.callbackAborted()) return HttpDownloader::FILE_ERROR;
+    if (!http.responseComplete()) {
+      LOG_ERR("HTTP", "wolfSSL incomplete: got %zu of %zu bytes", sink.downloaded, sink.total);
+      return HttpDownloader::HTTP_ERROR;
+    }
+    return HttpDownloader::OK;
+  }
+  LOG_ERR("HTTP", "too many redirects");
+  return HttpDownloader::HTTP_ERROR;
+}
+#endif
+
+#if !defined(FREEINK_NET_WOLFSSL)
 // Streams a GET body through sink.write in READ_CHUNK pieces. Uses the manual
 // open/fetch_headers/read path rather than esp_http_client_perform(): perform()
 // pushes the whole body through an event callback and reports a chunked body
@@ -84,8 +153,9 @@ HttpDownloader::DownloadError runGet(const std::string& url, const std::string&
  }
  int64_t contentLength = esp_http_client_fetch_headers(client);
  int status = esp_http_client_get_status_code(client);
-  for (int hop = 0; isRedirect(status) && hop < 5; ++hop) {
+  for (int hop = 0; isRedirect(status) && hop < MAX_REDIRECTS; ++hop) {
    if (esp_http_client_set_redirection(client) != ESP_OK) break;
+    esp_http_client_close(client);
    err = esp_http_client_open(client, 0);
    if (err != ESP_OK) {
      LOG_ERR("HTTP", "redirect open failed: %s", esp_err_to_name(err));
@@ -141,6 +211,20 @@ HttpDownloader::DownloadError runGet(const std::string& url, const std::string&
  }
  return HttpDownloader::OK;
 }
+#endif  // !FREEINK_NET_WOLFSSL
+
+// All HTTP(S) fetches go through wolfSSL when it is the active TLS stack: it
+// speaks TLS 1.3 and reads large bodies from servers where the esp_http_client/
+// mbedTLS path fails to connect or stalls mid-stream. Plain-http URLs still use a
+// WiFiClient inside runGetWolf, so this is safe for non-TLS targets too.
+HttpDownloader::DownloadError runGetSecure(const std::string& url, const std::string& username,
+                                           const std::string& password, Sink& sink) {
+#if defined(FREEINK_NET_WOLFSSL)
+  return runGetWolf(url, username, password, sink);
+#else
+  return runGet(url, username, password, sink);
+#endif
+}
 }  // namespace

 bool HttpDownloader::fetchUrl(const std::string& url, Stream& outContent, const std::string& username,
@@ -148,7 +232,7 @@ bool HttpDownloader::fetchUrl(const std::string& url, Stream& outContent, const
  LOG_DBG("HTTP", "Fetching: %s", url.c_str());
  Sink sink;
  sink.write = [&outContent](const uint8_t* data, size_t len) { return outContent.write(data, len) == len; };
-  return runGet(url, username, password, sink) == OK;
+  return runGetSecure(url, username, password, sink) == OK;
 }

 bool HttpDownloader::fetchUrl(const std::string& url, std::string& outContent, const std::string& username,
@@ -160,7 +244,7 @@ bool HttpDownloader::fetchUrl(const std::string& url, std::string& outContent, c
    outContent.append(reinterpret_cast<const char*>(data), len);
    return true;
  };
-  return runGet(url, username, password, sink) == OK;
+  return runGetSecure(url, username, password, sink) == OK;
 }

 bool HttpDownloader::fetchUrl(const std::string& url, const DataCallback& onData, const std::string& username,
@@ -168,7 +252,7 @@ bool HttpDownloader::fetchUrl(const std::string& url, const DataCallback& onData
  LOG_DBG("HTTP", "Fetching: %s", url.c_str());
  Sink sink;
  sink.write = onData;
-  return runGet(url, username, password, sink) == OK;
+  return runGetSecure(url, username, password, sink) == OK;
 }

 HttpDownloader::DownloadError HttpDownloader::downloadToFile(const std::string& url, const std::string& destPath,
@@ -190,7 +274,7 @@ HttpDownloader::DownloadError HttpDownloader::downloadToFile(const std::string&
  sink.cancelFlag = cancelFlag;
  sink.write = [&file](const uint8_t* data, size_t len) { return file.write(data, len) == len; };

-  const DownloadError result = runGet(url, username, password, sink);
+  const DownloadError result = runGetSecure(url, username, password, sink);
  // Close before any remove() on the same path; DESTRUCTOR_CLOSES_FILE would
  // otherwise close only after the remove.
  file.close();
@@ -2,15 +2,12 @@

 // clang-format off
 // HttpDownloader.h pulls Arduino/SdFat, whose macros collide with lwip's
-// ip4_addr.h unless seen before esp_http_client (which includes lwip). Pin this
-// order; clang-format would otherwise sort the local header last and break the
-// build.
+// ip4_addr.h unless seen first. Pin this order; clang-format would otherwise sort
+// the local header last and break the build.
 #include "HttpDownloader.h"
 #include <Logging.h>
 #include <ReleaseJsonParser.h>
-#include <esp_crt_bundle.h>
-#include <esp_http_client.h>
-#include <esp_https_ota.h>
+#include <esp_ota_ops.h>
 #include <esp_wifi.h>
 // clang-format on

@@ -18,10 +15,6 @@

 namespace {
 constexpr char latestReleaseUrl[] = "https://api.github.com/repos/crosspoint-reader/crosspoint-reader/releases/latest";
-
-esp_err_t http_client_set_header_cb(esp_http_client_handle_t http_client) {
-  return esp_http_client_set_header(http_client, "User-Agent", "CrossPoint-ESP32-" CROSSPOINT_VERSION);
-}
 }  // namespace

 OtaUpdater::OtaUpdaterError OtaUpdater::checkForUpdate() {
@@ -116,44 +109,39 @@ OtaUpdater::OtaUpdaterError OtaUpdater::installUpdate(ProgressCallback onProgres
    return UPDATE_OLDER_ERROR;
  }

-  esp_https_ota_handle_t ota_handle = NULL;
-  esp_err_t esp_err;
+  // esp_https_ota is hardwired to esp-tls/mbedTLS, whose precompiled build on this
+  // package can't negotiate TLS 1.3 (see SecureClient.h). Drive the OTA partition
+  // ourselves and stream the firmware through HttpDownloader, which runs over
+  // wolfSSL when FREEINK_NET_WOLFSSL is set, reusing its redirect handling for the
+  // GitHub -> CDN hop.
+  const esp_partition_t* updatePartition = esp_ota_get_next_update_partition(nullptr);
+  if (!updatePartition) {
+    LOG_ERR("OTA", "No OTA partition available");
+    return INTERNAL_UPDATE_ERROR;
+  }

-  esp_http_client_config_t client_config = {
-      .url = otaUrl.c_str(),
-      .timeout_ms = 15000,
-      // 4096 holds the github->CDN redirect headers (the 512 default truncates
-      // them); TX only carries our GET. Both are contiguous blocks contending
-      // with the TLS handshake on a tight internal arena, so keep them minimal.
-      .buffer_size = 4096,
-      .buffer_size_tx = 1024,
-      .skip_cert_common_name_check = true,
-      .crt_bundle_attach = esp_crt_bundle_attach,
-      .keep_alive_enable = true,
-  };
-
-  esp_https_ota_config_t ota_config = {
-      .http_config = &client_config,
-      .http_client_init_cb = http_client_set_header_cb,
-  };
+  esp_ota_handle_t otaHandle = 0;
+  esp_err_t esp_err = esp_ota_begin(updatePartition, OTA_SIZE_UNKNOWN, &otaHandle);
+  if (esp_err != ESP_OK) {
+    LOG_ERR("OTA", "esp_ota_begin failed: %s", esp_err_to_name(esp_err));
+    return INTERNAL_UPDATE_ERROR;
+  }

  /* For better timing and connectivity, we disable power saving for WiFi */
  esp_wifi_set_ps(WIFI_PS_NONE);

-  esp_err = esp_https_ota_begin(&ota_config, &ota_handle);
-  if (esp_err != ESP_OK) {
-    LOG_DBG("OTA", "HTTP OTA Begin Failed: %s", esp_err_to_name(esp_err));
-    return INTERNAL_UPDATE_ERROR;
-  }
-
+  processedSize = 0;
  int lastReportedPct = -1;
-  do {
-    esp_err = esp_https_ota_perform(ota_handle);
-    processedSize = esp_https_ota_get_image_len_read(ota_handle);
-    // Fire the callback only on whole-percent change. Without this it fired
-    // every ~100ms perform iteration, waking the render task whose framebuffer
-    // work contends with TLS on the same internal arena. E-ink can't repaint
-    // faster than a percent tick anyway.
+  bool flashOk = true;
+  const bool fetchOk = HttpDownloader::fetchUrl(otaUrl, [&](const uint8_t* data, size_t len) {
+    if (esp_ota_write(otaHandle, data, len) != ESP_OK) {
+      flashOk = false;
+      return false;  // abort the transfer
+    }
+    processedSize += len;
+    // Fire the callback only on whole-percent change. Per-chunk updates wake the
+    // render task, whose framebuffer work contends with TLS on the internal arena,
+    // and e-ink can't repaint faster than a percent tick anyway.
    if (onProgress && totalSize > 0) {
      const int pct = static_cast<int>(static_cast<uint64_t>(processedSize) * 100 / totalSize);
      if (pct != lastReportedPct) {
@@ -161,27 +149,27 @@ OtaUpdater::OtaUpdaterError OtaUpdater::installUpdate(ProgressCallback onProgres
        onProgress(ctx);
      }
    }
-    delay(100);  // TODO: should we replace this with something better?
-  } while (esp_err == ESP_ERR_HTTPS_OTA_IN_PROGRESS);
+    return true;
+  });

  /* Return back to default power saving for WiFi in case of failing */
  esp_wifi_set_ps(WIFI_PS_MIN_MODEM);

-  if (esp_err != ESP_OK) {
-    LOG_ERR("OTA", "esp_https_ota_perform Failed: %s", esp_err_to_name(esp_err));
-    esp_https_ota_finish(ota_handle);
-    return HTTP_ERROR;
+  if (!fetchOk || !flashOk) {
+    LOG_ERR("OTA", "Firmware install failed (%s)", flashOk ? "download" : "flash write");
+    esp_ota_abort(otaHandle);
+    return flashOk ? HTTP_ERROR : INTERNAL_UPDATE_ERROR;
  }

-  if (!esp_https_ota_is_complete_data_received(ota_handle)) {
-    LOG_ERR("OTA", "esp_https_ota_is_complete_data_received Failed: %s", esp_err_to_name(esp_err));
-    esp_https_ota_finish(ota_handle);
+  esp_err = esp_ota_end(otaHandle);  // verifies the written image
+  if (esp_err != ESP_OK) {
+    LOG_ERR("OTA", "esp_ota_end failed: %s", esp_err_to_name(esp_err));
    return INTERNAL_UPDATE_ERROR;
  }

-  esp_err = esp_https_ota_finish(ota_handle);
+  esp_err = esp_ota_set_boot_partition(updatePartition);
  if (esp_err != ESP_OK) {
-    LOG_ERR("OTA", "esp_https_ota_finish Failed: %s", esp_err_to_name(esp_err));
+    LOG_ERR("OTA", "esp_ota_set_boot_partition failed: %s", esp_err_to_name(esp_err));
    return INTERNAL_UPDATE_ERROR;
  }

@@ -1,6 +1,29 @@
 #include "UrlUtils.h"

+#include <cstdio>
+
 namespace UrlUtils {
+namespace {
+bool isHexDigit(const char c) { return (c >= '0' && c <= '9') || (c >= 'A' && c <= 'F') || (c >= 'a' && c <= 'f'); }
+
+bool shouldEncode(const unsigned char c) {
+  if (c <= 0x20 || c >= 0x7f) return true;
+  switch (c) {
+    case '"':
+    case '<':
+    case '>':
+    case '\\':
+    case '^':
+    case '`':
+    case '{':
+    case '|':
+    case '}':
+      return true;
+    default:
+      return false;
+  }
+}
+}  // namespace

 std::string ensureProtocol(const std::string& url) {
  if (url.find("://") == std::string::npos) {
@@ -22,18 +45,39 @@ std::string extractHost(const std::string& url) {
  return pathStart == std::string::npos ? url : url.substr(0, pathStart);
 }

+std::string encodeUnsafeUrlChars(const std::string& url) {
+  std::string out;
+  out.reserve(url.size());
+  for (size_t i = 0; i < url.size(); ++i) {
+    const unsigned char c = static_cast<unsigned char>(url[i]);
+    if (c == '%' && i + 2 < url.size() && isHexDigit(url[i + 1]) && isHexDigit(url[i + 2])) {
+      out += url[i];
+      out += url[i + 1];
+      out += url[i + 2];
+      i += 2;
+    } else if (c == '%' || shouldEncode(c)) {
+      char encoded[4];
+      snprintf(encoded, sizeof(encoded), "%%%02X", c);
+      out += encoded;
+    } else {
+      out += static_cast<char>(c);
+    }
+  }
+  return out;
+}
+
 std::string buildUrl(const std::string& serverUrl, const std::string& path) {
  // If path is already an absolute URL (has protocol), use it directly
  if (path.find("://") != std::string::npos) {
-    return path;
+    return encodeUnsafeUrlChars(path);
  }
  const std::string urlWithProtocol = ensureProtocol(serverUrl);
  if (path.empty()) {
-    return urlWithProtocol;
+    return encodeUnsafeUrlChars(urlWithProtocol);
  }
  if (path[0] == '/') {
    // Absolute path - use just the host
-    return extractHost(urlWithProtocol) + path;
+    return encodeUnsafeUrlChars(extractHost(urlWithProtocol) + path);
  }
  // Relative path - strip query string from base before appending
  std::string base = urlWithProtocol;
@@ -42,9 +86,9 @@ std::string buildUrl(const std::string& serverUrl, const std::string& path) {
    base.resize(queryPos);
  }
  if (base.back() == '/') {
-    return base + path;
+    return encodeUnsafeUrlChars(base + path);
  }
-  return base + "/" + path;
+  return encodeUnsafeUrlChars(base + "/" + path);
 }

 }  // namespace UrlUtils
@@ -13,6 +13,11 @@ std::string ensureProtocol(const std::string& url);
 */
 std::string extractHost(const std::string& url);

+/**
+ * Percent-encode raw characters that esp_http_client rejects in a URL.
+ */
+std::string encodeUnsafeUrlChars(const std::string& url);
+
 /**
 * Build full URL from server URL and path.
 * If path starts with /, it's an absolute path from the host root.