refactor: Replace libevent use in urlDecode with our own code

Author: fjahr

configure.ac

@@ -1706,7 +1706,6 @@ AM_CONDITIONAL([ENABLE_QT_TESTS], [test "$BUILD_TEST_QT" = "yes"])
 AM_CONDITIONAL([ENABLE_BENCH], [test "$use_bench" = "yes"])
 AM_CONDITIONAL([USE_QRCODE], [test "$use_qr" = "yes"])
 AM_CONDITIONAL([USE_LCOV], [test "$use_lcov" = "yes"])
-AM_CONDITIONAL([USE_LIBEVENT], [test "$use_libevent" = "yes"])
 AM_CONDITIONAL([HARDEN], [test "$use_hardening" = "yes"])
 AM_CONDITIONAL([ENABLE_SSE42], [test "$enable_sse42" = "yes"])
 AM_CONDITIONAL([ENABLE_SSE41], [test "$enable_sse41" = "yes"])

src/Makefile.am

@@ -679,6 +679,7 @@ libbitcoin_common_a_SOURCES = \
   common/run_command.cpp \
   common/settings.cpp \
   common/system.cpp \
+  common/url.cpp \
   compressor.cpp \
   core_read.cpp \
   core_write.cpp \
@@ -711,11 +712,6 @@ libbitcoin_common_a_SOURCES = \
   script/solver.cpp \
   warnings.cpp \
   $(BITCOIN_CORE_H)
-
-if USE_LIBEVENT
-libbitcoin_common_a_CPPFLAGS += $(EVENT_CFLAGS)
-libbitcoin_common_a_SOURCES += common/url.cpp
-endif
 #
 
 # util #

src/common/url.cpp

@@ -4,19 +4,41 @@
 
 #include <common/url.h>
 
-#include <event2/http.h>
-
-#include <cstdlib>
+#include <charconv>
 #include <string>
+#include <string_view>
+#include <system_error>
 
-std::string urlDecode(const std::string &urlEncoded) {
+std::string urlDecode(std::string_view urlEncoded)
+{
     std::string res;
-    if (!urlEncoded.empty()) {
-        char *decoded = evhttp_uridecode(urlEncoded.c_str(), false, nullptr);
-        if (decoded) {
-            res = std::string(decoded);
-            free(decoded);
+    res.reserve(urlEncoded.size());
+
+    for (size_t i = 0; i < urlEncoded.size(); ++i) {
+        char c = urlEncoded[i];
+        // Special handling for percent which should be followed by two hex digits
+        // representing an octet values, see RFC 3986, Section 2.1 Percent-Encoding
+        if (c == '%' && i + 2 < urlEncoded.size()) {
+            unsigned int decoded_value{0};
+            auto [p, ec] = std::from_chars(urlEncoded.data() + i + 1, urlEncoded.data() + i + 3, decoded_value, 16);
+
+            // Only if there is no error and the pointer is set to the end of
+            // the string, we can be sure both characters were valid hex
+            if (ec == std::errc{} && p == urlEncoded.data() + i + 3) {
+                // A null character terminates the string
+                if (decoded_value == 0) {
+                    return res;
+                }
+
+                res += static_cast<char>(decoded_value);
+                // Next two characters are part of the percent encoding
+                i += 2;
+                continue;
+            }
+            // In case of invalid percent encoding, add the '%' and continue
         }
+        res += c;
     }
+
     return res;
 }

src/common/url.h

@@ -6,8 +6,9 @@
 #define BITCOIN_COMMON_URL_H
 
 #include <string>
+#include <string_view>
 
-using UrlDecodeFn = std::string(const std::string& url_encoded);
+using UrlDecodeFn = std::string(std::string_view url_encoded);
 UrlDecodeFn urlDecode;
 extern UrlDecodeFn* const URL_DECODE;
 

src/wallet/rpc/util.cpp

@@ -11,6 +11,7 @@
 #include <wallet/context.h>
 #include <wallet/wallet.h>
 
+#include <string_view>
 #include <univalue.h>
 
 #include <boost/date_time/posix_time/posix_time.hpp>
@@ -61,9 +62,9 @@ bool ParseIncludeWatchonly(const UniValue& include_watchonly, const CWallet& wal
 
 bool GetWalletNameFromJSONRPCRequest(const JSONRPCRequest& request, std::string& wallet_name)
 {
-    if (URL_DECODE && request.URI.substr(0, WALLET_ENDPOINT_BASE.size()) == WALLET_ENDPOINT_BASE) {
+    if (URL_DECODE && request.URI.starts_with(WALLET_ENDPOINT_BASE)) {
         // wallet endpoint was used
-        wallet_name = URL_DECODE(request.URI.substr(WALLET_ENDPOINT_BASE.size()));
+        wallet_name = URL_DECODE(std::string_view{request.URI}.substr(WALLET_ENDPOINT_BASE.size()));
         return true;
     }
     return false;