refactor: Replace libevent use in urlDecode with our own code

2 files changed, 33 insertions, 10 deletions

diff --git a/src/common/url.cpp b/src/common/url.cpp
index 053e1a825c..d0bf4e0cbe 100644
--- a/src/common/url.cpp
+++ b/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;
 }
diff --git a/src/common/url.h b/src/common/url.h
index b16b8241af..7b0a944776 100644
--- a/src/common/url.h
+++ b/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;