From e5c2e251442fa5071cb16b446ce4f91131662a3c Mon Sep 17 00:00:00 2001
From: Johannes Tax <johannes.tax@grafana.com>
Date: Thu, 7 Mar 2024 16:16:16 +0100
Subject: [PATCH] Support URL-encoded values for `OTEL_EXPORTER_OTLP_HEADERS`
 (#2579)

---
 CHANGELOG.md                                  |  2 +
 exporters/otlp/src/otlp_grpc_client.cc        |  3 +-
 exporters/otlp/src/otlp_http_client.cc        |  3 +-
 .../ext/http/common/url_parser.h              | 44 +++++++++++++++++++
 ext/test/http/url_parser_test.cc              | 18 ++++++++
 5 files changed, 68 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 719def9844..ccb629074e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,6 +17,8 @@ Increment the:
 
 * [EXPORTER] Gzip compression support for OTLP/HTTP and OTLP/gRPC exporter
   [#2530](https://github.com/open-telemetry/opentelemetry-cpp/pull/2530)
+* [EXPORTER] Support URL-encoded values for `OTEL_EXPORTER_OTLP_HEADERS`
+  [#2579](https://github.com/open-telemetry/opentelemetry-cpp/pull/2579)
 
 Important changes:
 
diff --git a/exporters/otlp/src/otlp_grpc_client.cc b/exporters/otlp/src/otlp_grpc_client.cc
index f57e476955..90bbd41938 100644
--- a/exporters/otlp/src/otlp_grpc_client.cc
+++ b/exporters/otlp/src/otlp_grpc_client.cc
@@ -342,7 +342,8 @@ std::unique_ptr<grpc::ClientContext> OtlpGrpcClient::MakeClientContext(
 
   for (auto &header : options.metadata)
   {
-    context->AddMetadata(header.first, header.second);
+    context->AddMetadata(header.first,
+                         opentelemetry::ext::http::common::UrlDecoder::Decode(header.second));
   }
 
   return context;
diff --git a/exporters/otlp/src/otlp_http_client.cc b/exporters/otlp/src/otlp_http_client.cc
index 151873c221..4b4a92c2b0 100644
--- a/exporters/otlp/src/otlp_http_client.cc
+++ b/exporters/otlp/src/otlp_http_client.cc
@@ -948,7 +948,8 @@ OtlpHttpClient::createSession(
 
   for (auto &header : options_.http_headers)
   {
-    request->AddHeader(header.first, header.second);
+    request->AddHeader(header.first,
+                       opentelemetry::ext::http::common::UrlDecoder::Decode(header.second));
   }
   request->SetUri(http_uri_);
   request->SetSslOptions(options_.ssl_options);
diff --git a/ext/include/opentelemetry/ext/http/common/url_parser.h b/ext/include/opentelemetry/ext/http/common/url_parser.h
index 31da004003..5e18d85bb6 100644
--- a/ext/include/opentelemetry/ext/http/common/url_parser.h
+++ b/ext/include/opentelemetry/ext/http/common/url_parser.h
@@ -131,6 +131,50 @@ class UrlParser
   }
 };
 
+class UrlDecoder
+{
+public:
+  static std::string Decode(const std::string &encoded)
+  {
+    std::string result;
+    result.reserve(encoded.size());
+
+    for (size_t pos = 0; pos < encoded.size(); pos++)
+    {
+      if (encoded[pos] == '%')
+      {
+
+        // Invalid input: less than two characters left after '%'
+        if (encoded.size() < pos + 3)
+        {
+          return encoded;
+        }
+
+        char hex[3] = {0};
+        hex[0]      = encoded[++pos];
+        hex[1]      = encoded[++pos];
+
+        char *endptr;
+        long value = strtol(hex, &endptr, 16);
+
+        // Invalid input: no valid hex characters after '%'
+        if (endptr != &hex[2])
+        {
+          return encoded;
+        }
+
+        result.push_back(static_cast<char>(value));
+      }
+      else
+      {
+        result.push_back(encoded[pos]);
+      }
+    }
+
+    return result;
+  }
+};
+
 }  // namespace common
 
 }  // namespace http
diff --git a/ext/test/http/url_parser_test.cc b/ext/test/http/url_parser_test.cc
index e205ff6ef7..212c5655a7 100644
--- a/ext/test/http/url_parser_test.cc
+++ b/ext/test/http/url_parser_test.cc
@@ -134,3 +134,21 @@ TEST(UrlParserTests, BasicTests)
     ASSERT_EQ(url.query_, url_properties["query"]);
   }
 }
+
+TEST(UrlDecoderTests, BasicTests)
+{
+  std::map<std::string, std::string> testdata{
+      {"Authentication=Basic xxx", "Authentication=Basic xxx"},
+      {"Authentication=Basic%20xxx", "Authentication=Basic xxx"},
+      {"%C3%B6%C3%A0%C2%A7%C3%96abcd%C3%84", "öà§ÖabcdÄ"},
+      {"%2x", "%2x"},
+      {"%20", " "},
+      {"text%2", "text%2"},
+  };
+
+  for (auto &testsample : testdata)
+  {
+    ASSERT_EQ(http_common::UrlDecoder::Decode(testsample.first), testsample.second);
+    ASSERT_TRUE(http_common::UrlDecoder::Decode(testsample.first) == testsample.second);
+  }
+}