Issue 2162

example/Makefile

@@ -18,7 +18,7 @@ ZLIB_SUPPORT = -DCPPHTTPLIB_ZLIB_SUPPORT -lz
 BROTLI_DIR = $(PREFIX)/opt/brotli
 BROTLI_SUPPORT = -DCPPHTTPLIB_BROTLI_SUPPORT -I$(BROTLI_DIR)/include -L$(BROTLI_DIR)/lib -lbrotlicommon -lbrotlienc -lbrotlidec
 
-all: server client hello simplecli simplesvr upload redirect ssesvr ssecli benchmark one_time_request server_and_client
+all: server client hello simplecli simplesvr upload redirect ssesvr ssecli benchmark one_time_request server_and_client accept_header
 
 server : server.cc ../httplib.h Makefile
 	$(CXX) -o server $(CXXFLAGS) server.cc $(OPENSSL_SUPPORT) $(ZLIB_SUPPORT) $(BROTLI_SUPPORT)
@@ -56,9 +56,12 @@ one_time_request : one_time_request.cc ../httplib.h Makefile
 server_and_client : server_and_client.cc ../httplib.h Makefile
 	$(CXX) -o server_and_client $(CXXFLAGS) server_and_client.cc $(OPENSSL_SUPPORT) $(ZLIB_SUPPORT) $(BROTLI_SUPPORT)
 
+accept_header : accept_header.cc ../httplib.h Makefile
+	$(CXX) -o accept_header $(CXXFLAGS) accept_header.cc $(OPENSSL_SUPPORT) $(ZLIB_SUPPORT) $(BROTLI_SUPPORT)
+
 pem:
 	openssl genrsa 2048 > key.pem
 	openssl req -new -key key.pem | openssl x509 -days 3650 -req -signkey key.pem > cert.pem
 
 clean:
-	rm server client hello simplecli simplesvr upload redirect ssesvr ssecli benchmark one_time_request server_and_client *.pem
+	rm server client hello simplecli simplesvr upload redirect ssesvr ssecli benchmark one_time_request server_and_client accept_header *.pem

example/accept_header.cc

@@ -0,0 +1,134 @@
+#include "httplib.h"
+#include <iostream>
+
+int main() {
+    using namespace httplib;
+
+    // Example usage of parse_accept_header function
+    std::cout << "=== Accept Header Parser Example ===" << std::endl;
+
+    // Example 1: Simple Accept header
+    std::string accept1 = "text/html,application/json,text/plain";
+    std::vector<std::string> result1;
+    if (detail::parse_accept_header(accept1, result1)) {
+        std::cout << "\nExample 1: " << accept1 << std::endl;
+        std::cout << "Parsed order:" << std::endl;
+        for (size_t i = 0; i < result1.size(); ++i) {
+            std::cout << "  " << (i + 1) << ". " << result1[i] << std::endl;
+        }
+    } else {
+        std::cout << "\nExample 1: Failed to parse Accept header" << std::endl;
+    }
+
+    // Example 2: Accept header with quality values
+    std::string accept2 = "text/html;q=0.9,application/json;q=1.0,text/plain;q=0.8";
+    std::vector<std::string> result2;
+    if (detail::parse_accept_header(accept2, result2)) {
+        std::cout << "\nExample 2: " << accept2 << std::endl;
+        std::cout << "Parsed order (sorted by priority):" << std::endl;
+        for (size_t i = 0; i < result2.size(); ++i) {
+            std::cout << "  " << (i + 1) << ". " << result2[i] << std::endl;
+        }
+    } else {
+        std::cout << "\nExample 2: Failed to parse Accept header" << std::endl;
+    }
+
+    // Example 3: Browser-like Accept header
+    std::string accept3 = "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8";
+    std::vector<std::string> result3;
+    if (detail::parse_accept_header(accept3, result3)) {
+        std::cout << "\nExample 3: " << accept3 << std::endl;
+        std::cout << "Parsed order:" << std::endl;
+        for (size_t i = 0; i < result3.size(); ++i) {
+            std::cout << "  " << (i + 1) << ". " << result3[i] << std::endl;
+        }
+    } else {
+        std::cout << "\nExample 3: Failed to parse Accept header" << std::endl;
+    }
+
+    // Example 4: Invalid Accept header examples
+    std::cout << "\n=== Invalid Accept Header Examples ===" << std::endl;
+
+    std::vector<std::string> invalid_examples = {
+        "text/html;q=1.5,application/json",  // q > 1.0
+        "text/html;q=-0.1,application/json", // q < 0.0
+        "text/html;q=invalid,application/json", // invalid q value
+        "invalidtype,application/json",      // invalid media type
+        ",application/json"                  // empty entry
+    };
+
+    for (const auto& invalid_accept : invalid_examples) {
+        std::vector<std::string> temp_result;
+        std::cout << "\nTesting invalid: " << invalid_accept << std::endl;
+        if (detail::parse_accept_header(invalid_accept, temp_result)) {
+            std::cout << "  Unexpectedly succeeded!" << std::endl;
+        } else {
+            std::cout << "  Correctly rejected as invalid" << std::endl;
+        }
+    }
+
+    // Example 4: Server usage example
+    std::cout << "\n=== Server Usage Example ===" << std::endl;
+    Server svr;
+
+    svr.Get("/api/data", [](const Request& req, Response& res) {
+        // Get Accept header
+        auto accept_header = req.get_header_value("Accept");
+        if (accept_header.empty()) {
+            accept_header = "*/*";  // Default if no Accept header
+        }
+
+        // Parse accept header to get preferred content types
+        std::vector<std::string> preferred_types;
+        if (!detail::parse_accept_header(accept_header, preferred_types)) {
+            // Invalid Accept header
+            res.status = 400;  // Bad Request
+            res.set_content("Invalid Accept header", "text/plain");
+            return;
+        }
+
+        std::cout << "Client Accept header: " << accept_header << std::endl;
+        std::cout << "Preferred types in order:" << std::endl;
+        for (size_t i = 0; i < preferred_types.size(); ++i) {
+            std::cout << "  " << (i + 1) << ". " << preferred_types[i] << std::endl;
+        }
+
+        // Choose response format based on client preference
+        std::string response_content;
+        std::string content_type;
+
+        for (const auto& type : preferred_types) {
+            if (type == "application/json" || type == "application/*" || type == "*/*") {
+                response_content = "{\"message\": \"Hello, World!\", \"data\": [1, 2, 3]}";
+                content_type = "application/json";
+                break;
+            } else if (type == "text/html" || type == "text/*") {
+                response_content = "<html><body><h1>Hello, World!</h1><p>Data: 1, 2, 3</p></body></html>";
+                content_type = "text/html";
+                break;
+            } else if (type == "text/plain") {
+                response_content = "Hello, World!\nData: 1, 2, 3";
+                content_type = "text/plain";
+                break;
+            }
+        }
+
+        if (response_content.empty()) {
+            // No supported content type found
+            res.status = 406;  // Not Acceptable
+            res.set_content("No acceptable content type found", "text/plain");
+            return;
+        }
+
+        res.set_content(response_content, content_type);
+        std::cout << "Responding with: " << content_type << std::endl;
+    });
+
+    std::cout << "Server configured. You can test it with:" << std::endl;
+    std::cout << "  curl -H \"Accept: application/json\" http://localhost:8080/api/data" << std::endl;
+    std::cout << "  curl -H \"Accept: text/html\" http://localhost:8080/api/data" << std::endl;
+    std::cout << "  curl -H \"Accept: text/plain\" http://localhost:8080/api/data" << std::endl;
+    std::cout << "  curl -H \"Accept: text/html;q=0.9,application/json;q=1.0\" http://localhost:8080/api/data" << std::endl;
+
+    return 0;
+}

httplib.h

@@ -670,6 +670,7 @@ struct Request {
   std::function<bool()> is_connection_closed = []() { return true; };
 
   // for client
+  std::vector<std::string> accept_content_types;
   ResponseHandler response_handler;
   ContentReceiverWithProgress content_receiver;
   Progress progress;
@@ -2491,6 +2492,9 @@ bool parse_multipart_boundary(const std::string &content_type,
 
 bool parse_range_header(const std::string &s, Ranges &ranges);
 
+bool parse_accept_header(const std::string &s,
+                         std::vector<std::string> &content_types);
+
 int close_socket(socket_t sock);
 
 ssize_t send_socket(socket_t sock, const void *ptr, size_t size, int flags);
@@ -5026,6 +5030,123 @@ inline bool parse_range_header(const std::string &s, Ranges &ranges) try {
 } catch (...) { return false; }
 #endif
 
+inline bool parse_accept_header(const std::string &s,
+                                std::vector<std::string> &content_types) {
+  content_types.clear();
+
+  // Empty string is considered valid (no preference)
+  if (s.empty()) { return true; }
+
+  // Check for invalid patterns: leading/trailing commas or consecutive commas
+  if (s.front() == ',' || s.back() == ',' ||
+      s.find(",,") != std::string::npos) {
+    return false;
+  }
+
+  struct AcceptEntry {
+    std::string media_type;
+    double quality;
+    int order; // Original order in header
+  };
+
+  std::vector<AcceptEntry> entries;
+  int order = 0;
+  bool has_invalid_entry = false;
+
+  // Split by comma and parse each entry
+  split(s.data(), s.data() + s.size(), ',', [&](const char *b, const char *e) {
+    std::string entry(b, e);
+    entry = trim_copy(entry);
+
+    if (entry.empty()) {
+      has_invalid_entry = true;
+      return;
+    }
+
+    AcceptEntry accept_entry;
+    accept_entry.quality = 1.0; // Default quality
+    accept_entry.order = order++;
+
+    // Find q= parameter
+    auto q_pos = entry.find(";q=");
+    if (q_pos == std::string::npos) { q_pos = entry.find("; q="); }
+
+    if (q_pos != std::string::npos) {
+      // Extract media type (before q parameter)
+      accept_entry.media_type = trim_copy(entry.substr(0, q_pos));
+
+      // Extract quality value
+      auto q_start = entry.find('=', q_pos) + 1;
+      auto q_end = entry.find(';', q_start);
+      if (q_end == std::string::npos) { q_end = entry.length(); }
+
+      std::string quality_str =
+          trim_copy(entry.substr(q_start, q_end - q_start));
+      if (quality_str.empty()) {
+        has_invalid_entry = true;
+        return;
+      }
+
+      try {
+        accept_entry.quality = std::stod(quality_str);
+        // Check if quality is in valid range [0.0, 1.0]
+        if (accept_entry.quality < 0.0 || accept_entry.quality > 1.0) {
+          has_invalid_entry = true;
+          return;
+        }
+      } catch (...) {
+        has_invalid_entry = true;
+        return;
+      }
+    } else {
+      // No quality parameter, use entire entry as media type
+      accept_entry.media_type = entry;
+    }
+
+    // Remove additional parameters from media type
+    auto param_pos = accept_entry.media_type.find(';');
+    if (param_pos != std::string::npos) {
+      accept_entry.media_type =
+          trim_copy(accept_entry.media_type.substr(0, param_pos));
+    }
+
+    // Basic validation of media type format
+    if (accept_entry.media_type.empty()) {
+      has_invalid_entry = true;
+      return;
+    }
+
+    // Check for basic media type format (should contain '/' or be '*')
+    if (accept_entry.media_type != "*" &&
+        accept_entry.media_type.find('/') == std::string::npos) {
+      has_invalid_entry = true;
+      return;
+    }
+
+    entries.push_back(accept_entry);
+  });
+
+  // Return false if any invalid entry was found
+  if (has_invalid_entry) { return false; }
+
+  // Sort by quality (descending), then by original order (ascending)
+  std::sort(entries.begin(), entries.end(),
+            [](const AcceptEntry &a, const AcceptEntry &b) {
+              if (a.quality != b.quality) {
+                return a.quality > b.quality; // Higher quality first
+              }
+              return a.order < b.order; // Earlier order first for same quality
+            });
+
+  // Extract sorted media types
+  content_types.reserve(entries.size());
+  for (const auto &entry : entries) {
+    content_types.push_back(entry.media_type);
+  }
+
+  return true;
+}
+
 class MultipartFormDataParser {
 public:
   MultipartFormDataParser() = default;
@@ -7446,6 +7567,14 @@ Server::process_request(Stream &strm, const std::string &remote_addr,
   req.set_header("LOCAL_ADDR", req.local_addr);
   req.set_header("LOCAL_PORT", std::to_string(req.local_port));
 
+  if (req.has_header("Accept")) {
+    const auto &accept_header = req.get_header_value("Accept");
+    if (!detail::parse_accept_header(accept_header, req.accept_content_types)) {
+      res.status = StatusCode::BadRequest_400;
+      return write_response(strm, close_connection, req, res);
+    }
+  }
+
   if (req.has_header("Range")) {
     const auto &range_header_value = req.get_header_value("Range");
     if (!detail::parse_range_header(range_header_value, req.ranges)) {