feat: Implement POST form submission

Add full support for POST method form submissions alongside existing GET support.

Changes:
- Add HttpClient::post() method with configurable Content-Type
- Implement URL encoding for form data (RFC 3986 compliant)
- Update Browser::submit_form() to detect and handle both GET and POST methods
- Add proper form data encoding with special character handling
- Include Content-Type header for POST requests

Features:
- Automatic method detection from form's method attribute
- URL-encoded form data (application/x-www-form-urlencoded)
- Proper encoding of special characters (spaces, &, =, etc.)
- Status messages for form submission feedback
- History tracking for POST responses

Testing:
- Add test_post_form.html with GET, POST, and special character test cases
- Uses httpbin.org endpoints for validation

Resolves TODO at browser.cpp:238 - POST handling is now fully implemented.

src/browser.cpp

@@ -5,6 +5,8 @@
 #include <algorithm>
 #include <sstream>
 #include <map>
+#include <cctype>
+#include <cstdio>
 
 class Browser::Impl {
 public:
@@ -207,9 +209,27 @@ public:
         }
     }
 
+    // URL encode helper function
+    std::string url_encode(const std::string& value) {
+        std::string result;
+        for (unsigned char c : value) {
+            if (isalnum(c) || c == '-' || c == '_' || c == '.' || c == '~') {
+                result += c;
+            } else if (c == ' ') {
+                result += '+';
+            } else {
+                char hex[4];
+                snprintf(hex, sizeof(hex), "%%%02X", c);
+                result += hex;
+            }
+        }
+        return result;
+    }
+
     void submit_form(DomNode* button) {
         status_message = "Submitting form...";
-        // Simple GET implementation for now
+
+        // Find parent form
         DomNode* form = button->parent;
         while (form && form->element_type != ElementType::FORM) form = form->parent;
 
@@ -218,8 +238,8 @@ public:
             return;
         }
 
-        // Collect data
-        std::string query_string;
+        // Collect form data with URL encoding
+        std::string form_data;
         for (DomNode* field : current_tree.form_fields) {
             // Check if field belongs to this form
             DomNode* p = field->parent;
@@ -227,22 +247,60 @@ public:
             while(p) { if(p == form) { is_child = true; break; } p = p->parent; }
 
             if (is_child && !field->name.empty()) {
-                if (!query_string.empty()) query_string += "&";
-                query_string += field->name + "=" + field->value;
+                if (!form_data.empty()) form_data += "&";
+                form_data += url_encode(field->name) + "=" + url_encode(field->value);
             }
         }
 
         std::string target_url = form->action;
         if (target_url.empty()) target_url = current_url;
 
-        // TODO: Handle POST. For now, assume GET or append query string
-        if (target_url.find('?') == std::string::npos) {
-            target_url += "?" + query_string;
-        } else {
-            target_url += "&" + query_string;
-        }
+        // Check form method (default to GET if not specified)
+        std::string method = form->method;
+        std::transform(method.begin(), method.end(), method.begin(), ::toupper);
 
-        load_page(target_url);
+        if (method == "POST") {
+            // POST request
+            status_message = "Sending POST request...";
+            HttpResponse response = http_client.post(target_url, form_data);
+
+            if (!response.error_message.empty()) {
+                status_message = "Error: " + response.error_message;
+                return;
+            }
+
+            if (!response.is_success()) {
+                status_message = "Error: HTTP " + std::to_string(response.status_code);
+                return;
+            }
+
+            // Parse and render response
+            DocumentTree tree = html_parser.parse_tree(response.body, target_url);
+            current_tree = std::move(tree);
+            current_url = target_url;
+            rendered_lines = renderer.render_tree(current_tree, screen_width);
+            build_interactive_list();
+            scroll_pos = 0;
+            current_element_index = -1;
+
+            // Update history
+            if (history_pos < static_cast<int>(history.size()) - 1) {
+                history.erase(history.begin() + history_pos + 1, history.end());
+            }
+            history.push_back(current_url);
+            history_pos = history.size() - 1;
+
+            status_message = "Form submitted (POST)";
+        } else {
+            // GET request (default)
+            if (target_url.find('?') == std::string::npos) {
+                target_url += "?" + form_data;
+            } else {
+                target_url += "&" + form_data;
+            }
+            load_page(target_url);
+            status_message = "Form submitted (GET)";
+        }
     }
 
     void draw_status_bar() {

src/http_client.cpp

@@ -117,6 +117,95 @@ HttpResponse HttpClient::fetch(const std::string& url) {
     return response;
 }
 
+HttpResponse HttpClient::post(const std::string& url, const std::string& data,
+                              const std::string& content_type) {
+    HttpResponse response;
+    response.status_code = 0;
+
+    if (!pImpl->curl) {
+        response.error_message = "CURL not initialized";
+        return response;
+    }
+
+    curl_easy_reset(pImpl->curl);
+
+    // Re-apply settings
+    curl_easy_setopt(pImpl->curl, CURLOPT_URL, url.c_str());
+
+    // Set write callback
+    std::string response_body;
+    curl_easy_setopt(pImpl->curl, CURLOPT_WRITEFUNCTION, write_callback);
+    curl_easy_setopt(pImpl->curl, CURLOPT_WRITEDATA, &response_body);
+
+    // Set timeout
+    curl_easy_setopt(pImpl->curl, CURLOPT_TIMEOUT, pImpl->timeout);
+    curl_easy_setopt(pImpl->curl, CURLOPT_CONNECTTIMEOUT, 10L);
+
+    // Set user agent
+    curl_easy_setopt(pImpl->curl, CURLOPT_USERAGENT, pImpl->user_agent.c_str());
+
+    // Set redirect following
+    if (pImpl->follow_redirects) {
+        curl_easy_setopt(pImpl->curl, CURLOPT_FOLLOWLOCATION, 1L);
+        curl_easy_setopt(pImpl->curl, CURLOPT_MAXREDIRS, 10L);
+    }
+
+    // HTTPS support
+    curl_easy_setopt(pImpl->curl, CURLOPT_SSL_VERIFYPEER, 1L);
+    curl_easy_setopt(pImpl->curl, CURLOPT_SSL_VERIFYHOST, 2L);
+
+    // Cookie settings
+    if (!pImpl->cookie_file.empty()) {
+        curl_easy_setopt(pImpl->curl, CURLOPT_COOKIEFILE, pImpl->cookie_file.c_str());
+        curl_easy_setopt(pImpl->curl, CURLOPT_COOKIEJAR, pImpl->cookie_file.c_str());
+    } else {
+        curl_easy_setopt(pImpl->curl, CURLOPT_COOKIEFILE, "");
+    }
+
+    // Enable automatic decompression
+    curl_easy_setopt(pImpl->curl, CURLOPT_ACCEPT_ENCODING, "");
+
+    // Set POST method
+    curl_easy_setopt(pImpl->curl, CURLOPT_POST, 1L);
+
+    // Set POST data
+    curl_easy_setopt(pImpl->curl, CURLOPT_POSTFIELDS, data.c_str());
+    curl_easy_setopt(pImpl->curl, CURLOPT_POSTFIELDSIZE, data.length());
+
+    // Set Content-Type header
+    struct curl_slist* headers = nullptr;
+    std::string content_type_header = "Content-Type: " + content_type;
+    headers = curl_slist_append(headers, content_type_header.c_str());
+    curl_easy_setopt(pImpl->curl, CURLOPT_HTTPHEADER, headers);
+
+    // Perform request
+    CURLcode res = curl_easy_perform(pImpl->curl);
+
+    // Clean up headers
+    curl_slist_free_all(headers);
+
+    if (res != CURLE_OK) {
+        response.error_message = curl_easy_strerror(res);
+        return response;
+    }
+
+    // Get response code
+    long http_code = 0;
+    curl_easy_getinfo(pImpl->curl, CURLINFO_RESPONSE_CODE, &http_code);
+    response.status_code = static_cast<int>(http_code);
+
+    // Get Content-Type
+    char* resp_content_type = nullptr;
+    curl_easy_getinfo(pImpl->curl, CURLINFO_CONTENT_TYPE, &resp_content_type);
+    if (resp_content_type) {
+        response.content_type = resp_content_type;
+    }
+
+    response.body = std::move(response_body);
+
+    return response;
+}
+
 void HttpClient::set_timeout(long timeout_seconds) {
     pImpl->timeout = timeout_seconds;
 }

src/http_client.h

@@ -20,6 +20,8 @@ public:
     ~HttpClient();
 
     HttpResponse fetch(const std::string& url);
+    HttpResponse post(const std::string& url, const std::string& data,
+                     const std::string& content_type = "application/x-www-form-urlencoded");
     void set_timeout(long timeout_seconds);
     void set_user_agent(const std::string& user_agent);
     void set_follow_redirects(bool follow);

test_post_form.html

@@ -0,0 +1,31 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <title>POST Form Test</title>
+</head>
+<body>
+    <h1>Form Method Test</h1>
+
+    <h2>GET Form</h2>
+    <form action="https://httpbin.org/get" method="get">
+        <p>Name: <input type="text" name="name" value="John"></p>
+        <p>Email: <input type="text" name="email" value="john@example.com"></p>
+        <p><input type="submit" value="Submit GET"></p>
+    </form>
+
+    <h2>POST Form</h2>
+    <form action="https://httpbin.org/post" method="post">
+        <p>Username: <input type="text" name="username" value="testuser"></p>
+        <p>Password: <input type="password" name="password" value="secret123"></p>
+        <p>Message: <input type="text" name="message" value="Hello World"></p>
+        <p><input type="submit" value="Submit POST"></p>
+    </form>
+
+    <h2>Form with Special Characters</h2>
+    <form action="https://httpbin.org/post" method="post">
+        <p>Text: <input type="text" name="text" value="Hello & goodbye!"></p>
+        <p>Code: <input type="text" name="code" value="a=b&c=d"></p>
+        <p><input type="submit" value="Submit"></p>
+    </form>
+</body>
+</html>