Fix CGI form/cookie data handling and CGI URL encode/decode

- CGIFormData: fix broken setSize()+read() double-length bug that
  corrupted every parsed body with a leading run of garbage bytes
  (setSize(contentLength) pre-set length before read()/write()
  appended on top of it); switch content-type checks from exact
  equality to startsWith() since a real multipart Content-Type
  always carries a boundary= parameter; implement the previously
  empty multipart/form-data branch (ordinary fields only, file
  uploads deferred to a separate upload mechanism per TODO.txt);
  restore operator[] real lookup logic (was hardcoded to echo the
  key back); default-initialize formdata to NULL; fix mismatched
  include guard (leftover from an IMFFormData.h copy-paste); drop
  the unused IMFHeader.h include that pulled in a broken,
  unrelated StreamReader.h dependency.
- CGIFormattedData: parameterize the split delimiter (was hardcoded
  to &, which silently broke cookie parsing since HTTP_COOKIE uses
  ; not &) and trim whitespace on each split token.
- MString::toCGI()/fromCGI(): were unimplemented stubs (always
  returned an empty string); implemented proper CGI percent-encode
  / percent-decode + space plus-encoding, and fixed the one caller
  that discarded fromCGIs return value instead of using it.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

CGIFormData.cpp

@@ -1,28 +1,58 @@
 #include "CGIFormData.h"
-#include "IMFHeader.h"
 #include "malloc.h"
 
 namespace coreutils {
    
    CGIFormData::CGIFormData(int fd, ZString contentType, int contentLength, ZString boundary)
-     : contentType(contentType) { 
-      if(contentType == "application/x-www-form-urlencoded") {
-	 setSize(contentLength);
+     : contentType(contentType) {
+      if(contentType.startsWith("application/x-www-form-urlencoded")) {
 	 read(fd, contentLength);
 	 formdata = new CGIFormattedData(*this);
-      } else if(contentType == "multipart/form-data") {
-	 
+      } else if(contentType.startsWith("multipart/form-data")) {
+	 read(fd, contentLength);
+	 formdata = new CGIFormattedData();
 
+	 MString delimiter;
+	 delimiter << "--" << boundary;
+	 ZString body(*this);
+	 body.split(delimiter);
+
+	 for(int ix = 0; ix < body.getList().size(); ++ix) {
+	    ZString part = body[ix];
+	    if(part.getLength() == 0 || part.startsWith("--"))
+	      continue;
+
+	    int headerEnd = part.find("\r\n\r\n");
+	    if(headerEnd == -1)
+	      continue;
+
+	    ZString headers = part.substring(0, headerEnd);
+	    if(headers.find("filename=\"") != -1)
+	      // file uploads are out of scope here; handled via a separate upload mechanism.
+	      continue;
+
+	    int namePos = headers.find("name=\"");
+	    if(namePos == -1)
+	      continue;
+
+	    ZString afterName = headers.substring(namePos + 6);
+	    int nameEnd = afterName.find("\"");
+	    if(nameEnd == -1)
+	      continue;
+	    ZString name = afterName.substring(0, nameEnd);
+
+	    ZString value = part.substring(headerEnd + 4);
+	    value.trimCRLF();
+
+	    formdata->data[name] = value;
+	 }
       }
-      
-      
    }
 
    MString CGIFormData::operator[](ZString name) {
-//      if(contentType == "application/x-www-form-urlencoded") 
-//	return formdata[name];
-      MString temp(name);
-      return temp;
+      if(formdata == NULL)
+	return MString();
+      return (*formdata).data[name];
    }
-   
+
 }