Add StreamReader and rebuild Parser/LineParser/IMFHeader/IMFBoundary on it

Introduces StreamReader to accumulate socket data delivered in arbitrary
chunks into one buffer, so a Parser can build an object (a line, a header
block, a MIME boundary) that spans any number of packets without losing
its place. Parser is redesigned around this: no longer inherits MString
(was redundant with its own buffer member), takes a StreamReader&, and
drives a resumable COMPLETE/INCOMPLETE/DATA_AVAIL state-machine protocol
via doParse(). LineParser, IMFHeader, and IMFBoundary are rewritten as
real, working resumable parsers against the shared buffer instead of the
previous non-compiling stubs (mismatched constructors/return types, a
syntax error, checkParse() never implemented).

IMFFormData is left as the stub it already was, just restored to
compiling against the new IMFHeader signature - fully wiring it up needs
IMFMultipart/IMFText migrated to StreamReader too, out of scope here.

Verified with real runtime tests (not just compilation) covering data
split mid-line, mid-CRLF, mid-header-fold, and mid-boundary-marker across
separate feed() calls, plus StreamReader::compact(). Along the way fixed
a header-value bug (space after ':' wasn't skipped) and a double
cursor-offset subtraction bug in two places caused by forgetting that
ZString::getLength() is already cursor-relative, not the raw buffer size.

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

IMFHeader.cpp

@@ -1,32 +1,77 @@
 #include "IMFHeader.h"
 #include "Exception.h"
-#include "Log.h"
-#include <unistd.h>
 
 namespace coreutils {
 
-   IMFHeader::IMFHeader(int fd) {}
+   IMFHeader::IMFHeader(StreamReader &reader) : Parser(reader) {}
+
+   Parser::Status IMFHeader::parse() {
+      MString &buffer = reader.getBuffer();
+
+      switch (state) {
+
+       case NAME: {
+          if (buffer.eod())
+             return Status::INCOMPLETE;
+          if (buffer.getChar() == '\r') {
+             // ZString::getLength() is already cursor-relative.
+             if (buffer.getLength() < 2)
+                return Status::INCOMPLETE;
+             if (!buffer.ifNext(ZString("\r\n")))
+                throw coreutils::Exception("IMFHeader: expected CRLF at end of header block.");
+             return Status::COMPLETE;
+          }
+          name << buffer.getTokenInclude("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz-0123456789");
+          if (buffer.eod())
+             return Status::INCOMPLETE;
+          if (!buffer.ifNext(ZString(":")))
+             throw coreutils::Exception("IMFHeader: expected ':' in header name.");
+          state = SKIP_SPACE;
+          return Status::DATA_AVAIL;
+       }
+
+       case SKIP_SPACE:
+          while (!buffer.eod() && buffer.getChar() == ' ')
+             buffer.nextChar();
+          if (buffer.eod())
+             return Status::INCOMPLETE;
+          state = FIELD;
+          return Status::DATA_AVAIL;
 
-   virtual int parse() {
-      switch(state) {
-       case NAME:
-	 name << buffer.getTokenInclude("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz-0123456789");
-	 if(buffer.ifNext(":"))
-	  state = FIELD;
-	 else
-	   return 2;
        case FIELD:
-	 field << buffer.getTokenInclude("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz-;'\"0123456789");
-	 if(!buffer.ifNext("\r\n"))
-	   if(buffer.eod())
-	     return 2;
-	 // Right here is where we should check if next line is an extension to the previous line.
-	 
-      
-	 
+          field << buffer.getTokenExclude("\r\n");
+          if (buffer.eod())
+             return Status::INCOMPLETE;
+          if (!buffer.ifNext(ZString("\r\n")))
+             throw coreutils::Exception("IMFHeader: expected CRLF at end of header field.");
+          state = FOLD_CHECK;
+          return Status::DATA_AVAIL;
+
+       case FOLD_CHECK:
+          if (buffer.eod())
+             return Status::INCOMPLETE;
+          if (buffer.getChar() == ' ' || buffer.getChar() == '\t') {
+             buffer.nextChar();
+             field << " ";
+             state = SKIP_SPACE;
+             return Status::DATA_AVAIL;
+          }
+          commitField();
+          state = NAME;
+          return Status::DATA_AVAIL;
+
       }
-      
-      
+      throw coreutils::Exception("IMFHeader: unreachable state.");
    }
 
-}
+   void IMFHeader::commitField() {
+      headers[name] = field;
+      name = MString();
+      field = MString();
+   }
+
+   std::map<MString, MString> &IMFHeader::getHeaders() {
+      return headers;
+   }
+
+}