typedef struct { ... } *SilcBuffer, SilcBufferStruct;

    SILC Buffer object. Following short description of the fields
    of the buffer.

    unsiged char *head;

        Head of the allocated buffer. This is the start of the allocated
        data area and remains as same throughout the lifetime of the buffer.
        However, the end of the head area or the start of the currently valid
        data area is variable.

        --------------------------------
        | head  | data         | tail  |
        --------------------------------
        ^       ^

        Current head section in the buffer is sb->data - sb->head.

    unsigned char *data;

        Currently valid data area. This is the start of the currently valid
        main data area. The data area is variable in all directions.

        --------------------------------
        | head  | data         | tail  |
        --------------------------------
                ^              ^

        Current valid data area in the buffer is sb->tail - sb->data.

     unsigned char *tail;

        Tail of the buffer. This is the end of the currently valid data area
        or start of the tail area. The start of the tail area is variable.

        --------------------------------
        | head  | data         | tail  |
        --------------------------------
                               ^       ^

        Current tail section in the buffer is sb->end - sb->tail.

    unsigned char *end;

        End of the allocated buffer. This is the end of the allocated data
        area and remains as same throughout the lifetime of the buffer.
        Usually this field is not needed except when checking the size
        of the buffer.

        --------------------------------
        | head  | data         | tail  |
        --------------------------------
                                       ^

        Length of the entire buffer is (ie. truelen) sb->end - sb->head.

     Currently valid data area is considered to be the main data area in
     the buffer. However, the entire buffer is of course valid data and can
     be used as such. Usually head section of the buffer includes different
     kind of headers or similar. Data section includes the main data of
     the buffer. Tail section can be seen as a reserve space of the data
     section. Tail section can be pulled towards end, and thus the data
     section becomes larger.

 SILC Buffer is not thread-safe.  If the same SilcBuffer context must be
 used in multithreaded environment concurrency control must be employed.

    typedef struct SilcBufferObject {
      unsigned char *head;
      unsigned char *data;
      unsigned char *tail;
      unsigned char *end;
    } *SilcBuffer, SilcBufferStruct;