diff -r 862ab606ee06 -r 04c9f8d8f03b ucx/cx/buffer.h
--- a/ucx/cx/buffer.h	Sun Feb 16 17:38:07 2025 +0100
+++ b/ucx/cx/buffer.h	Tue Feb 25 21:12:11 2025 +0100
@@ -27,9 +27,9 @@
  */
 
 /**
- * \file buffer.h
+ * @file buffer.h
  *
- * \brief Advanced buffer implementation.
+ * @brief Advanced buffer implementation.
  *
  * Instances of CxBuffer can be used to read from or to write to like one
  * would do with a stream.
@@ -38,9 +38,9 @@
  * can be enabled. See the documentation of the macro constants for more
  * information.
  *
- * \author Mike Becker
- * \author Olaf Wintermann
- * \copyright 2-Clause BSD License
+ * @author Mike Becker
+ * @author Olaf Wintermann
+ * @copyright 2-Clause BSD License
  */
 
 #ifndef UCX_BUFFER_H
@@ -88,8 +88,73 @@
  */
 #define CX_BUFFER_COPY_ON_EXTEND 0x08
 
+/**
+ * Function pointer for cxBufferWrite that is compatible with cx_write_func.
+ * @see cx_write_func
+ */
+#define cxBufferWriteFunc  ((cx_write_func) cxBufferWrite)
+/**
+ * Function pointer for cxBufferRead that is compatible with cx_read_func.
+ * @see cx_read_func
+ */
+#define cxBufferReadFunc  ((cx_read_func) cxBufferRead)
+
+/**
+ * Configuration for automatic flushing.
+ */
+struct cx_buffer_flush_config_s {
+    /**
+     * The buffer may not extend beyond this threshold before starting to flush.
+     *
+     * Only used when the buffer uses #CX_BUFFER_AUTO_EXTEND.
+     * The threshold will be the maximum capacity the buffer is extended to
+     * before flushing.
+     */
+    size_t threshold;
+    /**
+     * The block size for the elements to flush.
+     */
+    size_t blksize;
+    /**
+     * The maximum number of blocks to flush in one cycle.
+     *
+     * @attention while it is guaranteed that cxBufferFlush() will not flush
+     * more blocks, this is not necessarily the case for cxBufferWrite().
+     * After performing a flush cycle, cxBufferWrite() will retry the write
+     * operation and potentially trigger another flush cycle, until the
+     * flush target accepts no more data.
+     */
+    size_t blkmax;
+
+    /**
+     * The target for write function.
+     */
+    void *target;
+
+    /**
+     * The write-function used for flushing.
+     * If NULL, the flushed content gets discarded.
+     */
+    cx_write_func wfunc;
+};
+
+/**
+ * Type alias for the flush configuration struct.
+ *
+ * @code
+ * struct cx_buffer_flush_config_s {
+ *     size_t threshold;
+ *     size_t blksize;
+ *     size_t blkmax;
+ *     void *target;
+ *     cx_write_func wfunc;
+ * };
+ * @endcode
+ */
+typedef struct cx_buffer_flush_config_s CxBufferFlushConfig;
+
 /** Structure for the UCX buffer data. */
-typedef struct {
+struct cx_buffer_s {
     /** A pointer to the buffer contents. */
     union {
         /**
@@ -103,6 +168,12 @@
     };
     /** The allocator to use for automatic memory management. */
     const CxAllocator *allocator;
+    /**
+     * Optional flush configuration
+     *
+     * @see cxBufferEnableFlushing()
+     */
+    CxBufferFlushConfig *flush;
     /** Current position of the buffer. */
     size_t pos;
     /** Current capacity (i.e. maximum size) of the buffer. */
@@ -110,40 +181,6 @@
     /** Current size of the buffer content. */
     size_t size;
     /**
-     * The buffer may not extend beyond this threshold before starting to flush.
-     * Default is \c SIZE_MAX (flushing disabled when auto extension is enabled).
-     */
-    size_t flush_threshold;
-    /**
-     * The block size for the elements to flush.
-     * Default is 4096 bytes.
-     */
-    size_t flush_blksize;
-    /**
-     * The maximum number of blocks to flush in one cycle.
-     * Zero disables flushing entirely (this is the default).
-     * Set this to \c SIZE_MAX to flush the entire buffer.
-     *
-     * @attention if the maximum number of blocks multiplied with the block size
-     * is smaller than the expected contents written to this buffer within one write
-     * operation, multiple flush cycles are performed after that write.
-     * That means the total number of blocks flushed after one write to this buffer may
-     * be larger than \c flush_blkmax.
-     */
-    size_t flush_blkmax;
-
-    /**
-     * The write function used for flushing.
-     * If NULL, the flushed content gets discarded.
-     */
-    cx_write_func flush_func;
-
-    /**
-     * The target for \c flush_func.
-     */
-    void *flush_target;
-
-    /**
      * Flag register for buffer features.
      * @see #CX_BUFFER_DEFAULT
      * @see #CX_BUFFER_FREE_CONTENTS
@@ -151,45 +188,46 @@
      * @see #CX_BUFFER_COPY_ON_WRITE
      */
     int flags;
-} cx_buffer_s;
+};
 
 /**
  * UCX buffer.
  */
-typedef cx_buffer_s CxBuffer;
+typedef struct cx_buffer_s CxBuffer;
 
 /**
  * Initializes a fresh buffer.
  *
- * You may also provide a read-only \p space, in which case
+ * You may also provide a read-only @p space, in which case
  * you will need to cast the pointer, and you should set the
  * #CX_BUFFER_COPY_ON_WRITE flag.
  *
  * You need to set the size manually after initialization, if
- * you provide \p space which already contains data.
+ * you provide @p space which already contains data.
  *
- * When you specify stack memory as \p space and decide to use
- * the auto-extension feature, you \em must use the
+ * When you specify stack memory as @p space and decide to use
+ * the auto-extension feature, you @em must use the
  * #CX_BUFFER_COPY_ON_EXTEND flag, instead of the
  * #CX_BUFFER_AUTO_EXTEND flag.
  *
- * \note You may provide \c NULL as argument for \p space.
+ * @note You may provide @c NULL as argument for @p space.
  * Then this function will allocate the space and enforce
  * the #CX_BUFFER_FREE_CONTENTS flag. In that case, specifying
  * copy-on-write should be avoided, because the allocated
  * space will be leaking after the copy-on-write operation.
  *
  * @param buffer the buffer to initialize
- * @param space pointer to the memory area, or \c NULL to allocate
+ * @param space pointer to the memory area, or @c NULL to allocate
  * new memory
  * @param capacity the capacity of the buffer
  * @param allocator the allocator this buffer shall use for automatic
  * memory management
- * (if \c NULL, a default stdlib allocator will be used)
+ * (if @c NULL, a default stdlib allocator will be used)
  * @param flags buffer features (see cx_buffer_s.flags)
  * @return zero on success, non-zero if a required allocation failed
  */
 cx_attr_nonnull_arg(1)
+cx_attr_export
 int cxBufferInit(
         CxBuffer *buffer,
         void *space,
@@ -199,6 +237,27 @@
 );
 
 /**
+ * Configures the buffer for flushing.
+ *
+ * Flushing can happen automatically when data is written
+ * to the buffer (see cxBufferWrite()) or manually when
+ * cxBufferFlush() is called.
+ *
+ * @param buffer the buffer
+ * @param config the flush configuration
+ * @retval zero success
+ * @retval non-zero failure
+ * @see cxBufferFlush()
+ * @see cxBufferWrite()
+ */
+cx_attr_nonnull
+cx_attr_export
+int cxBufferEnableFlushing(
+    CxBuffer *buffer,
+    CxBufferFlushConfig config
+);
+
+/**
  * Destroys the buffer contents.
  *
  * Has no effect if the #CX_BUFFER_FREE_CONTENTS feature is not enabled.
@@ -208,49 +267,52 @@
  * @see cxBufferInit()
  */
 cx_attr_nonnull
+cx_attr_export
 void cxBufferDestroy(CxBuffer *buffer);
 
 /**
  * Deallocates the buffer.
  *
  * If the #CX_BUFFER_FREE_CONTENTS feature is enabled, this function also destroys
- * the contents. If you \em only want to destroy the contents, use cxBufferDestroy().
+ * the contents. If you @em only want to destroy the contents, use cxBufferDestroy().
  *
- * \remark As with all free() functions, this accepts \c NULL arguments in which
+ * @remark As with all free() functions, this accepts @c NULL arguments in which
  * case it does nothing.
  *
  * @param buffer the buffer to deallocate
  * @see cxBufferCreate()
  */
+cx_attr_export
 void cxBufferFree(CxBuffer *buffer);
 
 /**
  * Allocates and initializes a fresh buffer.
  *
- * You may also provide a read-only \p space, in which case
+ * You may also provide a read-only @p space, in which case
  * you will need to cast the pointer, and you should set the
  * #CX_BUFFER_COPY_ON_WRITE flag.
- * When you specify stack memory as \p space and decide to use
- * the auto-extension feature, you \em must use the
+ * When you specify stack memory as @p space and decide to use
+ * the auto-extension feature, you @em must use the
  * #CX_BUFFER_COPY_ON_EXTEND flag, instead of the
  * #CX_BUFFER_AUTO_EXTEND flag.
  *
- * \note You may provide \c NULL as argument for \p space.
+ * @note You may provide @c NULL as argument for @p space.
  * Then this function will allocate the space and enforce
  * the #CX_BUFFER_FREE_CONTENTS flag.
  *
- * @param space pointer to the memory area, or \c NULL to allocate
+ * @param space pointer to the memory area, or @c NULL to allocate
  * new memory
  * @param capacity the capacity of the buffer
  * @param allocator the allocator to use for allocating the structure and the automatic
  * memory management within the buffer
- * (if \c NULL, a default stdlib allocator will be used)
+ * (if @c NULL, a default stdlib allocator will be used)
  * @param flags buffer features (see cx_buffer_s.flags)
- * @return a pointer to the buffer on success, \c NULL if a required allocation failed
+ * @return a pointer to the buffer on success, @c NULL if a required allocation failed
  */
 cx_attr_malloc
 cx_attr_dealloc(cxBufferFree, 1)
 cx_attr_nodiscard
+cx_attr_export
 CxBuffer *cxBufferCreate(
         void *space,
         size_t capacity,
@@ -269,7 +331,7 @@
  * are discarded.
  *
  * If the offset is negative, the contents are shifted to the left where the
- * first \p shift bytes are discarded.
+ * first @p shift bytes are discarded.
  * The new size of the buffer is the old size minus the absolute shift value.
  * If this value is larger than the buffer size, the buffer is emptied (but
  * not cleared, see the security note below).
@@ -277,11 +339,11 @@
  * The buffer position gets shifted alongside with the content but is kept
  * within the boundaries of the buffer.
  *
- * \note For situations where \c off_t is not large enough, there are specialized cxBufferShiftLeft() and
- * cxBufferShiftRight() functions using a \c size_t as parameter type.
+ * @note For situations where @c off_t is not large enough, there are specialized cxBufferShiftLeft() and
+ * cxBufferShiftRight() functions using a @c size_t as parameter type.
  *
- * \attention
- * Security Note: The shifting operation does \em not erase the previously occupied memory cells.
+ * @attention
+ * Security Note: The shifting operation does @em not erase the previously occupied memory cells.
  * But you can easily do that manually, e.g. by calling
  * <code>memset(buffer->bytes, 0, shift)</code> for a right shift or
  * <code>memset(buffer->bytes + buffer->size, 0, buffer->capacity - buffer->size)</code>
@@ -289,9 +351,13 @@
  *
  * @param buffer the buffer
  * @param shift the shift offset (negative means left shift)
- * @return 0 on success, non-zero if a required auto-extension or copy-on-write fails
+ * @retval zero success
+ * @retval non-zero if a required auto-extension or copy-on-write fails
+ * @see cxBufferShiftLeft()
+ * @see cxBufferShiftRight()
  */
 cx_attr_nonnull
+cx_attr_export
 int cxBufferShift(
         CxBuffer *buffer,
         off_t shift
@@ -303,10 +369,12 @@
  *
  * @param buffer the buffer
  * @param shift the shift offset
- * @return 0 on success, non-zero if a required auto-extension or copy-on-write fails
+ * @retval zero success
+ * @retval non-zero if a required auto-extension or copy-on-write fails
  * @see cxBufferShift()
  */
 cx_attr_nonnull
+cx_attr_export
 int cxBufferShiftRight(
         CxBuffer *buffer,
         size_t shift
@@ -318,10 +386,12 @@
  *
  * @param buffer the buffer
  * @param shift the positive shift offset
- * @return usually zero, except the buffer uses copy-on-write and the allocation fails
+ * @retval zero success
+ * @retval non-zero if the buffer uses copy-on-write and the allocation fails
  * @see cxBufferShift()
  */
 cx_attr_nonnull
+cx_attr_export
 int cxBufferShiftLeft(
         CxBuffer *buffer,
         size_t shift
@@ -331,23 +401,25 @@
 /**
  * Moves the position of the buffer.
  *
- * The new position is relative to the \p whence argument.
+ * The new position is relative to the @p whence argument.
  *
- * \li \c SEEK_SET marks the start of the buffer.
- * \li \c SEEK_CUR marks the current position.
- * \li \c SEEK_END marks the end of the buffer.
+ * @li @c SEEK_SET marks the start of the buffer.
+ * @li @c SEEK_CUR marks the current position.
+ * @li @c SEEK_END marks the end of the buffer.
  *
  * With an offset of zero, this function sets the buffer position to zero
- * (\c SEEK_SET), the buffer size (\c SEEK_END) or leaves the buffer position
- * unchanged (\c SEEK_CUR).
+ * (@c SEEK_SET), the buffer size (@c SEEK_END) or leaves the buffer position
+ * unchanged (@c SEEK_CUR).
  *
  * @param buffer the buffer
- * @param offset position offset relative to \p whence
- * @param whence one of \c SEEK_SET, \c SEEK_CUR or \c SEEK_END
- * @return 0 on success, non-zero if the position is invalid
+ * @param offset position offset relative to @p whence
+ * @param whence one of @c SEEK_SET, @c SEEK_CUR or @c SEEK_END
+ * @retval zero success
+ * @retval non-zero if the position is invalid
  *
  */
 cx_attr_nonnull
+cx_attr_export
 int cxBufferSeek(
         CxBuffer *buffer,
         off_t offset,
@@ -360,13 +432,14 @@
  * The data is deleted by zeroing it with a call to memset().
  * If you do not need that, you can use the faster cxBufferReset().
  *
- * \note If the #CX_BUFFER_COPY_ON_WRITE flag is set, this function
+ * @note If the #CX_BUFFER_COPY_ON_WRITE flag is set, this function
  * will not erase the data and behave exactly as cxBufferReset().
  *
  * @param buffer the buffer to be cleared
  * @see cxBufferReset()
  */
 cx_attr_nonnull
+cx_attr_export
 void cxBufferClear(CxBuffer *buffer);
 
 /**
@@ -379,17 +452,20 @@
  * @see cxBufferClear()
  */
 cx_attr_nonnull
+cx_attr_export
 void cxBufferReset(CxBuffer *buffer);
 
 /**
  * Tests, if the buffer position has exceeded the buffer size.
  *
  * @param buffer the buffer to test
- * @return true, if the current buffer position has exceeded the last
- * byte of the buffer's contents.
+ * @retval true if the current buffer position has exceeded the last
+ * byte of the buffer's contents
+ * @retval false otherwise
  */
 cx_attr_nonnull
 cx_attr_nodiscard
+cx_attr_export
 bool cxBufferEof(const CxBuffer *buffer);
 
 
@@ -400,9 +476,11 @@
  *
  * @param buffer the buffer
  * @param capacity the minimum required capacity for this buffer
- * @return 0 on success or a non-zero value on failure
+ * @retval zero the capacity was already sufficient or successfully increased
+ * @retval non-zero on allocation failure
  */
 cx_attr_nonnull
+cx_attr_export
 int cxBufferMinimumCapacity(
         CxBuffer *buffer,
         size_t capacity
@@ -411,30 +489,46 @@
 /**
  * Writes data to a CxBuffer.
  *
+ * If automatic flushing is not enabled, the data is simply written into the
+ * buffer at the current position and the position of the buffer is increased
+ * by the number of bytes written.
+ *
  * If flushing is enabled and the buffer needs to flush, the data is flushed to
  * the target until the target signals that it cannot take more data by
  * returning zero via the respective write function. In that case, the remaining
  * data in this buffer is shifted to the beginning of this buffer so that the
- * newly available space can be used to append as much data as possible. This
- * function only stops writing more elements, when the flush target and this
+ * newly available space can be used to append as much data as possible.
+ *
+ * This function only stops writing more elements, when the flush target and this
  * buffer are both incapable of taking more data or all data has been written.
- * The number returned by this function is the total number of elements that
- * could be written during the process. It does not necessarily mean that those
- * elements are still in this buffer, because some of them could have also be
- * flushed already.
+ *
+ * If, after flushing, the number of items that shall be written still exceeds
+ * the capacity or flush threshold, this function tries to write all items directly
+ * to the flush target, if possible.
  *
- * If automatic flushing is not enabled, the position of the buffer is increased
- * by the number of bytes written.
+ * The number returned by this function is the number of elements from
+ * @c ptr that could be written to either the flush target or the buffer
+ * (so it does not include the number of items that had been already in the buffer
+ * in were flushed during the process).
  *
- * \note The signature is compatible with the fwrite() family of functions.
+ * @attention
+ * When @p size is larger than one and the contents of the buffer are not aligned
+ * with @p size, flushing stops after all complete items have been flushed, leaving
+ * the mis-aligned part in the buffer.
+ * Afterward, this function only writes as many items as possible to the buffer.
+ *
+ * @note The signature is compatible with the fwrite() family of functions.
  *
  * @param ptr a pointer to the memory area containing the bytes to be written
  * @param size the length of one element
  * @param nitems the element count
  * @param buffer the CxBuffer to write to
  * @return the total count of elements written
+ * @see cxBufferAppend()
+ * @see cxBufferRead()
  */
 cx_attr_nonnull
+cx_attr_export
 size_t cxBufferWrite(
         const void *ptr,
         size_t size,
@@ -451,7 +545,7 @@
  * while additional data is added to the buffer occasionally.
  * Consequently, the position of the buffer is unchanged after this operation.
  *
- * \note The signature is compatible with the fwrite() family of functions.
+ * @note The signature is compatible with the fwrite() family of functions.
  *
  * @param ptr a pointer to the memory area containing the bytes to be written
  * @param size the length of one element
@@ -459,8 +553,10 @@
  * @param buffer the CxBuffer to write to
  * @return the total count of elements written
  * @see cxBufferWrite()
+ * @see cxBufferRead()
  */
 cx_attr_nonnull
+cx_attr_export
 size_t cxBufferAppend(
         const void *ptr,
         size_t size,
@@ -469,19 +565,79 @@
 );
 
 /**
+ * Performs a single flush-run on the specified buffer.
+ *
+ * Does nothing when the position in the buffer is zero.
+ * Otherwise, the data until the current position minus
+ * one is considered for flushing.
+ * Note carefully that flushing will never exceed the
+ * current @em position, even when the size of the
+ * buffer is larger than the current position.
+ *
+ * One flush run will try to flush @c blkmax many
+ * blocks of size @c blksize until either the @p buffer
+ * has no more data to flush or the write function
+ * used for flushing returns zero.
+ *
+ * The buffer is shifted left for that many bytes
+ * the flush operation has successfully flushed.
+ *
+ * @par Example 1
+ * Assume you have a buffer with size 340 and you are
+ * at position 200. The flush configuration is
+ * @c blkmax=4 and @c blksize=64 .
+ * Assume that the entire flush operation is successful.
+ * All 200 bytes on the left hand-side from the current
+ * position are written.
+ * That means, the size of the buffer is now 140 and the
+ * position is zero.
+ *
+ * @par Example 2
+ * Same as Example 1, but now the @c blkmax is 1.
+ * The size of the buffer is now 276 and the position is 136.
+ *
+ * @par Example 3
+ * Same as Example 1, but now assume the flush target
+ * only accepts 100 bytes before returning zero.
+ * That means, the flush operations manages to flush
+ * one complete block and one partial block, ending
+ * up with a buffer with size 240 and position 100.
+ *
+ * @remark Just returns zero when flushing was not enabled with
+ * cxBufferEnableFlushing().
+ *
+ * @remark When the buffer uses copy-on-write, the memory
+ * is copied first, before attempting any flush.
+ * This is, however, considered an erroneous use of the
+ * buffer, because it does not make much sense to put
+ * readonly data into an UCX buffer for flushing, instead
+ * of writing it directly to the target.
+ *
+ * @param buffer the buffer
+ * @return the number of successfully flushed bytes
+ * @see cxBufferEnableFlushing()
+ */
+cx_attr_nonnull
+cx_attr_export
+size_t cxBufferFlush(CxBuffer *buffer);
+
+/**
  * Reads data from a CxBuffer.
  *
  * The position of the buffer is increased by the number of bytes read.
  *
- * \note The signature is compatible with the fread() family of functions.
+ * @note The signature is compatible with the fread() family of functions.
  *
  * @param ptr a pointer to the memory area where to store the read data
  * @param size the length of one element
  * @param nitems the element count
  * @param buffer the CxBuffer to read from
  * @return the total number of elements read
+ * @see cxBufferWrite()
+ * @see cxBufferAppend()
  */
 cx_attr_nonnull
+cx_attr_export
 size_t cxBufferRead(
         void *ptr,
         size_t size,
@@ -495,25 +651,30 @@
  * The least significant byte of the argument is written to the buffer. If the
  * end of the buffer is reached and #CX_BUFFER_AUTO_EXTEND feature is enabled,
  * the buffer capacity is extended by cxBufferMinimumCapacity(). If the feature
- * is disabled or buffer extension fails, \c EOF is returned.
+ * is disabled or buffer extension fails, @c EOF is returned.
  *
  * On successful write, the position of the buffer is increased.
  *
+ * If you just want to write a null-terminator at the current position, you
+ * should use cxBufferTerminate() instead.
+ *
  * @param buffer the buffer to write to
  * @param c the character to write
- * @return the byte that has been written or \c EOF when the end of the stream is
+ * @return the byte that has been written or @c EOF when the end of the stream is
  * reached and automatic extension is not enabled or not possible
+ * @see cxBufferTerminate()
  */
 cx_attr_nonnull
+cx_attr_export
 int cxBufferPut(
         CxBuffer *buffer,
         int c
 );
 
 /**
- * Writes a terminating zero to a buffer.
+ * Writes a terminating zero to a buffer at the current position.
  *
- * On successful write, \em neither the position \em nor the size of the buffer is
+ * On successful write, @em neither the position @em nor the size of the buffer is
  * increased.
  *
  * The purpose of this function is to have the written data ready to be used as
@@ -523,17 +684,21 @@
  * @return zero, if the terminator could be written, non-zero otherwise
  */
 cx_attr_nonnull
+cx_attr_export
 int cxBufferTerminate(CxBuffer *buffer);
 
 /**
  * Writes a string to a buffer.
  *
+ * This is a convenience function for <code>cxBufferWrite(str, 1, strlen(str), buffer)</code>.
+ *
  * @param buffer the buffer
  * @param str the zero-terminated string
  * @return the number of bytes written
  */
 cx_attr_nonnull
 cx_attr_cstr_arg(2)
+cx_attr_export
 size_t cxBufferPutString(
         CxBuffer *buffer,
         const char *str
@@ -545,9 +710,10 @@
  * The current position of the buffer is increased after a successful read.
  *
  * @param buffer the buffer to read from
- * @return the character or \c EOF, if the end of the buffer is reached
+ * @return the character or @c EOF, if the end of the buffer is reached
  */
 cx_attr_nonnull
+cx_attr_export
 int cxBufferGet(CxBuffer *buffer);
 
 #ifdef __cplusplus