liblzma: Add lzma_str_to_filters, _from_filters, and _list_filters.

lzma_str_to_filters() uses static error messages which makes
them not very precise. It tells the position in the string
where an error occurred though which helps quite a bit if
applications take advantage of it. Dynamic error messages can
be added later with a new flag if it seems important enough.

src/liblzma/api/lzma/filter.h

@@ -454,3 +454,261 @@ extern LZMA_API(lzma_ret) lzma_filter_flags_decode(
 		lzma_filter *filter, const lzma_allocator *allocator,
 		const uint8_t *in, size_t *in_pos, size_t in_size)
 		lzma_nothrow lzma_attr_warn_unused_result;
+
+
+/***********
+ * Strings *
+ ***********/
+
+/**
+ * \brief       Allow or show all filters
+ *
+ * By default only the filters supported in the .xz format are accept by
+ * lzma_str_to_filters() or shown by lzma_str_list_filters().
+ */
+#define LZMA_STR_ALL_FILTERS    UINT32_C(0x01)
+
+
+/**
+ * \brief       Do not validate the filter chain in lzma_str_to_filters()
+ *
+ * By default lzma_str_to_filters() can return an error if the filter chain
+ * as a whole isn't usable in the .xz format or in the raw encoder or decoder.
+ * With this flag the validation is skipped (this doesn't affect the handling
+ * of the individual filter options).
+ */
+#define LZMA_STR_NO_VALIDATION  UINT32_C(0x02)
+
+
+/**
+ * \brief       Stringify encoder options
+ *
+ * Show the filter-specific options that the encoder will use.
+ * This may be useful for verbose diagnostic messages.
+ *
+ * Note that if options were decoded from .xz headers then the encoder options
+ * may be undefined. This flag shouldn't be used in such a situation.
+ */
+#define LZMA_STR_ENCODER        UINT32_C(0x10)
+
+
+/**
+ * \brief       Stringify decoder options
+ *
+ * Show the filter-specific options that the decoder will use.
+ * This may be useful for showing what filter options were decoded
+ * from file headers.
+ */
+#define LZMA_STR_DECODER        UINT32_C(0x20)
+
+
+/**
+ * \brief       Produce xz-compatible getopt_long() syntax
+ *
+ * That is, "delta:dist=2 lzma2:dict=4MiB,pb=1,lp=1" becomes
+ * "--delta=dist=2 --lzma2=dict=4MiB,pb=1,lp=1".
+ *
+ * This syntax is compatible with xz 5.0.0 as long as the filters and
+ * their options are supported too.
+ */
+#define LZMA_STR_GETOPT_LONG    UINT32_C(0x40)
+
+
+/**
+ * \brief       Use two dashes "--" instead of a space to separate filters
+ *
+ * That is, "delta:dist=2 lzma2:pb=1,lp=1" becomes
+ * "delta:dist=2--lzma2:pb=1,lp=1". This looks slightly odd but this
+ * kind of strings should be usable on the command line without quoting.
+ * However, it is possible that future versions with new filter options
+ * might produce strings that require shell quoting anyway as the exact
+ * set of possible characters isn't frozen for now.
+ *
+ * It is guaranteed that the single quote (') will never be used in
+ * filter chain strings (even if LZMA_STR_NO_SPACES isn't used).
+ */
+#define LZMA_STR_NO_SPACES      UINT32_C(0x80)
+
+
+/**
+ * \brief       Convert a string to a filter chain
+ *
+ * This tries to make it easier to write applications that allow users
+ * to set custom compression options. This only handles the filter
+ * configuration (including presets) but not the number of threads,
+ * block size, check type, or memory limits.
+ *
+ * The input string can be either a preset or a filter chain. Presets
+ * begin with a digit 0-9 and may be followed by zero or more flags
+ * which are lower-case letters. Currently only "e" is supported, matching
+ * LZMA_PRESET_EXTREME. For partial xz command line syntax compatibility,
+ * a preset string may start with a single dash "-".
+ *
+ * A filter chain consist of one or more "filtername:opt1=value1,opt2=value2"
+ * strings separated by one or more spaces. Leading and trailing spaces are
+ * ignored. All names and values must be lower-case. Extra commas in the
+ * option list are ignored. The order of filters is significant: when
+ * encoding, the uncompressed input data goes to the leftmost filter first.
+ * Normally "lzma2" is the last filter in the chain.
+ *
+ * If one wishes to avoid spaces, for example, to avoid shell quoting,
+ * it is possible to use two dashes "--" instead of spaces to separate
+ * the filters.
+ *
+ * For xz command line compatibility, each filter may be prefixed with
+ * two dashes "--" and the colon ":" separating the filter name from
+ * the options may be replaced with an equals sign "=".
+ *
+ * By default, only filters that can be used in the .xz format are accepted.
+ * To allow all filters (LZMA1) use the flag LZMA_STR_ALL_FILTERS.
+ *
+ * By default, very basic validation is done for the filter chain as a whole,
+ * for example, that LZMA2 is only used as the last filter in the chain.
+ * The validation isn't perfect though and it's possible that this function
+ * succeeds but using the filter chain for encoding or decoding will still
+ * result in LZMA_OPTIONS_ERROR. To disable this validation, use the flag
+ * LZMA_STR_NO_VALIDATION.
+ *
+ * The available filter names and their options are available via
+ * lzma_str_list_filters(). See the xz man page for the description
+ * of filter names and options.
+ *
+ * \param       str         User-supplied string describing a preset or
+ *                          a filter chain. If a default value is needed and
+ *                          you don't know what would be good, use "6" since
+ *                          that is the default preset in xz too.
+ * \param       error_pos   If this isn't NULL, this value will be set on
+ *                          both success and on all errors. This tells the
+ *                          location of the error in the string. This is
+ *                          an int to make it straightforward to use this
+ *                          as printf() field width. The value is guaranteed
+ *                          to be in the range [0, INT_MAX] even if strlen(str)
+ *                          somehow was greater than INT_MAX. On success this
+ *                          is equal to min(strlen(str), INT_MAX).
+ * \param       filters     An array of lzma_filter structures. There must
+ *                          be LZMA_FILTERS_MAX + 1 (that is, five) elements
+ *                          in the array. The old contents are ignored so it
+ *                          doesn't need to be initialized. This array is
+ *                          modified only if this function returns LZMA_OK.
+ *                          Once the allocated filter options are no longer
+ *                          needed, lzma_filters_free() can be used to free the
+ *                          options (it doesn't free the filters array itself).
+ * \param       flags       Bitwise-or of zero or more of the flags
+ *                          LZMA_STR_ALL_FILTERS and LZMA_STR_NO_VALIDATION.
+ * \param       allocator   lzma_allocator for custom allocator functions.
+ *                          Set to NULL to use malloc() and free().
+ *
+ * \return      On success, NULL is returned. On error, a statically-allocated
+ *              error message is returned which together with the error_pos
+ *              should give some idea what is wrong.
+ *
+ * For command line applications, below is an example how an error message
+ * can be displayed. Note the use of an empty string for the field width.
+ * If "^" was used there it would create an off-by-one error except at
+ * the very beginning of the line.
+ *
+ * \code{.c}
+ * const char *str = ...; // From user
+ * lzma_filter filters[LZMA_FILTERS_MAX + 1];
+ * int pos;
+ * const char *msg = lzma_str_to_filters(str, &pos, filters, 0, NULL);
+ * if (msg != NULL) {
+ *     printf("%s: Error in XZ compression options:\n", argv[0]);
+ *     printf("%s: %s\n", argv[0], str);
+ *     printf("%s: %*s^\n", argv[0], errpos, "");
+ *     printf("%s: %s\n", argv[0], msg);
+ * }
+ * \endcode
+ */
+extern LZMA_API(const char *) lzma_str_to_filters(
+		const char *str, int *error_pos, lzma_filter *filters,
+		uint32_t flags, const lzma_allocator *allocator)
+		lzma_nothrow lzma_attr_warn_unused_result;
+
+
+/**
+ * \brief       Convert a filter chain to a string
+ *
+ * Use cases:
+ *
+ *   - Verbose output showing the full encoder options to the user
+ *     (use LZMA_STR_ENCODER in flags)
+ *
+ *   - Showing the filters and options that are required to decode a file
+ *     (use LZMA_STR_DECODER in flags)
+ *
+ *   - Showing the filter names without any options in informational messages
+ *     where the technical details aren't important (no flags). In this case
+ *     the .options in the filters array are ignored and may be NULL even if
+ *     a filter has a mandatory options structure.
+ *
+ * Note that even if the filter chain was specified using a preset,
+ * the resulting filter chain isn't reversed to a preset. So if you
+ * specify "6" to lzma_str_to_filters() then lzma_str_from_filters()
+ * will produce a string containing "lzma2".
+ *
+ * \param       str         On success *str will be set to point an allocated
+ *                          string describing the given filter chain. Old
+ *                          value is ignored. On error *str is always set
+ *                          to NULL.
+ * \param       filters     Array of 1-4 filters and a terminating element
+ *                          with .id = LZMA_VLI_UNKNOWN.
+ * \param       flags       Bitwise-or of zero or more of the flags
+ *                          LZMA_STR_ENCODER, LZMA_STR_DECODER,
+ *                          LZMA_STR_GETOPT_LONG, and LZMA_STR_NO_SPACES.
+ * \param       allocator   lzma_allocator for custom allocator functions.
+ *                          Set to NULL to use malloc() and free().
+ *
+ * \return      - LZMA_OK
+ *              - LZMA_OPTIONS_ERROR: Empty filter chain
+ *                (filters[0].id == LZMA_VLI_UNKNOWN) or the filter chain
+ *                includes a Filter ID that is not supported by this function.
+ *              - LZMA_MEM_ERROR
+ *              - LZMA_PROG_ERROR
+ */
+extern LZMA_API(lzma_ret) lzma_str_from_filters(
+		char **str, const lzma_filter *filters, uint32_t flags,
+		const lzma_allocator *allocator)
+		lzma_nothrow lzma_attr_warn_unused_result;
+
+
+/**
+ * \brief       List available filters and/or their options (for help message)
+ *
+ * If a filter_id is given then only one line is created which contains the
+ * filter name. If LZMA_STR_ENCODER or LZMA_STR_DECODER is used then the
+ * options required for encoding or decoding are listed on the same line too.
+ *
+ * If filter_id is LZMA_VLI_UNKNOWN then all filters that can be used in
+ * the .xz format are listed:
+ *
+ *   - If neither LZMA_STR_ENCODER nor LZMA_STR_DECODER is used then
+ *     the supported filter names are listed on a single line separated
+ *     by spaces.
+ *
+ *   - If LZMA_STR_ENCODER or LZMA_STR_DECODER is used then filters and
+ *     the supported options are listed one filter per line. There won't
+ *     be a '\n' after the last filter.
+ *
+ *   - If LZMA_STR_ALL_FILTERS is used then the list will include also
+ *     those filters that cannot be used in the .xz format (LZMA1).
+ *
+ * \param       str         On success *str will be set to point an allocated
+ *                          string listing the filters and options. Old value
+ *                          is ignored. On error *str is always set to NULL.
+ * \param       filter_id   Filter ID or LZMA_VLI_UNKNOWN.
+ * \param       flags       Bitwise-or of zero or more of the flags
+ *                          LZMA_STR_ALL_FILTERS, LZMA_STR_ENCODER,
+ *                          LZMA_STR_DECODER, and LZMA_STR_GETOPT_LONG.
+ * \param       allocator   lzma_allocator for custom allocator functions.
+ *                          Set to NULL to use malloc() and free().
+ *
+ * \return      - LZMA_OK
+ *              - LZMA_OPTIONS_ERROR: Unsupported flags
+ *              - LZMA_MEM_ERROR
+ *              - LZMA_PROG_ERROR
+ */
+extern LZMA_API(lzma_ret) lzma_str_list_filters(
+		char **str, lzma_vli filter_id, uint32_t flags,
+		const lzma_allocator *allocator)
+		lzma_nothrow lzma_attr_warn_unused_result;

src/liblzma/common/Makefile.inc

@@ -19,6 +19,7 @@ liblzma_la_SOURCES += \
 	common/index.h \
 	common/stream_flags_common.c \
 	common/stream_flags_common.h \
+	common/string_conversion.c \
 	common/vli_size.c
 
 if COND_THREADS

src/liblzma/liblzma_generic.map

@@ -115,4 +115,7 @@ global:
 	lzma_stream_decoder_mt;
 	lzma_lzip_decoder;
 	lzma_filters_free;
+	lzma_str_to_filters;
+	lzma_str_from_filters;
+	lzma_str_list_filters;
 } XZ_5.2;

src/liblzma/liblzma_linux.map

@@ -130,4 +130,7 @@ global:
 	lzma_stream_decoder_mt;
 	lzma_lzip_decoder;
 	lzma_filters_free;
+	lzma_str_to_filters;
+	lzma_str_from_filters;
+	lzma_str_list_filters;
 } XZ_5.2;