keymap: add xkb_keymap_new_from_buffer()

The current API doesn't allow the caller to create keymaps from mmap()'ed
files. The problem is, xkb_keymap_new_from_string() requires a terminating
0 byte. However, there is no way to guarantee that when using mmap() so a
user currently has to copy the whole file just to get the terminating zero
byte (assuming they cannot use xkb_keymap_new_from_file()).

This adds a new entry xkb_keymap_new_from_buffer() which takes a memory
location and the buffer size in bytes.

Internally, we depend on yy_scan_{string,byte}() helpers. According to
flex documentation these already copy the input string because they are
wrappers around yy_scan_buffer().
yy_scan_buffer() on the other hand has some insane requirements. The
buffer must be writeable and the last two bytes must be ASCII-NUL. But the
buffer may contain other 0 bytes just fine.

Because we don't want these constraints in our public API,
xkb_keymap_new_from_buffer() needs to create a copy of the input memory.
But it then calls yy_scan_buffer() directly. Hence, we have the same
number of buffer-copies as with *_from_string() but without the
terminating 0 requirement.
The explicit yy_scan_buffer() call is preferred over yy_scan_byte() so the
buffer-copy operation is not hidden somewhere in flex.

Maybe some day we no longer depend on flex and can have a zero-copy API. A
user could mmap() a file and it would get parsed right from this buffer.
But until then, we shouldn't expose this limitation in the API but instead
provide an API that some day can work with zero-copy.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>

[ran: rebased on top of my branch]
Conflicts:
	Makefile.am
	src/xkbcomp/xkbcomp.c

Makefile.am

@@ -124,6 +124,7 @@ TESTS = \
 	test/context \
 	test/rules-file \
 	test/stringcomp \
+	test/buffercomp \
 	test/log
 TESTS_LDADD = libtest.la
 
@@ -134,6 +135,7 @@ test_context_LDADD = $(TESTS_LDADD)
 test_rules_file_CFLAGS = $(AM_CFLAGS) -Wno-declaration-after-statement
 test_rules_file_LDADD = $(TESTS_LDADD) -lrt
 test_stringcomp_LDADD = $(TESTS_LDADD)
+test_buffercomp_LDADD = $(TESTS_LDADD)
 test_log_LDADD = $(TESTS_LDADD)
 test_rmlvo_to_kccgst_LDADD = $(TESTS_LDADD)
 test_print_compiled_keymap_LDADD = $(TESTS_LDADD)

src/keymap.c

@@ -221,6 +221,43 @@ xkb_keymap_new_from_string(struct xkb_context *ctx,
     return keymap;
 }
 
+XKB_EXPORT struct xkb_keymap *
+xkb_keymap_new_from_buffer(struct xkb_context *ctx,
+                           const char *buffer, size_t length,
+                           enum xkb_keymap_format format,
+                           enum xkb_keymap_compile_flags flags)
+{
+    struct xkb_keymap *keymap;
+    const struct xkb_keymap_format_ops *ops;
+
+    ops = get_keymap_format_ops(format);
+    if (!ops || !ops->keymap_new_from_string) {
+        log_err_func(ctx, "unsupported keymap format: %d\n", format);
+        return NULL;
+    }
+
+    if (flags & ~(XKB_MAP_COMPILE_PLACEHOLDER)) {
+        log_err_func(ctx, "unrecognized flags: %#x\n", flags);
+        return NULL;
+    }
+
+    if (!buffer) {
+        log_err_func1(ctx, "no buffer specified\n");
+        return NULL;
+    }
+
+    keymap = xkb_keymap_new(ctx, format, flags);
+    if (!keymap)
+        return NULL;
+
+    if (!ops->keymap_new_from_buffer(keymap, buffer, length)) {
+        xkb_keymap_unref(keymap);
+        return NULL;
+    }
+
+    return keymap;
+}
+
 XKB_EXPORT struct xkb_keymap *
 xkb_keymap_new_from_file(struct xkb_context *ctx,
                          FILE *file,

src/keymap.h

@@ -440,6 +440,8 @@ struct xkb_keymap_format_ops {
                                   const struct xkb_rule_names *names);
     bool (*keymap_new_from_string)(struct xkb_keymap *keymap,
                                    const char *string);
+    bool (*keymap_new_from_buffer)(struct xkb_keymap *keymap,
+                                   const char *buffer, size_t length);
     bool (*keymap_new_from_file)(struct xkb_keymap *keymap, FILE *file);
     char *(*keymap_get_as_string)(struct xkb_keymap *keymap);
 };

src/xkbcomp/scanner.l

@@ -267,6 +267,38 @@ XkbParseString(struct xkb_context *ctx, const char *string,
     return xkb_file;
 }
 
+/*
+ * yy_scan_buffer() requires the last two bytes of \buf to be 0. These two bytes
+ * are not scanned. Other zero bytes in the buffer are scanned normally, though.
+ * Due to these terminating zeroes, \length must be greater than 2.
+ * Furthermore, the buffer must be writable and you cannot make any assumptions
+ * about it after the scanner finished.
+ * All this must be guaranteed by the caller of this function!
+ */
+XkbFile *
+XkbParseBuffer(struct xkb_context *ctx, char *buf, size_t length,
+               const char *file_name)
+{
+    yyscan_t scanner;
+    struct scanner_extra extra;
+    YY_BUFFER_STATE state;
+    XkbFile *xkb_file;
+
+    if (!init_scanner(&scanner, &extra, ctx, file_name))
+        return NULL;
+
+    xkb_file = NULL;
+    state = yy_scan_buffer(buf, length, scanner);
+    if (state) {
+        xkb_file = parse(ctx, scanner, NULL);
+        yy_delete_buffer(state, scanner);
+    }
+
+    clear_scanner(scanner);
+
+    return xkb_file;
+}
+
 XkbFile *
 XkbParseFile(struct xkb_context *ctx, FILE *file,
              const char *file_name, const char *map)

src/xkbcomp/xkbcomp-priv.h

@@ -48,6 +48,10 @@ XkbFile *
 XkbParseString(struct xkb_context *ctx, const char *string,
                const char *file_name);
 
+XkbFile *
+XkbParseBuffer(struct xkb_context *ctx, char *buf, size_t length,
+               const char *file_name);
+
 void
 FreeXkbFile(XkbFile *file);
 

src/xkbcomp/xkbcomp.c

@@ -113,6 +113,38 @@ text_v1_keymap_new_from_string(struct xkb_keymap *keymap, const char *string)
     return ok;
 }
 
+static bool
+text_v1_keymap_new_from_buffer(struct xkb_keymap *keymap,
+                               const char *buffer, size_t length)
+{
+    bool ok;
+    XkbFile *xkb_file;
+    char *buf;
+
+    buf = malloc(length + 2);
+    if (!buf) {
+        log_err(keymap->ctx, "Cannot allocate memory for keymap\n");
+        return NULL;
+    }
+
+    /* yy_scan_buffer requires two terminating zero bytes */
+    memcpy(buf, buffer, length);
+    buf[length] = 0;
+    buf[length + 1] = 0;
+
+    xkb_file = XkbParseBuffer(keymap->ctx, buf, length + 2, "input");
+    if (!xkb_file) {
+        log_err(keymap->ctx, "Failed to parse input xkb file\n");
+        free(buf);
+        return NULL;
+    }
+
+    ok = compile_keymap_file(keymap, xkb_file);
+    FreeXkbFile(xkb_file);
+    free(buf);
+    return ok;
+}
+
 static bool
 text_v1_keymap_new_from_file(struct xkb_keymap *keymap, FILE *file)
 {
@@ -133,6 +165,7 @@ text_v1_keymap_new_from_file(struct xkb_keymap *keymap, FILE *file)
 const struct xkb_keymap_format_ops text_v1_keymap_format_ops = {
     .keymap_new_from_names = text_v1_keymap_new_from_names,
     .keymap_new_from_string = text_v1_keymap_new_from_string,
+    .keymap_new_from_buffer = text_v1_keymap_new_from_buffer,
     .keymap_new_from_file = text_v1_keymap_new_from_file,
     .keymap_get_as_string = text_v1_keymap_get_as_string,
 };

test/.gitignore

@@ -7,6 +7,7 @@ state
 context
 rules-file
 stringcomp
+buffercomp
 keyseq
 log
 interactive

test/buffercomp.c

@@ -0,0 +1,90 @@
+/*
+ * Copyright © 2009 Dan Nicholson
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "test.h"
+
+#define DATA_PATH "keymaps/stringcomp.data"
+
+int
+main(int argc, char *argv[])
+{
+    struct xkb_context *ctx = test_get_context(0);
+    struct xkb_keymap *keymap;
+    char *original, *dump;
+
+    assert(ctx);
+
+    /* Load in a prebuilt keymap, make sure we can compile it from memory,
+     * then compare it to make sure we get the same result when dumping it
+     * to a string. */
+    original = test_read_file(DATA_PATH);
+    assert(original);
+
+    keymap = test_compile_buffer(ctx, original, strlen(original));
+    assert(keymap);
+
+    dump = xkb_keymap_get_as_string(keymap, XKB_KEYMAP_USE_ORIGINAL_FORMAT);
+    assert(dump);
+
+    if (!streq(original, dump)) {
+        fprintf(stderr,
+                "round-trip test failed: dumped map differs from original\n");
+        fprintf(stderr, "path to original file: %s\n",
+                test_get_path(DATA_PATH));
+        fprintf(stderr, "length: dumped %lu, original %lu\n",
+                (unsigned long) strlen(dump),
+                (unsigned long) strlen(original));
+        fprintf(stderr, "dumped map:\n");
+        fprintf(stderr, "%s\n", dump);
+        fflush(stderr);
+        assert(0);
+    }
+
+    free(original);
+    free(dump);
+    xkb_keymap_unref(keymap);
+
+    /* Make sure we can't (falsely claim to) compile an empty string. */
+    keymap = test_compile_buffer(ctx, "", 0);
+    assert(!keymap);
+
+    /* Make sure we can recompile our output for a normal keymap from rules. */
+    keymap = test_compile_rules(ctx, NULL, NULL,
+                                "ru,ca,de,us", ",multix,neo,intl", NULL);
+    assert(keymap);
+    dump = xkb_keymap_get_as_string(keymap, XKB_KEYMAP_USE_ORIGINAL_FORMAT);
+    assert(dump);
+    xkb_keymap_unref(keymap);
+    keymap = test_compile_buffer(ctx, dump, strlen(dump));
+    assert(keymap);
+    xkb_keymap_unref(keymap);
+    free(dump);
+
+    xkb_context_unref(ctx);
+
+    return 0;
+}

test/common.c

@@ -260,6 +260,21 @@ test_compile_string(struct xkb_context *context, const char *string)
     return keymap;
 }
 
+struct xkb_keymap *
+test_compile_buffer(struct xkb_context *context, const char *buf, size_t len)
+{
+    struct xkb_keymap *keymap;
+
+    keymap = xkb_keymap_new_from_buffer(context, buf, len,
+                                        XKB_KEYMAP_FORMAT_TEXT_V1, 0);
+    if (!keymap) {
+        fprintf(stderr, "Failed to compile keymap from memory buffer\n");
+        return NULL;
+    }
+
+    return keymap;
+}
+
 struct xkb_keymap *
 test_compile_rules(struct xkb_context *context, const char *rules,
                    const char *model, const char *layout,

test/test.h

@@ -69,6 +69,9 @@ test_compile_file(struct xkb_context *context, const char *path_rel);
 struct xkb_keymap *
 test_compile_string(struct xkb_context *context, const char *string);
 
+struct xkb_keymap *
+test_compile_buffer(struct xkb_context *context, const char *buf, size_t len);
+
 struct xkb_keymap *
 test_compile_rules(struct xkb_context *context, const char *rules,
                    const char *model, const char *layout, const char *variant,

xkbcommon/xkbcommon.h

@@ -740,6 +740,20 @@ xkb_keymap_new_from_string(struct xkb_context *context, const char *string,
                            enum xkb_keymap_format format,
                            enum xkb_keymap_compile_flags flags);
 
+/**
+ * Create a keymap from a memory buffer.
+ *
+ * This is just like xkb_keymap_new_from_string(), but takes a length argument
+ * so the input string does not have to be zero-terminated.
+ *
+ * @see xkb_keymap_new_from_string()
+ * @memberof xkb_keymap
+ */
+struct xkb_keymap *
+xkb_keymap_new_from_buffer(struct xkb_context *context, const char *buffer,
+                           size_t length, enum xkb_keymap_format format,
+                           enum xkb_keymap_compile_flags flags);
+
 /**
  * Take a new reference on a keymap.
  *