source: mainline/uspace/app/bithenge/transform.c@ 23db8aa

/*
 * Copyright (c) 2012 Sean Bartell
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/** @addtogroup bithenge
 * @{
 */
/**
 * @file
 * Transforms.
 */

#include <assert.h>
#include <errno.h>
#include <stdlib.h>
#include "blob.h"
#include "transform.h"

/** Initialize a new transform.
 * @param[out] self Transform to initialize.
 * @param[in] ops Operations provided by the transform.
 * @param num_params The number of parameters required. If this is nonzero, the
 * transform will get its own context with parameters, probably provided by a
 * param_wrapper. If this is zero, the existing outer context will be used with
 * whatever parameters it has, so they can be passed to any param_wrappers
 * within.
 * @return EOK or an error code from errno.h. */
int bithenge_init_transform(bithenge_transform_t *self,
    const bithenge_transform_ops_t *ops, int num_params)
{
        assert(ops);
        assert(ops->apply);
        assert(ops->destroy);
        self->ops = ops;
        self->refs = 1;
        self->num_params = num_params;
        return EOK;
}

static void transform_indestructible(bithenge_transform_t *self)
{
        assert(false);
}

typedef struct {
        bithenge_transform_t base;
        bithenge_transform_t *transform;
} param_transform_t;

static inline param_transform_t *transform_as_param(
    bithenge_transform_t *base)
{
        return (param_transform_t *)base;
}

static inline bithenge_transform_t *param_as_transform(
    param_transform_t *self)
{
        return &self->base;
}

static int param_transform_apply(bithenge_transform_t *base,
    bithenge_scope_t *scope, bithenge_node_t *in, bithenge_node_t **out)
{
        param_transform_t *self = transform_as_param(base);
        return bithenge_transform_apply(self->transform, scope, in, out);
}

static int param_transform_prefix_length(bithenge_transform_t *base,
    bithenge_scope_t *scope, bithenge_blob_t *in, aoff64_t *out)
{
        param_transform_t *self = transform_as_param(base);
        return bithenge_transform_prefix_length(self->transform, scope, in,
            out);
}

static void param_transform_destroy(bithenge_transform_t *base)
{
        param_transform_t *self = transform_as_param(base);
        bithenge_transform_dec_ref(self->transform);
        free(self);
}

static const bithenge_transform_ops_t param_transform_ops = {
        .apply = param_transform_apply,
        .prefix_length = param_transform_prefix_length,
        .destroy = param_transform_destroy,
};

/** Create a wrapper transform with a different number of parameters. Takes a
 * reference to @a transform, which it will use for all operations.
 * @param[out] out Holds the created transform.
 * @param transform The transform to wrap.
 * @param num_params The number of parameters to require.
 * @return EOK on success or an error code from errno.h. */
int bithenge_new_param_transform(bithenge_transform_t **out,
    bithenge_transform_t *transform, int num_params)
{
        assert(transform);
        assert(bithenge_transform_num_params(transform) == 0);
        assert(num_params != 0);

        int rc;
        param_transform_t *self = malloc(sizeof(*self));
        if (!self) {
                rc = ENOMEM;
                goto error;
        }
        rc = bithenge_init_transform(param_as_transform(self),
            &param_transform_ops, num_params);
        if (rc != EOK)
                goto error;
        self->transform = transform;
        *out = param_as_transform(self);
        return EOK;
error:
        bithenge_transform_dec_ref(transform);
        free(self);
        return rc;
}

static int ascii_apply(bithenge_transform_t *self, bithenge_scope_t *scope,
    bithenge_node_t *in, bithenge_node_t **out)
{
        int rc;
        if (bithenge_node_type(in) != BITHENGE_NODE_BLOB)
                return EINVAL;
        bithenge_blob_t *blob = bithenge_node_as_blob(in);
        aoff64_t size;
        rc = bithenge_blob_size(blob, &size);
        if (rc != EOK)
                return rc;

        char *buffer = malloc(size + 1);
        if (!buffer)
                return ENOMEM;
        aoff64_t size_read = size;
        rc = bithenge_blob_read(blob, 0, buffer, &size_read);
        if (rc != EOK) {
                free(buffer);
                return rc;
        }
        if (size_read != size) {
                free(buffer);
                return EINVAL;
        }
        buffer[size] = '\0';

        /* TODO: what if the OS encoding is incompatible with ASCII? */
        return bithenge_new_string_node(out, buffer, true);
}

static const bithenge_transform_ops_t ascii_ops = {
        .apply = ascii_apply,
        .destroy = transform_indestructible,
};

/** The ASCII text transform. */
bithenge_transform_t bithenge_ascii_transform = {
        &ascii_ops, 1, 0
};

static int invalid_apply(bithenge_transform_t *self, bithenge_scope_t *scope,
    bithenge_node_t *in, bithenge_node_t **out)
{
        return EINVAL;
}

static const bithenge_transform_ops_t invalid_ops = {
        .apply = invalid_apply,
        .destroy = transform_indestructible,
};

/** A transform that always raises an error. */
bithenge_transform_t bithenge_invalid_transform = {
        &invalid_ops, 1, 0
};

static int known_length_apply(bithenge_transform_t *self,
    bithenge_scope_t *scope, bithenge_node_t *in, bithenge_node_t **out)
{
        bithenge_node_t *length_node;
        int rc = bithenge_scope_get_param(scope, 0, &length_node);
        if (rc != EOK)
                return rc;
        if (bithenge_node_type(length_node) != BITHENGE_NODE_INTEGER) {
                bithenge_node_dec_ref(length_node);
                return EINVAL;
        }
        bithenge_int_t length = bithenge_integer_node_value(length_node);
        bithenge_node_dec_ref(length_node);

        if (bithenge_node_type(in) != BITHENGE_NODE_BLOB)
                return EINVAL;
        aoff64_t size;
        rc = bithenge_blob_size(bithenge_node_as_blob(in), &size);
        if (rc != EOK)
                return rc;
        if (length != (bithenge_int_t)size)
                return EINVAL;

        bithenge_node_inc_ref(in);
        *out = in;
        return EOK;
}

static int known_length_prefix_length(bithenge_transform_t *self,
    bithenge_scope_t *scope, bithenge_blob_t *in, aoff64_t *out)
{
        bithenge_node_t *length_node;
        int rc = bithenge_scope_get_param(scope, 0, &length_node);
        if (rc != EOK)
                return rc;
        if (bithenge_node_type(length_node) != BITHENGE_NODE_INTEGER) {
                bithenge_node_dec_ref(length_node);
                return EINVAL;
        }
        bithenge_int_t length = bithenge_integer_node_value(length_node);
        bithenge_node_dec_ref(length_node);

        *out = (aoff64_t)length;
        return EOK;
}

static const bithenge_transform_ops_t known_length_ops = {
        .apply = known_length_apply,
        .prefix_length = known_length_prefix_length,
        .destroy = transform_indestructible,
};

/** Pass through a blob, but require its length to equal the first argument. */
bithenge_transform_t bithenge_known_length_transform = {
        &known_length_ops, 1, 1
};

static int prefix_length_1(bithenge_transform_t *self, bithenge_scope_t *scope,
    bithenge_blob_t *blob, aoff64_t *out)
{
        *out = 1;
        return EOK;
}

static int prefix_length_2(bithenge_transform_t *self, bithenge_scope_t *scope,
    bithenge_blob_t *blob, aoff64_t *out)
{
        *out = 2;
        return EOK;
}

static int prefix_length_4(bithenge_transform_t *self, bithenge_scope_t *scope,
    bithenge_blob_t *blob, aoff64_t *out)
{
        *out = 4;
        return EOK;
}

static int prefix_length_8(bithenge_transform_t *self, bithenge_scope_t *scope,
    bithenge_blob_t *blob, aoff64_t *out)
{
        *out = 8;
        return EOK;
}

#define MAKE_UINT_TRANSFORM(NAME, TYPE, ENDIAN, PREFIX_LENGTH_FUNC)            \
        static int NAME##_apply(bithenge_transform_t *self,                    \
            bithenge_scope_t *scope, bithenge_node_t *in,                      \
            bithenge_node_t **out)                                             \
        {                                                                      \
                int rc;                                                        \
                if (bithenge_node_type(in) != BITHENGE_NODE_BLOB)              \
                        return EINVAL;                                         \
                bithenge_blob_t *blob = bithenge_node_as_blob(in);             \
                                                                               \
                /* Read too many bytes; success means the blob is too long. */ \
                TYPE val[2];                                                   \
                aoff64_t size = sizeof(val[0]) + 1;                            \
                rc = bithenge_blob_read(blob, 0, (char *)val, &size);          \
                if (rc != EOK)                                                 \
                        return rc;                                             \
                if (size != sizeof(val[0]))                                    \
                        return EINVAL;                                         \
                                                                               \
                return bithenge_new_integer_node(out, ENDIAN(val[0]));         \
        }                                                                      \
                                                                               \
        static const bithenge_transform_ops_t NAME##_ops = {                   \
                .apply = NAME##_apply,                                         \
                .prefix_length = PREFIX_LENGTH_FUNC,                           \
                .destroy = transform_indestructible,                           \
        };                                                                     \
                                                                               \
        bithenge_transform_t bithenge_##NAME##_transform = {                   \
                &NAME##_ops, 1, 0                                              \
        }

MAKE_UINT_TRANSFORM(uint8   , uint8_t ,                 , prefix_length_1);
MAKE_UINT_TRANSFORM(uint16le, uint16_t, uint16_t_le2host, prefix_length_2);
MAKE_UINT_TRANSFORM(uint16be, uint16_t, uint16_t_be2host, prefix_length_2);
MAKE_UINT_TRANSFORM(uint32le, uint32_t, uint32_t_le2host, prefix_length_4);
MAKE_UINT_TRANSFORM(uint32be, uint32_t, uint32_t_be2host, prefix_length_4);
MAKE_UINT_TRANSFORM(uint64le, uint64_t, uint32_t_le2host, prefix_length_8);
MAKE_UINT_TRANSFORM(uint64be, uint64_t, uint32_t_be2host, prefix_length_8);

static int zero_terminated_apply(bithenge_transform_t *self,
    bithenge_scope_t *scope, bithenge_node_t *in, bithenge_node_t **out)
{
        int rc;
        if (bithenge_node_type(in) != BITHENGE_NODE_BLOB)
                return EINVAL;
        bithenge_blob_t *blob = bithenge_node_as_blob(in);
        aoff64_t size;
        rc = bithenge_blob_size(blob, &size);
        if (rc != EOK)
                return rc;
        if (size < 1)
                return EINVAL;
        char ch;
        aoff64_t size_read = 1;
        rc = bithenge_blob_read(blob, size - 1, &ch, &size_read);
        if (rc != EOK)
                return rc;
        if (size_read != 1 || ch != '\0')
                return EINVAL;
        bithenge_blob_inc_ref(blob);
        return bithenge_new_subblob(out, blob, 0, size - 1);
}

static int zero_terminated_prefix_length(bithenge_transform_t *self,
    bithenge_scope_t *scope, bithenge_blob_t *blob, aoff64_t *out)
{
        int rc;
        char buffer[4096];
        aoff64_t offset = 0, size_read = sizeof(buffer);
        do {
                rc = bithenge_blob_read(blob, offset, buffer, &size_read);
                if (rc != EOK)
                        return rc;
                char *found = memchr(buffer, '\0', size_read);
                if (found) {
                        *out = found - buffer + offset + 1;
                        return EOK;
                }
                offset += size_read;
        } while (size_read == sizeof(buffer));
        return EINVAL;
}

static const bithenge_transform_ops_t zero_terminated_ops = {
        .apply = zero_terminated_apply,
        .prefix_length = zero_terminated_prefix_length,
        .destroy = transform_indestructible,
};

/** The zero-terminated data transform. */
bithenge_transform_t bithenge_zero_terminated_transform = {
        &zero_terminated_ops, 1, 0
};

static bithenge_named_transform_t primitive_transforms[] = {
        {"ascii", &bithenge_ascii_transform},
        {"known_length", &bithenge_known_length_transform},
        {"uint8", &bithenge_uint8_transform},
        {"uint16le", &bithenge_uint16le_transform},
        {"uint16be", &bithenge_uint16be_transform},
        {"uint32le", &bithenge_uint32le_transform},
        {"uint32be", &bithenge_uint32be_transform},
        {"uint64le", &bithenge_uint64le_transform},
        {"uint64be", &bithenge_uint64be_transform},
        {"zero_terminated", &bithenge_zero_terminated_transform},
        {NULL, NULL}
};

/** An array of named built-in transforms. */
bithenge_named_transform_t *bithenge_primitive_transforms = primitive_transforms;

typedef struct {
        bithenge_node_t base;
        bithenge_scope_t scope;
        struct struct_transform *transform;
        bithenge_blob_t *blob;
        aoff64_t *ends;
        size_t num_ends;
        bool prefix;
} struct_node_t;

typedef struct struct_transform {
        bithenge_transform_t base;
        bithenge_named_transform_t *subtransforms;
        size_t num_subtransforms;
} struct_transform_t;

static bithenge_node_t *struct_as_node(struct_node_t *node)
{
        return &node->base;
}

static struct_node_t *node_as_struct(bithenge_node_t *node)
{
        return (struct_node_t *)node;
}

static bithenge_transform_t *struct_as_transform(struct_transform_t *xform)
{
        return &xform->base;
}

static struct_transform_t *transform_as_struct(bithenge_transform_t *xform)
{
        return (struct_transform_t *)xform;
}

static int struct_node_field_offset(struct_node_t *self, aoff64_t *out,
    size_t index)
{
        if (index == 0) {
                *out = 0;
                return EOK;
        }
        index--;
        aoff64_t prev_offset =
            self->num_ends ? self->ends[self->num_ends - 1] : 0;
        for (; self->num_ends <= index; self->num_ends++) {
                bithenge_node_t *subblob_node;
                bithenge_blob_inc_ref(self->blob);
                int rc = bithenge_new_offset_blob(&subblob_node, self->blob,
                    prev_offset);
                if (rc != EOK)
                        return rc;

                bithenge_blob_t *subblob = bithenge_node_as_blob(subblob_node);
                aoff64_t field_size;
                rc = bithenge_transform_prefix_length(
                    self->transform->subtransforms[self->num_ends].transform,
                    &self->scope, subblob, &field_size);
                bithenge_node_dec_ref(subblob_node);
                if (rc != EOK)
                        return rc;

                prev_offset = self->ends[self->num_ends] =
                    prev_offset + field_size;
        }
        *out = self->ends[index];
        return EOK;
}

static int struct_node_subtransform(struct_node_t *self, bithenge_node_t **out,
    size_t index)
{
        aoff64_t start_pos, end_pos;
        int rc = struct_node_field_offset(self, &start_pos, index);
        if (rc != EOK)
                return rc;
        rc = struct_node_field_offset(self, &end_pos, index + 1);
        if (rc != EOK)
                return rc;

        bithenge_node_t *blob_node;
        bithenge_blob_inc_ref(self->blob);
        rc = bithenge_new_subblob(&blob_node, self->blob, start_pos,
            end_pos - start_pos);
        if (rc != EOK)
                return rc;

        rc = bithenge_transform_apply(
            self->transform->subtransforms[index].transform, &self->scope,
            blob_node, out);
        bithenge_node_dec_ref(blob_node);
        if (rc != EOK)
                return rc;

        return EOK;
}

static int struct_node_for_each(bithenge_node_t *base,
    bithenge_for_each_func_t func, void *data)
{
        int rc = EOK;
        struct_node_t *self = node_as_struct(base);
        bithenge_named_transform_t *subxforms =
            self->transform->subtransforms;

        for (size_t i = 0; subxforms[i].transform; i++) {
                bithenge_node_t *subxform_result;
                rc = struct_node_subtransform(self, &subxform_result, i);
                if (rc != EOK)
                        return rc;

                if (subxforms[i].name) {
                        bithenge_node_t *name_node;
                        rc = bithenge_new_string_node(&name_node,
                            subxforms[i].name, false);
                        if (rc == EOK) {
                                rc = func(name_node, subxform_result, data);
                                subxform_result = NULL;
                        }
                } else {
                        if (bithenge_node_type(subxform_result) !=
                            BITHENGE_NODE_INTERNAL) {
                                rc = EINVAL;
                        } else {
                                rc = bithenge_node_for_each(subxform_result,
                                    func, data);
                        }
                }
                bithenge_node_dec_ref(subxform_result);
                if (rc != EOK)
                        return rc;
        }

        if (!self->prefix) {
                aoff64_t blob_size, end_pos;
                rc = bithenge_blob_size(self->blob, &blob_size);
                if (rc != EOK)
                        return rc;
                rc = struct_node_field_offset(self, &end_pos,
                    self->transform->num_subtransforms);
                if (rc != EOK)
                        return rc;
                if (blob_size != end_pos) {
                        rc = EINVAL;
                        return rc;
                }
        }

        return rc;
}

static int struct_node_get(bithenge_node_t *base, bithenge_node_t *key,
    bithenge_node_t **out)
{
        struct_node_t *self = node_as_struct(base);

        if (bithenge_node_type(key) != BITHENGE_NODE_STRING) {
                bithenge_node_dec_ref(key);
                return ENOENT;
        }
        const char *name = bithenge_string_node_value(key);

        for (size_t i = 0; self->transform->subtransforms[i].transform; i++) {
                if (self->transform->subtransforms[i].name
                    && !str_cmp(name, self->transform->subtransforms[i].name)) {
                        bithenge_node_dec_ref(key);
                        return struct_node_subtransform(self, out, i);
                }
        }

        for (size_t i = 0; self->transform->subtransforms[i].transform; i++) {
                if (self->transform->subtransforms[i].name)
                        continue;
                bithenge_node_t *subxform_result;
                int rc = struct_node_subtransform(self, &subxform_result, i);
                if (rc != EOK) {
                        bithenge_node_dec_ref(key);
                        return rc;
                }
                if (bithenge_node_type(subxform_result) !=
                    BITHENGE_NODE_INTERNAL) {
                        bithenge_node_dec_ref(subxform_result);
                        bithenge_node_dec_ref(key);
                        return EINVAL;
                }
                bithenge_node_inc_ref(key);
                rc = bithenge_node_get(subxform_result, key, out);
                bithenge_node_dec_ref(subxform_result);
                if (rc != ENOENT) {
                        bithenge_node_dec_ref(key);
                        return rc;
                }
        }

        bithenge_node_dec_ref(key);
        return ENOENT;
}

static void struct_node_destroy(bithenge_node_t *base)
{
        struct_node_t *node = node_as_struct(base);

        /* We didn't inc_ref for the scope in struct_transform_make_node, so
         * make sure it doesn't try to dec_ref. */
        node->scope.current_node = NULL;
        bithenge_scope_destroy(&node->scope);

        bithenge_transform_dec_ref(struct_as_transform(node->transform));
        bithenge_blob_dec_ref(node->blob);
        free(node->ends);
        free(node);
}

static const bithenge_internal_node_ops_t struct_node_ops = {
        .for_each = struct_node_for_each,
        .get = struct_node_get,
        .destroy = struct_node_destroy,
};

static int struct_transform_make_node(struct_transform_t *self,
    bithenge_node_t **out, bithenge_scope_t *scope, bithenge_blob_t *blob,
    bool prefix)
{
        struct_node_t *node = malloc(sizeof(*node));
        if (!node)
                return ENOMEM;

        bithenge_scope_init(&node->scope);
        int rc = bithenge_scope_copy(&node->scope, scope);
        if (rc != EOK) {
                free(node);
                return rc;
        }

        node->ends = malloc(sizeof(*node->ends) * self->num_subtransforms);
        if (!node->ends) {
                bithenge_scope_destroy(&node->scope);
                free(node);
                return ENOMEM;
        }

        rc = bithenge_init_internal_node(struct_as_node(node),
            &struct_node_ops);
        if (rc != EOK) {
                bithenge_scope_destroy(&node->scope);
                free(node->ends);
                free(node);
                return rc;
        }

        bithenge_transform_inc_ref(struct_as_transform(self));
        bithenge_blob_inc_ref(blob);
        node->transform = self;
        node->blob = blob;
        node->prefix = prefix;
        node->num_ends = 0;
        *out = struct_as_node(node);

        /* We should inc_ref(*out) here, but that would make a cycle. Instead,
         * we leave it 1 too low, so that when the only remaining use of *out
         * is the scope, *out will be destroyed. Also see the comment in
         * struct_node_destroy. */
        bithenge_scope_set_current_node(&node->scope, *out);

        return EOK;
}

static int struct_transform_apply(bithenge_transform_t *base,
    bithenge_scope_t *scope, bithenge_node_t *in, bithenge_node_t **out)
{
        struct_transform_t *self = transform_as_struct(base);
        if (bithenge_node_type(in) != BITHENGE_NODE_BLOB)
                return EINVAL;
        return struct_transform_make_node(self, out, scope,
            bithenge_node_as_blob(in), false);
}

static int struct_transform_prefix_length(bithenge_transform_t *base,
    bithenge_scope_t *scope, bithenge_blob_t *blob, aoff64_t *out)
{
        struct_transform_t *self = transform_as_struct(base);
        bithenge_node_t *struct_node;
        int rc = struct_transform_make_node(self, &struct_node, scope, blob,
            true);
        if (rc != EOK)
                return rc;

        rc = struct_node_field_offset(node_as_struct(struct_node), out,
            self->num_subtransforms);
        bithenge_node_dec_ref(struct_node);
        return rc;
}

static void free_subtransforms(bithenge_named_transform_t *subtransforms)
{
        for (size_t i = 0; subtransforms[i].transform; i++) {
                free((void *)subtransforms[i].name);
                bithenge_transform_dec_ref(subtransforms[i].transform);
        }
        free(subtransforms);
}

static void struct_transform_destroy(bithenge_transform_t *base)
{
        struct_transform_t *self = transform_as_struct(base);
        free_subtransforms(self->subtransforms);
        free(self);
}

static bithenge_transform_ops_t struct_transform_ops = {
        .apply = struct_transform_apply,
        .prefix_length = struct_transform_prefix_length,
        .destroy = struct_transform_destroy,
};

/** Create a struct transform. The transform will apply its subtransforms
 * sequentially to a blob to create an internal node. Each result is either
 * given a key from @a subtransforms or, if the name is NULL, the result's keys
 * and values are merged into the struct transform's result. This function
 * takes ownership of @a subtransforms and the names and references therein.
 * @param[out] out Stores the created transform.
 * @param subtransforms The subtransforms and field names.
 * @return EOK on success or an error code from errno.h. */
int bithenge_new_struct(bithenge_transform_t **out,
    bithenge_named_transform_t *subtransforms)
{
        int rc;
        struct_transform_t *self = malloc(sizeof(*self));
        if (!self) {
                rc = ENOMEM;
                goto error;
        }
        rc = bithenge_init_transform(struct_as_transform(self),
            &struct_transform_ops, 0);
        if (rc != EOK)
                goto error;
        self->subtransforms = subtransforms;
        self->num_subtransforms = 0;
        for (self->num_subtransforms = 0;
            subtransforms[self->num_subtransforms].transform;
            self->num_subtransforms++);
        *out = struct_as_transform(self);
        return EOK;
error:
        free_subtransforms(subtransforms);
        free(self);
        return rc;
}

typedef struct {
        bithenge_transform_t base;
        bithenge_transform_t **xforms;
        size_t num;
} compose_transform_t;

static bithenge_transform_t *compose_as_transform(compose_transform_t *xform)
{
        return &xform->base;
}

static compose_transform_t *transform_as_compose(bithenge_transform_t *xform)
{
        return (compose_transform_t *)xform;
}

static int compose_apply(bithenge_transform_t *base, bithenge_scope_t *scope,
    bithenge_node_t *in, bithenge_node_t **out)
{
        int rc;
        compose_transform_t *self = transform_as_compose(base);
        bithenge_node_inc_ref(in);

        /* i ranges from (self->num - 1) to 0 inside the loop. */
        for (size_t i = self->num; i--; ) {
                bithenge_node_t *tmp;
                rc = bithenge_transform_apply(self->xforms[i], scope, in,
                    &tmp);
                bithenge_node_dec_ref(in);
                if (rc != EOK)
                        return rc;
                in = tmp;
        }

        *out = in;
        return rc;
}

static int compose_prefix_length(bithenge_transform_t *base,
    bithenge_scope_t *scope, bithenge_blob_t *blob, aoff64_t *out)
{
        compose_transform_t *self = transform_as_compose(base);
        return bithenge_transform_prefix_length(self->xforms[self->num - 1],
            scope, blob, out);
}

static void compose_destroy(bithenge_transform_t *base)
{
        compose_transform_t *self = transform_as_compose(base);
        for (size_t i = 0; i < self->num; i++)
                bithenge_transform_dec_ref(self->xforms[i]);
        free(self->xforms);
        free(self);
}

static const bithenge_transform_ops_t compose_transform_ops = {
        .apply = compose_apply,
        .prefix_length = compose_prefix_length,
        .destroy = compose_destroy,
};

/** Create a composition of multiple transforms. When the result is applied to a
 * node, each transform is applied in turn, with the last transform applied
 * first. @a xforms may contain any number of transforms or no transforms at
 * all. This function takes ownership of @a xforms and the references therein.
 * @param[out] out Holds the result.
 * @param[in] xforms The transforms to apply.
 * @param num The number of transforms.
 * @return EOK on success or an error code from errno.h. */
int bithenge_new_composed_transform(bithenge_transform_t **out,
    bithenge_transform_t **xforms, size_t num)
{
        if (num == 0) {
                /* TODO: optimize */
        } else if (num == 1) {
                *out = xforms[0];
                free(xforms);
                return EOK;
        }

        int rc;
        compose_transform_t *self = malloc(sizeof(*self));
        if (!self) {
                rc = ENOMEM;
                goto error;
        }
        rc = bithenge_init_transform(compose_as_transform(self),
            &compose_transform_ops, 0);
        if (rc != EOK)
                goto error;
        self->xforms = xforms;
        self->num = num;
        *out = compose_as_transform(self);
        return EOK;
error:
        for (size_t i = 0; i < num; i++)
                bithenge_transform_dec_ref(xforms[i]);
        free(xforms);
        free(self);
        return rc;
}

/** @}
 */