[people/ms/libloc.git] / src / database.c

/*
        libloc - A library to determine the location of someone on the Internet

        Copyright (C) 2017 IPFire Development Team <info@ipfire.org>

        This library is free software; you can redistribute it and/or
        modify it under the terms of the GNU Lesser General Public
        License as published by the Free Software Foundation; either
        version 2.1 of the License, or (at your option) any later version.

        This library is distributed in the hope that it will be useful,
        but WITHOUT ANY WARRANTY; without even the implied warranty of
        MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
        Lesser General Public License for more details.
*/

#include <arpa/inet.h>
#include <ctype.h>
#include <errno.h>
#include <netinet/in.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <time.h>
#include <unistd.h>

#ifdef HAVE_ENDIAN_H
#  include <endian.h>
#endif

#include <openssl/err.h>
#include <openssl/evp.h>
#include <openssl/pem.h>

#include <loc/libloc.h>
#include <loc/as.h>
#include <loc/compat.h>
#include <loc/country.h>
#include <loc/database.h>
#include <loc/format.h>
#include <loc/network.h>
#include <loc/private.h>
#include <loc/stringpool.h>

struct loc_database {
        struct loc_ctx* ctx;
        int refcount;

        FILE* f;

        unsigned int version;
        time_t created_at;
        off_t vendor;
        off_t description;
        off_t license;

        char* signature;
        size_t signature_length;

        // ASes in the database
        struct loc_database_as_v0* as_v0;
        size_t as_count;

        // Network tree
        struct loc_database_network_node_v0* network_nodes_v0;
        size_t network_nodes_count;

        // Networks
        struct loc_database_network_v0* networks_v0;
        size_t networks_count;

        // Countries
        struct loc_database_country_v0* countries_v0;
        size_t countries_count;

        struct loc_stringpool* pool;
};

#define MAX_STACK_DEPTH 256

struct loc_node_stack {
        off_t offset;
        int i; // Is this node 0 or 1?
        int depth;
};

struct loc_database_enumerator {
        struct loc_ctx* ctx;
        struct loc_database* db;
        enum loc_database_enumerator_mode mode;
        int refcount;

        // Search string
        char* string;
        char country_code[3];
        uint32_t asn;
        enum loc_network_flags flags;

        // Index of the AS we are looking at
        unsigned int as_index;

        // Network state
        struct in6_addr network_address;
        struct loc_node_stack network_stack[MAX_STACK_DEPTH];
        int network_stack_depth;
        unsigned int* networks_visited;
};

static int loc_database_read_magic(struct loc_database* db) {
        struct loc_database_magic magic;

        // Read from file
        size_t bytes_read = fread(&magic, 1, sizeof(magic), db->f);

        // Check if we have been able to read enough data
        if (bytes_read < sizeof(magic)) {
                ERROR(db->ctx, "Could not read enough data to validate magic bytes\n");
                DEBUG(db->ctx, "Read %zu bytes, but needed %zu\n", bytes_read, sizeof(magic));
                return -ENOMSG;
        }

        // Compare magic bytes
        if (memcmp(LOC_DATABASE_MAGIC, magic.magic, strlen(LOC_DATABASE_MAGIC)) == 0) {
                DEBUG(db->ctx, "Magic value matches\n");

                // Parse version
                db->version = be16toh(magic.version);
                DEBUG(db->ctx, "Database version is %u\n", db->version);

                return 0;
        }

        ERROR(db->ctx, "Database format is not compatible\n");

        // Return an error
        return 1;
}

static int loc_database_read_as_section_v0(struct loc_database* db,
                const struct loc_database_header_v0* header) {
        off_t as_offset  = be32toh(header->as_offset);
        size_t as_length = be32toh(header->as_length);

        DEBUG(db->ctx, "Reading AS section from %jd (%zu bytes)\n", (intmax_t)as_offset, as_length);

        if (as_length > 0) {
                db->as_v0 = mmap(NULL, as_length, PROT_READ,
                        MAP_SHARED, fileno(db->f), as_offset);

                if (db->as_v0 == MAP_FAILED)
                        return -errno;
        }

        db->as_count = as_length / sizeof(*db->as_v0);

        INFO(db->ctx, "Read %zu ASes from the database\n", db->as_count);

        return 0;
}

static int loc_database_read_network_nodes_section_v0(struct loc_database* db,
                const struct loc_database_header_v0* header) {
        off_t network_nodes_offset  = be32toh(header->network_tree_offset);
        size_t network_nodes_length = be32toh(header->network_tree_length);

        DEBUG(db->ctx, "Reading network nodes section from %jd (%zu bytes)\n",
                (intmax_t)network_nodes_offset, network_nodes_length);

        if (network_nodes_length > 0) {
                db->network_nodes_v0 = mmap(NULL, network_nodes_length, PROT_READ,
                        MAP_SHARED, fileno(db->f), network_nodes_offset);

                if (db->network_nodes_v0 == MAP_FAILED)
                        return -errno;
        }

        db->network_nodes_count = network_nodes_length / sizeof(*db->network_nodes_v0);

        INFO(db->ctx, "Read %zu network nodes from the database\n", db->network_nodes_count);

        return 0;
}

static int loc_database_read_networks_section_v0(struct loc_database* db,
                const struct loc_database_header_v0* header) {
        off_t networks_offset  = be32toh(header->network_data_offset);
        size_t networks_length = be32toh(header->network_data_length);

        DEBUG(db->ctx, "Reading networks section from %jd (%zu bytes)\n",
                (intmax_t)networks_offset, networks_length);

        if (networks_length > 0) {
                db->networks_v0 = mmap(NULL, networks_length, PROT_READ,
                        MAP_SHARED, fileno(db->f), networks_offset);

                if (db->networks_v0 == MAP_FAILED)
                        return -errno;
        }

        db->networks_count = networks_length / sizeof(*db->networks_v0);

        INFO(db->ctx, "Read %zu networks from the database\n", db->networks_count);

        return 0;
}

static int loc_database_read_countries_section_v0(struct loc_database* db,
                const struct loc_database_header_v0* header) {
        off_t countries_offset  = be32toh(header->countries_offset);
        size_t countries_length = be32toh(header->countries_length);

        DEBUG(db->ctx, "Reading countries section from %jd (%zu bytes)\n",
                (intmax_t)countries_offset, countries_length);

        if (countries_length > 0) {
                db->countries_v0 = mmap(NULL, countries_length, PROT_READ,
                        MAP_SHARED, fileno(db->f), countries_offset);

                if (db->countries_v0 == MAP_FAILED)
                        return -errno;
        }

        db->countries_count = countries_length / sizeof(*db->countries_v0);

        INFO(db->ctx, "Read %zu countries from the database\n",
                db->countries_count);

        return 0;
}

static int loc_database_read_header_v0(struct loc_database* db) {
        struct loc_database_header_v0 header;

        // Read from file
        size_t size = fread(&header, 1, sizeof(header), db->f);

        if (size < sizeof(header)) {
                ERROR(db->ctx, "Could not read enough data for header\n");
                return -ENOMSG;
        }

        // Copy over data
        db->created_at  = be64toh(header.created_at);
        db->vendor      = be32toh(header.vendor);
        db->description = be32toh(header.description);
        db->license     = be32toh(header.license);

        // Read signature
        db->signature_length = be32toh(header.signature_length);
        if (db->signature_length) {
                // Check for a plausible signature length
                if (db->signature_length > LOC_SIGNATURE_MAX_LENGTH) {
                        ERROR(db->ctx, "Signature too long: %ld\n", db->signature_length);
                        return -EINVAL;
                }

                DEBUG(db->ctx, "Reading signature of %ld bytes\n",
                        db->signature_length);

                db->signature = malloc(db->signature_length);
                for (unsigned int i = 0; i < db->signature_length; i++)
                        db->signature[i] = header.signature[i];
        }

        // Open pool
        off_t pool_offset  = be32toh(header.pool_offset);
        size_t pool_length = be32toh(header.pool_length);

        int r = loc_stringpool_open(db->ctx, &db->pool,
                db->f, pool_length, pool_offset);
        if (r)
                return r;

        // AS section
        r = loc_database_read_as_section_v0(db, &header);
        if (r)
                return r;

        // Network Nodes
        r = loc_database_read_network_nodes_section_v0(db, &header);
        if (r)
                return r;

        // Networks
        r = loc_database_read_networks_section_v0(db, &header);
        if (r)
                return r;

        // countries
        r = loc_database_read_countries_section_v0(db, &header);
        if (r)
                return r;

        return 0;
}

static int loc_database_read_header(struct loc_database* db) {
        switch (db->version) {
                case 0:
                        return loc_database_read_header_v0(db);

                default:
                        ERROR(db->ctx, "Incompatible database version: %u\n", db->version);
                        return 1;
        }
}

static int loc_database_read(struct loc_database* db, FILE* f) {
        clock_t start = clock();

        int fd = fileno(f);

        // Clone file descriptor
        fd = dup(fd);
        if (!fd) {
                ERROR(db->ctx, "Could not duplicate file descriptor\n");
                return -1;
        }

        // Reopen the file so that we can keep our own file handle
        db->f = fdopen(fd, "r");
        if (!db->f) {
                ERROR(db->ctx, "Could not re-open database file\n");
                return -1;
        }

        // Rewind to the start of the file
        rewind(db->f);

        // Read magic bytes
        int r = loc_database_read_magic(db);
        if (r)
                return r;

        // Read the header
        r = loc_database_read_header(db);
        if (r)
                return r;

        clock_t end = clock();

        INFO(db->ctx, "Opened database in %.4fms\n",
                (double)(end - start) / CLOCKS_PER_SEC * 1000);

        return 0;
}

LOC_EXPORT int loc_database_new(struct loc_ctx* ctx, struct loc_database** database, FILE* f) {
        // Fail on invalid file handle
        if (!f)
                return -EINVAL;

        struct loc_database* db = calloc(1, sizeof(*db));
        if (!db)
                return -ENOMEM;

        // Reference context
        db->ctx = loc_ref(ctx);
        db->refcount = 1;

        DEBUG(db->ctx, "Database object allocated at %p\n", db);

        int r = loc_database_read(db, f);
        if (r) {
                loc_database_unref(db);
                return r;
        }

        *database = db;

        return 0;
}

LOC_EXPORT struct loc_database* loc_database_ref(struct loc_database* db) {
        db->refcount++;

        return db;
}

static void loc_database_free(struct loc_database* db) {
        int r;

        DEBUG(db->ctx, "Releasing database %p\n", db);

        // Removing all ASes
        if (db->as_v0) {
                r = munmap(db->as_v0, db->as_count * sizeof(*db->as_v0));
                if (r)
                        ERROR(db->ctx, "Could not unmap AS section: %s\n", strerror(errno));
        }

        // Remove mapped network sections
        if (db->networks_v0) {
                r = munmap(db->networks_v0, db->networks_count * sizeof(*db->networks_v0));
                if (r)
                        ERROR(db->ctx, "Could not unmap networks section: %s\n", strerror(errno));
        }

        // Remove mapped network nodes section
        if (db->network_nodes_v0) {
                r = munmap(db->network_nodes_v0, db->network_nodes_count * sizeof(*db->network_nodes_v0));
                if (r)
                        ERROR(db->ctx, "Could not unmap network nodes section: %s\n", strerror(errno));
        }

        loc_stringpool_unref(db->pool);

        // Free signature
        if (db->signature)
                free(db->signature);

        // Close database file
        if (db->f)
                fclose(db->f);

        loc_unref(db->ctx);
        free(db);
}

LOC_EXPORT struct loc_database* loc_database_unref(struct loc_database* db) {
        if (--db->refcount > 0)
                return NULL;

        loc_database_free(db);
        return NULL;
}

LOC_EXPORT int loc_database_verify(struct loc_database* db, FILE* f) {
        // Cannot do this when no signature is available
        if (!db->signature) {
                DEBUG(db->ctx, "No signature available to verify\n");
                return 1;
        }

        // Start the stopwatch
        clock_t start = clock();

        // Load public key
        EVP_PKEY* pkey = PEM_read_PUBKEY(f, NULL, NULL, NULL);
        if (!pkey) {
                char* error = ERR_error_string(ERR_get_error(), NULL);
                ERROR(db->ctx, "Could not parse public key: %s\n", error);

                return -1;
        }

        int r = 0;

        EVP_MD_CTX* mdctx = EVP_MD_CTX_new();

        // Initialise hash function
        EVP_DigestVerifyInit(mdctx, NULL, NULL, NULL, pkey);

        // Reset file to start
        rewind(db->f);

        // Read magic
        struct loc_database_magic magic;
        fread(&magic, 1, sizeof(magic), db->f);

        // Feed magic into the hash
        EVP_DigestVerifyUpdate(mdctx, &magic, sizeof(magic));

        // Read the header
        struct loc_database_header_v0 header_v0;

        switch (db->version) {
                case 0:
                        fread(&header_v0, 1, sizeof(header_v0), db->f);

                        // Clear signature
                        for (unsigned int i = 0; i < sizeof(header_v0.signature); i++) {
                                header_v0.signature[i] = '\0';
                        }

                        // Feed header into the hash
                        EVP_DigestVerifyUpdate(mdctx, &header_v0, sizeof(header_v0));
                        break;

                default:
                        ERROR(db->ctx, "Cannot compute hash for database with format %d\n",
                                db->version);
                        r = -EINVAL;
                        goto CLEANUP;
        }

        // Walk through the file in chunks of 64kB
        char buffer[64 * 1024];

        while (!feof(db->f)) {
                size_t bytes_read = fread(buffer, 1, sizeof(buffer), db->f);

                EVP_DigestVerifyUpdate(mdctx, buffer, bytes_read);
        }

        // Finish
        r = EVP_DigestVerifyFinal(mdctx,
                (unsigned char*)db->signature, db->signature_length);

        if (r == 0) {
                DEBUG(db->ctx, "The signature is valid\n");
        } else if (r == 1) {
                DEBUG(db->ctx, "The signature is invalid\n");
        } else {
                ERROR(db->ctx, "Error verifying the signature: %s\n",
                        ERR_error_string(ERR_get_error(), NULL));
        }

        clock_t end = clock();
        DEBUG(db->ctx, "Signature checked in %.4fms\n",
                (double)(end - start) / CLOCKS_PER_SEC * 1000);

CLEANUP:
        // Cleanup
        EVP_MD_CTX_free(mdctx);
        EVP_PKEY_free(pkey);

        return r;
}

LOC_EXPORT time_t loc_database_created_at(struct loc_database* db) {
        return db->created_at;
}

LOC_EXPORT const char* loc_database_get_vendor(struct loc_database* db) {
        return loc_stringpool_get(db->pool, db->vendor);
}

LOC_EXPORT const char* loc_database_get_description(struct loc_database* db) {
        return loc_stringpool_get(db->pool, db->description);
}

LOC_EXPORT const char* loc_database_get_license(struct loc_database* db) {
        return loc_stringpool_get(db->pool, db->license);
}

LOC_EXPORT size_t loc_database_count_as(struct loc_database* db) {
        return db->as_count;
}

// Returns the AS at position pos
static int loc_database_fetch_as(struct loc_database* db, struct loc_as** as, off_t pos) {
        if ((size_t)pos >= db->as_count)
                return -EINVAL;

        DEBUG(db->ctx, "Fetching AS at position %jd\n", (intmax_t)pos);

        int r;
        switch (db->version) {
                case 0:
                        r = loc_as_new_from_database_v0(db->ctx, db->pool, as, db->as_v0 + pos);
                        break;

                default:
                        return -1;
        }

        if (r == 0) {
                DEBUG(db->ctx, "Got AS%u\n", loc_as_get_number(*as));
        }

        return r;
}

// Performs a binary search to find the AS in the list
LOC_EXPORT int loc_database_get_as(struct loc_database* db, struct loc_as** as, uint32_t number) {
        off_t lo = 0;
        off_t hi = db->as_count - 1;

        // Save start time
        clock_t start = clock();

        while (lo <= hi) {
                off_t i = (lo + hi) / 2;

                // Fetch AS in the middle between lo and hi
                int r = loc_database_fetch_as(db, as, i);
                if (r)
                        return r;

                // Check if this is a match
                uint32_t as_number = loc_as_get_number(*as);
                if (as_number == number) {
                        clock_t end = clock();

                        // Log how fast this has been
                        DEBUG(db->ctx, "Found AS%u in %.4fms\n", as_number,
                                (double)(end - start) / CLOCKS_PER_SEC * 1000);

                        return 0;
                }

                // If it wasn't, we release the AS and
                // adjust our search pointers
                loc_as_unref(*as);

                if (as_number < number) {
                        lo = i + 1;
                } else
                        hi = i - 1;
        }

        // Nothing found
        *as = NULL;

        return 1;
}

// Returns the network at position pos
static int loc_database_fetch_network(struct loc_database* db, struct loc_network** network,
                struct in6_addr* address, unsigned int prefix, off_t pos) {
        if ((size_t)pos >= db->networks_count) {
                DEBUG(db->ctx, "Network ID out of range: %jd/%jd\n",
                        (intmax_t)pos, (intmax_t)db->networks_count);
                return -EINVAL;
        }


        DEBUG(db->ctx, "Fetching network at position %jd\n", (intmax_t)pos);

        int r;
        switch (db->version) {
                case 0:
                        r = loc_network_new_from_database_v0(db->ctx, network,
                                address, prefix, db->networks_v0 + pos);
                        break;

                default:
                        return -1;
        }

        if (r == 0) {
                char* string = loc_network_str(*network);
                DEBUG(db->ctx, "Got network %s\n", string);
                free(string);
        }

        return r;
}

static int __loc_database_node_is_leaf(const struct loc_database_network_node_v0* node) {
        return (node->network != htobe32(0xffffffff));
}

static int __loc_database_lookup_handle_leaf(struct loc_database* db, const struct in6_addr* address,
                struct loc_network** network, struct in6_addr* network_address, unsigned int prefix,
                const struct loc_database_network_node_v0* node) {
        off_t network_index = be32toh(node->network);

        DEBUG(db->ctx, "Handling leaf node at %jd (%jd)\n", (intmax_t)(node - db->network_nodes_v0), (intmax_t)network_index);

        // Fetch the network
        int r = loc_database_fetch_network(db, network,
                network_address, prefix, network_index);
        if (r) {
                ERROR(db->ctx, "Could not fetch network %jd from database\n", (intmax_t)network_index);
                return r;
        }

        // Check if the given IP address is inside the network
        r = loc_network_match_address(*network, address);
        if (r) {
                DEBUG(db->ctx, "Searched address is not part of the network\n");

                loc_network_unref(*network);
                *network = NULL;
                return 1;
        }

        // A network was found and the IP address matches
        return 0;
}

// Searches for an exact match along the path
static int __loc_database_lookup(struct loc_database* db, const struct in6_addr* address,
                struct loc_network** network, struct in6_addr* network_address,
                const struct loc_database_network_node_v0* node, unsigned int level) {
        int r;
        off_t node_index;

        // Follow the path
        int bit = in6_addr_get_bit(address, level);
        in6_addr_set_bit(network_address, level, bit);

        if (bit == 0)
                node_index = be32toh(node->zero);
        else
                node_index = be32toh(node->one);

        // If the node index is zero, the tree ends here
        // and we cannot descend any further
        if (node_index > 0) {
                // Check boundaries
                if ((size_t)node_index >= db->network_nodes_count)
                        return -EINVAL;

                // Move on to the next node
                r = __loc_database_lookup(db, address, network, network_address,
                        db->network_nodes_v0 + node_index, level + 1);

                // End here if a result was found
                if (r == 0)
                        return r;

                // Raise any errors
                else if (r < 0)
                        return r;

                DEBUG(db->ctx, "No match found below level %u\n", level);
        } else {
                DEBUG(db->ctx, "Tree ended at level %u\n", level);
        }

        // If this node has a leaf, we will check if it matches
        if (__loc_database_node_is_leaf(node)) {
                r = __loc_database_lookup_handle_leaf(db, address, network, network_address, level, node);
                if (r <= 0)
                        return r;
        }

        return 1;
}

LOC_EXPORT int loc_database_lookup(struct loc_database* db,
                struct in6_addr* address, struct loc_network** network) {
        struct in6_addr network_address;
        memset(&network_address, 0, sizeof(network_address));

        *network = NULL;

        // Save start time
        clock_t start = clock();

        int r = __loc_database_lookup(db, address, network, &network_address,
                db->network_nodes_v0, 0);

        clock_t end = clock();

        // Log how fast this has been
        DEBUG(db->ctx, "Executed network search in %.4fms\n",
                (double)(end - start) / CLOCKS_PER_SEC * 1000);

        return r;
}

LOC_EXPORT int loc_database_lookup_from_string(struct loc_database* db,
                const char* string, struct loc_network** network) {
        struct in6_addr address;

        int r = loc_parse_address(db->ctx, string, &address);
        if (r)
                return r;

        return loc_database_lookup(db, &address, network);
}

// Returns the country at position pos
static int loc_database_fetch_country(struct loc_database* db,
                struct loc_country** country, off_t pos) {
        if ((size_t)pos >= db->countries_count)
                return -EINVAL;

        DEBUG(db->ctx, "Fetching country at position %jd\n", (intmax_t)pos);

        int r;
        switch (db->version) {
                case 0:
                        r = loc_country_new_from_database_v0(db->ctx, db->pool, country, db->countries_v0 + pos);
                        break;

                default:
                        return -1;
        }

        if (r == 0) {
                DEBUG(db->ctx, "Got country %s\n", loc_country_get_code(*country));
        }

        return r;
}

// Performs a binary search to find the country in the list
LOC_EXPORT int loc_database_get_country(struct loc_database* db,
                struct loc_country** country, const char* code) {
        off_t lo = 0;
        off_t hi = db->countries_count - 1;

        // Save start time
        clock_t start = clock();

        while (lo <= hi) {
                off_t i = (lo + hi) / 2;

                // Fetch country in the middle between lo and hi
                int r = loc_database_fetch_country(db, country, i);
                if (r)
                        return r;

                // Check if this is a match
                const char* cc = loc_country_get_code(*country);
                int result = strcmp(code, cc);

                if (result == 0) {
                        clock_t end = clock();

                        // Log how fast this has been
                        DEBUG(db->ctx, "Found country %s in %.4fms\n", cc,
                                (double)(end - start) / CLOCKS_PER_SEC * 1000);

                        return 0;
                }

                // If it wasn't, we release the country and
                // adjust our search pointers
                loc_country_unref(*country);

                if (result > 0) {
                        lo = i + 1;
                } else
                        hi = i - 1;
        }

        // Nothing found
        *country = NULL;

        return 1;
}

// Enumerator

LOC_EXPORT int loc_database_enumerator_new(struct loc_database_enumerator** enumerator,
                struct loc_database* db, enum loc_database_enumerator_mode mode) {
        struct loc_database_enumerator* e = calloc(1, sizeof(*e));
        if (!e)
                return -ENOMEM;

        // Reference context
        e->ctx = loc_ref(db->ctx);
        e->db = loc_database_ref(db);
        e->mode = mode;
        e->refcount = 1;

        // Initialise graph search
        //e->network_stack[++e->network_stack_depth] = 0;
        e->network_stack_depth = 1;
        e->networks_visited = calloc(db->network_nodes_count, sizeof(*e->networks_visited));

        DEBUG(e->ctx, "Database enumerator object allocated at %p\n", e);

        *enumerator = e;
        return 0;
}

LOC_EXPORT struct loc_database_enumerator* loc_database_enumerator_ref(struct loc_database_enumerator* enumerator) {
        enumerator->refcount++;

        return enumerator;
}

static void loc_database_enumerator_free(struct loc_database_enumerator* enumerator) {
        DEBUG(enumerator->ctx, "Releasing database enumerator %p\n", enumerator);

        // Release all references
        loc_database_unref(enumerator->db);
        loc_unref(enumerator->ctx);

        if (enumerator->string)
                free(enumerator->string);

        // Free network search
        free(enumerator->networks_visited);

        free(enumerator);
}

LOC_EXPORT struct loc_database_enumerator* loc_database_enumerator_unref(struct loc_database_enumerator* enumerator) {
        if (!enumerator)
                return NULL;

        if (--enumerator->refcount > 0)
                return enumerator;

        loc_database_enumerator_free(enumerator);
        return NULL;
}

LOC_EXPORT int loc_database_enumerator_set_string(struct loc_database_enumerator* enumerator, const char* string) {
        enumerator->string = strdup(string);

        // Make the string lowercase
        for (char *p = enumerator->string; *p; p++)
                *p = tolower(*p);

        return 0;
}

LOC_EXPORT int loc_database_enumerator_set_country_code(struct loc_database_enumerator* enumerator, const char* country_code) {
        // Set empty country code
        if (!country_code || !*country_code) {
                *enumerator->country_code = '\0';
                return 0;
        }

        // Treat A1, A2, A3 as special country codes,
        // but perform search for flags instead
        if (strcmp(country_code, "A1") == 0) {
                return loc_database_enumerator_set_flag(enumerator,
                        LOC_NETWORK_FLAG_ANONYMOUS_PROXY);
        } else if (strcmp(country_code, "A2") == 0) {
                return loc_database_enumerator_set_flag(enumerator,
                        LOC_NETWORK_FLAG_SATELLITE_PROVIDER);
        } else if (strcmp(country_code, "A3") == 0) {
                return loc_database_enumerator_set_flag(enumerator,
                        LOC_NETWORK_FLAG_ANYCAST);
        }

        // Country codes must be two characters
        if (!loc_country_code_is_valid(country_code))
                return -EINVAL;

        for (unsigned int i = 0; i < 3; i++) {
                enumerator->country_code[i] = country_code[i];
        }

        return 0;
}

LOC_EXPORT int loc_database_enumerator_set_asn(
                struct loc_database_enumerator* enumerator, unsigned int asn) {
        enumerator->asn = asn;

        return 0;
}

LOC_EXPORT int loc_database_enumerator_set_flag(
                struct loc_database_enumerator* enumerator, enum loc_network_flags flag) {
        enumerator->flags |= flag;

        return 0;
}

LOC_EXPORT int loc_database_enumerator_next_as(
                struct loc_database_enumerator* enumerator, struct loc_as** as) {
        *as = NULL;

        // Do not do anything if not in AS mode
        if (enumerator->mode != LOC_DB_ENUMERATE_ASES)
                return 0;

        struct loc_database* db = enumerator->db;

        while (enumerator->as_index < db->as_count) {
                // Fetch the next AS
                int r = loc_database_fetch_as(db, as, enumerator->as_index++);
                if (r)
                        return r;

                r = loc_as_match_string(*as, enumerator->string);
                if (r == 1) {
                        DEBUG(enumerator->ctx, "AS%d (%s) matches %s\n",
                                loc_as_get_number(*as), loc_as_get_name(*as), enumerator->string);

                        return 0;
                }

                // No match
                loc_as_unref(*as);
                *as = NULL;
        }

        // Reset the index
        enumerator->as_index = 0;

        // We have searched through all of them
        return 0;
}

static int loc_database_enumerator_stack_push_node(
                struct loc_database_enumerator* e, off_t offset, int i, int depth) {
        // Do not add empty nodes
        if (!offset)
                return 0;

        // Check if there is any space left on the stack
        if (e->network_stack_depth >= MAX_STACK_DEPTH) {
                ERROR(e->ctx, "Maximum stack size reached: %d\n", e->network_stack_depth);
                return -1;
        }

        // Increase stack size
        int s = ++e->network_stack_depth;

        DEBUG(e->ctx, "Added node %jd to stack (%d)\n", (intmax_t)offset, depth);

        e->network_stack[s].offset = offset;
        e->network_stack[s].i = i;
        e->network_stack[s].depth = depth;

        return 0;
}

LOC_EXPORT int loc_database_enumerator_next_network(
                struct loc_database_enumerator* enumerator, struct loc_network** network) {
        // Reset network
        *network = NULL;

        // Do not do anything if not in network mode
        if (enumerator->mode != LOC_DB_ENUMERATE_NETWORKS)
                return 0;

        int r;

        DEBUG(enumerator->ctx, "Called with a stack of %u nodes\n",
                enumerator->network_stack_depth);

        // Perform DFS
        while (enumerator->network_stack_depth > 0) {
                DEBUG(enumerator->ctx, "Stack depth: %u\n", enumerator->network_stack_depth);

                // Get object from top of the stack
                struct loc_node_stack* node = &enumerator->network_stack[enumerator->network_stack_depth];

                // Remove the node from the stack if we have already visited it
                if (enumerator->networks_visited[node->offset]) {
                        enumerator->network_stack_depth--;
                        continue;
                }

                // Mark the bits on the path correctly
                in6_addr_set_bit(&enumerator->network_address,
                        (node->depth > 0) ? node->depth - 1 : 0, node->i);

                DEBUG(enumerator->ctx, "Looking at node %jd\n", (intmax_t)node->offset);
                enumerator->networks_visited[node->offset]++;

                // Pop node from top of the stack
                struct loc_database_network_node_v0* n =
                        enumerator->db->network_nodes_v0 + node->offset;

                // Add edges to stack
                r = loc_database_enumerator_stack_push_node(enumerator,
                        be32toh(n->one), 1, node->depth + 1);

                if (r)
                        return r;

                r = loc_database_enumerator_stack_push_node(enumerator,
                        be32toh(n->zero), 0, node->depth + 1);

                if (r)
                        return r;

                // Check if this node is a leaf and has a network object
                if (__loc_database_node_is_leaf(n)) {
                        off_t network_index = be32toh(n->network);

                        DEBUG(enumerator->ctx, "Node has a network at %jd\n", (intmax_t)network_index);

                        // Fetch the network object
                        r = loc_database_fetch_network(enumerator->db, network,
                                &enumerator->network_address, node->depth, network_index);

                        // Break on any errors
                        if (r)
                                return r;

                        // Check if we are interested in this network

                        // Skip if the country code does not match
                        if (*enumerator->country_code &&
                                        !loc_network_match_country_code(*network, enumerator->country_code)) {
                                loc_network_unref(*network);
                                *network = NULL;

                                continue;
                        }

                        // Skip if the ASN does not match
                        if (enumerator->asn &&
                                        !loc_network_match_asn(*network, enumerator->asn)) {
                                loc_network_unref(*network);
                                *network = NULL;

                                continue;
                        }

                        // Skip if flags do not match
                        if (enumerator->flags &&
                                        !loc_network_match_flag(*network, enumerator->flags)) {
                                loc_network_unref(*network);
                                *network = NULL;
                        }

                        return 0;
                }
        }

        // Reached the end of the search

        // Mark all nodes as non-visited
        for (unsigned int i = 0; i < enumerator->db->network_nodes_count; i++)
                enumerator->networks_visited[i] = 0;

        return 0;
}