mod_upload_progress.c

#include <stdint.h>
#include <ctype.h>
#include <ap_config.h>
#include <http_core.h>
#include <http_log.h>
#include <http_protocol.h>
#include <http_request.h>
#include <apr_version.h>
#include <apr_pools.h>
#include <apr_strings.h>
#include "unixd.h"

#if APR_HAS_SHARED_MEMORY
#include "apr_rmm.h"
#include "apr_shm.h"
#else
#error "APR_HAS_SHARED_MEMORY required for upload_progress module"
#endif

#if APR_HAVE_UNISTD_H
#include <unistd.h>
#endif

#include "ap_backports.h"

#ifndef PROGRESS_ID
#  define PROGRESS_ID "X-Progress-ID"
#endif
#ifndef JSON_CB_PARAM
#  define JSON_CB_PARAM "callback"
#endif
#ifndef CACHE_FILENAME
#  define CACHE_FILENAME "/tmp/upload_progress_cache"
#endif
#ifndef PROGRESS_EXPIRES
/* shared memory entries not updated in PROGRESS_EXPIRES seconds
   will be reused when needed */
#  define PROGRESS_EXPIRES 60
#endif
#ifndef UP_DEBUG
#  define UP_DEBUG 0
#endif

#ifndef ARG_ALLOWED_PROGRESSID
#  define ARG_ALLOWED_PROGRESSID "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_:./!{}"
#endif
#ifndef ARG_ALLOWED_JSONPCALLBACK
#  define ARG_ALLOWED_JSONPCALLBACK "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789._$"
#endif
#ifndef ARG_MINLEN_PROGRESSID
#  define ARG_MINLEN_PROGRESSID 8
#endif
#ifndef ARG_MAXLEN_PROGRESSID
#  define ARG_MAXLEN_PROGRESSID 128
#endif
#define UP_STRINGIFY(arg) #arg
#define UP_TOSTRING(arg) UP_STRINGIFY(arg)
#define UP_ID_FMT "." UP_TOSTRING(ARG_MAXLEN_PROGRESSID) "s"
#ifndef ARG_MINLEN_JSONPCALLBACK
#  define ARG_MINLEN_JSONPCALLBACK 1
#endif
#ifndef ARG_MAXLEN_JSONPCALLBACK
/* This limit is set by most JS implementations on identifier length */
#  define ARG_MAXLEN_JSONPCALLBACK 64
#endif

#if UP_DEBUG > 0
#  if UP_DEBUG > 1
#    define up_log(m,s,err,srv,fmtstr,...) ap_log_error( m, s, err, srv, "pid:%" APR_PID_T_FMT " " fmtstr, getpid(), ##__VA_ARGS__ )
#  else
#    define up_log(...) ap_log_error( __VA_ARGS__ )
#  endif
#else
#  define up_log(...)
#endif

#define CACHE_LOCK() do {                                  \
    if (config->cache_lock) {                              \
        char errbuf[200];                                  \
        up_log(APLOG_MARK, APLOG_DEBUG, 0, server, "CACHE_LOCK()"); \
        apr_status_t status = apr_global_mutex_lock(config->cache_lock);        \
        if (status != APR_SUCCESS) {                          \
            ap_log_error(APLOG_MARK, APLOG_CRIT, status, server, \
                       "%s", apr_strerror(status, errbuf, sizeof(errbuf))); \
        }                                                  \
    } \
} while (0)

#define CACHE_UNLOCK() do {                                \
    if (config->cache_lock)                               \
    {	\
        up_log(APLOG_MARK, APLOG_DEBUG, 0, server, "CACHE_UNLOCK()"); \
        apr_global_mutex_unlock(config->cache_lock);      \
    }	\
} while (0)

typedef struct {
    int track_enabled;
    int report_enabled;
} DirConfig;

typedef struct upload_progress_node_s{
    apr_off_t length;
    apr_off_t received;
    int err_status;
    time_t started_at;
    apr_off_t speed; /* bytes per second */
    time_t updated_at;
    int done;
    char key[ARG_MAXLEN_PROGRESSID];
} upload_progress_node_t;

typedef struct {
    apr_time_t cache_updated_at;
    upload_progress_node_t node;
} upload_progress_req_t;

typedef struct {
    int count;
    int active;
} upload_progress_cache_t;

typedef struct {
    apr_global_mutex_t *cache_lock;
    char *lock_file;           /* filename for shm lock mutex */
    apr_size_t cache_bytes;
    apr_shm_t *cache_shm;
    char *cache_file;
    upload_progress_cache_t *cache;
    int *list; /* static array of node indexes, list begins with indexes of active nodes */
    upload_progress_node_t *nodes; /* all nodes allocated at once */
} ServerConfig;

static void upload_progress_cache_write(server_rec *, upload_progress_node_t *);
static upload_progress_node_t *find_node(server_rec *, const char *);
static apr_status_t upload_progress_cleanup(void *);
static const char *get_progress_id(request_rec *, int *);

extern module AP_MODULE_DECLARE_DATA upload_progress_module;

static server_rec *global_server = NULL;

static inline ServerConfig *get_server_config(server_rec *s)
{
    return (ServerConfig *)ap_get_module_config(s->module_config, &upload_progress_module);
}

static inline DirConfig *get_dir_config(request_rec *r)
{
    return (DirConfig *)ap_get_module_config(r->per_dir_config, &upload_progress_module);
}

static inline upload_progress_req_t *get_request_config(request_rec *r)
{
    return (upload_progress_req_t *)ap_get_module_config(r->request_config, &upload_progress_module);
}


static int upload_progress_handle_request(request_rec *r)
{
    server_rec *server = r->server;
/**/up_log(APLOG_MARK, APLOG_DEBUG, 0, server, "upload_progress_handle_request()");

    DirConfig *dir = get_dir_config(r);

    if (!dir || (dir->track_enabled <= 0)) {
        return DECLINED;
    }
    if (r->method_number != M_POST) {
        ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, server,
                     "Upload Progress: Non-POST request in trackable location: %s.", r->uri);
        return DECLINED;
    }

    int param_error;
    const char *id = get_progress_id(r, &param_error);

    if (id) {
        ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, server,
                     "Upload Progress: Upload id='%s' in trackable location: %s.", id, r->uri);

        upload_progress_req_t *reqinfo = (upload_progress_req_t *)apr_pcalloc(r->pool,
                                       sizeof(upload_progress_req_t));
        upload_progress_node_t *node = NULL;
        if (reqinfo) {
            reqinfo->cache_updated_at = apr_time_now();
            upload_progress_node_t *node = &(reqinfo->node);

            strncpy(node->key, id, ARG_MAXLEN_PROGRESSID);
            time_t t = time(NULL);

            node->received = 0;
            node->done = 0;
            node->err_status = 0;
            node->started_at = t;
            node->speed = 0;
            node->updated_at = t;
            const char *content_length = apr_table_get(r->headers_in, "Content-Length");
            node->length = 1;
            /* Content-Length is missing is case of chunked transfer encoding */
            if (content_length)
                sscanf(content_length, "%" APR_OFF_T_FMT, &(node->length));
        }

        ap_set_module_config(r->request_config, &upload_progress_module, reqinfo);
        apr_pool_cleanup_register(r->pool, r, upload_progress_cleanup, apr_pool_cleanup_null);
        ap_add_input_filter("UPLOAD_PROGRESS", NULL, r, r->connection);

        upload_progress_cache_write(server, node);

    } else if (param_error < 0) {
        ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, server,
                     "Upload Progress: Upload with invalid ID in trackable location: %s.", r->uri);
        /*
        return HTTP_BAD_REQUEST;
        return HTTP_NOT_FOUND;
        */

    } else {
        ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, server,
                     "Upload Progress: Upload without ID in trackable location: %s.", r->uri);
    }

    return DECLINED;
}

static const char *report_upload_progress_cmd(cmd_parms *cmd, void *config, int arg)
{
/**/up_log(APLOG_MARK, APLOG_DEBUG, 0, global_server, "report_upload_progress_cmd()");
    DirConfig *dir = (DirConfig *)config;
    dir->report_enabled = arg ? 1 : -1;
    return NULL;
}

static const char *track_upload_progress_cmd(cmd_parms *cmd, void *config, int arg)
{
/**/up_log(APLOG_MARK, APLOG_DEBUG, 0, global_server, "track_upload_progress_cmd()");
    DirConfig *dir = (DirConfig *)config;
    dir->track_enabled = arg ? 1 : -1;
    return NULL;
}

static const char* upload_progress_shared_memory_size_cmd(cmd_parms *cmd,
                                                 void *dummy, const char *arg)
{
/**/up_log(APLOG_MARK, APLOG_DEBUG, 0, global_server, "upload_progress_shared_memory_size_cmd()");
    ServerConfig *config = get_server_config(cmd->server);

    long long int n = atoi(arg);

    if (n <= 0) {
        return "UploadProgressSharedMemorySize should be positive";
    }

    config->cache_bytes = (apr_size_t)n;

    return NULL;
}

static void *upload_progress_create_dir_config(apr_pool_t *p, char *dirspec)
{
/**/up_log(APLOG_MARK, APLOG_DEBUG, 0, global_server, "upload_progress_create_dir_config()");
    DirConfig *dir = (DirConfig *)apr_pcalloc(p, sizeof(DirConfig));
    dir->track_enabled = 0;
    dir->report_enabled = 0;
    return dir;
}

static void *upload_progress_merge_dir_config(apr_pool_t *p, void *basev, void *overridev)
{
    DirConfig *new = (DirConfig *)apr_pcalloc(p, sizeof(DirConfig));
    DirConfig *override = (DirConfig *)overridev;
    DirConfig *base = (DirConfig *)basev;
    new->track_enabled = (override->track_enabled == 0) ? base->track_enabled :
                             (override->track_enabled > 0 ? 1 : -1);
    new->report_enabled = (override->report_enabled == 0) ? base->report_enabled :
                              (override->report_enabled > 0 ? 1 : -1);
    return new;
}

static void *upload_progress_create_server_config(apr_pool_t *p, server_rec *s)
{
    if (!global_server) global_server = s;
/**/up_log(APLOG_MARK, APLOG_DEBUG, 0, global_server, "upload_progress_create_server_config()");
    ServerConfig *config = (ServerConfig *)apr_pcalloc(p, sizeof(ServerConfig));
    config->cache_file = apr_pstrdup(p, CACHE_FILENAME);
    config->cache_bytes = 51200;
    return config;
}

static void *upload_progress_merge_server_config(apr_pool_t *p, void *basev,
                                    void *overridesv)
{
    return basev;
}

static int read_request_status(request_rec *r)
{
    int status;

    if (r) {
        /* error status rendered in status line is preferred because passenger
           clobbers request_rec->status when exception occurs */
        /* FIXME: Shouldn't we read r->status instead as it's already preparsed? */
        status = r->status_line ? atoi(r->status_line) : 0;
        if (!ap_is_HTTP_VALID_RESPONSE(status))
            status = r->status;
        return status;
    } else {
        return 0;
    }
}

static int track_upload_progress(ap_filter_t *f, apr_bucket_brigade *bb,
                           ap_input_mode_t mode, apr_read_type_e block,
                           apr_off_t readbytes)
{
    server_rec *server = f->r->server;
/**/up_log(APLOG_MARK, APLOG_DEBUG, 0, server, "track_upload_progress()");

    apr_status_t rv = ap_get_brigade(f->next, bb, mode, block, readbytes);

    upload_progress_req_t *reqinfo = get_request_config(f->r);
    if (!reqinfo) {
        up_log(APLOG_MARK, APLOG_DEBUG, 0, server, "Request config not available");
        return rv;
    }
    upload_progress_node_t *node = &(reqinfo->node);

    time_t t = time(NULL);
    node->updated_at = t;
    if (rv == APR_SUCCESS) {
        apr_off_t length;
        apr_brigade_length(bb, 1, &length);
        node->received += length;
        if (node->received > node->length) /* handle chunked transfer */
            node->length = node->received;
        int upload_time = t - node->started_at;
        if (upload_time > 0) {
            node->speed = node->received / upload_time;
        }
    } else {
        node->err_status = read_request_status(f->r);
        reqinfo->cache_updated_at = 0; /* force cache update */
    }

    apr_time_t now = apr_time_now();
    if ((now - reqinfo->cache_updated_at) > apr_time_from_msec(500)) {
        reqinfo->cache_updated_at = now;
        upload_progress_cache_write(server, node);
    }

    return rv;
}

static int check_request_argument(const char *value, int len, char *allowed, int minlen, int maxlen) {
    /* Check the length of the argument */
    if (len > maxlen) return -1;
    if (len < minlen) return -2;
    /* If no whitelist given, assume everything whitelisted */
    if (!allowed) return 0;
    /* Check each char to be in the whitelist */
    if (strspn(value, allowed) < len) return -3;
    return 0;
}

static char *get_param_value(char *p, const char *param_name, int *len) {
    char pn1[3] = {toupper(param_name[0]), tolower(param_name[0]), 0};
    int pn_len = strlen(param_name);
    char *val_end;
    static char *param_sep = "&";

    while (p) {
        if ((strncasecmp(p, param_name, pn_len) == 0) && (p[pn_len] == '='))
            break;
        if (*p) p++;
        p = strpbrk(p, pn1);
    }
    if (p) {
        p += (pn_len + 1);
        *len = strcspn(p, param_sep);
    }
    return p;
}

static const char *get_progress_id(request_rec *r, int *param_error) {
    int len;

    /* try to find progress id in http headers */
    const char *id  = apr_table_get(r->headers_in, PROGRESS_ID);
    if (id) {
        *param_error = check_request_argument(id, strlen(id), ARG_ALLOWED_PROGRESSID,
            ARG_MINLEN_PROGRESSID, ARG_MAXLEN_PROGRESSID);
        if (*param_error) return NULL;
        return id;
    }

    /* if progress id not found in headers, check request args (query string) */
    id = get_param_value(r->args, PROGRESS_ID, &len);
    if (id) {
        *param_error = check_request_argument(id, len, ARG_ALLOWED_PROGRESSID,
            ARG_MINLEN_PROGRESSID, ARG_MAXLEN_PROGRESSID);
        if (*param_error) return NULL;
        return apr_pstrndup(r->connection->pool, id, len);
    }

    *param_error = 1; /* not found */
    return NULL;
}

static const char *get_json_callback_param(request_rec *r, int *param_error) {
    char *val;
    int len;

    val = get_param_value(r->args, JSON_CB_PARAM, &len);
    if (val) {
        *param_error = check_request_argument(val, len, ARG_ALLOWED_JSONPCALLBACK,
            ARG_MINLEN_JSONPCALLBACK, ARG_MAXLEN_JSONPCALLBACK);
        if (*param_error) return NULL;
        return apr_pstrndup(r->connection->pool, val, len);
    }

    *param_error = 1; /* not found */
    return NULL;
}

static inline int check_node(upload_progress_node_t *node, const char *key) {
    return ((node) && (strncasecmp(node->key, key, ARG_MAXLEN_PROGRESSID) == 0)) ? 1 : 0;
}

static upload_progress_node_t *find_node(server_rec *server, const char *key) {
/**/up_log(APLOG_MARK, APLOG_DEBUG, 0, server, "find_node()");

    ServerConfig *config = get_server_config(server);
    upload_progress_cache_t *cache = config->cache;
    upload_progress_node_t *node, *nodes = config->nodes;
    int *list = config->list;
    int active = cache->active;
    int i;

    for (i = 0; i < active; i++) {
        node = &nodes[list[i]];
        if (check_node(node, key))
          return node;
    }
    return NULL;
}

static apr_status_t upload_progress_cleanup(void *data)
{
    request_rec *r = (request_rec *)data;
    server_rec *server = r->server;
/**/up_log(APLOG_MARK, APLOG_DEBUG, 0, server, "upload_progress_cleanup()");

    upload_progress_req_t *reqinfo = get_request_config(r);
    if (!reqinfo) {
        up_log(APLOG_MARK, APLOG_DEBUG, 0, server, "Request config not available");
        return APR_SUCCESS;
    }
    upload_progress_node_t *node = &(reqinfo->node);
    node->err_status = read_request_status(r);
    node->updated_at = time(NULL);
    node->done = 1;
    upload_progress_cache_write(server, node);

    return APR_SUCCESS;
}

static void upload_progress_cache_write(server_rec *server, upload_progress_node_t *new_data)
{
    if (!new_data) return;
    ServerConfig *config = get_server_config(server);

    CACHE_LOCK();
    upload_progress_node_t *node = find_node(server, new_data->key);
    time_t now = time(NULL);
#define EXPIRED(node,now) ((now - node->updated_at) > PROGRESS_EXPIRES)
    if (node) {
        /* reuse node if: request finished, expired, or same started_at as node */
        if (node->started_at == new_data->started_at || node->done || EXPIRED(node, now)) {
            memcpy(node, new_data, sizeof(upload_progress_node_t));
            up_log(APLOG_MARK, APLOG_DEBUG, 0, server,
                         "Upload Progress: Reused existing node with id='%" UP_ID_FMT "'.", node->key);
        } else {
            ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, server,
                         "Upload Progress: Upload with id='%" UP_ID_FMT "' already exists, ignoring.", node->key);
        }
    } else {

        up_log(APLOG_MARK, APLOG_DEBUG, 0, server, "cleaning expired cache nodes");

        upload_progress_cache_t *cache = config->cache;
        upload_progress_node_t *nodes = config->nodes;
        int *list = config->list;
        int i, tmp;

        /* check active nodes list, if expired node found
           then swap it with last active and shrink active list by one */
        for (i = 0; i < cache->active; i++) {
            node = &nodes[list[i]];
            if (EXPIRED(node, now)) {
                cache->active -= 1;
                tmp = list[cache->active];
                list[cache->active] = list[i];
                list[i] = tmp;
                i--;
            }
        }

        if (cache->active < cache->count) {
            node = &config->nodes[config->list[cache->active]];
            cache->active += 1;
            memcpy(node, new_data, sizeof(upload_progress_node_t));
            up_log(APLOG_MARK, APLOG_DEBUG, 0, server,
                   "Upload Progress: Added upload with id='%" UP_ID_FMT "' to list.", node->key);
        } else {
            ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, server, "Cache full");
        }

    }
    CACHE_UNLOCK();

}

static apr_status_t upload_progress_cache_init(apr_pool_t *pool, ServerConfig *config)
{
/**/up_log(APLOG_MARK, APLOG_DEBUG, 0, global_server, "upload_progress_cache_init()");

    apr_status_t result;
    apr_size_t size;
    int nodes_cnt, i;

    if (config->cache_file) {
        /* Remove any existing shm segment with this name. */
        apr_shm_remove(config->cache_file, pool);
        unlink(config->cache_file);
    }

    size = APR_ALIGN_DEFAULT(config->cache_bytes);
    result = apr_shm_create(&config->cache_shm, size, config->cache_file, pool);
    if (result != APR_SUCCESS) {
        return result;
    }

    /* Determine the usable size of the shm segment. */
    size = apr_shm_size_get(config->cache_shm);
    nodes_cnt = (size - sizeof(upload_progress_cache_t)) /
                (sizeof(int) + sizeof(upload_progress_node_t));

    /* init cache */
    config->cache = (upload_progress_cache_t *)apr_shm_baseaddr_get(config->cache_shm);
    config->list = (int *)(config->cache + 1);
    config->nodes = (upload_progress_node_t *)(config->list + nodes_cnt);
    config->cache->count = nodes_cnt;
    config->cache->active = 0;
    for (i = 0; i < nodes_cnt; i++) config->list[i] = i;

    ap_log_error(APLOG_MARK, APLOG_INFO, 0, global_server,
                 "Upload Progress: monitoring max %i simultaneous uploads, id (%s) length %i..%i",
                 nodes_cnt, PROGRESS_ID, ARG_MINLEN_PROGRESSID, ARG_MAXLEN_PROGRESSID);

    return APR_SUCCESS;
}

static int upload_progress_init(apr_pool_t *p, apr_pool_t *plog,
                    apr_pool_t *ptemp,
                    server_rec *s) {
/**/up_log(APLOG_MARK, APLOG_DEBUG, 0, s, "upload_progress_init()");

    apr_status_t result;

    ServerConfig *config = get_server_config(s);

    void *data;
    const char *userdata_key = "upload_progress_init";

    /* upload_progress_init will be called twice. Don't bother
     * going through all of the initialization on the first call
     * because it will just be thrown away.*/
    apr_pool_userdata_get(&data, userdata_key, s->process->pool);
    if (!data) {
        apr_pool_userdata_set((const void *)1, userdata_key,
                               apr_pool_cleanup_null, s->process->pool);

        /* If the cache file already exists then delete it.  Otherwise we are
         * going to run into problems creating the shared memory. */
        if (config->cache_file) {
            char *lck_file = apr_pstrcat(ptemp, config->cache_file, ".lck",
                                         NULL);
            up_log(APLOG_MARK, APLOG_DEBUG, 0, s, "Upload Progress: Remove lock file");
            apr_file_remove(lck_file, ptemp);
        }
        return OK;
    }

    /* initializing cache if shared memory size is not zero and we already
     * don't have shm address
     */
    if (!config->cache_shm && config->cache_bytes > 0) {
        result = upload_progress_cache_init(p, config);
        if (result != APR_SUCCESS) {
            ap_log_error(APLOG_MARK, APLOG_ERR, result, s,
                         "Upload Progress cache: could not create shared memory segment");
            return DONE;
        }

        if (config->cache_file) {
            config->lock_file = apr_pstrcat(p, config->cache_file, ".lck",
                                        NULL);
        }

        result = apr_global_mutex_create(&config->cache_lock,
                                         config->lock_file, APR_LOCK_DEFAULT,
                                         p);
        if (result != APR_SUCCESS) {
            return result;
        }

#ifdef AP_NEED_SET_MUTEX_PERMS
        result = ap_unixd_set_global_mutex_perms(config->cache_lock);
        if (result != APR_SUCCESS) {
            ap_log_error(APLOG_MARK, APLOG_CRIT, result, s,
                         "Upload progress cache: failed to set mutex permissions");
            return result;
        }
#endif

    } else {
        ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, s,
                     "Upload Progress cache: cache size is zero, disabling "
                     "shared memory cache");
    }

    return(OK);
}

static int reportuploads_handler(request_rec *r)
{ 
    server_rec *server = r->server;
/**/up_log(APLOG_MARK, APLOG_DEBUG, 0, server, "reportuploads_handler()");

    upload_progress_node_t upload, *found;
    int param_error;
    char *response;
    DirConfig *dir = get_dir_config(r);

    if (!dir || (dir->report_enabled <= 0)) {
        return DECLINED;
    }
    if (r->method_number != M_GET) {
        return HTTP_METHOD_NOT_ALLOWED;
    }

    /* get the tracking id if any */
    const char *id = get_progress_id(r, &param_error);

    if (id == NULL) {
        if (param_error < 0) {
            ap_log_error(APLOG_MARK, APLOG_INFO, 0, server,
                         "Upload Progress: Report requested with invalid id. uri=%s", r->uri);
            return HTTP_BAD_REQUEST;
        } else {
            ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, server,
                         "Upload Progress: Report requested without id. uri=%s", r->uri);
            return HTTP_NOT_FOUND;
        }
    }

    ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, server,
                 "Upload Progress: Report requested with id='%s'. uri=%s", id, r->uri);

    ServerConfig *config = get_server_config(server);

    CACHE_LOCK();
    found = find_node(server, id);
    if (found) {
        up_log(APLOG_MARK, APLOG_DEBUG, 0, server,
                     "Node with id=%s found for report", id);
        memcpy(&upload, found, sizeof(upload));
    } else {
        up_log(APLOG_MARK, APLOG_DEBUG, 0, server,
                     "Node with id=%s not found for report", id);
    }
    CACHE_UNLOCK();

    ap_set_content_type(r, "application/json");

    apr_table_set(r->headers_out, "Expires", "Mon, 28 Sep 1970 06:00:00 GMT");
    apr_table_set(r->headers_out, "Cache-Control", "no-cache");

    /* There are 4 possibilities
     * request not yet started: found = false
     * request in error:        err_status >= NGX_HTTP_SPECIAL_RESPONSE
     * request finished:        done = true
     * request not yet started but registered:        length==0 && rest ==0
     * request in progress:     rest > 0
     */

    if (!found) {
        response = apr_psprintf(r->pool, "{ \"state\" : \"starting\", \"uuid\" : \"%s\" }", id);
    } else if (upload.err_status >= HTTP_BAD_REQUEST  ) {
        response = apr_psprintf(r->pool, "{ "
            "\"state\": \"error\", "
            "\"status\": %d, "
            "\"uuid\": \"%s\" "
            "}", upload.err_status, id);
    } else if (upload.done) {
        response = apr_psprintf(r->pool, "{ "
            "\"state\": \"done\", "
            "\"size\": %" APR_OFF_T_FMT ", "
            "\"speed\": %" APR_OFF_T_FMT ", "
            "\"started_at\": %li, "
            "\"completed_at\": %li, "
            "\"uuid\": \"%s\" "
            "}", upload.length, upload.speed, upload.started_at, upload.updated_at, id);
    } else if (upload.received == 0) {
        response = apr_psprintf(r->pool, "{ \"state\" : \"starting\", \"uuid\" : \"%s\" }", id);
    } else {
        time_t eta = 0, t = time(NULL);
        if (upload.speed > 0) eta = upload.started_at + upload.length / upload.speed;
        if (eta <= t) eta = t + 1;
        response = apr_psprintf(r->pool, "{ "
            "\"state\": \"uploading\", "
            "\"received\": %" APR_OFF_T_FMT ", "
            "\"size\": %" APR_OFF_T_FMT ", "
            "\"speed\": %" APR_OFF_T_FMT ", "
            "\"started_at\": %li, "
            "\"eta\": %li, "
            "\"uuid\": \"%s\" "
            "}", upload.received, upload.length, upload.speed, upload.started_at, eta, id);
    }

    char *completed_response;

    /* get the jsonp callback if any */
    const char *jsonp = get_json_callback_param(r, &param_error);

    if (param_error < 0) {
        ap_log_error(APLOG_MARK, APLOG_INFO, 0, server,
                     "Upload Progress: Report requested with invalid JSON-P callback. uri=%s", r->uri);
        return HTTP_BAD_REQUEST;
    }

    up_log(APLOG_MARK, APLOG_DEBUG, 0, server,
                       "Upload Progress: JSON-P callback: %s.", jsonp);

    // fix up response for jsonp request, if needed
    if (jsonp) {
        completed_response = apr_psprintf(r->pool, "%s(%s);\r\n", jsonp, response);
    } else {
        completed_response = apr_psprintf(r->pool, "%s\r\n", response);
    }

    ap_rputs(completed_response, r);

    return OK;
}

static void upload_progress_child_init(apr_pool_t *p, server_rec *s)
{
/**/up_log(APLOG_MARK, APLOG_DEBUG, 0, s, "upload_progress_child_init()");

    apr_status_t rv;
    ServerConfig *config = get_server_config(s);

    if (!config->cache_lock) {
        ap_log_error(APLOG_MARK, APLOG_CRIT, 0, s, "Global mutex not set.");
        return;
    }

    rv = apr_global_mutex_child_init(&config->cache_lock, config->lock_file, p);
    if (rv != APR_SUCCESS) {
        ap_log_error(APLOG_MARK, APLOG_CRIT, rv, s,
                     "Failed to initialise global mutex %s in child process %"
                     APR_PID_T_FMT ".", config->lock_file, getpid());
    }

    if (!config->cache_shm) {
        rv = apr_shm_attach(&config->cache_shm, config->cache_file, p);
        if (rv != APR_SUCCESS) {
            ap_log_error(APLOG_MARK, APLOG_CRIT, rv, s, "Failed to attach to "
                         "shared memory file '%s'", config->cache_file);
            return;
        }
    }

    config->cache = (upload_progress_cache_t *)apr_shm_baseaddr_get(config->cache_shm);
    config->list = (int *)(config->cache + 1);
    config->nodes = (upload_progress_node_t *)(config->list + config->cache->count);
}

static const command_rec upload_progress_cmds[] =
{
    AP_INIT_FLAG("TrackUploads", track_upload_progress_cmd, NULL, OR_AUTHCFG,
                 "Track upload progress in this location"),
    AP_INIT_FLAG("ReportUploads", report_upload_progress_cmd, NULL, OR_AUTHCFG,
                 "Report upload progress in this location"),
    AP_INIT_TAKE1("UploadProgressSharedMemorySize", upload_progress_shared_memory_size_cmd, NULL, RSRC_CONF,
                 "Size of shared memory used to keep uploads data, default 100KB"),
    { NULL }
};

static void upload_progress_register_hooks (apr_pool_t *p)
{
/**/up_log(APLOG_MARK, APLOG_DEBUG, 0, global_server, "upload_progress_register_hooks()");

    ap_hook_fixups(upload_progress_handle_request, NULL, NULL, APR_HOOK_FIRST);
    ap_hook_handler(reportuploads_handler, NULL, NULL, APR_HOOK_FIRST);
    ap_hook_post_config(upload_progress_init, NULL, NULL, APR_HOOK_MIDDLE);
    ap_hook_child_init(upload_progress_child_init, NULL, NULL, APR_HOOK_MIDDLE);
    ap_register_input_filter("UPLOAD_PROGRESS", track_upload_progress, NULL, AP_FTYPE_RESOURCE);
}

module AP_MODULE_DECLARE_DATA upload_progress_module =
{
    STANDARD20_MODULE_STUFF,
    upload_progress_create_dir_config,
    upload_progress_merge_dir_config,
    upload_progress_create_server_config,
    upload_progress_merge_server_config,
    upload_progress_cmds,
    upload_progress_register_hooks,      /* callback for registering hooks */
};