sandbox/mod_arm4/mod_arm4.c

/* Copyright 2000-2004 The Apache Software Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/* INSTRUMENT_HANDLER_HACK
 * Use arm_fixups and arm_logger as a poor man's way to call 
 * arm_block_transaction/arm_unblock_transaction across a call to a handler. 
 * The correct way to instrument block/unblock transactions is to modify 
 * each handler that sends requests outside the httpd process to call the
 * optional hooks, arm_ap_block_transaction() and arm_ap_unblock_transaction().
 * We can selectively turn on the request for block/unblock instrumentation by
 * setting the ArmInstrumentHandler directive inside  <Directory> or <Location> containers.
 */

#include "httpd.h"
#include "http_config.h"
#include "http_core.h"
#include "http_log.h"
#include "http_main.h"
#include "http_protocol.h"
#include "util_script.h"
#include "apr.h"
#include "apr_strings.h"
#include "apr_base64.h"
#include "http_request.h"
#include "mod_arm4.h"
#include <stdio.h>

#ifdef WIN32
#define DEFAULT_ARM4_LIBRARY_NAME "libarm4.dll"
#elif defined(_AIX)
#ifdef __64BIT__
#define DEFAULT_ARM4_LIBRARY_NAME "libarm4.a(shr_64.o)"
#else
#define DEFAULT_ARM4_LIBRARY_NAME "libarm4.a(shr.o)"
#endif
/* End AIX */
#else
#define DEFAULT_ARM4_LIBRARY_NAME "libarm4.so"
#endif

#include "arm4.h"

#if !defined(APR_UINT64_T_HEX_FMT)
#if defined(LINUX)
#define APR_UINT64_T_HEX_FMT "llx"
#elif defined(WIN32)
#define APR_UINT64_T_HEX_FMT "I64x"
#endif
#endif

/*
 * Define the dynamically loadable API to the ARM client library 
 */
APR_DECLARE_OPTIONAL_FN(void, arm_ap_block_transaction, (const void *));
APR_DECLARE_OPTIONAL_FN(void, arm_ap_unblock_transaction, (const void *));

arm_register_application_t  ap_arm_register_application;
arm_register_transaction_t  ap_arm_register_transaction;
arm_register_metric_t       ap_arm_register_metric;
arm_start_application_t     ap_arm_start_application;
arm_stop_application_t      ap_arm_stop_application;
arm_destroy_application_t   ap_arm_destroy_application;
arm_start_transaction_t     ap_arm_start_transaction;
arm_stop_transaction_t      ap_arm_stop_transaction;
arm_update_transaction_t    ap_arm_update_transaction;
arm_discard_transaction_t   ap_arm_discard_transaction;
arm_block_transaction_t     ap_arm_block_transaction;
arm_unblock_transaction_t   ap_arm_unblock_transaction;
arm_report_transaction_t    ap_arm_report_transaction;
arm_bind_thread_t           ap_arm_bind_thread;
arm_unbind_thread_t         ap_arm_unbind_thread;
arm_generate_correlator_t   ap_arm_generate_correlator;
arm_get_correlator_length_t ap_arm_get_correlator_length;
arm_get_correlator_flags_t  ap_arm_get_correlator_flags;
arm_get_arrival_time_t      ap_arm_get_arrival_time;
arm_get_error_message_t     ap_arm_get_error_message;
arm_is_charset_supported_t  ap_arm_is_charset_supported;

/* Module declaration */
#define ARM_MODULE arm4_module
module AP_MODULE_DECLARE_DATA ARM_MODULE;

/* Per server config */
#define DEFAULT_TRAN_NAME "HTTP Request"
#define DEFAULT_APP_NAME  "Apache HTTP Server"
#define DEFAULT_PLUGINTYPE  "Apache"
typedef struct server_config {
    arm_id_t app_id;
    arm_id_t tran_id;
    arm_app_start_handle_t app_handle;
    const char* libname;

    char *app_name;
    char *tran_name;
} server_config_t;

/* Per dir config */
typedef struct dir_config {
    int instrument_handler;
} dir_config_t;

/* Per request config */
typedef struct request_config {
    arm_tran_start_handle_t   tran_handle;
    arm_tran_block_handle_t   block_handle;
    arm_subbuffer_arrival_time_t sb_arrival_time;
} request_config_t;

static int module_is_disabled = 0;

/* 
 * Convert binary data into a hex string.
 * in  - Input data in binary format.  It's length must be len+1.
 * out - Output data in Hex String.  It must be pre-allocated.
 *       It's length must be at least len*2+1.
 * len - The amount of Byte that are going to be converted.
 */
static void stringify(unsigned char *in, unsigned char *out, int len)
{
    int i;
    char to_hex[] = { '0', '1', '2', '3', '4', '5', '6', '7',
                      '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', } ;

    for(i=0; i<len;i++) {
        out[2*i] = to_hex[(in[i]>>4) & 0x0f];
        out[1+2*i] = to_hex[in[i] & 0x0f];
    }

    out[2*len] = '\0';
}

/*
 * Convert hex String into binary data.
 * in  - Input data in Hex String.  It's length must be len*2+1.
 * out - Output data in binary.  It must be pre-allocated.  It's length must be
 *       at least len+1.
 * len - len*2+1 will be the number of byte converted.
 */
static void destringify(const unsigned char *in, unsigned char *out, int orig_len)
{
    int len=0;
    int i;
    int maxlen = orig_len * 2 + 1;

    while((in[len] != '\0') && isxdigit(in[len]) && (len < maxlen)) {
        len++;
    }

    /*
     * if (in[len] != '\0') at this point we're ignoring trailing non xdigit chars
     * also, len should be even, but we're not checking ...
     */
    for(i=0;i<(len/2);i++) {
        if(isdigit(in[2*i])) {
            if(isdigit(in[1+2*i])) {
                out[i] = ((in[2*i]-'0')<<4)|(0x0f & (in[1+2*i]-'0'));
            }
            else  {
                out[i] = ((in[2*i]-'0')<<4)|(0x0f & (10+toupper(in[1+2*i])-'A'));
            }
        }
        else {
            if(isdigit(in[1+2*i])) {
                out[i] = ((10+toupper(in[2*i])-'A')<<4)|(0x0f & (in[1+2*i]-'0'));
            }
            else {
                out[i] = ((10+toupper(in[2*i])-'A')<<4) |
                  (0x0f & (10+toupper(in[1+2*i])-'A'));
            }
        }
    }
}

/*
 *   This is to change the correlator into a string so it can be passed
 *   in the request header to a downstream application.(Inefficient version)
 *
 *   Note: arm_correlator_get_length(corr_out) should be at least
 *         2*arm_correlator_get_length(corr_in)+1
 */
static void stringify_Correlator(arm_correlator_t* corr_in, unsigned char* corr_out)
{
    unsigned char *in;
    arm_correlator_length_t len = 0;
    ap_arm_get_correlator_length(corr_in, &len);
    in = (unsigned char *)corr_in;

    stringify(in, corr_out, len);
}

/*
 * pconf pool cleanup
 */
static apr_status_t mod_arm4_cleanup(void *dv)
{
    server_config_t *sconf;
    server_rec *s = dv;
    char *sname = s->server_hostname;
    arm_error_t arm_rc;

    sconf = ap_get_module_config(s->module_config, &arm4_module);
    /* End the Application for this process */
    arm_rc = ap_arm_stop_application(sconf->app_handle, 0, NULL);
    if (arm_rc < 0) {
        ap_log_error(APLOG_MARK, APLOG_WARNING, 0, s, 
                     "mod_arm: arm_stop_application failed with rc = %d", arm_rc);
    }
    /** app must be destroyed */
    arm_rc = ap_arm_destroy_application(&(sconf->app_id), 0, NULL);
    if (arm_rc < 0) {
        ap_log_error(APLOG_MARK, APLOG_WARNING, 0, s, 
                     "mod_arm: arm_destroy_application failed with rc = %d", arm_rc);
    }

    return APR_SUCCESS;
}

#define LOAD_SYMBOL(symbol) \
{ \
   rv = apr_dso_sym((void**)&ap_##symbol,libhandle,#symbol); \
   if (rv != APR_SUCCESS)  { \
      ap_log_error(APLOG_MARK, APLOG_ERR, rv, s, "Failed to load symbol %s in library %s", #symbol, libname);  \
      return rv; \
    } \
}
static apr_status_t load_library(apr_pool_t *p, server_rec *s, const char *libname)
{
    apr_status_t rv;
    apr_dso_handle_t *libhandle;

    rv = apr_dso_load(&libhandle, libname, p);
    if (rv != APR_SUCCESS) {
        ap_log_error(APLOG_MARK, APLOG_ERR, rv, s, "Failed to load library %s", libname);
        return rv;
    }

    LOAD_SYMBOL(arm_register_application);
    LOAD_SYMBOL(arm_register_transaction);
    LOAD_SYMBOL(arm_register_metric);

    LOAD_SYMBOL(arm_start_application);
    LOAD_SYMBOL(arm_stop_application);
    LOAD_SYMBOL(arm_destroy_application)

    LOAD_SYMBOL(arm_start_transaction);
    LOAD_SYMBOL(arm_stop_transaction);
    LOAD_SYMBOL(arm_update_transaction);
    LOAD_SYMBOL(arm_discard_transaction);
    LOAD_SYMBOL(arm_block_transaction);
    LOAD_SYMBOL(arm_unblock_transaction);
    LOAD_SYMBOL(arm_report_transaction);

    LOAD_SYMBOL(arm_bind_thread);
    LOAD_SYMBOL(arm_unbind_thread);

    LOAD_SYMBOL(arm_generate_correlator);
    LOAD_SYMBOL(arm_get_correlator_length);
    LOAD_SYMBOL(arm_get_correlator_flags);

    LOAD_SYMBOL(arm_get_arrival_time);
    LOAD_SYMBOL(arm_get_error_message);
    LOAD_SYMBOL(arm_is_charset_supported);

    /* Register a cleanup against the open handle */

    return APR_SUCCESS;
}

/*
 * Build the app_instance parameter passed on the arm_start_application()
 * call. app_instance should be of the form:
 * hostname/PID=pid
 */
static char* build_app_instance(apr_pool_t *p, server_rec *s, int max_len)
{
    char *app_instance;
    char *pid_str;
    pid_t pid = getpid();
    
    pid_str = apr_itoa(p, pid);
    app_instance = apr_pstrndup(p,
                                apr_pstrcat(p, s->server_hostname,"/PID=",pid_str,NULL),
                                max_len);
    ap_log_error(APLOG_MARK, APLOG_NOTICE, 0, s, 
                 "mod_arm: pid: %d app_instance: %s", pid, app_instance);
    return app_instance;
}

/* This function is called during server initialisation by each process
 * which can serve a request. 
 */
static int register_application(apr_pool_t *p, server_rec *s)
{
    apr_status_t                    rv;
    arm_error_t                     arm_rc;
    server_config_t                 *sconf;

    arm_buffer4_t                   api_buff4;    /*ARM buffer4*/
    arm_subbuffer_t                 *subbuf;
    arm_subbuffer_app_identity_t    *sb_appl_identity;
    arm_subbuffer_tran_identity_t   *sb_tran_identity;

    char *app_group;
    char *app_instance;
    
    arm_property_t appl_identity_properties[1];

    const arm_char_t *tran_context_names[] = {
        "ServerVersion",
        "HostInfo",
        "RemoteAddress",
        "RemoteUser",
        "Scheme",
        "Port",
        "QueryString",
        "Protocol",
        "ServerName"
    };

    /*
     * Set up the per process config record to hold the application and transaction
     * type handles.
     */
    sconf = ap_get_module_config(s->module_config, &arm4_module);

    /* Load the ARM4 client library */
    ap_log_error(APLOG_MARK, APLOG_INFO, 0, s, "mod_arm: Loading the ARM4 client library %s", sconf->libname);
    rv = load_library(p, s, sconf->libname);
    if (rv != APR_SUCCESS) {
        ap_log_error(APLOG_MARK, APLOG_ERR, 0, s, 
                     "mod_arm: Failed to load the ARM4 client library %s. mod_arm4_ap20 is disabled.", 
                     sconf->libname);
        module_is_disabled = 1;
        return OK;
    }

    ap_log_error(APLOG_MARK, APLOG_INFO, 0, s, "mod_arm: Initializing ARM client.");

    /* 
     * Register application class with arm agent 
     */
    appl_identity_properties[0].name = "PluginType";
    appl_identity_properties[0].value = DEFAULT_PLUGINTYPE;
    
    sb_appl_identity = apr_pcalloc(p, sizeof(*sb_appl_identity));
    
    sb_appl_identity->header.format = ARM_SUBBUFFER_APP_IDENTITY;
    sb_appl_identity->identity_property_count = 1;
    sb_appl_identity->identity_property_array = &appl_identity_properties[0];
    sb_appl_identity->context_name_count = 0;
    sb_appl_identity->context_name_array = NULL;

    subbuf = (arm_subbuffer_t *) sb_appl_identity;
    api_buff4.count = 1;
    api_buff4.subbuffer_array = &subbuf;
     
    arm_rc = ap_arm_register_application(sconf->app_name, ARM_ID_NONE, 
                                         ARM_FLAG_NONE, &api_buff4,
                                         &(sconf->app_id));
    if (arm_rc < 0) {
        ap_log_error(APLOG_MARK, APLOG_ERR, 0, s, 
                     "mod_arm: arm_register_application() failed with rc = %d. mod_arm4_ap20 is disabled.", 
                     arm_rc);
        module_is_disabled = 1;
        return OK;
    }

    /* Register the cleanup which calls arm_stop_application() when pconf 
     * is destroyed 
     */
    apr_pool_cleanup_register(p, s, mod_arm4_cleanup, apr_pool_cleanup_null);

    /* Register transaction class with arm agent. Begin by setting up the 
     * transaction type buffer
     */
    sb_tran_identity = apr_pcalloc(p, sizeof(*sb_tran_identity));

    sb_tran_identity->header.format = ARM_SUBBUFFER_TRAN_IDENTITY;
    sb_tran_identity->identity_property_count = 0;
    sb_tran_identity->identity_property_array = NULL;
    sb_tran_identity->context_name_count = 9;
    sb_tran_identity->context_name_array = &tran_context_names[0];
    sb_tran_identity->uri = NULL;

    subbuf = (arm_subbuffer_t *) sb_tran_identity;
    api_buff4.count = 1;
    api_buff4.subbuffer_array = &subbuf;

    arm_rc = ap_arm_register_transaction(&(sconf->app_id),
                                         sconf->tran_name,
                                         ARM_ID_NONE,
                                         ARM_FLAG_NONE, 
                                         &api_buff4,
                                         &(sconf->tran_id));
    if (arm_rc < 0) {
        ap_log_error(APLOG_MARK, APLOG_ERR, 0, s, 
                     "mod_arm: arm_register_transaction() failed with rc = %d. mod_arm4_ap20 is disabled", 
                     arm_rc);
        module_is_disabled = 1;
        return OK;
    }
 
    /* Start the application instance
     */
    app_group = apr_pstrndup(p,ap_get_server_version(),ARM_PROPERTY_VALUE_MAX_CHARS);
    app_instance = build_app_instance(p, s, ARM_PROPERTY_VALUE_MAX_CHARS);
    arm_rc = ap_arm_start_application(&(sconf->app_id),
                                      app_group,
                                      app_instance,
                                      ARM_FLAG_NONE, 
                                      ARM_BUF4_NONE,
                                      &(sconf->app_handle));
    if (arm_rc < 0) {
        ap_log_error(APLOG_MARK, APLOG_ERR, 0, s, 
                     "mod_arm: arm_start_application() failed with rc = %d. mod_arm4_ap20 is disabled", arm_rc);
        module_is_disabled = 1;
        return OK;
    }
 
    ap_log_error(APLOG_MARK, APLOG_INFO, 0, s, "mod_arm: ARM client initialized for server %s", 
                 s->server_hostname);

    return OK;
}
static void arm_child_init(apr_pool_t *p, server_rec *s)
{
    register_application(p, s);
}

/*
 * This function gets called to create a per-server configuration
 * record.  It will always be called for the "default" server.
 *
 * The return value is a pointer to the created module-specific
 * structure.
 */
static void *arm_create_server_config(apr_pool_t *p, server_rec *s)
{
    server_config_t *sconf;

    ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, s, 
                 "mod_arm: Entering arm_create_server_config()");

    sconf = (server_config_t *) apr_pcalloc(p, sizeof(*sconf));
    sconf->libname = DEFAULT_ARM4_LIBRARY_NAME;
    sconf->tran_name = DEFAULT_TRAN_NAME;
    sconf->app_name = DEFAULT_APP_NAME;
    return sconf;
}

/* Create the per-dir config
 */
static void *arm_create_dir_config(apr_pool_t *p, char *s)
{
    dir_config_t *dconf =  apr_pcalloc(p, sizeof (dir_config_t));
    dconf->instrument_handler = 0;
    return dconf;
}
static void *arm_merge_dir_config(apr_pool_t *p, void *basev, void *addv)
{
    dir_config_t *base = (dir_config_t*) basev;
    dir_config_t *add = (dir_config_t*) addv;
    dir_config_t *new = apr_pcalloc(p, sizeof(dir_config_t));

    new->instrument_handler = add->instrument_handler;
    return new;
}

/*
 * This function is a request pool cleanup to notify the ARM agent
 * the transaction has ended.
 */
static apr_status_t stop_transaction(void *arg)
{
    request_rec *r = (request_rec *) arg;
    arm_error_t arm_rc;
    arm_tran_status_t tran_status;
    request_config_t *rconf;

#if 0
    /* This check was needed when this code was called during the
     * logging phase. Leave in for documentation.
     */
    if (module_is_disabled) {
        return DECLINED;
    }
#endif

    rconf = (request_config_t *) ap_get_module_config(r->request_config, &arm4_module);

    if (r->status >= 500) {
        tran_status = ARM_STATUS_ABORTED;   /* Server errors */
    }
    else if (r->status >= 400) {
        tran_status = ARM_STATUS_FAILED;    /* Client Errors */
    }
    else {
        tran_status = ARM_STATUS_GOOD;      /* No Error */
    }

    arm_rc = ap_arm_stop_transaction(rconf->tran_handle,
                                     tran_status,
                                     0,
                                     NULL);

    if (arm_rc < 0) {
        ap_log_rerror(APLOG_MARK, APLOG_WARNING, 0, r, 
                      "mod_arm4: arm_stop_transaction() failed with rc: %x "
                      "Start handle: %"APR_UINT64_T_HEX_FMT"", arm_rc, rconf->tran_handle);
    }
    else {
        ap_log_rerror(APLOG_MARK, APLOG_DEBUG, 0, r, 
                      "mod_arm4: arm_stop_transaction() handle: %"APR_UINT64_T_HEX_FMT", rc: %x", 
                      rconf->tran_handle, arm_rc);
    }
    return APR_SUCCESS;
}

/* Record the HTTP request arrival time for use in the arm_start_transaction()
 * call made after all access/auth checks have been made
 */
static int arm_post_read_request(request_rec *r)
{
    request_config_t *rconf;

    if (module_is_disabled) {
        return DECLINED;
    }

    /* Set up the per-request config structure */
    rconf = apr_pcalloc(r->pool, sizeof(*rconf));
    rconf->sb_arrival_time.header.format = ARM_SUBBUFFER_ARRIVAL_TIME;
    ap_arm_get_arrival_time(&(rconf->sb_arrival_time.opaque_time));

    ap_set_module_config(r->request_config, &arm4_module, rconf); 

    return DECLINED;
}

/* ArmLoadLibrary <library name>
 */
static const char *arm_load_library(cmd_parms *parms, 
                                    void *dummy, 
                                    const char *arg)
{
    server_config_t *sconf;
    char *libname;
    const char *c;

    sconf = ap_get_module_config(parms->server->module_config, &arm4_module);
    if (!arg) {
        return "ArmLoadLibrary requires an ARM library name as an argument";
    }
    libname = apr_pstrdup(parms->pool, arg);

    c = strrchr(arg, '.');
#ifdef _AIX
    /* AIX presents it's shared objects in an archive file. Tweak the libname
     * argument appropriately 
     */
    if (c && !strcasecmp(c, ".a")) {
#ifdef __64BIT__
        libname = apr_pstrcat(parms->pool, arg, "(shr_64.o)", NULL);
#else
        libname = apr_pstrcat(parms->pool, arg, "(shr.o)", NULL);
#endif
    }
#endif

    sconf->libname = libname;
    return NULL;
}

/* ArmTransactionName <name>
 */
static const char *arm_set_transaction_name(cmd_parms *parms, void *d, const char *arg)
{
    server_config_t *sconf = ap_get_module_config(parms->server->module_config, &arm4_module);
    sconf->tran_name = apr_pstrdup(parms->pool, arg);
    return NULL;
}

/* ArmApplicationName <name>
 */
static const char *arm_set_application_name(cmd_parms *parms, void *d, const char *arg)
{
    server_config_t *sconf = ap_get_module_config(parms->server->module_config, &arm4_module);
    sconf->app_name = apr_pstrdup(parms->pool, arg);
    return NULL;
}

/* ArmInstrumentHandler on|off
 */
static const char *arm_instrument_handler(cmd_parms *parms, void *dconfv, const char *arg)
{
    dir_config_t *dconf = (dir_config_t *) dconfv;

    if (!strcasecmp(arg, "on")) {
        dconf->instrument_handler = 1;
    }
    else {
        dconf->instrument_handler = 0;
    }
    return NULL;
}

static const command_rec arm_commands[] = {
    AP_INIT_TAKE1("ArmLoadLibrary", arm_load_library, NULL, RSRC_CONF | EXEC_ON_READ,
      "the name of the ARM4 agent shared library."),
    AP_INIT_TAKE1("ArmTransactionName", arm_set_transaction_name, NULL, RSRC_CONF,
      "the transaction name registered with the ARM agent. Default: HTTP Request"),
    AP_INIT_TAKE1("ArmApplicationName", arm_set_application_name, NULL, RSRC_CONF,
      "the application name registered with the the ARM agent. Default: Apache HTTP Server"),
    AP_INIT_TAKE1("ArmInstrumentHandler", arm_instrument_handler, NULL, RSRC_CONF | ACCESS_CONF,
      "on|off. ArmInstrumentHandler on causes arm_block|unblock_transaction to be called across content handlers. Default: off"),
    { NULL }
};
void arm_ap_unblock_transaction(const void *vr)
{
    arm_error_t arm_rc;
    request_config_t *rconf;
    request_rec *r = (request_rec *) vr;

    if (module_is_disabled) {
        return;
    }

    rconf = (request_config_t *) ap_get_module_config(r->request_config, &arm4_module);    
    if (!rconf) {
        /* We can hit this case while processing a subrequest. Checking for rconf
         * NULL is faster check than checking for subrequest
         */
        return;
    }
    arm_rc = ap_arm_unblock_transaction(rconf->tran_handle, rconf->block_handle, 0, NULL);

    ap_log_rerror(APLOG_MARK, APLOG_DEBUG, 0, r,
                  "mod_arm4: arm_unblocked_transaction() handle:  %"APR_UINT64_T_HEX_FMT", "     
                  "block_handle: %"APR_UINT64_T_HEX_FMT", rc: %x",     
                  rconf->tran_handle, rconf->block_handle, arm_rc);

    return;
}

/*
 * Begin definition of optional functions. These functions are used to enable a module to
 * interface to the ARM client w/o needing to be responsible for making sure the ARM client
 * library is loaded, initialized, etc.
 */
void arm_ap_block_transaction(const void *vr)
{
    arm_error_t arm_rc;
    request_rec *r = (request_rec*) vr;
    request_config_t *rconf;
    /*    arm_tran_block_handle_t *block_handle = apr_pcalloc(r->pool, sizeof(arm_tran_block_handle_t)); */

    if (module_is_disabled) {
        return;
    }
    rconf = (request_config_t *) ap_get_module_config(r->request_config, &arm4_module);
    if (!rconf) {
        /* We can hit this case while processing a subrequest. Checking for rconf
         * NULL is faster check than checking for subrequest
         */
        return;
    }

    arm_rc = ap_arm_block_transaction(rconf->tran_handle, 0, NULL, &rconf->block_handle);
    ap_log_rerror(APLOG_MARK, APLOG_DEBUG, 0, r,
                  "mod_arm4: arm_block_transaction() handle:  %"APR_UINT64_T_HEX_FMT", "     
                  "block_handle: %"APR_UINT64_T_HEX_FMT", rc: %x",     
                  rconf->tran_handle, rconf->block_handle, arm_rc);
    return;
}

#ifdef USE_CAP_ARM_APPLICATION
/*
 * Some ARM agents (on AIX) authorize users to ARM 4 interfaces thru 
 * Posix capabilities. For those systems, identify this application as
 * an ARM Application and propagate the capabilities to the child 
 * processes.
 */
static void set_process_capability(server_rec *s)
{
    cap_t mycap;
    cap_flag_value_t capflag;
    int cap_array[2];

    /*
     * Test if the CAP_ARM_APPLICATION can be set on this version
     * of the operating system.  First, get the process' current
     * capabilities.
     */
    mycap = (cap_t) cap_get_proc();
    if (!mycap) {
        ap_log_error(APLOG_MARK, APLOG_ERR, errno, s, 
                     "mod_arm: cap_get_proc failed.");
        return;
    }

    if (cap_get_flag(mycap, CAP_ARM_APPLICATION, CAP_EFFECTIVE, &capflag)) {
        ap_log_error(APLOG_MARK, APLOG_ERR, errno, s, 
                     "mod_arm: cap_get_flag failed. This OS does not support "
                     "CAP_ARM_APPLICATION.");
        goto exit;
    }

    /*
     * Add CAP_ARM_APPLICATION capability to current process.
     * Always set CAP_PROPAGATE capability. Don't let errors
     * prevent the server from starting.
     */
    cap_array[0] = CAP_PROPAGATE;
    cap_array[1] = CAP_ARM_APPLICATION;

    if (cap_set_flag(mycap, CAP_EFFECTIVE, 2, cap_array, CAP_SET)) {
        ap_log_error(APLOG_MARK, APLOG_ERR, errno, s, 
                     "mod_arm: CAP_EFFECTIVE failed.");
    }

    if (cap_set_flag(mycap, CAP_INHERITABLE, 2, cap_array, CAP_SET)) {
        ap_log_error(APLOG_MARK, APLOG_ERR, errno, s, 
                     "mod_arm: CAP_INHERITABLE failed.");
    }

    if (cap_set_flag(mycap, CAP_PERMITTED, 2, cap_array, CAP_SET)) {
        ap_log_error(APLOG_MARK, APLOG_ERR, errno, s, 
                     "mod_arm: CAP_PERMITTED failed.");
    }   

    /* Set the process's capabilities, you must be root to do this */
    if (cap_set_proc(mycap)) {
        ap_log_error(APLOG_MARK, APLOG_ERR, errno, s, 
                     "mod_arm: cap_set_proc() call failed.");
    }
    
exit:
    /* Free the capability allocated by cap_get_proc() */
    cap_free(mycap);
    
    return;
}
#endif

static int arm_post_config(apr_pool_t *p,
                           apr_pool_t *plog,
                           apr_pool_t *ptemp,
                           server_rec *s)
{
#ifdef USE_CAP_ARM_APPLICATION
    set_process_capability(s);
#endif
    return OK;
}

/* arm_fixups:
 * Call arm_start_transaction() in this hook rather than in post_read_request
 * because RemoteUser is not known until after access/auth checks have been 
 * run.
 */
static int arm_fixups(request_rec *r)
{
    dir_config_t     *dconf;
    server_config_t  *sconf;
    request_config_t *rconf;
    arm_error_t arm_rc;
    apr_uri_t uri_parts;

    unsigned char *stringified_correlator;
    const char *stringified_parent_correlator;
    arm_correlator_t *correlator;
    arm_correlator_t *parent_correlator;

    const arm_char_t *attribvalues[9];
    arm_buffer4_t cvbuf;  
    arm_subbuffer_t *subbuf[2];
    arm_subbuffer_tran_context_t *sb_tran_values;

    if (module_is_disabled) {
        return DECLINED;
    }

    /* Start the request only the first time we see it. If we see it again
     * after alias or redirect we don't want to start another one. If you'd
     * rather do classification on the aliased or redirected URL you'll have
     * to change this.
     */
    if (!ap_is_initial_req(r)) {
        return DECLINED;
    }
    sconf = ap_get_module_config(r->server->module_config, &arm4_module);

    rconf = (request_config_t *) ap_get_module_config(r->request_config, &arm4_module);    
    if (!rconf) {
        /* We can hit this case while processing a subrequest. Checking for rconf
         * NULL is faster check than checking for subrequest
         */
        return DECLINED;
    }

    /* Initialize the arm_subbuffer_tran_context_t
     */
    apr_uri_parse(r->pool, ap_construct_url(r->pool,r->uri,r), &uri_parts);
    attribvalues[0] = apr_pstrdup(r->pool, ap_get_server_version());
    attribvalues[1] = uri_parts.hostinfo;
    attribvalues[2] = r->connection->remote_ip;
    attribvalues[3] = r->user;
    attribvalues[4] = uri_parts.scheme;
    attribvalues[5] = apr_psprintf(r->pool, "%u", ap_get_server_port(r));
    attribvalues[6] = apr_pstrdup(r->pool, r->args); /* Query string */
    attribvalues[7] = "HTTP 1.1"; /* Protocol */
    attribvalues[8] = ap_get_server_name(r);

    sb_tran_values = apr_pcalloc(r->pool, sizeof(*sb_tran_values));
    sb_tran_values->header.format = ARM_SUBBUFFER_TRAN_CONTEXT;
    sb_tran_values->context_value_count = 9;
    sb_tran_values->context_value_array = &attribvalues[0];
    sb_tran_values->uri = r->uri;
    subbuf[0] = (arm_subbuffer_t *) sb_tran_values;

    /* arm_subbuffer_arrival_time_t was initialized in the post_read_request hook
     */
    subbuf[1] = (arm_subbuffer_t *) &rconf->sb_arrival_time;

    cvbuf.count = 2;
    cvbuf.subbuffer_array = &subbuf[0];

    correlator = (arm_correlator_t *) apr_pcalloc(r->pool, ARM_CORR_MAX_LENGTH);

    /* Check for an ARM_CORRELATOR header field on the inbound request, set the
     * parent_correlator.
     */
    parent_correlator = NULL;
    stringified_parent_correlator = apr_table_get(r->headers_in, "ARM_CORRELATOR");
    if (stringified_parent_correlator) {
        int len;

        /* Do some simple validity checks on the correlator string. Ignore invalid
         * correlators.
         */
        len = strlen(stringified_parent_correlator);
        if (len > 2*ARM_CORR_MAX_LENGTH) {
            /* Length error: exceeded max len */
            ap_log_rerror(APLOG_MARK, APLOG_WARNING, 0, r,
                          "mod_arm: Inbound ARM_CORRELATOR failed length check. Length is %d. Correlator: %s ...",
                          len, apr_pstrndup(r->pool, stringified_parent_correlator, 20));
        }
        else if (len % 2) {
            /* Length error: odd length */
            ap_log_rerror(APLOG_MARK, APLOG_WARNING, 0, r,
                          "mod_arm: Inbound ARM_CORRELATOR failed length check. Correlator contains odd number of characters. Correlator: %s ...",
                          apr_pstrndup(r->pool, stringified_parent_correlator, 20));
        }
        else {
            len = (len/2);
            parent_correlator = (arm_correlator_t *) apr_pcalloc(r->pool, ARM_CORR_MAX_LENGTH);
            destringify((const unsigned char*)stringified_parent_correlator, (unsigned char*) parent_correlator, len);
            ap_log_rerror(APLOG_MARK, APLOG_DEBUG, 0, r,
                          "mod_arm: Received ARM_CORRELATOR header field. Correlator: %s ...",
                          apr_pstrndup(r->pool, stringified_parent_correlator, 20));
        }
    }

    /* ARM_FLAG_BIND_THREAD is only valid if the same thread calls 
     * arm_start_transaction() and arm_stop_transaction(). This assumption
     * breaks when httpd supports non-blocking event driven or async 
     * i/o.
     */
    arm_rc = ap_arm_start_transaction(sconf->app_handle,
                                      &(sconf->tran_id),
                                      parent_correlator,
                                      ARM_FLAG_BIND_THREAD,
                                      &cvbuf,
                                      &rconf->tran_handle,
                                      correlator);
    if (arm_rc < 0) {
        ap_log_rerror(APLOG_MARK, APLOG_WARNING, 0, r, 
                      "mod_arm: arm_start_transaction() failed with rc = %x", arm_rc);
    }
    else {
        /* Register the stop_transaction only if the call to 
         * start_transaction is successful.
         */
        apr_pool_cleanup_register(r->pool, r, stop_transaction, 
                                  apr_pool_cleanup_null);
        stringified_correlator = (unsigned char *) apr_pcalloc(r->pool, (2*ARM_CORR_MAX_LENGTH+1));
        stringify_Correlator(correlator, stringified_correlator);
    }

    ap_log_rerror(APLOG_MARK, APLOG_DEBUG, 0, r,
                  "mod_arm4: arm_start_transaction() handle: %"APR_UINT64_T_HEX_FMT", rc: %x\n"
                  "\tcorrelator: %s\n"
                  "\tconstructed url: %s\n"
                  "\tattr::ServerVersion: %s\n"
                  "\tattr::Hostinfo: %s\n"
                  "\tattr::RemoteAddress: %s\n"
                  "\tattr::RemoteUser: %s\n"
                  "\tattr::Scheme: %s\n"
                  "\tattr::Port: %s\n"
                  "\tattr::QueryString: %s\n"
                  "\tattr::Protocol: %s\n"
                  "\tattr::ServerName: %s\n",
                  rconf->tran_handle, arm_rc, 
                  stringified_correlator, 
                  ap_construct_url(r->pool, r->uri, r),
                  attribvalues[0], 
                  attribvalues[1], 
                  attribvalues[2], 
                  attribvalues[3], 
                  attribvalues[4],
                  attribvalues[5],
                  attribvalues[6],
                  attribvalues[7],
                  attribvalues[8]);

    /* TODO: Develop config driven or huristic for when to add the ARM_CORRELATOR.
     * For now, always add the correlator.
     */
    apr_table_set(r->headers_in, "ARM_CORRELATOR", (char*) stringified_correlator);
    apr_table_set(r->err_headers_out, "ARM_CORRELATOR", (char*) stringified_correlator); /* Is this necessary? */

    /* Poor man's way to bracket the call to the handler with
     * arm_block_transaction()/arm_unblock_transaction() calls. The 
     * arm_unblock_transaction() is called in the logging phase.  If you
     * can live with the potential inacuracies with this method, you can
     * eliminate the need to instrument each and every handler with block/unblock
     * calls.
     */
    dconf = (dir_config_t *) ap_get_module_config(r->per_dir_config, &arm4_module);
    if (dconf->instrument_handler) {
        arm_ap_block_transaction(r);
    }
    return DECLINED;
}

/* arm_logger(): poor man's arm_unblock_tranaction()
 * TODO: Consider implementing this call in a simple output filter that
 *       sets high in the stack.
 */
static int arm_logger(request_rec *r)
{
    dir_config_t *dconf;

    if (module_is_disabled) {
        return DECLINED;
    }
    dconf = (dir_config_t *) ap_get_module_config(r->per_dir_config, &arm4_module);
    if (dconf->instrument_handler) {
        arm_ap_unblock_transaction(r);
    }
    return DECLINED;
}


static void arm_register_hooks(apr_pool_t *p)
{
    ap_hook_post_config(arm_post_config, NULL, NULL, APR_HOOK_MIDDLE);
    ap_hook_fixups(arm_fixups, NULL, NULL, APR_HOOK_REALLY_FIRST);
    ap_hook_log_transaction(arm_logger, NULL, NULL, APR_HOOK_LAST);
    ap_hook_post_read_request(arm_post_read_request, NULL, NULL, APR_HOOK_MIDDLE);
    ap_hook_child_init(arm_child_init, NULL, NULL, APR_HOOK_MIDDLE);
    APR_REGISTER_OPTIONAL_FN(arm_ap_block_transaction);
    APR_REGISTER_OPTIONAL_FN(arm_ap_unblock_transaction);
}

module AP_MODULE_DECLARE_DATA ARM_MODULE =
{
    STANDARD20_MODULE_STUFF,
    arm_create_dir_config,      /* per-directory config creator */
    arm_merge_dir_config,       /* dir config merger */
    arm_create_server_config,   /* server config creator */
    NULL,                       /* server config merger */
    arm_commands,               /* command table */
    arm_register_hooks,         /* register hooks*/
};
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