Hi Tobias,

Am 08.08.2009 11:49, schrieb Tobias Oetiker:
> Hi Benny,
>
> the patch seems sane to me from looking at your code ... I will be
> glad to include it if you can provide a version that applies to
>
>   svn://svn.oetiker.ch/rrdtool/trunk/program
>   
As the version available in the public download directory and the SVN
differ quite a bit, I had some work on merging in my changes, thus you
might notice some differences between the old and the new API extension
patch. In particular I chose to rename the API function from
rrd_dump_opt_cb_r to rrd_dump_cb_r. I furthermore hope I didn't miss any
changes made in the SVN when I merged the files.
> also you should add a section to doc/librrd.pod explaining this new
> access method ...
>   
The API documentation explains the usage of this interface using the
internally used rrd_dump_opt_cb_fileout callback which should, because
of its simplicity, be a well-enough example.
> cheers
> tobi
>   
IDK if the rrd_dump_opt_r function should be exported too (and not only
used internally wrapped by rrd_dump and rrd_dump_r).?

Anyway: The working patch, based on revision 1886 is attached. If there
are any questions left, feel free to contact me.

Regards,
BenBE.
Index: CONTRIBUTORS
===================================================================
--- CONTRIBUTORS	(Revision 1886)
+++ CONTRIBUTORS	(Arbeitskopie)
@@ -9,6 +9,7 @@
 Amos Shapira <amos with gezernet.co.il>
 Andreas Kroomaa <andre with ml.ee>
 Andrew Turner <turner with mint.net> (LAST consolidator)
+Benny Baumann <benbe with geshi.org) rrd_dump with callback support
 Bernard Fischer <bfischer with syslog.ch> 64bit stuff, --alt-autoscale-max
 Bernhard Fischer <rep dot dot dot nop with gmail.com> MMAP rewrite
 Bill Fenner <fenner with research.att.com>
Index: doc/librrd.pod
===================================================================
--- doc/librrd.pod	(Revision 1886)
+++ doc/librrd.pod	(Arbeitskopie)
@@ -58,4 +58,41 @@
     rrd_free_ptrs(&arr, &arr_size);
     /* here, arr == NULL && arr_size == 0 */
 
+=item B<rrd_dump_cr_r(char *filename, int opt_header, rrd_output_callback_t cb, void *user)>
+
+In some situations it is necessary to get the output of C<rrd_dump> without
+writing it to a file or the standard output. In such cases an application
+can ask B<rrd_dump_cb_r> to call an user-defined function each time there
+is output to be stored somewhere. This can be used, to e.g. directly feed
+an XML parser with the dumped output or transfer the resulting string
+in memory.
+
+The arguments for B<rrd_dump_cb_r> are the same as for B<rrd_dump_opt_r>
+except that the output filename parameter is replaced by the user-defined
+callback function and an additional parameter for the callback function
+that is passed untouched, i.e. to store information about the callback state
+needed for the user-defined callback to function properly.
+
+Recent versions of B<rrd_dump_opt_r> internally use this callback mechanism
+to write their output to the file provided by the user.
+
+    size_t rrd_dump_opt_cb_fileout(
+        const void *data,
+        size_t len,
+        void *user)
+    {
+        return fwrite(data, 1, len, (FILE *)user);
+    }
+
+The associated call for B<rrd_dump_cb_r> looks like
+
+    res = rrd_dump_cb_r(filename, opt_header,
+        rrd_dump_opt_cb_fileout, (void *)out_file);
+
+where the last parameter specifies the file handle B<rrd_dump_opt_cb_fileout>
+should write to. There's no specific condition for the callback to detect
+when it is called for the first time, nor for the last time. If you require
+this for initialization and cleanup you should do those tasks before and
+after calling B<rrd_dump_cr_r> respectively.
+
 =back
Index: src/rrd.h
===================================================================
--- src/rrd.h	(Revision 1886)
+++ src/rrd.h	(Arbeitskopie)
@@ -130,6 +130,10 @@
         struct rrd_info_t *next;
     } rrd_info_t;
 
+    typedef size_t (* rrd_output_callback_t)(
+    const void *,
+    size_t,
+    void *);
 
 /* main function blocks */
     int       rrd_create(
@@ -252,6 +256,12 @@
     const char *filename,
     int rraindex);
 
+    int rrd_dump_cb_r(
+    const char *filename,
+    int opt_header,
+    rrd_output_callback_t cb,
+    void *user);
+
 /* Transplanted from rrd_parsetime.h */
     typedef enum {
         ABSOLUTE_TIME,
Index: src/rrd_dump.c
===================================================================
--- src/rrd_dump.c	(Revision 1886)
+++ src/rrd_dump.c	(Arbeitskopie)
@@ -49,123 +49,172 @@
 #include <locale.h>
 #endif
 
-
 #if !(defined(NETWARE) || defined(WIN32))
 extern char *tzname[2];
 #endif
 
-static int rrd_dump_opt_r(
+//Local prototypes
+size_t rrd_dump_opt_cb_fileout(
+    const void *data,
+    size_t len,
+    void *user);
+
+
+int rrd_dump_cb_r(
     const char *filename,
-    char *outname,
-    int opt_header)
+    int opt_header,
+    rrd_output_callback_t cb,
+    void *user)
 {
     unsigned int i, ii, ix, iii = 0;
     time_t    now;
     char      somestring[255];
+    char      somestring_buf[255];
     rrd_value_t my_cdp;
     off_t     rra_base, rra_start, rra_next;
     rrd_file_t *rrd_file;
-    FILE     *out_file;
     rrd_t     rrd;
     rrd_value_t value;
     struct tm tm;
     char *old_locale = "";
 
+    //Check if we got a (valid) callback method
+    if (!cb) {
+        return (-1);
+    }
+
     rrd_init(&rrd);
+
     rrd_file = rrd_open(filename, &rrd, RRD_READONLY | RRD_READAHEAD);
     if (rrd_file == NULL) {
         rrd_free(&rrd);
         return (-1);
     }
 
-    out_file = NULL;
-    if (outname) {
-        if (!(out_file = fopen(outname, "w"))) {
-            return (-1);
-        }
-    } else {
-        out_file = stdout;
-    }
 #ifdef HAVE_SETLOCALE
     old_locale = setlocale(LC_NUMERIC, "C");
 #endif
 
     if (opt_header == 1) {
-        fputs("<?xml version=\"1.0\" encoding=\"utf-8\"?>\n", out_file);
-        fputs
-            ("<!DOCTYPE rrd SYSTEM \"http://oss.oetiker.ch/rrdtool/rrdtool.dtd\";>\n",
-             out_file);
-	fputs("<!-- Round Robin Database Dump -->\n", out_file);
-	fputs("<rrd>\n", out_file);
+        cb("<?xml version=\"1.0\" encoding=\"utf-8\"?>\n", 
+            strlen("<?xml version=\"1.0\" encoding=\"utf-8\"?>\n"), user);
+        cb("<!DOCTYPE rrd SYSTEM \"http://oss.oetiker.ch/rrdtool/rrdtool.dtd\";>\n",
+            strlen("<!DOCTYPE rrd SYSTEM \"http://oss.oetiker.ch/rrdtool/rrdtool.dtd\";>\n"), user);
+        cb("<!-- Round Robin Database Dump -->\n", 
+            strlen("<!-- Round Robin Database Dump -->\n"), user);
+        cb("<rrd>\n", 
+            strlen("<rrd>\n"), user);
     } else if (opt_header == 2) {
-    	fputs("<?xml version=\"1.0\" encoding=\"utf-8\"?>\n", out_file);
-	fputs("<!-- Round Robin Database Dump -->\n", out_file);
-	fputs("<rrd xmlns=\"http://oss.oetiker.ch/rrdtool/rrdtool-dump.xml\"; xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\"\n";, out_file);
-	fputs("\txsi:schemaLocation=\"http://oss.oetiker.ch/rrdtool/rrdtool-dump.xml http://oss.oetiker.ch/rrdtool/rrdtool-dump.xsd\";>\n", out_file);
+        cb("<?xml version=\"1.0\" encoding=\"utf-8\"?>\n", 
+            strlen("<?xml version=\"1.0\" encoding=\"utf-8\"?>\n"), user);
+        cb("<!-- Round Robin Database Dump -->\n", 
+            strlen("<!-- Round Robin Database Dump -->\n"), user);
+        cb("<rrd xmlns=\"http://oss.oetiker.ch/rrdtool/rrdtool-dump.xml\"; xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\"\n";, 
+            strlen("<rrd xmlns=\"http://oss.oetiker.ch/rrdtool/rrdtool-dump.xml\"; xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\"\n";), user);
+        cb("\txsi:schemaLocation=\"http://oss.oetiker.ch/rrdtool/rrdtool-dump.xml http://oss.oetiker.ch/rrdtool/rrdtool-dump.xsd\";>\n", 
+            strlen("\txsi:schemaLocation=\"http://oss.oetiker.ch/rrdtool/rrdtool-dump.xml http://oss.oetiker.ch/rrdtool/rrdtool-dump.xsd\";>\n"), user);
     } else {
-    	fputs("<!-- Round Robin Database Dump -->\n", out_file);
-    	fputs("<rrd>\n", out_file);
+        cb("<!-- Round Robin Database Dump -->\n", 
+            strlen("<!-- Round Robin Database Dump -->\n"), user);
+        cb("<rrd>\n", 
+            strlen("<rrd>\n"), user);
     }
 
+    cb("<!-- Round Robin Database Dump -->", 
+        strlen("<!-- Round Robin Database Dump -->"), user);
+
+    cb("<rrd>", 
+        strlen("<rrd>"), user);
+
     if (atoi(rrd.stat_head->version) <= 3) {
-        fprintf(out_file, "\t<version>%s</version>\n", RRD_VERSION3);
+        snprintf(somestring, 255, "\t<version>%s</version>\n", RRD_VERSION3);
     } else {
-        fprintf(out_file, "\t<version>%s</version>\n", RRD_VERSION);
+        snprintf(somestring, 255, "\t<version>%s</version>\n", RRD_VERSION);
     }
-    fprintf(out_file, "\t<step>%lu</step> <!-- Seconds -->\n",
-            rrd.stat_head->pdp_step);
+    cb(somestring, strlen(somestring), user);
+    
+    snprintf(somestring, 255, "\t<step>%lu</step> <!-- Seconds -->\n",
+        rrd.stat_head->pdp_step);
+    cb(somestring, strlen(somestring), user);
+
 #ifdef HAVE_STRFTIME
     localtime_r(&rrd.live_head->last_up, &tm);
-    strftime(somestring, 200, "%Y-%m-%d %H:%M:%S %Z", &tm);
+    strftime(somestring, 255, "%Y-%m-%d %H:%M:%S %Z", &tm);
 #else
 # error "Need strftime"
 #endif
-    fprintf(out_file, "\t<lastupdate>%lld</lastupdate> <!-- %s -->\n\n",
-            (long long) rrd.live_head->last_up, somestring);
+    snprintf(somestring_buf, 255, "\t<lastupdate>%lld</lastupdate> <!-- %s -->\n\n",
+        (long long) rrd.live_head->last_up, somestring);
+    cb(somestring_buf, strlen(somestring_buf), user);
     for (i = 0; i < rrd.stat_head->ds_cnt; i++) {
-        fprintf(out_file, "\t<ds>\n");
-        fprintf(out_file, "\t\t<name>%s</name>\n", rrd.ds_def[i].ds_nam);
-        fprintf(out_file, "\t\t<type>%s</type>\n", rrd.ds_def[i].dst);
+        cb("\t<ds>\n", 
+            strlen("\t<ds>\n"), user);
+
+        snprintf(somestring_buf, 255, "\t\t<name> %s </name>\n", rrd.ds_def[i].ds_nam);
+        cb(somestring_buf, strlen(somestring_buf), user);
+
+        snprintf(somestring_buf, 255, "\t\t<type> %s </type>\n", rrd.ds_def[i].dst);
+        cb(somestring_buf, strlen(somestring_buf), user);
+
         if (dst_conv(rrd.ds_def[i].dst) != DST_CDEF) {
-            fprintf(out_file,
-                    "\t\t<minimal_heartbeat>%lu</minimal_heartbeat>\n",
+            snprintf(somestring_buf, 255, "\t\t<minimal_heartbeat>%lu</minimal_heartbeat>\n",
                     rrd.ds_def[i].par[DS_mrhb_cnt].u_cnt);
+            cb(somestring_buf, strlen(somestring_buf), user);
+
             if (isnan(rrd.ds_def[i].par[DS_min_val].u_val)) {
-                fprintf(out_file, "\t\t<min>NaN</min>\n");
+                snprintf(somestring_buf, 255, "\t\t<min>NaN</min>\n");
             } else {
-                fprintf(out_file, "\t\t<min>%0.10e</min>\n",
-                        rrd.ds_def[i].par[DS_min_val].u_val);
+                snprintf(somestring_buf, 255, "\t\t<min>%0.10e</min>\n",
+                    rrd.ds_def[i].par[DS_min_val].u_val);
             }
+            cb(somestring_buf, strlen(somestring_buf), user);
+            
             if (isnan(rrd.ds_def[i].par[DS_max_val].u_val)) {
-                fprintf(out_file, "\t\t<max>NaN</max>\n");
+                snprintf(somestring_buf, 255, "\t\t<max>NaN</max>\n");
             } else {
-                fprintf(out_file, "\t\t<max>%0.10e</max>\n",
-                        rrd.ds_def[i].par[DS_max_val].u_val);
+                snprintf(somestring_buf, 255, "\t\t<max>%0.10e</max>\n",
+                    rrd.ds_def[i].par[DS_max_val].u_val);
             }
+            cb(somestring_buf, strlen(somestring_buf), user);
         } else {        /* DST_CDEF */
             char     *str = NULL;
 
             rpn_compact2str((rpn_cdefds_t *) &(rrd.ds_def[i].par[DS_cdef]),
-                            rrd.ds_def, &str);
-            fprintf(out_file, "\t\t<cdef>%s</cdef>\n", str);
+                rrd.ds_def, &str);
+
+            //Splitting into 3 writes to avoid allocating memory
+            //This is better compared to snprintf as str may be of arbitrary size
+            cb("\t\t<cdef> ", strlen("\t\t<cdef>"), user);
+            cb(str, strlen(str), user);
+            cb(" </cdef>\n", strlen("</cdef>\n"), user);
+
             free(str);
         }
-        fprintf(out_file, "\n\t\t<!-- PDP Status -->\n");
-        fprintf(out_file, "\t\t<last_ds>%s</last_ds>\n",
-                rrd.pdp_prep[i].last_ds);
+
+        cb("\n\t\t<!-- PDP Status -->\n",
+            strlen("\n\t\t<!-- PDP Status -->\n"), user);
+        snprintf(somestring_buf, 255, "\t\t<last_ds>%s</last_ds>\n",
+            rrd.pdp_prep[i].last_ds);
+        cb(somestring_buf, strlen(somestring_buf), user);
+
         if (isnan(rrd.pdp_prep[i].scratch[PDP_val].u_val)) {
-            fprintf(out_file, "\t\t<value>NaN</value>\n");
+            snprintf(somestring_buf, 255, "\t\t<value>NaN</value>\n");
         } else {
-            fprintf(out_file, "\t\t<value>%0.10e</value>\n",
-                    rrd.pdp_prep[i].scratch[PDP_val].u_val);
+            snprintf(somestring_buf, 255, "\t\t<value>%0.10e</value>\n",
+                rrd.pdp_prep[i].scratch[PDP_val].u_val);
         }
-        fprintf(out_file, "\t\t<unknown_sec>%lu</unknown_sec>\n",
-                rrd.pdp_prep[i].scratch[PDP_unkn_sec_cnt].u_cnt);
+        cb(somestring_buf, strlen(somestring_buf), user);
 
-        fprintf(out_file, "\t</ds>\n\n");
+        snprintf(somestring_buf, 255, "\t\t<unknown_sec> %lu </unknown_sec>\n",
+            rrd.pdp_prep[i].scratch[PDP_unkn_sec_cnt].u_cnt);
+        cb(somestring_buf, strlen(somestring_buf), user);
+
+        cb("\t</ds>\n\n",
+            strlen("\t</ds>\n\n"), user);
     }
 
-    fputs("<!-- Round Robin Archives -->\n", out_file);
+    cb("<!-- Round Robin Archives -->\n", 
+        strlen("<!-- Round Robin Archives -->\n"), user);
 
     rra_base = rrd_file->header_len;
     rra_next = rra_base;
@@ -177,182 +226,224 @@
         rra_start = rra_next;
         rra_next += (rrd.stat_head->ds_cnt
                      * rrd.rra_def[i].row_cnt * sizeof(rrd_value_t));
-        fprintf(out_file, "\t<rra>\n");
-        fprintf(out_file, "\t\t<cf>%s</cf>\n", rrd.rra_def[i].cf_nam);
-        fprintf(out_file,
-                "\t\t<pdp_per_row>%lu</pdp_per_row> <!-- %lu seconds -->\n\n",
-                rrd.rra_def[i].pdp_cnt,
-                rrd.rra_def[i].pdp_cnt * rrd.stat_head->pdp_step);
+
+        cb("\t<rra>\n",
+            strlen("\t<rra>\n"), user);
+
+        snprintf(somestring_buf, 255, 
+            "\t\t<cf>%s</cf>\n", rrd.rra_def[i].cf_nam);
+        cb(somestring_buf, strlen(somestring_buf), user);
+
+        snprintf(somestring_buf, 255, 
+            "\t\t<pdp_per_row>%lu</pdp_per_row> <!-- %lu seconds -->\n\n",
+            rrd.rra_def[i].pdp_cnt, 
+            rrd.rra_def[i].pdp_cnt * rrd.stat_head->pdp_step);
+        cb(somestring_buf, strlen(somestring_buf), user);
+
         /* support for RRA parameters */
-        fprintf(out_file, "\t\t<params>\n");
+        cb("\t\t<params>\n", 
+            strlen("\t\t<params>\n"), user);
+
         switch (cf_conv(rrd.rra_def[i].cf_nam)) {
         case CF_HWPREDICT:
         case CF_MHWPREDICT:
-            fprintf(out_file, "\t\t<hw_alpha>%0.10e</hw_alpha>\n",
+            snprintf(somestring_buf, 255, "\t\t<hw_alpha>%0.10e</hw_alpha>\n",
                     rrd.rra_def[i].par[RRA_hw_alpha].u_val);
-            fprintf(out_file, "\t\t<hw_beta>%0.10e</hw_beta>\n",
+            cb(somestring_buf, strlen(somestring_buf), user);
+
+            snprintf(somestring_buf, 255, "\t\t<hw_beta>%0.10e</hw_beta>\n",
                     rrd.rra_def[i].par[RRA_hw_beta].u_val);
-            fprintf(out_file,
+            cb(somestring_buf, strlen(somestring_buf), user);
+
+            snprintf(somestring_buf, 255, 
                     "\t\t<dependent_rra_idx>%lu</dependent_rra_idx>\n",
                     rrd.rra_def[i].par[RRA_dependent_rra_idx].u_cnt);
+            cb(somestring_buf, strlen(somestring_buf), user);
             break;
         case CF_SEASONAL:
         case CF_DEVSEASONAL:
-            fprintf(out_file,
+            snprintf(somestring_buf, 255, 
                     "\t\t<seasonal_gamma>%0.10e</seasonal_gamma>\n",
                     rrd.rra_def[i].par[RRA_seasonal_gamma].u_val);
-            fprintf(out_file,
+            cb(somestring_buf, strlen(somestring_buf), user);
+
+            snprintf(somestring_buf, 255, 
                     "\t\t<seasonal_smooth_idx>%lu</seasonal_smooth_idx>\n",
                     rrd.rra_def[i].par[RRA_seasonal_smooth_idx].u_cnt);
+            cb(somestring_buf, strlen(somestring_buf), user);
+
             if (atoi(rrd.stat_head->version) >= 4) {
-                fprintf(out_file,
-                        "\t\t<smoothing_window>%0.10e</smoothing_window>\n",
-                        rrd.rra_def[i].par[RRA_seasonal_smoothing_window].
-                        u_val);
+                snprintf(somestring_buf, 255, 
+                    "\t\t<smoothing_window>%0.10e</smoothing_window>\n",
+                    rrd.rra_def[i].par[RRA_seasonal_smoothing_window].u_val);
+                cb(somestring_buf, strlen(somestring_buf), user);
             }
-            fprintf(out_file,
+            snprintf(somestring_buf, 255, 
                     "\t\t<dependent_rra_idx>%lu</dependent_rra_idx>\n",
                     rrd.rra_def[i].par[RRA_dependent_rra_idx].u_cnt);
+            cb(somestring_buf, strlen(somestring_buf), user);
             break;
         case CF_FAILURES:
-            fprintf(out_file, "\t\t<delta_pos>%0.10e</delta_pos>\n",
+            snprintf(somestring_buf, 255, "\t\t<delta_pos>%0.10e</delta_pos>\n",
                     rrd.rra_def[i].par[RRA_delta_pos].u_val);
-            fprintf(out_file, "\t\t<delta_neg>%0.10e</delta_neg>\n",
+            cb(somestring_buf, strlen(somestring_buf), user);
+
+            snprintf(somestring_buf, 255, "\t\t<delta_neg>%0.10e</delta_neg>\n",
                     rrd.rra_def[i].par[RRA_delta_neg].u_val);
-            fprintf(out_file, "\t\t<window_len>%lu</window_len>\n",
+            cb(somestring_buf, strlen(somestring_buf), user);
+
+            snprintf(somestring_buf, 255, "\t\t<window_len>%lu</window_len>\n",
                     rrd.rra_def[i].par[RRA_window_len].u_cnt);
-            fprintf(out_file,
+            cb(somestring_buf, strlen(somestring_buf), user);
+
+            snprintf(somestring_buf, 255, 
                     "\t\t<failure_threshold>%lu</failure_threshold>\n",
                     rrd.rra_def[i].par[RRA_failure_threshold].u_cnt);
+            cb(somestring_buf, strlen(somestring_buf), user);
+
             /* fall thru */
         case CF_DEVPREDICT:
-            fprintf(out_file,
+            snprintf(somestring_buf, 255, 
                     "\t\t<dependent_rra_idx>%lu</dependent_rra_idx>\n",
                     rrd.rra_def[i].par[RRA_dependent_rra_idx].u_cnt);
+            cb(somestring_buf, strlen(somestring_buf), user);
             break;
         case CF_AVERAGE:
         case CF_MAXIMUM:
         case CF_MINIMUM:
         case CF_LAST:
         default:
-            fprintf(out_file, "\t\t<xff>%0.10e</xff>\n",
+            snprintf(somestring_buf, 255, "\t\t<xff>%0.10e</xff>\n",
                     rrd.rra_def[i].par[RRA_cdp_xff_val].u_val);
+            cb(somestring_buf, strlen(somestring_buf), user);
             break;
         }
-        fprintf(out_file, "\t\t</params>\n");
-        fprintf(out_file, "\t\t<cdp_prep>\n");
+
+        cb("\t\t</params>\n",
+            strlen("\t\t</params>\n"), user);
+        cb("\t\t<cdp_prep>\n",
+            strlen("\t\t<cdp_prep>\n"), user);
+
         for (ii = 0; ii < rrd.stat_head->ds_cnt; ii++) {
             unsigned long ivalue;
 
-            fprintf(out_file, "\t\t\t<ds>\n");
+            cb("\t\t\t<ds>\n",
+                strlen("\t\t\t<ds>\n"), user);
             /* support for exporting all CDP parameters */
             /* parameters common to all CFs */
             /* primary_val and secondary_val do not need to be saved between updates
              * so strictly speaking they could be omitted.
              * However, they can be useful for diagnostic purposes, so are included here. */
-            value = rrd.cdp_prep[i * rrd.stat_head->ds_cnt
-                                 + ii].scratch[CDP_primary_val].u_val;
+            value = rrd.cdp_prep[i * rrd.stat_head->ds_cnt + ii].
+                scratch[CDP_primary_val].u_val;
             if (isnan(value)) {
-                fprintf(out_file,
-                        "\t\t\t<primary_value>NaN</primary_value>\n");
+                snprintf(somestring_buf, 255, 
+                    "\t\t\t<primary_value>NaN</primary_value>\n");
             } else {
-                fprintf(out_file,
-                        "\t\t\t<primary_value>%0.10e</primary_value>\n",
-                        value);
+                snprintf(somestring_buf, 255, 
+                    "\t\t\t<primary_value>%0.10e</primary_value>\n", value);
             }
-            value =
-                rrd.cdp_prep[i * rrd.stat_head->ds_cnt +
-                             ii].scratch[CDP_secondary_val].u_val;
+            cb(somestring_buf, strlen(somestring_buf), user);
+
+            value = rrd.cdp_prep[i * rrd.stat_head->ds_cnt + ii].
+                scratch[CDP_secondary_val].u_val;
             if (isnan(value)) {
-                fprintf(out_file,
-                        "\t\t\t<secondary_value>NaN</secondary_value>\n");
+                snprintf(somestring_buf, 255, 
+                    "\t\t\t<secondary_value>NaN</secondary_value>\n");
             } else {
-                fprintf(out_file,
-                        "\t\t\t<secondary_value>%0.10e</secondary_value>\n",
-                        value);
+                snprintf(somestring_buf, 255, 
+                    "\t\t\t<secondary_value>%0.10e</secondary_value>\n", value);
             }
+            cb(somestring_buf, strlen(somestring_buf), user);
+
             switch (cf_conv(rrd.rra_def[i].cf_nam)) {
             case CF_HWPREDICT:
             case CF_MHWPREDICT:
-                value =
-                    rrd.cdp_prep[i * rrd.stat_head->ds_cnt +
-                                 ii].scratch[CDP_hw_intercept].u_val;
+                value = rrd.cdp_prep[i * rrd.stat_head->ds_cnt + ii].
+                    scratch[CDP_hw_intercept].u_val;
                 if (isnan(value)) {
-                    fprintf(out_file, "\t\t\t<intercept>NaN</intercept>\n");
+                    snprintf(somestring_buf, 255, 
+                        "\t\t\t<intercept>NaN</intercept>\n");
                 } else {
-                    fprintf(out_file,
-                            "\t\t\t<intercept>%0.10e</intercept>\n", value);
+                    snprintf(somestring_buf, 255, 
+                        "\t\t\t<intercept>%0.10e</intercept>\n", value);
                 }
-                value =
-                    rrd.cdp_prep[i * rrd.stat_head->ds_cnt +
-                                 ii].scratch[CDP_hw_last_intercept].u_val;
+                cb(somestring_buf, strlen(somestring_buf), user);
+
+                value = rrd.cdp_prep[i * rrd.stat_head->ds_cnt + ii].
+                    scratch[CDP_hw_last_intercept].u_val;
                 if (isnan(value)) {
-                    fprintf(out_file,
-                            "\t\t\t<last_intercept>NaN</last_intercept>\n");
+                    snprintf(somestring_buf, 255, 
+                        "\t\t\t<last_intercept>NaN</last_intercept>\n");
                 } else {
-                    fprintf(out_file,
-                            "\t\t\t<last_intercept>%0.10e</last_intercept>\n",
-                            value);
+                    snprintf(somestring_buf, 255, 
+                        "\t\t\t<last_intercept>%0.10e</last_intercept>\n", value);
                 }
-                value =
-                    rrd.cdp_prep[i * rrd.stat_head->ds_cnt +
-                                 ii].scratch[CDP_hw_slope].u_val;
+                cb(somestring_buf, strlen(somestring_buf), user);
+
+                value = rrd.cdp_prep[i * rrd.stat_head->ds_cnt + ii].
+                    scratch[CDP_hw_slope].u_val;
                 if (isnan(value)) {
-                    fprintf(out_file, "\t\t\t<slope>NaN</slope>\n");
+                    snprintf(somestring_buf, 255, 
+                        "\t\t\t<slope>NaN</slope>\n");
                 } else {
-                    fprintf(out_file, "\t\t\t<slope>%0.10e</slope>\n",
-                            value);
+                    snprintf(somestring_buf, 255, 
+                        "\t\t\t<slope>%0.10e</slope>\n", value);
                 }
-                value =
-                    rrd.cdp_prep[i * rrd.stat_head->ds_cnt +
-                                 ii].scratch[CDP_hw_last_slope].u_val;
+                cb(somestring_buf, strlen(somestring_buf), user);
+
+                value = rrd.cdp_prep[i * rrd.stat_head->ds_cnt + ii].
+                    scratch[CDP_hw_last_slope].u_val;
                 if (isnan(value)) {
-                    fprintf(out_file,
-                            "\t\t\t<last_slope>NaN</last_slope>\n");
+                    snprintf(somestring_buf, 255, 
+                        "\t\t\t<last_slope>NaN</last_slope>\n");
                 } else {
-                    fprintf(out_file,
-                            "\t\t\t<last_slope>%0.10e</last_slope>\n",
-                            value);
+                    snprintf(somestring_buf, 255, 
+                        "\t\t\t<last_slope>%0.10e</last_slope>\n", value);
                 }
-                ivalue =
-                    rrd.cdp_prep[i * rrd.stat_head->ds_cnt +
-                                 ii].scratch[CDP_null_count].u_cnt;
-                fprintf(out_file, "\t\t\t<nan_count>%lu</nan_count>\n",
-                        ivalue);
-                ivalue =
-                    rrd.cdp_prep[i * rrd.stat_head->ds_cnt +
-                                 ii].scratch[CDP_last_null_count].u_cnt;
-                fprintf(out_file,
-                        "\t\t\t<last_nan_count>%lu</last_nan_count>\n",
-                        ivalue);
+                cb(somestring_buf, strlen(somestring_buf), user);
+
+                ivalue = rrd.cdp_prep[i * rrd.stat_head->ds_cnt + ii].
+                    scratch[CDP_null_count].u_cnt;
+                snprintf(somestring_buf, 255, 
+                    "\t\t\t<nan_count>%lu</nan_count>\n", ivalue);
+                cb(somestring_buf, strlen(somestring_buf), user);
+
+                ivalue = rrd.cdp_prep[i * rrd.stat_head->ds_cnt + ii].
+                    scratch[CDP_last_null_count].u_cnt;
+                snprintf(somestring_buf, 255, 
+                    "\t\t\t<last_nan_count>%lu</last_nan_count>\n", ivalue);
+                cb(somestring_buf, strlen(somestring_buf), user);
                 break;
             case CF_SEASONAL:
             case CF_DEVSEASONAL:
-                value =
-                    rrd.cdp_prep[i * rrd.stat_head->ds_cnt +
-                                 ii].scratch[CDP_hw_seasonal].u_val;
+                value = rrd.cdp_prep[i * rrd.stat_head->ds_cnt + ii].
+                    scratch[CDP_hw_seasonal].u_val;
                 if (isnan(value)) {
-                    fprintf(out_file, "\t\t\t<seasonal>NaN</seasonal>\n");
+                    snprintf(somestring_buf, 255, 
+                        "\t\t\t<seasonal>NaN</seasonal>\n");
                 } else {
-                    fprintf(out_file, "\t\t\t<seasonal>%0.10e</seasonal>\n",
-                            value);
+                    snprintf(somestring_buf, 255, 
+                        "\t\t\t<seasonal>%0.10e</seasonal>\n", value);
                 }
-                value =
-                    rrd.cdp_prep[i * rrd.stat_head->ds_cnt +
-                                 ii].scratch[CDP_hw_last_seasonal].u_val;
+                cb(somestring_buf, strlen(somestring_buf), user);
+
+                value = rrd.cdp_prep[i * rrd.stat_head->ds_cnt + ii].
+                    scratch[CDP_hw_last_seasonal].u_val;
                 if (isnan(value)) {
-                    fprintf(out_file,
-                            "\t\t\t<last_seasonal>NaN</last_seasonal>\n");
+                    snprintf(somestring_buf, 255, 
+                        "\t\t\t<last_seasonal>NaN</last_seasonal>\n");
                 } else {
-                    fprintf(out_file,
-                            "\t\t\t<last_seasonal>%0.10e</last_seasonal>\n",
-                            value);
+                    snprintf(somestring_buf, 255, 
+                        "\t\t\t<last_seasonal>%0.10e</last_seasonal>\n", value);
                 }
-                ivalue =
-                    rrd.cdp_prep[i * rrd.stat_head->ds_cnt +
-                                 ii].scratch[CDP_init_seasonal].u_cnt;
-                fprintf(out_file, "\t\t\t<init_flag>%lu</init_flag>\n",
-                        ivalue);
+                cb(somestring_buf, strlen(somestring_buf), user);
+
+                ivalue = rrd.cdp_prep[i * rrd.stat_head->ds_cnt + ii].
+                    scratch[CDP_init_seasonal].u_cnt;
+                snprintf(somestring_buf, 255, 
+                    "\t\t\t<init_flag>%lu</init_flag>\n", ivalue);
+                cb(somestring_buf, strlen(somestring_buf), user);
                 break;
             case CF_DEVPREDICT:
                 break;
@@ -366,13 +457,16 @@
                                                                     ds_cnt +
                                                                     ii].
                                                        scratch);
-                fprintf(out_file, "\t\t\t<history> ");
+                cb("\t\t\t<history> ", 
+                    strlen("\t\t\t<history> "), user);
                 for (vidx = 0;
-                     vidx < rrd.rra_def[i].par[RRA_window_len].u_cnt;
-                     ++vidx) {
-                    fprintf(out_file, "%d", violations_array[vidx]);
+                    vidx < rrd.rra_def[i].par[RRA_window_len].u_cnt;
+                    ++vidx) {
+                    snprintf(somestring_buf, 255, "%d", violations_array[vidx]);
+                    cb(somestring_buf, strlen(somestring_buf), user);
                 }
-                fprintf(out_file, " </history>\n");
+                cb(" </history>\n",
+                    strlen(" </history>\n"), user);
             }
                 break;
             case CF_AVERAGE:
@@ -380,26 +474,31 @@
             case CF_MINIMUM:
             case CF_LAST:
             default:
-                value =
-                    rrd.cdp_prep[i * rrd.stat_head->ds_cnt +
-                                 ii].scratch[CDP_val].u_val;
+                value = rrd.cdp_prep[i * rrd.stat_head->ds_cnt + ii].scratch[CDP_val].u_val;
                 if (isnan(value)) {
-                    fprintf(out_file, "\t\t\t<value>NaN</value>\n");
+                    snprintf(somestring_buf, 255, 
+                        "\t\t\t<value>NaN</value>\n");
                 } else {
-                    fprintf(out_file, "\t\t\t<value>%0.10e</value>\n",
-                            value);
+                    snprintf(somestring_buf, 255, 
+                        "\t\t\t<value>%0.10e</value>\n", value);
                 }
-                fprintf(out_file,
-                        "\t\t\t<unknown_datapoints>%lu</unknown_datapoints>\n",
-                        rrd.cdp_prep[i * rrd.stat_head->ds_cnt +
-                                     ii].scratch[CDP_unkn_pdp_cnt].u_cnt);
+                cb(somestring_buf, strlen(somestring_buf), user);
+
+                snprintf(somestring_buf, 255, 
+                    "\t\t\t<unknown_datapoints>%lu</unknown_datapoints>\n",
+                    rrd.cdp_prep[i * rrd.stat_head->ds_cnt + ii].
+                        scratch[CDP_unkn_pdp_cnt].u_cnt);
+                cb(somestring_buf, strlen(somestring_buf), user);
                 break;
             }
-            fprintf(out_file, "\t\t\t</ds>\n");
+            cb("\t\t\t</ds>\n",
+                strlen("\t\t\t</ds>\n"), user);
         }
-        fprintf(out_file, "\t\t</cdp_prep>\n");
+        cb("\t\t</cdp_prep>\n",
+            strlen("\t\t</cdp_prep>\n"), user);
 
-        fprintf(out_file, "\t\t<database>\n");
+        cb("\t\t<database>\n",
+            strlen("\t\t<database>\n"), user);
         rrd_seek(rrd_file, (rra_start + (rrd.rra_ptr[i].cur_row + 1)
                             * rrd.stat_head->ds_cnt
                             * sizeof(rrd_value_t)), SEEK_SET);
@@ -419,36 +518,75 @@
             timer++;
 #if HAVE_STRFTIME
             localtime_r(&now, &tm);
-            strftime(somestring, 200, "%Y-%m-%d %H:%M:%S %Z", &tm);
+            strftime(somestring, 255, "%Y-%m-%d %H:%M:%S %Z", &tm);
 #else
 # error "Need strftime"
 #endif
-            fprintf(out_file, "\t\t\t<!-- %s / %lld --> <row>", somestring,
-                    (long long) now);
+            snprintf(somestring_buf, 255, 
+                "\t\t\t<!-- %s / %lld --> <row>",  somestring, (long long) now);
+            cb(somestring_buf, strlen(somestring_buf), user);
             for (iii = 0; iii < rrd.stat_head->ds_cnt; iii++) {
                 rrd_read(rrd_file, &my_cdp, sizeof(rrd_value_t) * 1);
                 if (isnan(my_cdp)) {
-                    fprintf(out_file, "<v>NaN</v>");
+                    snprintf(somestring_buf, 255, "<v>NaN</v>");
                 } else {
-                    fprintf(out_file, "<v>%0.10e</v>", my_cdp);
-                };
+                    snprintf(somestring_buf, 255, "<v>%0.10e</v>", my_cdp);
+                }
+                cb(somestring_buf, strlen(somestring_buf), user);
             }
-            fprintf(out_file, "</row>\n");
+            cb("</row>\n",
+                strlen("</row>\n"), user);
         }
-        fprintf(out_file, "\t\t</database>\n\t</rra>\n");
+        cb("\t\t</database>\n\t</rra>\n",
+            strlen("\t\t</database>\n\t</rra>\n"), user);
+    }
 
-    }
-    fprintf(out_file, "</rrd>\n");
+    cb("</rrd>\n",
+        strlen("</rrd>\n"), user);
+
     rrd_free(&rrd);
-    if (out_file != stdout) {
-        fclose(out_file);
-    }
+
 #ifdef HAVE_SETLOCALE
     setlocale(LC_NUMERIC, old_locale);
 #endif
+
     return rrd_close(rrd_file);
 }
 
+size_t rrd_dump_opt_cb_fileout(
+    const void *data,
+    size_t len,
+    void *user)
+{
+    return fwrite(data, 1, len, (FILE *)user);
+}
+
+int rrd_dump_opt_r(
+    const char *filename,
+    char *outname,
+    int opt_noheader)
+{
+    FILE     *out_file;
+    int       res;
+
+    out_file = NULL;
+    if (outname) {
+        if (!(out_file = fopen(outname, "w"))) {
+            return (-1);
+        }
+    } else {
+        out_file = stdout;
+    }
+
+    res = rrd_dump_cb_r(filename, opt_noheader, rrd_dump_opt_cb_fileout, (void *)out_file);
+
+    if (out_file != stdout) {
+        fclose(out_file);
+    }
+
+    return res;
+}
+
 /* backward compatibility with 1.2.x */
 int rrd_dump_r(
     const char *filename,

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