bugfix resizing the format output buffer

src/format.c

@@ -1454,20 +1454,21 @@ FMT_Estimate_RecsPerTx(void)
 }
 
 static inline void
-fmt_resize(size_t curlen)
+fmt_resize(size_t length)
 {
-    if (curlen > obuf_sz) {
-        do { obuf_sz <<= 1; } while (curlen > obuf_sz);
+    /* Add 1 since we'll be appending a NUL byte */
+    if (length + 1 > obuf_sz) {
+        do { obuf_sz <<= 1; } while (length + 1 > obuf_sz);
         obuf = realloc(obuf, obuf_sz);
         AN(obuf);
     }
 }
 
 char *
-FMT_Format(tx_t *tx, size_t *curlen)
+FMT_Format(tx_t *tx, size_t *length)
 {
     compiled_fmt_t fmt;
-    char *p = obuf;
+    size_t curlen = 0;
 
     CHECK_OBJ_NOTNULL(tx, TX_MAGIC);
     assert(tx->state == TX_SUBMITTED);
@@ -1488,31 +1489,27 @@ FMT_Format(tx_t *tx, size_t *curlen)
 
     tx->state = TX_FORMATTING;
 
-    /* Start curlen at 1, because we'll be appending a NUL byte */
-    *p = '\0';
-    *curlen = 1;
+    *obuf = '\0';
     for (int i = 0; i < fmt.n; i++) {
         char *s = NULL;
         size_t len = 0;
 
         if (fmt.str[i] != NULL) {
-            *curlen += fmt.strlen[i];
-            fmt_resize(*curlen);
-            memcpy(p, fmt.str[i], fmt.strlen[i]);
-            p += fmt.strlen[i];
+            fmt_resize(curlen + fmt.strlen[i]);
+            memcpy(obuf + curlen, fmt.str[i], fmt.strlen[i]);
+            curlen += fmt.strlen[i];
         }
         if (fmt.formatter[i] != NULL) {
             (fmt.formatter[i])(tx, &fmt.args[i], &s, &len);
             if (s != NULL && len != 0) {
-                *curlen += len;
-                fmt_resize(*curlen);
-                memcpy(p, s, len);
-                p += len;
+                fmt_resize(curlen + len);
+                memcpy(obuf + curlen, s, len);
+                curlen += len;
             }
         }
     }
-    *p = '\0';
-    *curlen -= 1;
+    obuf[curlen] = '\0';
+    *length = curlen;
 
     assert(tx->state == TX_FORMATTING);
     tx->state = TX_WRITTEN;

src/test/test_format.c

@@ -2333,6 +2333,45 @@ static const char
     return NULL;
 }
 
+static const char
+*test_long_output(void)
+{
+#define NFORMATS 8193
+#define XID 47114711
+#define xstr(s) #s
+#define str(s) xstr(s)
+    char err[1024], *os;
+    int status;
+    tx_t tx;
+    size_t len;
+    struct vsb *exp;
+
+    printf("... testing long formatted output\n");
+
+    exp = VSB_new_auto();
+    VSB_clear(config.cformat);
+    for (int i = 0; i < NFORMATS; i++) {
+        VSB_cat(config.cformat, "%{vxid}x");
+        VSB_cat(exp, str(XID));
+    }
+    VSB_putc(exp, '\n');
+    VSB_finish(config.cformat);
+    VSB_finish(exp);
+    status = FMT_Init(err);
+    VMASSERT(status == 0, "FMT_Init: %s", err);
+
+    tx.magic = TX_MAGIC;
+    tx.state = TX_SUBMITTED;
+    tx.type = VSL_t_req;
+    tx.vxid = 47114711;
+
+    os = FMT_Format(&tx, &len);
+    MASSERT(len == NFORMATS * (sizeof(str(XID)) - 1) + 1);
+    MASSERT(strncmp(os, VSB_data(exp), len) == 0);
+
+    return NULL;
+}
+
 static const char
 *all_tests(void)
 {
@@ -2366,6 +2405,7 @@ static const char
     mu_run_test(test_format_p_vxid);
     mu_run_test(test_FMT_Fini);
     mu_run_test(test_FMT_interface);
+    mu_run_test(test_long_output);
 
     return NULL;
 }