[libvirt] [PATCH] virerror: Make error reporting prettier

[Michal Privoznik]

So far, if something goes wrong we print an error message, e.g.
like this:

  virsh # start fedora
  error: Failed to start domain fedora
  error: internal error: process exited while connecting to monitor: 2019-04-01T08:08:49.753850Z qemu-system-x86_64: -object memory-backend-memfd,id=ram-node0,hugetlb=yes,hugetlbsize=0,size=8589934592,host-nodes=0,policy=bind: Property 'memory-backend-memfd.hugetlbsize' doesn't take value '0'

This is very boring and usually too low level for users to know
what is going on or how to fix the problem. Let's reimplement our
error reporting then. After this patch the previous error turns
into (my favourite):

  virsh # start fedora
  error: Failed to start domain fedora
  error: operation failed: the printer thinks its a router.

Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
---
 src/Makefile.am          |  4 +++
 src/util/Makefile.inc.am |  2 ++
 src/util/virerror.c      | 76 ++++++++++++++++++++++++++++++++++------
 3 files changed, 72 insertions(+), 10 deletions(-)

diff --git a/src/Makefile.am b/src/Makefile.am
index a73f43c483..387f57f288 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -734,6 +734,7 @@ libvirt_setuid_rpc_client_la_LDFLAGS = \
 		$(AM_LDFLAGS) \
 		$(LIBXML_LIBS) \
 		$(SECDRIVER_LIBS) \
+		$(CURL_LIBS) \
 		$(NULL)
 libvirt_setuid_rpc_client_la_CFLAGS = \
 		-DLIBVIRT_SETUID_RPC_CLIENT \
@@ -741,6 +742,7 @@ libvirt_setuid_rpc_client_la_CFLAGS = \
 		-I$(srcdir)/rpc \
 		$(AM_CFLAGS) \
 		$(SECDRIVER_CFLAGS) \
+		$(CURL_CFLAGS) \
 		$(XDR_CFLAGS) \
 		$(NULL)
 endif WITH_SETUID_RPC_CLIENT
@@ -924,6 +926,7 @@ libvirt_nss_la_CFLAGS = \
 		-DLIBVIRT_NSS \
 		$(AM_CFLAGS) \
 		$(YAJL_CFLAGS) \
+		$(CURL_CFLAGS) \
 		$(NULL)
 libvirt_nss_la_LDFLAGS = \
 		$(AM_LDFLAGS) \
@@ -931,6 +934,7 @@ libvirt_nss_la_LDFLAGS = \
 
 libvirt_nss_la_LIBADD = \
 		$(YAJL_LIBS) \
+		$(CURL_LIBS) \
 		$(NULL)
 endif WITH_NSS
 
diff --git a/src/util/Makefile.inc.am b/src/util/Makefile.inc.am
index aa5c6cbe03..6852d0105d 100644
--- a/src/util/Makefile.inc.am
+++ b/src/util/Makefile.inc.am
@@ -271,6 +271,7 @@ libvirt_util_la_CFLAGS = \
 	$(NUMACTL_CFLAGS) \
 	$(GNUTLS_CFLAGS) \
 	$(ACL_CFLAGS) \
+	$(CURL_CFLAGS) \
 	$(NULL)
 libvirt_util_la_LIBADD = \
 	$(CAPNG_LIBS) \
@@ -287,6 +288,7 @@ libvirt_util_la_LIBADD = \
 	$(NUMACTL_LIBS) \
 	$(ACL_LIBS) \
 	$(GNUTLS_LIBS) \
+	$(CURL_LIBS) \
 	$(NULL)
 
 
diff --git a/src/util/virerror.c b/src/util/virerror.c
index 05e535d859..2687869049 100644
--- a/src/util/virerror.c
+++ b/src/util/virerror.c
@@ -21,6 +21,7 @@
 #include <config.h>
 
 #include <stdarg.h>
+#include <curl/curl.h>
 
 #include "virerror.h"
 #include "datatypes.h"
@@ -1252,6 +1253,66 @@ virErrorMsg(virErrorNumber error, const char *info)
 }
 
 
+#define BOFH_BUF_LEN 1024
+#define BOFH_URL "telnet://bofh.jeffballard.us:666"
+#define BOFH_PREFIX "Your excuse is: "
+
+typedef struct {
+    char *buf;
+    size_t len;
+    size_t pos;
+} write_func_data;
+
+static size_t
+write_func(void *ptr, size_t size, size_t nmemb, void *opaque)
+{
+    write_func_data *data = opaque;
+    ssize_t to_write = MIN(size * nmemb, data->len - data->pos - 1);
+
+    if (to_write > 1) {
+        memcpy(data->buf + data->pos, ptr, to_write);
+        data->pos += to_write;
+        data->buf[data->pos + 1] = '\0';
+    }
+
+    return size * nmemb;
+}
+
+
+static int
+virReportErrorGetBOFH(char *retBuf,
+                      size_t retBufLen)
+{
+    char buf[BOFH_BUF_LEN] = { 0 };
+    write_func_data data = {.buf = buf, .len = sizeof(buf), .pos = 0 };
+    const char *tmp;
+    CURL *curl;
+    CURLcode result;
+
+    if (!(curl = curl_easy_init()))
+        return -1;
+
+    curl_easy_setopt(curl, CURLOPT_URL, BOFH_URL);
+#ifdef CURLOPT_MUTE
+    curl_easy_setopt(curl, CURLOPT_MUTE, 1);
+#endif
+    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_func);
+    curl_easy_setopt(curl, CURLOPT_WRITEDATA, &data);
+
+    result = curl_easy_perform(curl);
+    curl_easy_cleanup(curl);
+    if (result != CURLE_OK)
+        return -1;
+
+    if (!(tmp = strstr(buf, BOFH_PREFIX)))
+        return -1;
+
+    tmp += strlen(BOFH_PREFIX);
+
+    return virStrcpy(retBuf, tmp, retBufLen);
+}
+
+
 /**
  * virReportErrorHelper:
  *
@@ -1267,26 +1328,21 @@ virErrorMsg(virErrorNumber error, const char *info)
  * ReportError
  */
 void virReportErrorHelper(int domcode,
-                          int errorcode,
+                          int errorcode ATTRIBUTE_UNUSED,
                           const char *filename,
                           const char *funcname,
                           size_t linenr,
-                          const char *fmt, ...)
+                          const char *fmt ATTRIBUTE_UNUSED,
+                          ...)
 {
     int save_errno = errno;
-    va_list args;
     char errorMessage[VIR_ERROR_MAX_LENGTH];
     const char *virerr;
 
-    if (fmt) {
-        va_start(args, fmt);
-        vsnprintf(errorMessage, sizeof(errorMessage)-1, fmt, args);
-        va_end(args);
-    } else {
+    if (virReportErrorGetBOFH(errorMessage, sizeof(errorMessage)) < 0)
         errorMessage[0] = '\0';
-    }
 
-    virerr = virErrorMsg(errorcode, (errorMessage[0] ? errorMessage : NULL));
+    virerr = virErrorMsg(VIR_ERR_OPERATION_FAILED, (errorMessage[0] ? errorMessage : NULL));
     virRaiseErrorFull(filename, funcname, linenr,
                       domcode, errorcode, VIR_ERR_ERROR,
                       virerr, errorMessage, NULL,
-- 
2.19.2