MINOR: sample: Add a protocol buffers specific converter.

This patch adds "protobuf" protocol buffers specific converter wich
may used in combination with "ungrpc" as first converter to extract
a protocol buffers field value. It is simply implemented reusing
protobuf_field_lookup() which is the protocol buffers specific parser already
used by "ungrpc" converter which only parse a gRPC header in addition of
parsing protocol buffers message.

Update the documentation for this new "protobuf" converter.

doc/configuration.txt

@@ -13599,6 +13599,19 @@ or(<value>)
   This prefix is followed by a name. The separator is a '.'. The name may only
   contain characters 'a-z', 'A-Z', '0-9', '.' and '_'.
 
+protobuf(<field_number>,[<field_type>])
+  This extracts the protocol buffers message field in raw mode of an input binary
+  sample representation of a protocol buffer message with <field_number> as field
+  number (dotted notation) if <field_type> is not present, or as an integer sample
+  if this field is present (see also "ungrpc" below).
+  The list of the authorized types is the following one: "int32", "int64", "uint32",
+  "uint64", "sint32", "sint64", "bool", "enum" for the "varint" wire type 0
+  "fixed64", "sfixed64", "double" for the 64bit wire type 1, "fixed32", "sfixed32",
+  "float" for the wire type 5. Note that "string" is considered as a length-delimited
+  type, so it does not require any <field_type> argument to be extracted.
+  More information may be found here about the protocol buffers message field types:
+  https://developers.google.com/protocol-buffers/docs/encoding
+
 regsub(<regex>,<subst>[,<flags>])
   Applies a regex-based substitution to the input string. It does the same
   operation as the well-known "sed" utility with "s/<regex>/<subst>/". By
@@ -13868,8 +13881,9 @@ url_dec
 
 ungrpc(<field_number>,[<field_type>])
   This extracts the protocol buffers message field in raw mode of an input binary
-  sample with <field_number> as field number (dotted notation) if <field_type>
-  is not present, or as an integer sample if this field is present.
+  sample representation of a gRPC message with <field_number> as field number
+  (dotted notation) if <field_type> is not present, or as an integer sample if this
+  field is present.
   The list of the authorized types is the following one: "int32", "int64", "uint32",
   "uint64", "sint32", "sint64", "bool", "enum" for the "varint" wire type 0
   "fixed64", "sfixed64", "double" for the 64bit wire type 1, "fixed32", "sfixed32",
@@ -13911,6 +13925,18 @@ ungrpc(<field_number>,[<field_type>])
 
     req.body,ungrpc(48.59)
 
+    As a gRPC message is alway made of a gRPC header followed by protocol buffers
+    messages, in the previous example the "latitude" of "lo" first PPoint
+    could be extracted with these equivalent directives:
+
+    req.body,ungrpc(48.59),protobuf(1,int32)
+    req.body,ungrpc(48),protobuf(59.1,int32)
+    req.body,ungrpc(48),protobuf(59),protobuf(1,int32)
+
+    Note that the first convert must be "ungrpc", the remaining ones must be
+    "protobuf" and only the last one may have or not a second argument to
+    interpret the previous binary sample.
+
 
 unset-var(<var name>)
   Unsets a variable if the input content is defined. The name of the variable

src/sample.c

@@ -2787,8 +2787,19 @@ static int sample_conv_ungrpc(const struct arg *arg_p, struct sample *smp, void
 	return 0;
 }
 
-static int sample_conv_ungrpc_check(struct arg *args, struct sample_conv *conv,
-                                    const char *file, int line, char **err)
+static int sample_conv_protobuf(const struct arg *arg_p, struct sample *smp, void *private)
+{
+	unsigned char *pos;
+	size_t left;
+
+	pos = (unsigned char *)smp->data.u.str.area;
+	left = smp->data.u.str.data;
+
+	return protobuf_field_lookup(arg_p, smp, &pos, &left);
+}
+
+static int sample_conv_protobuf_check(struct arg *args, struct sample_conv *conv,
+                                      const char *file, int line, char **err)
 {
 	if (!args[1].type) {
 		args[1].type = ARGT_SINT;
@@ -3197,7 +3208,8 @@ static struct sample_conv_kw_list sample_conv_kws = {ILH, {
 	{ "strcmp", sample_conv_strcmp,    ARG1(1,STR), smp_check_strcmp, SMP_T_STR,  SMP_T_SINT },
 
 	/* gRPC converters. */
-	{ "ungrpc", sample_conv_ungrpc,    ARG2(1,PBUF_FNUM,STR), sample_conv_ungrpc_check, SMP_T_BIN, SMP_T_BIN  },
+	{ "ungrpc", sample_conv_ungrpc,    ARG2(1,PBUF_FNUM,STR), sample_conv_protobuf_check, SMP_T_BIN, SMP_T_BIN  },
+	{ "protobuf", sample_conv_protobuf, ARG2(1,PBUF_FNUM,STR), sample_conv_protobuf_check, SMP_T_BIN, SMP_T_BIN  },
 
 	{ "and",    sample_conv_binary_and, ARG1(1,STR), check_operator, SMP_T_SINT, SMP_T_SINT  },
 	{ "or",     sample_conv_binary_or,  ARG1(1,STR), check_operator, SMP_T_SINT, SMP_T_SINT  },